Transverse momentum spectra and nuclear modification factors of charged particles in Xe-Xe collisions at root s(NN)=5.44 TeV

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DOI: 10.1016/j.physletb.2018.10.052

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by Elsevier. All rights reserved.

DIRETORIA DE TRATAMENTO DA INFORMAÇÃO

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Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Transverse

momentum

spectra

and

nuclear

modification

factors

of charged

particles

in

Xe–Xe

collisions

at

√

s

_NN

=

5

.

44 TeV

.

ALICE

Collaboration



a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received24May2018

Receivedinrevisedform26September 2018

Accepted24October2018 Availableonline31October2018 Editor: M.Doser

Transverse momentum (pT) spectraof charged particlesatmid-pseudorapidity inXe–Xe collisions at √_s

NN=5.44 TeV measured withthe ALICE apparatusatthe LargeHadronCollider are reported. The kinematic range0.15

<

pT<50GeV/c and |

η

|

<

0.8 iscovered. Resultsare presented innineclasses of collision centralityin the 0–80%range. For comparison, app reference at the collisionenergy of √_s=5

.44 TeV isobtainedbyinterpolatingbetweenexistingppmeasurementsat√s=5.02 and7 TeV. ThenuclearmodificationfactorsincentralXe–Xecollisions andPb–Pbcollisionsatasimilar center-of-mass energyof√sNN=5.02 TeV,andinadditionat2.76 TeV,atanalogousrangesofchargedparticle multiplicitydensitydNch/d

η

showaremarkablesimilarityatpT>10 GeV/c.Thecentralitydependence of the ratio of the average transverse momentum pT in Xe–Xe collisions over Pb–Pb collision at √

s=5.02 TeV iscomparedtohydrodynamicalmodelcalculations.

©2018TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Transverse momentum (pT) spectra ofcharged particles carry

essential information aboutthe high-density deconfined state of strongly-interacting matter commonly denoted as quark–gluon plasma,thatisformedinhigh-energynucleus–nucleus(A–A) colli-sions [1].Relativistichydrodynamicsisabletomodeltheevolution ofthismedium [2,3].

At low to intermediate pT, typically in the range of up to

10 GeV

/

c, chargedparticle productionis governedby the collec-tive expansion of the system, which is observed in the shapes of single-particle transverse-momentum spectra [4,5] and multi-particle correlations [2]. However, there is presently an intense debate as to whether the strikingly similar signatures observed insmallcollision systems (ppandp–A) are alsoof hydrodynam-ical origin [6–14]. A key ingredient of calculations in relativistic hydrodynamics is the initial energy density [2,15,16]. The num-ber of produced particles and the volume of the medium are approximatelyproportional to thenumberof nucleons Npart that

participateinthecollision [17–19].Thus, theparticledensityper unit volume is roughly independent of Npart. As a consequence,

particlespectraat smalltransversemomentum shouldbe similar innucleus–nucleuscollisions, independentlyofthemassnumber, whencomparedatsimilarvaluesof

N

part [20].

At high pT,typically above 10 GeV

/

c, particles originate from

parton fragmentationand are sensitive to the amount of energy

 _{E-mailaddress:alice -publications @cern .ch.}

loss that thepartons sufferwhenpropagating inthe medium. In a simplified model, the energy loss depends on the number of scattering centers, which is roughly proportional to the energy density,andonthepathlength thatthepartonpropagatesinthe medium [21].Forelasticcollisions,thedependenceislinear,while formediuminducedgluonradiation,itisquadratic [22].A descrip-tionofexperimentaldataliesinbetweenthosetwo [23].

For hard processes, the production yield NAA in nucleus–

nucleus (A–A) collisions is expected to scale with the average nuclear overlapfunction



TAA



whencompared totheproduction

crosssection

σ

ppinppcollisions.Intheabsenceofnucleareffects,

thenuclearmodificationfactor

RAA

(

pT

)

=

1



TAA



·

dNAA

(

pT

)/

dpT d

σ

pp

(

pT

)/

dpT (1)

equals unity. The average nuclear overlap function is defined as the average number of binary nucleon-nucleon collisions



Ncoll



per inelasticnucleon-nucleoncrosssectionandisestimatedviaa Glaubermodelcalculation [24].AttheLargeHadronCollider(LHC), particleproductionisobservedtobestronglysuppressedinPb–Pb collisions by a factorofup to 7–8around pT

=

6–7 GeV

/

c with

alineardecreaseofthesuppressionfactorathigher pT butstill a

substantialsuppressionevenabove100 GeV

/

c [5,25].

The LHC produced for the first time collisions of xenon nu-cleiatacenter-of-massenergyof

√

sNN

=

5

.

44 TeV duringa pilot

run with 6 hours of stable beams in October 2017. This allows for studying the dependence of particle production on the colli-sionsystemsizewherexenonneatlybridgesthegapbetweendata

https://doi.org/10.1016/j.physletb.2018.10.052

0370-2693/©2018TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

Table 1

AveragedvaluesofdNch/dη,Npart,NcollandTAAforninecentralityclassesofXe–Xecollisions[18,19] at

√

sNN=5.44 TeV,anddNch/dηforPb–Pbcollisionsat√sNN=5.02 TeV [30].Thevaluesfor dNch/dηare measuredintherange|η|<0.5.

Centrality (%) dNch/dηXe–Xe Npart Ncoll TAA (mb−1) dNch/dηPb–Pb 0–5 1167±26 236±2 949±53 13.9±0.8 1943±54 5–10 939±24 207±2 737±46 10.8±0.7 1586±46 10–20 706±17 165±2 511±26 7.5±0.5 1180±31 20–30 478±11 118±3 303±28 4.4±0.4 786±20 30–40 315±8 82±3 171±19 2.5±0.3 512±15 40–50 198±5 55±3 92±11 1.3±0.2 318±12 50–60 118±3 34±2 46±6 0.7±0.1 183±8 60–70 65±2 20±2 22±3 0.32±0.04 96±6 70–80 32±1 11±1 10±1 0.14±0.02 45±3

frompp, p–PbandPb–Pbcollisions. Here,theatomicmass num-bersare A

=

129 forxenon,andA

=

208 forleadwithhalf-density radii of the nuclear-charge distribution of r

= (

5

.

36

±

0

.

1

)

fm and(6

.

62

±

0

.

06) fm,respectively [24,26]. The parameters ofthe nuclear-chargedensitydistributionfor129_{Xearenotyetmeasured}

butwereextrapolatedfromneighboringisotopesandarethusless preciselyknownthanfor208Pb.While208Pbisasphericalnucleus,

129_{Xehasadeformationparameterof}

_β

2

= (

0

.

18

±

0

.

02

)

.

This article reports transverse momentum spectra of charged particles at mid-pseudorapidity in Xe–Xe collisions at

√

sNN

=

5

.

44 TeV measured with the ALICE apparatus atthe LHC in the kinematic range 0

.

15

<

pT

<

50 GeV

/

c and

|

η

|

<

0

.

8 for nine

classesofcollisioncentrality,coveringthemostcentral80%ofthe hadronic cross section. It is organized as follows: Section 2 de-scribestheexperimentalsetupanddataanalysis.Systematic uncer-taintiesarediscussedinSect.3.Resultsandcomparisontomodel calculationsarepresentedinSect.4.AsummaryisgiveninSect.5. 2. Experimentanddataanalysis

Collisionsofxenonnucleiwere recordedatanaverage instan-taneous luminosity of about 2

·

10−25cm−2s−1 and a hadronic interaction rateof80–150 s−1_{. A detaileddescription ofthe}

AL-ICEexperimentalapparatuscanbefoundelsewhere [27].

2.1. Trigger and event selection

Aminimum-biasinteractiontriggerwasoptimizedforhigh effi-ciencyonhadroniccollisions.Itrequiredsignalsfrombothforward scintillator arrays covering 2

.

8

<

η

<

5

.

1 (V0A) and

−

3

.

7

<

η

<

−

1

.

7 (V0C). Additionally, coincidence withsignalsfromtwo neu-tron Zero-Degree Calorimeters (ZDC), ZNA and ZNC, at

|

η

|

>

8

.

7 wasrequiredinorderto removecontamination from electromag-netic processes. Here A and C denote opposite sides of the ex-perimentalongthe beamline.The offlineeventselectionwas op-timized to reject beam-induced background. Background events were efficiently rejected by exploiting the timing signals in the two V0 detectors. Parasitic collisions are removed by using the correlationbetweenthesumandthedifferenceinarrivaltimesas measuredineachoftheneutronZDCs.Intotal,1

.

1

·

106 minimum-biascollisionspasstheeventselectionandwerefurtheranalyzed. This analysis is based on tracking information from the In-ner Tracking System (ITS) [28] and the Time Projection Cham-ber (TPC) [29] which are located in the central barrel of ALICE. A solenoidalmagnetprovides momentumdispersioninthe direc-tiontransversetothebeamaxis.Thenominalfieldstrengthinthe ALICEcentral barrelis0.5 T.However, inordertoextendparticle trackingandidentificationtothelowestpossiblemomenta,itwas reducedto0.2 TinXe–Xecollisions.

TheITS is comprisedof sixcylindricallayers of silicon detec-torswithradiibetween3.9and43.0 cm.Thetwoinnermostlayers,

withaverageradiiof3.9cmand7.6 cm,areequippedwithSilicon Pixel Detectors (SPD); the two intermediate layers, with average radiiof15.0 cmand23.9 cm,areequippedwithSiliconDrift De-tectors (SDD) and the two outermost layers, with average radii of 38.0cm and43.0 cm, are equippedwith double-sided Silicon Strip Detectors (SSD). The large cylindrical TPC hasan active ra-dial range fromabout85 to250 cm andan overall length along the beam directionof 500 cm. It covers the full azimuth in the pseudo-rapidityrange

|

η

|

<

0

.

9 andprovidestrackreconstruction with up to 159 points along the trajectory of a charged particle aswell asparticle identificationvia the measurement ofspecific energyloss dE

/

dx.

The collision vertex is determined using reconstructed parti-cletrajectories inthe TPCincluding hitsin theITS. All collisions with a reconstructed vertex position within

±

10 cm along the beam directionfrom the nominalinteraction point are accepted. Thecollisioncentralityisdefinedasthepercentileofthehadronic crosssectioncorrespondingtothemeasuredchargedparticle mul-tiplicity.The centralitydetermination isbasedon thesumof the amplitudesoftheV0AandV0Csignals[18,19].Averagedquantities characterizing a centrality class such as the number of partici-pants Npart,thenumberofbinarycollisions Ncoll,andthenuclear

overlapfunction TAA arecalculated astheaverageoverall events

inthisclassbyfittingtheexperimentaldistributionwithaGlauber MonteCarlomodelthatemploysnegativebinomialdistributionsto modelmultiplicityproduction [18,19] (seeTable1).Theanalysisis restrictedtothe0–80%centralityrangeinordertoensurethat ef-fectsoftriggerinefficiency andcontaminationby electromagnetic processesarenegligible.

2.2. Track selection

Primarychargedparticleswithinthekinematicrange

|

η

|

<

0

.

8 and0

.

15

<

pT

<

50 GeV/c are measured.Here, primaries are

de-finedasallchargedparticleswithaproperlifetime

τ

largerthan 1 cm/c that are either produced directly in the primary beam-beaminteraction,orfromdecaysofparticles with

τ

smallerthan 1 cm/c, excludingparticles produced ininteractions withthe de-tectormaterial [31].Thetrackselectionisoptimizedforbesttrack qualityandminimumcontaminationfromsecondaryparticles.The selection criteria are identical to those of the previous analysis ofPb–Pb collisionsat

√

sNN

=

5

.

02 TeV [5] except forthe

follow-ingchangesintheparameterizationonthetransversemomentum dependence.Thegeometrical tracklength intheTPCfiducial vol-ume [29] is

L

/(

1 cm

) >

130

− (

pT

/(

1 GeV

/

c

))

−0.7,andthedistance

ofclosestapproachtotheprimaryvertexinthetransverseplaneis

|

DCAxy

|/(

1 cm

) <

0

.

0119

+

0

.

049

(

pT

/(

1 GeV

/

c

))

−1.Thesechanges

reflectdifferencesinparticletrackingduetothereducedmagnetic field.Inordertorejectfaketracksthatcontaminatethespectrum, especially athigh pT,another selection isintroduced:the

matrix ofthe trackfit must be lessthan ten timesthe standard deviation,whenaveragedoveralltracksatthatmomentum.

2.3. Corrections

Thedoubly-differentialtransversemomentumspectrainXe–Xe collisionsarenormalizedbythenumberofevents

N

evineach

cen-tralityclass,andaregivenby

1 Nev d2Nch d

η

dpT

≡

Nrec_ch

(

η

,



pT

)

Nev

· 

η



pT

·

δ

pT

(

pT

)

α

(

pT

)

·

ε

(

pT

)

,

(2) where

N

rec

ch istherawyieldofreconstructedprimarycharged

par-ticlesin each interval ofpseudo-rapidity andtransverse momen-tum

(

η

,



pT

)

. The symbols

α

(

pT

)

and

ε

(

pT

)

are the

cor-rectionfactorsfordetectoracceptanceandtrackingefficiency, re-spectively.The correctiondueto thefinitetransverse-momentum resolution in the reconstruction of primary charged particles is denotedby

δ

pT

(

pT

)

.Theefficienciesfortrigger,eventvertex

re-construction andtrackingare estimatedusingMonteCarlo simu-lationswithHIJING[32] astheeventgeneratorandGEANT3 [33] forparticle propagationand simulation ofthe detectorresponse. The triggerandvertexselectionsare fullyefficient forthewhole centralityrangeusedintheanalysis.

Contaminationfromsecondarychargedparticles,i.e.fromweak decaysandinteractionsinthedetectormaterial,issubtractedfrom the raw spectrum by employing a data driven method [5]. Re-constructed trajectoriesofprimary chargedparticles point tothe collisionvertex,whilechargedparticlesfromweakdecaysand par-ticlesgeneratedinthedetectormaterialpreferentially pointaway from it. In order to distinguish between primary and secondary particles, the distance ofclosest approach to the collision vertex inradialdirection, DCAxy,is used.Amulti-templatefunctionthat

consistsoftemplatesforprimaryparticles,secondaryparticles pro-ducedfromweakdecaysandsecondaryparticlesfrominteractions inthedetectormaterialisfittedtotheDCAxydistributionsineach

pTinterval.

The primary charged particle reconstruction efficiency is ob-tained from the Monte Carlo simulation. As discussed in detail in [5], this efficiencydepends on the relative abundances ofthe various primary particles species. These relative abundances are adjusted inthe simulation using a data-driven re-weighting pro-cedure. The particle composition in Xe–Xe collisions is not yet known.However,bulkparticleproductionscaleswiththeaverage chargedparticlemultiplicity density,



dNch

/

dη



,independently of

the collision system [34]. In Xe–Xe collisions, the weights from existing analyses [35–37,4,5] with Pb–Pb collisions at

√

sNN

=

2

.

76 TeV atequivalentvaluesin



dNch

/

dη



areapplied.

The acceptance times tracking efficiency for charged pions, chargedkaons and (anti-)protons for5% most central Xe–Xe col-lisions isshown inFig. 1asa function ofthe particletransverse momentumandcomparedto 10–20%Pb–Pbcollisions at

√

sNN

=

5

.

02 TeV.Thetwocentralityclasseshavesimilarmultiplicity den-sities. The particular shape witha dip at pT

∼

0

.

4 GeV

/

c arises

fromthe geometricallengthselectionthat isespeciallyvisiblefor pions.This dipcorresponds toparticles that crossthe TPCsector boundariesundersmall angles.The decreaseat low valuesof pT

is dueto curling trajectoriesin the magnetic field which do not reach therequired minimumtracklength in theTPC anddueto energylossandabsorptioninthedetectormaterial.InPb–Pb colli-sions,themagneticfieldwassetto B

=

0

.

5 T,whichresultsinthe dipbeingpositionedaround1 GeV

/

c. Atlarge pT,above7 GeV

/

c,

thetrackingefficiencyisreducedby anincreasedlocaltrack den-sity, i.e.high pT particlesare preferentially produced within jets,

leadingtoaslightdecreaseinthetrackfindingperformance.

Fig. 1. Transversemomentum dependenceofthe acceptancetimestracking effi-ciency for the5% mostcentral Xe–Xecollisions and comparisontothe 10–20% centralityclassforPb–Pbcollisions.Thetwocentralityclasseshavesimilar mul-tiplicitydensities.

The transverse momentum ofprimary chargedparticles is re-constructed fromthe trackcurvatureasmeasured bytheITSand theTPC [38].Thefinitemomentumresolutionmodifiesthe recon-structed charged-particlespectrumandisestimatedbythe corre-spondingcovariancematrixelementoftheKalmanfit.Therelative

pT resolution,

σ

(

pT

)/

pT,dependsonthemomentumandamounts

toapproximately4.5%atpT

=

0

.

15 GeV

/

c, itshowsaminimumof

1.5% around pT

=

1

.

0 GeV

/

c, and increaseslinearlyforlarger pT,

approaching 9.3% at50 GeV

/

c. The centrality dependenceof the relative

p

Tresolutionisnegligible.Toaccountforthefinite

p

T

res-olution, correction factors to thespectra are determinedfrom an unfolding procedureasdescribed in[5],usingBayesian unfolding atlow pT andabin-by-bin correctionatlarge pT.The pT

depen-dent correction factorsare applied to themeasured pT spectrum

anddepend slightlyon collisioncentrality becauseofthe change in the slope ofthe spectrum athigh pT.At transverse momenta

below10 GeV

/

c,

δ

pT deviatessignificantly fromunity onlyatthe

lowest momentum interval of 0

.

15

≤

pT

<

0

.

2 GeV

/

c where it

amounts to 0.5% for all centrality classes, and by up to 3% (4%) in0–5%(70–80%)centralcollisionsabove10 GeV

/

c.

The statistical uncertainty ofthe spectra is dominated by the statisticaluncertainty inthe rawdata.It islargestat thehighest momentumintervalof40–50 GeV

/

c and amountsto28%(38%)for the0–5%(30–40%)centralityclasswhilethecontributionfromthe MonteCarloefficiencyis2%(4%)orless.

2.4. pp reference at

√

s

=

5

.

44 TeV

The pT-differential inelastic cross section in pp collisions at

√

s

=

5

.

44 TeV is needed to measure the corresponding nuclear modificationfactor.Astherearenomeasurementsofppcollisions at this energy, a referenceis obtained by interpolating pp refer-ences as measured at

√

s

=

5

.

02 TeV and

√

s

=

7 TeV assuming a power-lawdependence ineach pT interval,

d

σ

/

dpT

(

√

s

)

∝

√

sn.

The value of thefree parameter n varies between0

.

35 and 1.75, depending on pT.Thisapproach isa combinationofthe

Fig. 2. Ratioof pT-differential inelasticcross sections inpp collisions at √s= 5.44 TeV over5.02 TeV usingapowerlawinterpolationandtheeventgenerator PYTHIA 8.

pT

<

5 GeV

/

c as usedin [39].Thestatisticaluncertaintyofthepp

referenceisinterpolatedbetweenthereferencesat

√

s

=

5

.

02 TeV and7 TeV assumingalsoapower-lawdependenceandisassigned totheinterpolatedreference.Itamountsto7.8%atthemomentum intervalof30–50 GeV

/

c.

Asan alternative approach,the scaling ofthe measured cross section at

√

s

=

5

.

02 TeV to

√

s

=

5

.

44 TeV byusing theratioof spectraatthosetwoenergiesobtainedwiththePYTHIA 8(Monash tune)event generator [40] is studied. The ratio of the pp refer-encesat

√

s

=

5

.

44 TeV from thepower-law interpolationandat

√

s

=

5

.

02 TeV is shownin Fig.2 together with resultsobtained withthealternativemethod.Thespectrumisharderathigher col-lisionenergy,withasmallchangeinthetotalcrosssectionof4% below1 GeV

/

c and an increase of about 10% at transverse mo-mentaabove10 GeV

/

c.

3. Systematicuncertainties

Forthetotalsystematicuncertainty,allcontributionsareadded inquadratureandaresummarizedinTable2.

The effectof the selection of events based on the vertex po-sitionis studiedby comparing thefully corrected pT spectra

ob-tainedwithalternativevertexselectionscorresponding to

±

5 cm,

and

±

20 cm. The difference in the fully corrected pT spectra is

lessthan0.3%forcentralcollisions andlessthan0.5%for periph-eralcollisions.

In order to test the description of the detector response and thetrackreconstructioninthesimulation,allcriteriafortrack se-lectionare varied within theranges asdescribed in theprevious publication [5].Afull analysisisperformedby varyingone selec-tioncriterionatatime.Themaximumchangeinthecorrected pT

spectrum isthen considered assystematic uncertainty.The over-all systematic uncertainty related to track selection is obtained fromsummingupallindividual contributionsquadraticallyandit amountsto0.6–3.0%,dependingon pTandcentrality.

Thesystematicuncertaintyonthe secondary-particle contami-nation isestimatedbyvarying thefitmodelusingtwotemplates, i.e. forprimariesandsecondaries,orthreetemplates,i.e. primaries, secondaries from interactions in the detector material and sec-ondaries from weak decays of K0_s and



, aswell asvarying the fit ranges. The maximum difference between data and the two-component-template fit is summed in quadrature together with thedifferencebetweenresultsobtainedfromthetwo- and three-component-template fits. The systematic uncertainty due to the contamination fromsecondariesisdecreasing withincreasing pT.

Itdominatesatlow

p

Twithvaluesupto4%andisnegligibleabove

2 GeV

/

c.

Thesystematicuncertaintyontheprimaryparticlecomposition istakenfrom [5].Anadditionaluncertaintyisestimatedby assum-ing theparticlecomposition fromaneighboring



dNch

/

dη



range

tothe matchedone inthePb–Pbanalysisandisadded quadrati-cally.Thesumpeaksaround3 GeV

/

c with amaximumof5%(less than2%)forthe0–5%(70–80%)centralityclass.

In order to estimate the systematic uncertainty due to the tracking efficiency, the track matching betweenthe TPC andthe ITS informationin data andMonte Carlois compared after scal-ing the fraction of secondary particles obtained from the fits to the DCAxy distributions [5]. The difference in the TPC-ITS

track-matchingefficiencybetweendataandsimulationisassignedtothe corresponding systematicuncertainty(seeTable2). Itamounts to 2%incentralcollisions,andupto3.5%inperipheralcollisions.

ThematerialbudgetinALICEat

η

≈

0 amountsto

(

11

.

4

±

0

.

5

)

% inradiationlengthsforprimary chargedparticlesthat have suffi-cient tracklength inthe TPC [38].A difference intheamount of detectormaterialleadstodifferentamountsofsecondaryparticles thatareproduced.Afterthesubtractionofthecontributiondueto secondariesusingthethree-componentDCAxyfits,thedifferences

onthesecondarycorrectionfactorisnegligible.Avariationofthe materialbudget withinabovelimitsleads toa pT dependent

sys-tematicuncertaintyonthetrackingefficiencyof0.1–0.3%.

Theuncertaintyduetothefinite

p

T resolutionathighpTis

es-timated using the azimuthal dependence of the 1/pT spectra for

Table 2

Contributionstothesystematicuncertaintyinunitsofpercentforthe0–5%,30–40%,and70–80%centralityclassesinXe– Xecollisions.ThenumbersareaveragedinthepTintervalsfrom0.2–0.5 GeV/c (left),1–2 GeV/c (middle)and40–50 GeV/c (right).ForthepT-dependentsum,contributionsareaddedinquadrature.

Centrality (%) 0–5 (%) 30–40 (%) 70–80 (%)

pTrange (GeV/c) 0.2–0.5/1–2/40–50 0.2–0.5/1–2/40–50 0.2–0.5/1–2/40–50 Source

Vertex selection 0.2/0.2/0.2 0.8/0.8/0.8 0.8/0.8/0.8 Track selection 1.6/0.9/1.2 0.9/0.6/0.8 0.9/0.5/1.0 Secondary particles 1.4/0.2/negl. 0.8/0.2/negl. 0.6/0.2/negl. Particle composition 0.3/1.7/0.7 0.4/1.9/1.0 0.7/0.6/0.6 Tracking efficiency 1.9/1.2/0.4 2.2/1.2/0.4 2.2/1.4/0.6 Material budget 0.3/0.3/0.1 0.3/0.3/0.1 0.3/0.3/0.1

pTresolution negl./negl./0.5 negl./negl./0.7 negl./negl./0.9 Sum, pTdependent: 3.1/2.4/1.5 2.8/2.5/1.8 2.8/1.9/2.1 Centrality selection 0.1 0.8 3.2

positivelyandnegativelychargedparticles.Therelativeshiftofthe spectraforoppositelychargedparticlesalong1/pT determinesthe

size of uncertainty fora givenangle. The RMS of the 1/pT shift

asdistributed over the full azimuthis used as an additional in-creaseofthe pT resolution.Forthelowest pT bintheuncertainty

isestimatedfromtheunfoldingprocedureappliedtoMonteCarlo simulations.Theuncertaintyduetothefinite pT resolutionis

sig-nificantonlyatthelowestandhighestmomentabinsandamounts to0.5%atthelowst pT binforallcentralities and0.5% (0.9%)for

the0–5%(70–80%)centralityclass.

The uncertainty due to the centrality determination is esti-matedbychangingthefractionofthevisiblecrosssection

(

90

.

0

±

0

.

5

)

%. The uncertainty is estimatedfromthe variation of the re-sulting pT spectra and amounts to

∼

0.1% and

∼

3.2% for central

(0–5%)andperipheral(70–80%)collisions,respectively.

Thesystematicuncertaintyoftheppreferenceat

√

s

=

5

.

44 TeV has two contributions, which are added quadratically. For each

pT interval, the systematic uncertainty of the pp references at

√

s

=

5

.

02 TeV and

√

s

=

7 TeV areinterpolatedto

√

s

=

5

.

44 TeV by usinga power-law. Thiscorresponds tointerpolating between theupperandlowerboundariesoftheexperimentaldatapointsas givenby theirsystematicuncertainties.Itassumesfullcorrelation ofsystematicuncertaintiesatbothenergies.

Thedifferencebetweentheinterpolatedreferenceandtheone usingthePYTHIA 8eventgenerator isassignedastheother con-tributiontothesystematicuncertaintyintheppreference,ineach

pT interval. The systematicuncertaintyin thepp referencehasa

minimum of 2.2% around 1 GeV

/

c and reaches its maximum of 7.7%atthehighestmomentumbin.

4. Results

Thetransverse momentumspectra ofchargedparticlesin Xe– Xe collisions are shownin the top panel of Fig. 3 for nine cen-trality classes together with the interpolated pp reference spec-trumat

√

s

=

5

.

44 TeV. The latteris obtained fromthe interpo-lated pT-differential cross section by dividing it by the

interpo-lated inelastic nucleon-nucleon cross section of

(

68

.

4

±

0

.

5

)

mb at

√

s

=

5

.

44 TeV [24]. In the most-peripheralcollisions, the pT

spectrum issimilar to that ofpp collisions andexhibitsa power law behavior that is characteristic of hard-parton scattering and vacuumfragmentation. Withincreasingcollisioncentrality,the pT

differentialcrosssectionisprogressivelydepletedabove5 GeV

/

c.

Systematic uncertainties are shown in the bottom panel. At momenta between0.4 and10 GeV

/

c, the systematic uncertainty is dominated by the contribution from tracking and amounts to about2–3%.ItisalmostindependentofpTabove10 GeV

/

c with a

valueof1.4%(2.1%)forthe0–5%(70–80%)centralityclass. Inordertodeterminethenuclear modificationfactor RAA,the

interpolated pT-differential pp cross section is scaled by the

av-eragenuclear overlap function



TAA



.The resulting nuclear

mod-ification factor as a function of transverse momentum is shown inFig.4 forninecentrality classesandcomparedto resultsfrom Pb–Pb collisions [5]. The overall normalization uncertainties for

RAA are indicated by vertical bars around unity. The

uncertain-tiesoftheppreferenceandthecentralitydeterminationareadded in quadrature. The latter is larger for Xe–Xe collisions than for Pb–Pbbecauseofthelesspreciselyknownnuclear-charge-density distribution ofthe deformed 129_{Xe andthe resulting larger}

rela-tive uncertainty in



TAA



[18,19]. The nuclear modification factor

exhibitsa strong centrality dependencewith a minimumaround

pT

=

6–7 GeV

/

c and an almost linearrise above.In particular, in

the 5% mostcentral Xe–Xe collisions, atthe minimum,the yield is suppressed by a factor of about 6 with respect to the scaled pp reference. The nuclear modification factor reaches a value of

Fig. 3. TransversemomentumspectraofchargedparticlesinXe–Xecollisionsat

√

sNN=5.44 TeV inninecentralityclassestogetherwiththeinterpolatedpp refer-encespectrumat√s=5.44 TeV (toppanel)andsystematicuncertainties(bottom panel).

0.6 at the highest measured transverse-momentum interval of 30–50 GeV

/

c. Forcomparison,thenuclearmodificationfactor

R

AA

inPb–Pbcollisionsat

√

sNN

=

5

.

02 TeV isshowninFig.4asopen

circles forthe same centralityclassesas Xe–Xe.In both collision systems,asimilarcharacteristic

p

Tdependenceof

R

AAisobserved.

InPb–Pbcollisions,thesuppressionofhigh-momentumparticlesis apparentlystrongerforthesamecentralityclassbutstillin agree-mentwithXe–Xecollisionswithinuncertainties.

Nuclear modificationfactors from Xe–Xe andPb–Pb collisions andtheirratiosatsimilarrangesof



dNch

/

dη



areshowninFig.5.

In5% mostcentralXe–Xecollisions,the nuclearmodification fac-tor is remarkably well matched by 10–20% central Pb–Pb colli-sions over the entire pT range. ln the 30–40% Xe–Xe (40–50%

Pb–Pb) centrality class, again agreement is found within uncer-tainties.Thesefindingsofmatchingnuclearmodificationfactorsat similarrangesof



dNch

/

dη



areinagreementwithresultsfromthe

studyoffractionalmomentumlossofhigh-pTpartonsatRHICand

LHCenergies [41].

A comparison of the nuclear modification factors as a func-tion of



dNch

/

dη



in Xe–Xe and Pb–Pb collisions for three

dif-ferent regions of pT (low, medium, andhigh)is shownin Fig.6.

A remarkable similarity in RAA is observed between Xe–Xe

col-lision at

√

sNN

=

5

.

44 TeV and Pb–Pb collisions at

√

sNN

=

5

.

02

and 2.76 TeV when compared at identical ranges in



dNch

/

dη



,

for



dNch

/

dη

 >

400. This holds both at low momentum where

thehydrodynamicalexpansionofthemediumdominatesthe spec-trumandathighmomentum,wherepartonenergylossinsidethe

Fig. 4. NuclearmodificationfactorinXe–Xeat√sNN=5.44 TeV (filledcircles)andPb–Pbcollisions [5] at√sNN=5.02 TeV (opencircles)forninecentralityclasses.The verticallines(brackets)representthestatistical(systematic)uncertainties.Theoverallnormalizationuncertaintyisshownasafilledboxaroundunity.

Fig. 5. ComparisonofnuclearmodificationfactorsinXe–Xecollisions(filledcircles) andPb–Pbcollisions(opencircles) forsimilarrangesindNch/dηforthe 0–5% (left)and30–40%(right)Xe–Xecentralityclasses.Theverticallines(brackets) rep-resentthestatistical(systematic)uncertainties.

medium drives the spectral shape. At



dNch

/

dη

 <

400, the

val-ues of RAA still agree within rather large uncertainties although

nodefinitiveconclusioncanbedrawnbecause,inparticular,event selectionandgeometrybiasescouldaffectthespectrumin periph-eralA–Acollisions [42].

In a simplified radiative energy loss scenario when assum-ingidenticalthermalizationtimes [43,44],theaverageenergyloss



E



is proportional to the density of scattering centers in the medium,whichinturnisproportionaltotheenergydensity

ε

,and to thesquare ofthe pathlength L of theparton inthemedium,



E



∝

ε

·

L2 _{[22].The energydensitycan beestimatedfromthe}

average charged-particle multiplicity density [45] per transverse area,

ε

∝ 

dNch

/

dη

 /

AT. In central collisions, the initial

trans-verse area AT is related to the radius r of the colliding nuclei,

AT

=

π

·

r2 [22]. Therefore,the comparisonof themeasured RAA

valuesinthetwocollidingsystemscouldenableatestofthepath lengthdependenceofmedium-inducedpartonenergyloss [46].

Tofurtheraddressbulkproduction,theaveragetransverse mo-mentum



pT



intherangefrom0–10 GeV

/

c is derived.The

spec-tra are extrapolated downto pT

=

0 by fittinga Hagedorn

func-tion [47] in the range 0

.

15 GeV

/

c

<

pT

<

1 GeV

/

c. The relative

fractionoftheextrapolatedparticleyieldamountsto8%(11%)for the0–5%(70–80%)centralityclass.Statisticaluncertaintiesin



pT



are negligible. Systematic uncertainties are estimated by varying each source of systematic uncertainty in the spectra at a time, by varying thefitrange to0

.

15GeV

/

c

<

pT

<

0

.

5 GeV

/

c, andby

changingtheinterpolationrangeto0–0.2 GeV

/

c. Allcontributions arethenaddedquadratically.Therelativesystematicuncertaintyis 1.8%(1.3%)forthe0–5%(70–80%)centralityclass.

The average transverse momentum is presented in the top panelofFig.7forXe–Xecollisionsat

√

s

=

5

.

44 TeV (squares)and Pb–Pb collisions at

√

s

=

5

.

02 TeV (diamonds)for nine centrality classes.An increase of



pT



with centralityisvisiblein both

col-Fig. 6. ComparisonofthenuclearmodificationfactorinXe–Xeand Pb–Pb colli-sionsintegratedoveridenticalregionsinpTasafunctionofdNch/dη.Thevertical bracketsindicatethequadraticsumofthetotalsystematicuncertaintyinthe mea-surementandtheoverallnormalizationuncertaintyinTAA.Thehorizontalbars reflecttheRMSofthedistributionineachbin.Thedashedlinesshowresultsfrom power-lawfitstothedataandaredrawntoguidetheeye.

lisionsystemsandisattributedtotheincreasingtransverseradial flow. Thebottompanel ofFig.7 showsthe ratiosof



pT



inboth

collisionsystems.The ratioisflat withinuncertainties butallows forrelativevariations ofuptotwopercent.Comparisontoresults fromhydrodynamical calculations [43] are shown by the hashed areasforpions,kaonsandprotons.Whilethecalculationsarenot abletopredict absoluteparticlespectra,predictions aremadefor the relative difference in



pT



betweenboth collision systems in

ordertostudythesystemsizedependence.Thepredictedtrendof alarger



pT



in5%mostcentralXe–Xecollisionandcontinuously

lower values towards the 40–50% centrality class are consistent withthedata.

5. Summary

Transverse momentum spectra and nuclear modification fac-tors of chargedparticles in Xe–Xe collisions at

√

sNN

=

5

.

44 TeV

in the kinematic range 0

.

15

<

pT

<

50 GeV

/

c and

|

η

|

<

0

.

8 are

reportedfornine centralityclasses,inthe0–80%range.App ref-erence at

√

s

=

5

.

44 TeV is obtained by the interpolation ofthe existingspectraat

√

s

=

5

.

02 and7 TeV.Whencomparingnuclear modification factors at similar ranges of averaged charged parti-cle multiplicity densities, a remarkable similarity between cen-tral Xe–Xe collisions andPb–Pb collisions at a similar center-of-massenergyof

√

sNN

=

5

.

02 TeV and at2.76 TeV isobserved for

Fig. 7. AveragetransversemomentuminthepT-range0–10 GeV/c forXe–Xe colli-sionsat√s=5.44 TeV (squares)andPb–Pbcollisionsat√s=5.02 TeV (diamonds) forninecentralityclasses(top)andtheirratios(bottom).Theverticalbrackets indi-catesystematicuncertainties.Thehashedareasshowresultsfromhydrodynamical calculationsbyGiacaloneetal. [43].



dNch

/

dη

 >

400.Thecentralitydependenceoftheratioofthe

av-erage transversemomentum



pT



inXe–Xe collisions over Pb–Pb

collisions isflatwithin uncertaintiesbutallows forrelative varia-tionsofuptotwopercent.Predictionsfromhydrodynamical calcu-lationsthattakeintoaccountthesignificantlydifferentgeometries ofbothcollisionsystemsareconsistentwiththedata.

Acknowledgements

The ALICE collaboration would like to thank G. Giacalone, J. Noronha-Hostler, M. Luzum, and J.-Y. Ollitrault for providing the resultsoftheirhydrodynamicalcalculationspriortopublication.

The ALICECollaboration would like to thank all its engineers andtechniciansfortheirinvaluablecontributionstothe construc-tionoftheexperimentandtheCERNacceleratorteamsforthe out-standingperformanceoftheLHCcomplex.TheALICECollaboration gratefully acknowledges the resources and support provided by all Grid centresandthe WorldwideLHC ComputingGrid (WLCG) collaboration. The ALICE Collaboration acknowledges the follow-ingfundingagenciesfortheirsupportinbuildingandrunningthe ALICEdetector:A.I.AlikhanyanNationalScienceLaboratory (Yere-vanPhysics Institute)Foundation (ANSL),State Committeeof Sci-enceandWorld FederationofScientists(WFS), Armenia;Austrian AcademyofSciencesandNationalstiftungfürForschung, Technolo-gie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Universidade Federal do Rio Grande do Sul (UFRGS), Fi-nanciadoradeEstudoseProjetos(Finep)andFundaçãodeAmparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil; Ministry of Science & Technology of China (MSTC), National Natural Science Foundation of China (NSFC) and Ministry of Education of China (MOEC), China;Ministry of Science and Education, Croatia; Min-istryofEducation,Youth andSportsofthe CzechRepublic, Czech Republic; The Danish Council for Independent Research | Natu-ral Sciences, the Carlsberg Foundation and Danish National Re-search Foundation (DNRF), Denmark; Helsinki Institute ofPhysics

(HIP),Finland;Commissariatàl’EnergieAtomique(CEA)and Insti-tut Nationalde Physique Nucléaire etde Physique des Particules (IN2P3)andCentre National de laRecherche Scientifique (CNRS), France; Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and GSI Helmholtzzentrum für Schw-erionenforschung GmbH, Germany; General Secretariat for Re-search andTechnology,Ministry ofEducation, Researchand Reli-gions,Greece;NationalResearch,DevelopmentandInnovation Of-fice,Hungary;DepartmentofAtomicEnergy,GovernmentofIndia (DAE),DepartmentofScienceandTechnology,GovernmentofIndia (DST),University Grants Commission, Governmentof India(UGC) andCouncil ofScientificandIndustrialResearch(CSIR), India; In-donesian Institute of Science, Indonesia; Centro Fermi - Museo StoricodellaFisicaeCentroStudieRicercheEnricoFermiand Isti-tutoNazionalediFisicaNucleare(INFN),Italy;Institutefor Innova-tiveScienceandTechnology,NagasakiInstituteofAppliedScience (IIST),Japan Societyforthe PromotionofScience(JSPS)KAKENHI andJapanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan; Consejo Nacional de Ciencia (CONA-CYT)yTecnología,throughFondodeCooperaciónInternacionalen CienciayTecnología (FONCICYT)andDirección Generalde Asun-tosdelPersonalAcademico(DGAPA),Mexico;Nederlandse Organ-isatievoorWetenschappelijk Onderzoek(NWO),Netherlands; The ResearchCouncil ofNorway, Norway;CommissiononScienceand TechnologyforSustainableDevelopmentintheSouth(COMSATS), Pakistan;PontificiaUniversidadCatólicadelPerú,Peru;Ministryof ScienceandHigherEducationandNationalScienceCentre,Poland; KoreaInstituteofScienceandTechnologyInformationandNational ResearchFoundationofKorea(NRF),RepublicofKorea;Ministryof EducationandScientificResearch,Institute ofAtomicPhysicsand RomanianNationalAgencyforScience,TechnologyandInnovation, Romania; Joint Institute for Nuclear Research (JINR), Ministry of EducationandScienceoftheRussianFederationandNational Re-search Centre Kurchatov Institute, Russia; Ministry of Education, Science,Researchand SportoftheSlovak Republic, Slovakia; Na-tionalResearchFoundationofSouthAfrica,SouthAfrica;Centrode AplicacionesTecnológicasyDesarrolloNuclear(CEADEN), Cubaen-ergía,CubaandCentrodeInvestigacionesEnergéticas, Medioambi-entalesyTecnológicas(CIEMAT),Spain;SwedishResearchCouncil (VR)andKnut&AliceWallenbergFoundation(KAW),Sweden; Eu-ropean Organization for Nuclear Research, Switzerland; National Scienceand Technology DevelopmentAgency (NSDTA), Suranaree University of Technology (SUT) and Office of the Higher Educa-tionCommissionunderNRUprojectofThailand,Thailand;Turkish Atomic Energy Agency (TAEK), Turkey; NationalAcademy of Sci-encesofUkraine,Ukraine;ScienceandTechnologyFacilities Coun-cil (STFC), United Kingdom; National Science Foundation of the UnitedStatesofAmerica(NSF)andU.S.DepartmentofEnergy, Of-ficeofNuclearPhysics(DOENP),UnitedStatesofAmerica. References

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ALICECollaboration

S. Acharya

138

,

F.T.-. Acosta

22

,

D. Adamová

94

,

J. Adolfsson

81

,

M.M. Aggarwal

98

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G. Aglieri Rinella

36

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M. Agnello

33

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N. Agrawal

49

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Z. Ahammed

138

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S.U. Ahn

77

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S. Aiola

143

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A. Akindinov

65

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M. Al-Turany

104

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S.N. Alam

138

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D.S.D. Albuquerque

120

,

D. Aleksandrov

88

,

B. Alessandro

59

,

R. Alfaro Molina

73

,

Y. Ali

16

,

A. Alici

11

,

54

,

29

,

A. Alkin

3

,

J. Alme

24

,

T. Alt

70

,

L. Altenkamper

24

,

I. Altsybeev

137

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C. Andrei

48

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D. Andreou

36

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H.A. Andrews

108

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A. Andronic

141

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104

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M. Angeletti

36

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V. Anguelov

102

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C. Anson

17

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T. Antiˇci ´c

105

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F. Antinori

57

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P. Antonioli

54

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R. Anwar

124

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N. Apadula

80

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L. Aphecetche

112

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H. Appelshäuser

70

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S. Arcelli

29

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R. Arnaldi

59

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O.W. Arnold

103

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115

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I.C. Arsene

23

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M. Arslandok

102

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B. Audurier

112

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A. Augustinus

36

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R. Averbeck

104

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M.D. Azmi

18

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A. Badalà

56

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Y.W. Baek

61

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42

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S. Bagnasco

59

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R. Bailhache

70

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R. Bala

99

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A. Baldisseri

134

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M. Ball

44

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R.C. Baral

86

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A.M. Barbano

28

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R. Barbera

30

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F. Barile

53

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L. Barioglio

28

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G.G. Barnaföldi

142

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L.S. Barnby

93

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V. Barret

131

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P. Bartalini

7

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K. Barth

36

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E. Bartsch

70

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N. Bastid

131

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S. Basu

140

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G. Batigne

112

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B. Batyunya

76

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P.C. Batzing

23

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J.L. Bazo Alba

109

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I.G. Bearden

89

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H. Beck

102

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C. Bedda

64

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N.K. Behera

61

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I. Belikov

133

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F. Bellini

36

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H. Bello Martinez

2

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R. Bellwied

124

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L.G.E. Beltran

118

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V. Belyaev

92

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G. Bencedi

142

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S. Beole

28

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A. Bercuci

48

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Y. Berdnikov

96

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D. Berenyi

142

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R.A. Bertens

127

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D. Berzano

36

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59

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L. Betev

36

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P.P. Bhaduri

138

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A. Bhasin

99

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I.R. Bhat

99

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H. Bhatt

49

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B. Bhattacharjee

43

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J. Bhom

116

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A. Bianchi

28

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L. Bianchi

124

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N. Bianchi

52

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J. Bielˇcík

39

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J. Bielˇcíková

94

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A. Bilandzic

115

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103

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G. Biro

142

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R. Biswas

4

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S. Biswas

4

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J.T. Blair

117

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D. Blau

88

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C. Blume

70

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G. Boca

135

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F. Bock

36

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A. Bogdanov

92

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L. Boldizsár

142

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M. Bombara

40

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G. Bonomi

136

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M. Bonora

36

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H. Borel

134

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A. Borissov

20

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141

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M. Borri

126

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E. Botta

28

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C. Bourjau

89

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L. Bratrud

70

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P. Braun-Munzinger

104

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M. Bregant

119

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T.A. Broker

70

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M. Broz

39

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E.J. Brucken

45

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E. Bruna

59

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G.E. Bruno

36

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35

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D. Budnikov

106

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H. Buesching

70

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S. Bufalino

33

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P. Buhler

111

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P. Buncic

36

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O. Busch

130

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Z. Buthelezi

74

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J.B. Butt

16

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J.T. Buxton

19

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J. Cabala

114

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D. Caffarri

90

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H. Caines

143

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A. Caliva

104

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E. Calvo Villar

109

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R.S. Camacho

2

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P. Camerini

27

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A.A. Capon

111

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F. Carena

36

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W. Carena

36

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F. Carnesecchi

29

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11

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J. Castillo Castellanos

134

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A.J. Castro

127

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E.A.R. Casula

55

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C. Ceballos Sanchez

9

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S. Chandra

138

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B. Chang

125

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W. Chang

7

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S. Chapeland

36

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M. Chartier

126

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S. Chattopadhyay

138

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S. Chattopadhyay

107

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A. Chauvin

103

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115

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C. Cheshkov

132

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B. Cheynis

132

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V. Chibante Barroso

36

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D.D. Chinellato

120

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S. Cho

61

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P. Chochula

36

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T. Chowdhury

131

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P. Christakoglou

90

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C.H. Christensen

89

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P. Christiansen

81

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T. Chujo

130

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S.U. Chung

20

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C. Cicalo

55

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L. Cifarelli

11

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29

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F. Cindolo

54

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J. Cleymans

123

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F. Colamaria

53

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D. Colella

66

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36

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53

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A. Collu

80

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M. Colocci

29

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M. Concas

59

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i

,

G. Conesa Balbastre

79

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Z. Conesa del Valle

62

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J.G. Contreras

39

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T.M. Cormier

95

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Y. Corrales Morales

59

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P. Cortese

34

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M.R. Cosentino

121

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F. Costa

36

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S. Costanza

135

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J. Crkovská

62

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P. Crochet

131

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E. Cuautle

71

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L. Cunqueiro

141

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95

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T. Dahms

103

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115

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A. Dainese

57

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M.C. Danisch

102

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A. Danu

69

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D. Das

107

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I. Das

107

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S. Das

4

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A. Dash

86

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S. Dash

49

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S. De

50

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A. De Caro

32

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G. de Cataldo

53

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C. de Conti

119

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J. de Cuveland

41

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A. De Falco

26

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D. De Gruttola

11

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32

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N. De Marco

59

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S. De Pasquale

32

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R.D. De Souza

120

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D. Di Bari

35

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A. Di Mauro

36

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B. Di Ruzza

57

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R.A. Diaz

9

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T. Dietel

123

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P. Dillenseger

70

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Y. Ding

7

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R. Divià

36

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Ø. Djuvsland

24

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A. Dobrin

36

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D. Domenicis Gimenez

119

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B. Dönigus

70

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O. Dordic

23

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L.V.R. Doremalen

64

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A.K. Dubey

139

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A. Dubla

104

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L. Ducroux

132

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S. Dudi

98

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A.K. Duggal

98

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M. Dukhishyam

86

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P. Dupieux

131

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R.J. Ehlers

143

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D. Elia

53

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E. Endress

109

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H. Engel

75

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E. Epple

143

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B. Erazmus

112

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F. Erhardt

97

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M.R. Ersdal

24

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B. Espagnon

62

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G. Eulisse

36

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J. Eum

20

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D. Evans

108

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S. Evdokimov

91

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L. Fabbietti

103

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115

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M. Faggin

31

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J. Faivre

79

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A. Fantoni

52

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M. Fasel

95

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L. Feldkamp

141

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A. Feliciello

59

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G. Feofilov

137

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A. Fernández Téllez

2

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A. Ferretti

28

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A. Festanti

31

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36

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V.J.G. Feuillard

102

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J. Figiel

116

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M.A.S. Figueredo

119

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S. Filchagin

106

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D. Finogeev

63

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F.M. Fionda

24

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G. Fiorenza

53

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M. Floris

36

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S. Foertsch

74

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P. Foka

104

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S. Fokin

88

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E. Fragiacomo

60

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A. Francescon

36

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A. Francisco

112

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U. Frankenfeld

104

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G.G. Fronze

28

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U. Fuchs

36

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C. Furget

79

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A. Furs

63

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M. Fusco Girard

32

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J.J. Gaardhøje

89

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M. Gagliardi

28

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A.M. Gago

109

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K. Gajdosova

89

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M. Gallio

28

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C.D. Galvan

118

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P. Ganoti

84

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C. Garabatos

104

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E. Garcia-Solis

12

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K. Garg

30

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C. Gargiulo

36

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P. Gasik

115

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103

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E.F. Gauger

117

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M.B. Gay Ducati

72

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M. Germain

112

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J. Ghosh

107

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P. Ghosh

138

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S.K. Ghosh

4

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P. Gianotti

52

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P. Giubellino

104

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59

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P. Giubilato

31

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P. Glässel

102

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D.M. Goméz Coral

73

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A. Gomez Ramirez

75

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V. Gonzalez

104

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P. González-Zamora

2

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S. Gorbunov

41

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L. Görlich

116

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S. Gotovac

37

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V. Grabski

73

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L.K. Graczykowski

139

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K.L. Graham

108

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L. Greiner

80

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A. Grelli

64

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C. Grigoras

36

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V. Grigoriev

92

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A. Grigoryan

1

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S. Grigoryan

76

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J.M. Gronefeld

104

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F. Grosa

33

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J.F. Grosse-Oetringhaus

36

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R. Grosso

104

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R. Guernane

79

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B. Guerzoni

29

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M. Guittiere

112

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K. Gulbrandsen

89

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T. Gunji

129

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A. Gupta

99

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R. Gupta

99

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I.B. Guzman

2

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R. Haake

36

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M.K. Habib

104

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C. Hadjidakis

62

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H. Hamagaki

82

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G. Hamar

142

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J.C. Hamon

133

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R. Hannigan

117

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M.R. Haque

64

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J.W. Harris

143

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A. Harton

12

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H. Hassan

79

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D. Hatzifotiadou

54

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11

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S. Hayashi

129

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S.T. Heckel

70

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E. Hellbär

70

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H. Helstrup

38

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A. Herghelegiu

48

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E.G. Hernandez

2

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G. Herrera Corral

10

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F. Herrmann

141

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K.F. Hetland

38

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T.E. Hilden

45

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H. Hillemanns

36

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C. Hills

126

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B. Hippolyte

133

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B. Hohlweger

103

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D. Horak

39

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S. Hornung

104

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R. Hosokawa

130

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79

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P. Hristov

36

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C. Huang

62

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C. Hughes

127

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P. Huhn

70

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T.J. Humanic

19

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H. Hushnud

107

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N. Hussain

43

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T. Hussain

18

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D. Hutter

41

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21

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J.P. Iddon

126

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71

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R. Ilkaev

106

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M. Inaba

130

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M. Ippolitov

88

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M.S. Islam

107

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M. Ivanov

104

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V. Ivanov

96

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V. Izucheev

91

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B. Jacak

80

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N. Jacazio

29

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P.M. Jacobs

80

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M.B. Jadhav

49

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S. Jadlovska

114

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J. Jadlovsky

114

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S. Jaelani

64

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C. Jahnke

119

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115

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M.J. Jakubowska

139

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M.A. Janik

139

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C. Jena

86

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M. Jercic

97

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R.T. Jimenez Bustamante

104

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M. Jin

124

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P.G. Jones

108

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A. Jusko

108

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P. Kalinak

66

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A. Kalweit

36

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J.H. Kang

144

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V. Kaplin

92

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S. Kar

7

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A. Karasu Uysal

78

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O. Karavichev

63

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T. Karavicheva

63

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P. Karczmarczyk

36

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E. Karpechev

63

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U. Kebschull

75

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R. Keidel

47

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D.L.D. Keijdener

64

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M. Keil

36

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B. Ketzer

44

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Z. Khabanova

90

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S. Khan

18

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S.A. Khan

138

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A. Khanzadeev

96

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Y. Kharlov

91

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A. Khatun

18

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A. Khuntia

50

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M.M. Kielbowicz

116

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B. Kileng

38

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B. Kim

130

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D. Kim

144

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D.J. Kim

125

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E.J. Kim

14

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H. Kim

144

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J.S. Kim

42

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J. Kim

102

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M. Kim

61

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102

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S. Kim

21

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T. Kim

144

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T. Kim

144

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S. Kirsch

41

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I. Kisel

41

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S. Kiselev

65

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A. Kisiel

139

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J.L. Klay

6

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C. Klein

70

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J. Klein

36

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59

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C. Klein-Bösing

141

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S. Klewin

102

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A. Kluge

36

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M.L. Knichel

36

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A.G. Knospe

124

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C. Kobdaj

113

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M. Kofarago

142

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M.K. Köhler

102

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T. Kollegger

104

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N. Kondratyeva

92

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E. Kondratyuk

91

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A. Konevskikh

63

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M. Konyushikhin

140

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O. Kovalenko

85

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V. Kovalenko

137

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M. Kowalski

116

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I. Králik

66

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A. Kravˇcáková

40

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L. Kreis

104

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M. Krivda

66

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108

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F. Krizek

94

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M. Krüger

70

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E. Kryshen

96

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M. Krzewicki

41

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A.M. Kubera

19

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V. Kuˇcera

94

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61

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C. Kuhn

133

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P.G. Kuijer

90

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J. Kumar

49

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L. Kumar

98

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S. Kumar

49

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S. Kundu

86

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P. Kurashvili

85

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A. Kurepin

63

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A.B. Kurepin

63

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A. Kuryakin

106

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S. Kushpil

94

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M.J. Kweon

61

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Y. Kwon

144

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S.L. La Pointe

41

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P. La Rocca

30

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Y.S. Lai

80

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I. Lakomov

36

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R. Langoy

122

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K. Lapidus

143

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C. Lara

75

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A. Lardeux

23

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P. Larionov

52

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E. Laudi

36

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R. Lavicka

39

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R. Lea

27

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L. Leardini

102

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S. Lee

144

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F. Lehas

90

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S. Lehner

111

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J. Lehrbach

41

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R.C. Lemmon

93

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E. Leogrande

64

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I. León Monzón

118

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P. Lévai

142

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X. Li

13

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7

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J. Lien

122

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R. Lietava

108

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B. Lim

20

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S. Lindal

23

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V. Lindenstruth

41

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S.W. Lindsay

126

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C. Lippmann

104

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M.A. Lisa

19

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V. Litichevskyi

45

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A. Liu

80

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H.M. Ljunggren

81

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W.J. Llope

140

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D.F. Lodato

64

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V. Loginov

92

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C. Loizides

80

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95

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P. Loncar

37

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X. Lopez

131

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E. López Torres

9

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A. Lowe

142

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P. Luettig

70

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J.R. Luhder

141

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M. Lunardon

31

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G. Luparello

60

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36

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63

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M. Mager

36

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S.M. Mahmood

23

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133

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R.D. Majka

143

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M. Malaev

96

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Q.W. Malik

23

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L. Malinina

76

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ii

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D. Mal’Kevich

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P. Malzacher

104

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A. Mamonov

106

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V. Manko

88

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F. Manso

131

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V. Manzari

53

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7

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M. Marchisone

74

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128

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132

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J. Mareš

68

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27

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54

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J. Margutti

64

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104

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36

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2

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G. Martínez García

112

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M. Martinez Pedreira

36

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104

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M. Masera

28

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55

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L. Massacrier

62

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E. Masson

112

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