EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP-2012-060
Submitted to: Physics Letters B
Measurement of the WW cross section in
√
s
= 7 TeV
pp
collisions with the ATLAS detector and
limits on anomalous gauge couplings
The ATLAS Collaboration
Abstract
This Letter reports a measurement of the WW production cross section in
√
s
= 7 TeV pp collisions
using data corresponding to an integrated luminosity of 1.02 fb
−1collected with the ATLAS detector.
Using leptonic decays of oppositely charged W bosons, the total measured cross section is σ(pp →
WW)
= 54.4 ± 4.0 (stat.) ± 3.9 (syst.) ± 2.0 (lumi.) pb, consistent with the Standard Model prediction of
σ(pp → WW) = 44.4 ± 2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted
from a fit to the transverse-momentum distribution of the leading charged lepton in the event.
Measurement of the WW cross section in
√
s
= 7 TeV pp collisions with the
ATLAS detector and limits on anomalous gauge couplings
The ATLAS Collaboration
Abstract
This Letter reports a measurement of the WW production cross section in √s = 7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb−1collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is σ(pp → WW)= 54.4 ± 4.0 (stat.) ± 3.9 (syst.) ± 2.0 (lumi.) pb, consistent with the Standard Model prediction of σ(pp → WW)= 44.4 ± 2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event.
Keywords:
1. Introduction
Measurements of WW production at the LHC pro-vide important tests of the Standard Model (SM), in par-ticular of the WWZ and WWγ triple gauge couplings (TGCs) resulting from the non-Abelian nature of the SU(2)L × U(1)Y symmetry group. Precise measure-ments of TGCs are sensitive probes of new physics in the electroweak sector and are complementary to direct searches. Furthermore, since WW production is a back-ground to possible new processes such as the production of the SM Higgs boson, a precise measurement of the WWcross section is an important step in the search for new physics.
This Letter describes the measurements of the WW cross section and of TGCs in pp collisions at √s = 7 TeV. The dominant SM WW production mechanisms are s-channel and t-channel quark-antiquark annihila-tion, with a 3% contribution from gluon-gluon fusion. The cross section is measured in the fiducial phase space of the detector using WW → lνlν decays in final states with electrons and muons, and is extrapolated to the to-tal phase space. The fiducial phase space includes geo-metric and kinematic acceptance. The total production cross section of oppositely charged W bosons is mea-sured according to the equation [1]
σ(pp → WW) = Ndata− Nbg AWWCWWLB
, (1)
where Ndata and Nbg are the number of observed data
events and estimated background events, respectively, AWWis the kinematic and geometric acceptance, CWWis the ratio of the number of measured events to the num-ber of events produced in the fiducial phase space, L is the integrated luminosity of the data sample, and B is the branching ratio for both W bosons to decay to eν or µν (including decays through tau leptons with addi-tional neutrinos). The fiducial cross section is defined as σ × AWW× B [1].
Previous measurements of WW production using the CMS and ATLAS detectors, both based on the data recorded in 2010 and corresponding to an integrated luminosity of 36 pb−1, have found σ(pp → WW) = 41.1 ± 15.3 (stat.) ± 5.8 (syst.) ± 4.5 (lumi.) pb [2] and
σ(pp → WW) = 41+20
−16(stat.) ± 5 (syst.) ± 1 (lumi.) pb [3], respectively. CMS has additionally used these data to set limits on anomalous gauge-coupling parameters at higher center of mass energies than corresponding mea-surements at the Tevatron [4] and LEP [5].
2. ATLAS detector
The ATLAS detector [6] consists of an inner track-ing system (inner detector, or ID) surrounded by a su-perconducting solenoid providing a 2 T magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer (MS) incorporating three large supercon-ducting toroid magnets arranged with an eight-fold az-imuthal coil symmetry around the calorimeters. The ID
consists of silicon pixel and microstrip detectors, sur-rounded by a transition radiation tracker. The electro-magnetic calorimeter is a lead/liquid-argon (LAr) detec-tor. Hadron calorimetry is based on two different detec-tor technologies, with scintilladetec-tor tiles or LAr as active media, and with either steel, copper, or tungsten as the absorber material. The MS comprises three layers of chambers for the trigger and for track measurements.
A three-level trigger system is used to select events. The level-1 trigger is implemented in hardware and uses a subset of detector information to reduce the event rate to a design value of at most 75 kHz. This is followed by two software-based trigger levels, level-2 and the event filter, which together reduce the event rate to about 200 Hz recorded for analysis.
The nominal pp interaction point at the centre of the detector is defined as the origin of a right-handed co-ordinate system. The positive x-axis is defined by the direction from the interaction point to the centre of the LHC ring, with the positive y-axis pointing upwards, while the z-axis is along the beam direction. The az-imuthal angle φ is measured around the beam axis and the polar angle θ is the angle from the z-axis. The pseu-dorapidity is defined as η= − ln tan(θ/2).
3. Data sample and event selection
The data used for this analysis correspond to an inte-grated luminosity of 1.02 ± 0.04 fb−1[7], recorded be-tween April and June of 2011. Events are selected with triggers requiring either a single electron with pT > 20 GeV and |η| < 2.5 or a single muon with pT > 18 GeV and |η| < 2.4. Additional data collected with a trigger requiring a single muon with pT > 40 GeV, |η| < 1.05, and looser identification criteria are used to increase efficiency. The combination of triggers results in ≈ 100% (98%) trigger efficiency for events with WW decays to eνµν and eνeν (µνµν) passing the selection described below.
The WW event selection begins with the identifica-tion of electrons and muons, requiring exactly two of these particles with opposite charge. Electrons are re-constructed with a clustering algorithm in the electro-magnetic calorimeter and matched to an ID track. To distinguish electrons from hadrons, selection criteria [8] are applied based on the quality of the position and mo-mentum match between the extrapolated track and the calorimeter cluster, the consistency of the longitudinal and lateral shower profiles with an incident electron, and the observed transition radiation in the TRT. Elec-trons are required to lie within the fiducial regions of the calorimeters (|η| < 1.37 or 1.52 < |η| < 2.47), have
pT > 25 GeV (pT > 20 GeV for the lower pT elec-tron in the eνeν decay channel), and be isolated in the calorimeter and tracker. Calorimeter isolation requires the summed transverse energies deposited in calorime-ter cells, excluding those belonging to the electron clus-ter, in a cone of radius ∆R = p(∆η)2+ (∆φ)2 = 0.3 around the electron direction to be < 4 GeV. Tracker isolation requires the summed pTof ID tracks in a cone of radius∆R = 0.2 centered on and excluding the elec-tron track to be < 10% of the elecelec-tron pT.
The muon reconstruction algorithm begins with a track from the MS to determine the muon’s η, and then combines it with an ID track to determine the muon’s momentum [9]. Muons are required to have pT > 20 GeV and |η| < 2.4, and in the µνµν channel at least one muon must have pT > 25 GeV. Decays of hadrons to muons are suppressed using calorimeter and track iso-lation. The calorimeter isolation requires the summed transverse energies deposited in calorimeter cells in a cone of radius ∆R = 0.2 around the muon track to be less than 15% of the muon’s pT. The track isolation requirement is the same as for electrons. The tracks as-sociated with muon and electron candidates must have longitudinal and transverse impact parameters consis-tent with originating from the primary reconstructed vertex. The primary vertex is defined as the vertex with the highestP p2
Tof associated ID tracks.
The presence of neutrinos is characterized by an im-balance of transverse momentum in the event. The missing transverse momentum (Emiss
T ) is the modulus of the event −~pT vector, calculated by summing the transverse momentum determined from each calorime-ter cell’s energy and direction with respect to the pri-mary vertex. Cells with |η| < 4.5 are used in the cal-culation and a correction is applied to account for the momentum of measured muons.
Misreconstructed leptons and jets, as well as leptons from tau decays, are suppressed by applying cuts on ETmiss× sin∆φ when ∆φ < π/2. Here, ∆φ is the az-imuthal angle between the missing transverse momen-tum and the nearest charged lepton or jet; small∆φ in-dicates that EmissT is dominated by a mismeasured lepton or jet, or by the presence of neutrinos in the direction of the lepton or jet, as would occur in a tau decay. The lower cuts on Emiss
T , or E miss
T × sin∆φ for ∆φ < π/2, are 25 GeV in the eνµν channel, 40 GeV in the eνeν chan-nel, and 45 GeV in the µνµν channel. The thresholds in the eνeν and µνµν channels are more stringent than in the eνµν channel to suppress the background from Drell-Yan (DY) production of ee and µµ pairs.
by vetoing events containing a reconstructed jet with pT > 25 GeV and |η| < 4.5. Jets are reconstructed with the anti-kt algorithm [10] with a radius parame-ter of R = 0.4. A further 30% reduction of top-quark background is achieved by rejecting events with a jet with pT > 20 GeV, |η| < 2.5, and identified as originat-ing from a b-quark (b-jet). The identification of b-jets combines information from the impact parameters and the reconstructed vertices of tracks within the jet [11]. The additional b-jet rejection reduces WW acceptance by 1.3%.
Resonances with dilepton decays are removed by re-quiring ee and µµ invariant masses to be greater than 15 GeV and not within 15 GeV of the Z-boson mass. To suppress backgrounds from heavy-flavour hadron de-cays, events with an eµ invariant mass below 10 GeV are also removed. The complete event selection yields 202 eνµν, 59 eνeν, and 64 µνµν candidates.
4. Background estimation
The selected data sample contains 26 ± 3% back-ground to the WW production process (Table 1). In decreasing order of size, the main background pro-cesses are: DY production of dileptons, with significant Emiss
T arising from misreconstructed jet(s) or charged lepton(s); t¯t and tWb production, where the b-quarks in the WWb¯b final state are not rejected by the jet veto; (W → lν)+ jet, where the jet is misidentified as a lep-ton; WZ → lνll production, where one lepton is not reconstructed; (W → lν)+ γ, where the photon con-verts in the inner detector and is misreconstructed as an electron; ZZ → llνν production; and cosmic-ray muons overlapping a pp collision (which is negligible).
Backgrounds are estimated using a combination of Monte Carlo (MC) samples including a full geant [12] simulation of the ATLAS detector [13], and control samples (independent of the measurement sample) from data. The simulation includes the modeling of multiple ppinteractions in the same bunch crossing (pile-up), as well as corrections (determined from data) to improve the modeling of reconstructed objects.
The DY background is estimated using the alpgen [14] Monte Carlo generator interfaced to pythia [15] for parton showering. To test the modeling of Emiss
T , data are compared to simulated Z/γ∗events where the lepton pair forms an invariant mass within 15 GeV of the Z-boson mass. The DY MC accurately models the number of events above the thresholds on Emiss
T or E
miss
T × sin∆φ used to select WW events, after subtracting the ≈ 20% non-DY contributions. A 12% relative systematic
un-certainty on the DY prediction is taken from the statisti-cal precision of the MC validation in the control sample.
Jet Multiplicity 0 1 2 3 4 5 6 7 8 9 Events 0 100 200 300 400 500 600 700 800 900 ATLAS -1 Ldt = 1.02 fb ∫ = 7 TeV s Data ν l ν l → WW Drell-Yan Top W+jets/Dijet Diboson stat+syst σ
Figure 1: The multiplicity distribution of jets with pT > 25 GeV for
the combined dilepton channels, after all WW selection cuts except the jet veto requirement. The systematic uncertainties shown in the >0-jet bins include only those on the integrated luminosity and the theoretical cross sections.
Background from top-quark production arises when the final-state b-quarks have low transverse momen-tum (pT < 20 GeV), are not identified as b-jets (for 20 < pT < 25 GeV), or are in the far forward region (|η| > 4.5). To model this background, mc@nlo [16] samples of t¯t and AcerMC [17] samples of tWb pro-duction are used, respectively, with corrections derived from the data. An overall normalization factor is deter-mined from the ratio of events in data to those predicted by the top-quark MC using the WW selection without any jet rejection. This sample is dominated by top-quark decays, as shown in Fig. 1; a 24% contribution from other processes is subtracted in the normalization. The subtraction of the WW component is based on the SM prediction of WW production, with an uncertainty that covers the difference between the prediction and the cross section measurement reported in this Letter. The relative cross sections of t¯t to tWb are set by the gen-erator calculations of σ = 164.6 pb and σ = 15.6 pb, respectively.
A key aspect of the top-quark background prediction is the modeling of the jet veto acceptance. To reduce the associated uncertainties, a data-based correction is de-rived using a top-quark-dominated sample based on the WW selection but with the requirement of at least one b-jet with pT > 25 GeV [18]. In this sample, the ratio P1of events with one jet to the total number of events is sensitive to the modeling of the jet energy spectrum in top-quark events. A multiplicative correction based on
Table 1: The estimated background event yields in the selected WW data sample. The first uncertainty is statistical, the second systematic.
Production process eνµν selection eνeν selection µνµν selection
DY 13.0 ± 2.1 ± 1.6 12.5 ± 2.3 ± 1.4 10.9 ± 2.5 ± 1.4
Top 11.9 ± 1.8 ± 2.4 3.1 ± 0.5 ± 0.6 3.8 ± 0.6 ± 0.8
W+ jet 10.0 ± 1.6 ± 2.1 4.1 ± 1.3 ± 0.9 4.2 ± 1.1 ± 1.3
Diboson 5.1 ± 1.0 ± 0.7 2.1 ± 0.8 ± 0.3 2.9 ± 0.4 ± 0.4
Total background 40.0 ± 3.3 ± 3.6 21.7 ± 2.8 ± 1.8 21.8 ± 2.8 ± 2.1
the ratio Pdata
1 /P
MC
1 is applied to reduce the uncertainties resulting from the jet veto requirement. The residual un-certainty on the background prediction due to jet energy scale and resolution is small (4%) compared to uncer-tainties from the b-quark identification efficiency (6%), parton shower modeling (12%), statistical uncertainty on the Pdata
1 /P
MC
1 -based correction (12%), and unmod-eled t¯t-tWb interference and higher order QCD correc-tions (15%). As a cross-check, the normalization of the top-quark background is extracted from a fit to the jet multiplicity distribution; the result is consistent with the primary estimate.
The W+ jet process contributes to the selected sam-ple when one or more hadrons in the jet decay to, or are misidentified as, a charged lepton. Jets reconstructed as electrons or muons predominantly arise from misiden-tification or heavy-flavour quark decays, respectively. This background is estimated with a pass-to-fail ratio fe ( fµ), defined as the ratio of the number of electron (muon) candidates passing the electron (muon) identi-fication criteria to the number of candidates failing the criteria. These ratios are measured in data samples dom-inated by hadronic jets collected with a trigger requir-ing an electromagnetic cluster or a muon candidate. All candidates are required to pass a loose set of selection criteria, including an isolation requirement. The mea-sured feand fµare then applied as multiplicative factors to events satisfying all WW selection cuts except with one lepton failing the identification criteria but passing the looser criteria.
The above procedure measures fe and fµ ratios av-eraged over misidentified jets and heavy-flavour quark decays in jet-dominated samples. If, for example, the ratio fediffers for these two contributions, the W + jet prediction could be biased. To address this issue, two sets of loose criteria are applied to electron candidates, one based on the track and the shower profile and ex-pected to enhance the misidentification fraction, and the other based on the isolation and expected to enhance the heavy flavour fraction. The feratio is measured for these criteria separately in events where there is an
addi-tional b-jet and events where there is no such jet. From the combination of measurements, the heavy-flavour and misidentification contributions are separated; the re-sulting W + jet background is consistent with that ob-tained using the inclusive fe for the misidentification and heavy-flavour components. A similar separation is not performed for fµ, since heavy-flavour decays domi-nate the contribution of background muons from the W + jet process.
The systematic uncertainty on the W+ jet prediction is dominated by a 30% variation of the ratios feand fµ with the jet pTthreshold. This variation is sensitive to the relative fraction of quarks and gluons in the samples used to measure feand fµ, and thus encompasses poten-tial differences in feand fµratios between these samples and those used to estimate the W+ jet background.
Several alternative methods are used to check the W + jet prediction and give consistent results. The first method applies the measured fe and fµratios to an in-clusive W + jets data sample, and then determines the fraction of expected events with no additional jets using W+ jets Monte Carlo events with two identified leptons. The second method defines different sets of “loose” lep-ton criteria and independently measures efficiencies for lepton identification and rates for misidentified or de-caying hadrons to pass the standard identification crite-ria. Background from dijet production is estimated with this method and is found to be small; it is implicitly in-cluded in the primary estimate.
Monte Carlo estimates of the Wγ, WZ, and ZZ back-grounds are obtained using a combination of alpgen and pythia (for Wγ) and herwig [19] with jimmy [20] (for the others), normalized to the next-to-leading order (NLO) cross sections calculated with mcfm [21]. The O(10%) systematic uncertainty on these backgrounds is domi-nated by the uncertainty on the jet energy scale.
5. WW acceptance modeling
The WW total cross section measurement requires the knowledge of the AWW and CWW factors given in
Eq. 1. The acceptance factor AWW is defined as the ra-tio of generated WW events in the fiducial phase space to those in the total phase space. The correction fac-tor CWW is defined as the ratio of measured events to generator-level events in the fiducial phase space. The value of this ratio is determined primarily by lepton trig-ger and identification efficiencies, with a small contribu-tion from differences in generated and measured phase space due to detector resolutions. The fiducial phase space is defined at generator level as:
• Muon pT > 20 GeV and |η| < 2.4 (pT > 25 GeV for at least one muon in the µνµν channel); • Electron pT > 20 GeV and either |η| < 1.37 or
1.52 < |η| < 2.47 (pT > 25 GeV in the eνµν nel and for at least one electron in the eνeν chan-nel);
• No anti-ktjet (R = 0.4) with pT > 25 GeV, |η| < 4.5, and∆R(e,jet) > 0.3;
• No anti-kt jet with pT > 20 GeV, |η| < 2.5, ∆R(e,jet) > 0.3, and ∆R(b,jet) < 0.3, where the b-quark has pT> 5 GeV;
• Neutrino |P~p
T| or |P~pT| × sin∆φ (for ∆φ < π/2) > 45, 40, 25 GeV in the µνµν, eνeν and eνµν chan-nels, respectively (∆φ is the azimuthal angle be-tween the neutrinoP~p
T and the nearest charged lepton);
• m`` > 15 (10) GeV in the µνµν and eνeν channels (eνµν channel);
• |m``−mZ|> 15 GeV in the µνµν and eνeν channels, where mZ is the Z boson mass. To reduce the depen-dence on the model of QED final-state radiation, the electron and muon pT include contributions from pho-tons within∆R = 0.1 of the lepton direction.
Estimates of AWW and CWW are based on samples of
q¯q → WW and gg → WW events generated with
mc@nlo and gg2WW [22], respectively. Initial parton momenta are modeled with CTEQ 6.6 [23] parton distri-bution functions (PDFs). The underlying event and par-ton showering are modeled with jimmy, and hadroniza-tion and tau-lepton decays with herwig. Data-based cor-rections measured with W and Z boson data are applied to reduce uncertainties, as described below. Because the corrections are applied to WW MC samples, residual uncertainties on the fiducial cross section measurement are based on the kinematics of SM WW production.
The combined factor AWW× CWW is estimated sepa-rately for each leptonic decay channel, including decays
to tau leptons (Table 2). Tau-lepton decays to hadrons are not included in the denominator for the acceptances in the table. The impact of pile-up is modeled by adding pythia-generated low-Q2events to the WW MC accord-ing to the distribution of the number of additional colli-sions in the same bunch crossing in the data. Effects on detector response from nearby bunches are also mod-eled using this distribution.
A correction to the q ¯q → WW MC modeling of the jet veto is derived using Z-boson data. The fraction of Z-boson events with no additional jets is compared be-tween data and mc@nlo simulated samples. The ratio of this fraction in data to the fraction in the MC is applied as a multiplicative correction factor of 0.963 to the WW MC. The correction reduces the uncertainties due to jet energy scale and resolution to 1.1%. A theoretical un-certainty of 5.0% on the jet veto acceptance contributes the largest uncertainty to AWW, as shown in Table 3.
Contributions to Emiss
T include energy from the in-teracting protons’ remnants (the underlying event), and from pile-up. The dominant uncertainty arises from the detector response to the underlying event, and is evaluated by varying the individual calorimeter cell en-ergy deposits in the MC [24]. To determine the un-certainty due to additional pp interactions in the same bunch crossing as the hard-scattering process, the event ~pTmeasured with the calorimeter is compared between data and MC in Z → µµ events. The mean |~pT| as a function of the number of reconstructed vertices agrees to within 3% between data and MC, yielding a negli-gible uncertainty on the WW acceptance. The effect of collisions from other bunch crossings is studied by split-ting Z-boson samples in data and MC according to the bunch position in the LHC train, and by smearing Emiss
T in the simulation samples to match the acceptance of a given Emiss
T cut in the data samples. The resulting uncer-tainty on the WW acceptance is small.
The efficiencies for triggering, reconstructing, and identifying charged leptons are measured as a function of lepton pTand η using Z boson events and (for elec-trons) W boson events [1]. Corrections to the MC de-rived from these data are within 1% of unity for trigger and muon identification efficiencies and deviate from unity by up to 11% at low pT for the electron identi-fication efficiency. Uncertainties on the corrections are largely due to the limited number of events available for the measurements and, in case of electron identification, from the estimate of the jet background contamination.
Finally, there are small uncertainties on the WW pro-duction model. Uncertainties on PDFs are determined using the CTEQ eigenvectors and the acceptance dif-ferences between the CTEQ 6.6 and MSTW 2008 PDF
Table 2: The total WW acceptance AWW× CWWin the individual decay channels, and the expected number of SM WW events (NWW) for an
integrated luminosity of 1.02 fb−1.
eνµν selection eνeν selection µνµν selection
WW → eνµν WW → lντν WW → eνeν WW → eντν WW →µνµν WW →µντν
AWW× CWW 10.8% 3.0% 4.4% 1.1% 7.6% 1.6%
NWW 114.9 12.0 23.4 2.3 40.3 3.3
Table 3: Relative uncertainties, in percent, on the estimate of the product AWW× CWWfor the individual WW decay channels. The uncertainty on
AWW(CWW) receives contributions from the last three (first six) sources.
Relative uncertainty (%)
Source of uncertainty eνµν selection eνeν selection µνµν selection
Trigger efficiency 1.0 1.0 1.0
Lepton efficiency 2.3 4.1 1.8
Lepton pTscale and resolution 0.4 1.0 0.1
ETmissmodeling 0.6 1.0 2.2
Jet energy scale and resolution 1.1 1.1 1.1
Lepton acceptance 2.0 2.1 1.6
Jet veto acceptance 5.0 5.0 5.0
PDFs 1.4 1.2 1.2
Total 6.2 7.2 6.2
sets [25]. The impact of unmodeled higher-order contri-butions is estimated by varying the renormalization and factorization scales coherently by factors of 2 and 1/2.
The total acceptance uncertainty on the three chan-nels combined is 6.2%.
6. Cross section results
The WW cross section is measured in the fiducial phase space and extrapolated to the total phase space. The total cross section is defined in Eq. 1, while the fiducial cross section is
σfid=
Ndata− Nbg
LCWW
. (2)
Uncertainties on the fiducial cross section measurement result from modeling lepton and jet efficiency, energy scale and resolution, and ETmiss (the first five rows of Table 3). Small uncertainties of 1.4% (µνµν and eνeν channels) and 0.5% (eνµν channel) arise from the im-pact of QCD renormalization and factorization scale variations on lepton momenta (included in the sixth row of Table 3). Table 4 shows CWW and the other compo-nents of the cross section measurements for each chan-nel. The measurements are performed by minimizing a likelihood fit to the observed data with respect to the
WW and background predictions for the three chan-nels combined. The measured cross sections are consis-tent with the SM predictions, differing by +1.7σ (eνµν channel),+1.3σ (eνeν channel) and −0.1σ (µνµν chan-nel). Contributions from a hypothetical SM Higgs bo-son would be small: 2.9, 0.9, and 1.8 events in the eνµν, eνeν and µνµν channels, respectively, for a Higgs boson mass of 125 GeV.
The AWW uncertainty comes from PDFs and scale variations affecting the lepton and jet veto acceptances (the last three rows of Table 3). The combined AWW × CWW and the total measured cross section in each chan-nel are shown in Table 4. The contribution of leptons from tau decays is included. The channels are combined by maximizing a log likelihood, yielding
σ(pp → WW) =
54.4 ± 4.0 (stat.) ± 3.9 (syst.) ± 2.0 (lumi.) pb, to be compared with the NLO SM prediction of σ(pp → WW) = 44.4 ± 2.8 pb [16, 22]. Figure 2 shows the following distributions for data and MC: Emiss
T , trans-verse mass, the azimuthal angle between the charged leptons [∆φ(l, l)], and invariant mass of the charged leptons [m``]. The transverse mass is mT(llEmissT ) =
Table 4: The measured total (σ(pp → WW)) and fiducial (σfid) cross sections and the components used in the calculations, as well as the SM
predictions for the fiducial cross sections (σSM
fid). The first uncertainty is statistical and the second systematic. The 3.7% relative uncertainty on the
integrated luminosity is the third uncertainty on the measured cross sections. The uncertainties on σSM
fid are highly correlated between the channels.
eνµν selection eνeν selection µνµν selection
Data 202 59 64 Background 40.0 ± 3.3 ± 3.6 21.7 ± 2.8 ± 1.8 21.8 ± 2.8 ± 2.1 CWW 0.541 ± 0.005 ± 0.022 0.396 ± 0.005 ± 0.019 0.721 ± 0.005 ± 0.025 AWW 0.161 ± 0.001 ± 0.008 0.089 ± 0.001 ± 0.005 0.082 ± 0.001 ± 0.004 AWW× CWW 0.087 ± 0.001 ± 0.005 0.035 ± 0.001 ± 0.003 0.059 ± 0.001 ± 0.004 σ(pp → WW) [pb] 56.3 ± 4.9 ± 3.9 ± 2.1 64.1 ± 13.0 ± 7.4 ± 2.4 43.2 ± 8.1 ± 4.5 ± 1.6 σfid[fb] 294 ± 26 ± 15 ± 11 92.0 ± 18.9 ± 9.4 ± 3.4 57.2 ± 10.8 ± 5.2 ± 2.1 σSM fid [fb] 230 ± 19 63.4 ± 5.3 59.0 ± 4.7 [GeV] T miss E 0 20 40 60 80 100 120 140 Events / 10 GeV 0 20 40 60 80 100 120 ATLAS -1 Ldt = 1.02 fb ∫ = 7 TeV s Data ν l ν l → WW Drell-Yan Top W+jets/Dijet Diboson stat+syst σ ) [GeV] T miss (llE T m 50 100 150 200 250 300 Events / 20 GeV 0 20 40 60 80 100 120 ATLAS -1 Ldt = 1.02 fb ∫ = 7 TeV s Data ν l ν l → WW Drell-Yan Top W+jets/Dijet Diboson stat+syst σ (ll) φ ∆ 0 0.5 1 1.5 2 2.5 3 Events / 0.4 0 20 40 60 80 100 ∫Ldt = 1.02 fbATLAS -1 = 7 TeV s Data ν l ν l → WW Drell-Yan Top W+jets/Dijet Diboson stat+syst σ [GeV] ll m 0 50 100 150 200 250 300 Events / 15 GeV 0 10 20 30 40 50 60 70 80 ATLAS -1 Ldt = 1.02 fb ∫ = 7 TeV s Data ν l ν l → WW Drell-Yan Top W+jets/Dijet Diboson stat+syst σ
Figure 2: The EmissT (top left), mT(top right),∆φ(l, l) (bottom left) and m``(bottom right) distributions for the combined dilepton channels after
all selection requirements. The data (dots) are compared to the expectation from WW and the backgrounds (histograms). The W+ jet and dijet backgrounds are estimated using data. The hashed region shows the ±1σ uncertainty band on the expectation.
q (pl1 T+ p l2 T+ E miss T )2−P(p l1 i + p l2 i + E miss i )2, where the sum runs over the x and y coordinates and l1and l2refer to the two charged leptons.
7. Anomalous triple-gauge couplings
The s-channel production of WW events occurs via the triple-gauge couplings WWγ and WWZ.
Contribu-tions to these couplings from new physics processes at a high energy scale would affect the measured cross sec-tion, particularly at high momentum transfer [26]. Be-low the energy scale of these new physics processes, an effective Lagrangian can be used to describe the effect of non-SM processes on the WWV (V = γ, Z) couplings. Assuming the dominant non-SM contributions conserve Cand P, the general Lagrangian for WWV couplings is
LWWV/gWWV = igV1(Wµν†WµVν− Wµ†VνWµν)+ ikVWµ†WνVµν+miλ2V
W
W뵆WνµVνλ, (3) where gWWγ = −e, gWWZ = −e cot θW, Vµν = ∂µVν− ∂νVµ and Wµν = ∂µWν −∂νWµ. The SM couplings are gV1 = kV = 1 and λV = 0. Individually, non-zero couplings lead to divergent cross sections at high √
s, and non-SM values of the gV1 or kVcouplings break the gauge cancellation of processes at high momentum transfer. To regulate this behavior, a suppression factor depending on a scaleΛ with the general form
λ( ˆs) = λ
(1+ ˆs/Λ2)2, (4)
is defined for λ,∆g1≡ g1− 1 and∆k ≡ k − 1. Here, λ is the coupling value at low energy and
√
ˆs is the invariant mass of the WW pair. The gγ1coupling is fixed to its SM value by electromagnetic gauge invariance.
To reduce the number of WWV coupling parameters, three specific scenarios are considered. The first is the “LEP scenario” [27, 28], where anomalous couplings arise from dimension-6 operators and electroweak sym-metry breaking occurs via a light SM Higgs boson. This leads to the relations
∆kγ= −cos 2θ
W sin2θW
(∆kZ−∆gZ1) and λγ= λZ, (5)
leaving three free parameters (∆gZ
1, ∆kZ, λZ). The pa-rameter space can be further reduced by requiring equal couplings of the SU(2) and U(1) gauge bosons to the Higgs boson in the dimension-6 operators. This adds the constraint∆gZ1 = ∆kγ/(2 cos2θW) and is referred to as the “HISZ scenario” [27]. A third “Equal Coupling scenario” assumes common couplings for the WWZ and WWγ vertices (∆kZ= ∆kγ, λZ= λγ,∆gZ1 = ∆g
γ 1= 0). The differential cross section as a function of the in-variant mass of the WW pair is the most direct probe of anomalous couplings, particularly at high invariant mass. The mass can not be fully reconstructed but is correlated with the momentum of the individual leptons.
[GeV] T Lepton p 20 40 60 80 100 120 140 Events / 20 GeV 0 50 100 150
∫
Ldt = 1.02 fb-1, s = 7 TeV ATLAS Data SM WW =0.1 Z κ ∆ =0.15 γ λ = Z λ =0.2 Z 1 g ∆ Background stat+syst σFigure 3: The pTdistribution of the highest-pTcharged lepton in WW
final states. Shown are the data (dots), the background (shaded his-togram), SM WW plus background (solid hishis-togram), and the follow-ing WW anomalous couplfollow-ings added to the background:∆kZ = 0.1
(dashed histogram), λZ = λγ= 0.15 (dotted histogram), and ∆gZ1 =
0.2 (dash-dotted histogram). The last bin corresponds to pT > 120
GeV.
The pTdistribution of the highest-pT charged lepton is therefore a sensitive probe of anomalous TGCs and is used in a binned likelihood fit to extract the values of the anomalous couplings preferred by the data (Fig. 3). The dependence of the distribution on specific anomalous couplings is modeled by reweighting the mc@nlo SM WWMC to the predictions of the BHO generator [29] at the matrix-element level. Figure 3 demonstrates the sen-sitivity to anomalous TGCs at high lepton pT; the cou-pling measurement is negligibly affected by the excess in the data at low pT. The fiducial cross section is mea-sured in the last bin of Fig. 3. The result σfid(pT ≥ 120 GeV) = 5.6+5.4−4.4 (stat.) ± 2.9 (syst.) ± 0.2 (lumi.) fb is consistent with the SM WW prediction of σfid(pT≥ 120 GeV)= 12.2 ± 1.0 fb.
Table 5 and Fig. 4 show the results of the coupling fits to one and two parameters respectively in the LEP scenario, withΛ = 3 TeV and the other parameter(s) set to the SM value(s). One-dimensional limits on λZin the HISZ and Equal Coupling scenarios are the same as in the LEP scenario. In the HISZ scenario, the 95% CL limits on∆kZare [−0.049, 0.072] and [−0.037, 0.069] for Λ = 3 TeV and Λ = ∞, respectively. The cor-responding limits in the Equal Coupling scenario are [−0.089, 0.096] and [−0.065, 0.102], respectively.
The anomalous coupling limits in the LEP scenario are compared with limits obtained from CMS, CDF, D0
Table 5: 95% CL limits on anomalous TGCs in the LEP scenario assuming the other couplings are set to their SM values. Λ ∆gZ 1 ∆kZ λZ 3 TeV [−0.064, 0.096] [−0.100, 0.067] [−0.090, 0.086] ∞ [−0.052, 0.082] [−0.071, 0.071] [−0.079, 0.077] Z κ ∆ -0.2 -0.1 0 0.1 0.2 Z λ -0.2 -0.1 0 0.1 0.2
∫
Ldt = 1.02 fb-1, s = 7 TeV ATLAS LEP Scenario ∞ = Λ 95% CL 68% CL Z κ ∆ -0.2 -0.1 0 0.1 0.2 Z 1 g ∆ -0.2 -0.1 0 0.1 0.2∫
Ldt = 1.02 fb-1, s = 7 TeV ATLAS LEP Scenario ∞ = Λ 95% CL 68% CL Z λ -0.2 -0.1 0 0.1 0.2 Z 1 g ∆ -0.2 -0.1 0 0.1 0.2∫
Ldt = 1.02 fb-1, s = 7 TeV ATLAS LEP Scenario ∞ = Λ 95% CL 68% CLFigure 4: Two-dimensional fits to the anomalous couplings in the LEP scenario:∆kZvs. λZ(left),∆kZvs.∆gZ1 (middle), and λZvs.∆gZ1(right).
and the combined LEP results in Fig. 5. The sensitiv-ity of this result is significantly greater than that of the Tevatron due to the higher center-of-mass energy and higher WW production cross section. It is also compa-rable to the combined results from LEP, which include data from four detectors and all WW decay channels.
8. Summary
Using 1.02 fb−1 of √s = 7 TeV pp data, the pp → WWcross section has been measured with the ATLAS detector in the fully leptonic decay channel. The mea-sured total cross section of 54.4 ± 5.9 pb is consistent with the SM prediction of 44.4 ± 2.8 pb and is the most precise measurement to date. In addition, a first mea-surement of the WW cross section in a fiducial phase space region has been presented. Limits on anomalous couplings have been derived in three scenarios using the pT distribution of the leading charged lepton. No sig-nificant deviation is observed with respect to the SM prediction. These limits are competitive with previous results and are sensitive to a higher mass scale for new physical processes.
9. Acknowledgements
We thank CERN for the very successful operation of the LHC, as well as the support staff from our
institu-tions without whom ATLAS could not be operated effi-ciently.
We acknowledge the support of ANPCyT, Ar-gentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET and ERC,
European Union; IN2P3-CNRS, CEA-DSM/IRFU,
France; GNAS, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Mo-rocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slo-vakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foun-dation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America.
The crucial computing support from all WLCG part-ners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
95% CL limits from WW production
ATLAS (1.02 fb-1, Λ=3TeV) ATLAS (1.02 fb-1, Λ=∞) ) ∞ = Λ , -1 CMS (36 pb LEP =2TeV) Λ , -1 CDF (3.6 fb =2TeV) Λ , -1 D0 (1.1 fb Z
κ
∆
Zλ
1 Zg
∆
Figure 5: Anomalous TGC limits from ATLAS, D0 and LEP (based on the LEP scenario) and CDF and CMS (based on the HISZ scenario), as obtained from WW production measurements.
(Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Tai-wan), RAL (UK) and BNL (USA) and in the Tier-2 fa-cilities worldwide.
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T. Cuhadar Donszelmann140, M. Curatolo47, C.J. Curtis17, C. Cuthbert151, P. Cwetanski61, H. Czirr142, P. Czodrowski43, Z. Czyczula177, S. D’Auria53, M. D’Onofrio74, A. D’Orazio133a,133b, P.V.M. Da Silva23a, C. Da Via83, W. Dabrowski37, A. Dafinca119, T. Dai88, C. Dallapiccola85, M. Dam35, M. Dameri50a,50b, D.S. Damiani138, H.O. Danielsson29, D. Dannheim100, V. Dao49, G. Darbo50a, G.L. Darlea25b, W. Davey20, T. Davidek127, N. Davidson87, R. Davidson72, E. Davies119,c, M. Davies94, A.R. Davison78, Y. Davygora58a, E. Dawe143, I. Dawson140, J.W. Dawson5,∗, R.K. Daya-Ishmukhametova22, K. De7, R. de Asmundis103a, S. De Castro19a,19b, P.E. De Castro Faria Salgado24, S. De Cecco79, J. de Graat99, N. De Groot105, P. de Jong106, C. De La Taille116, H. De la Torre81, B. De Lotto165a,165c, L. de Mora72, L. De Nooij106, D. De Pedis133a,
A. De Salvo133a, U. De Sanctis165a,165c, A. De Santo150, J.B. De Vivie De Regie116, G. De Zorzi133a,133b, S. Dean78, W.J. Dearnaley72, R. Debbe24, C. Debenedetti45, B. Dechenaux55, D.V. Dedovich65, J. Degenhardt121,
C. Del Papa165a,165c, J. Del Peso81, T. Del Prete123a,123b, T. Delemontex55, M. Deliyergiyev75, A. Dell’Acqua29, L. Dell’Asta21, M. Della Pietra103a,i, D. della Volpe103a,103b, M. Delmastro4, N. Delruelle29, P.A. Delsart55, C. Deluca149, S. Demers177, M. Demichev65, B. Demirkoz11,k, J. Deng164, S.P. Denisov129, D. Derendarz38, J.E. Derkaoui136d, F. Derue79, P. Dervan74, K. Desch20, E. Devetak149, P.O. Deviveiros106, A. Dewhurst130, B. DeWilde149, S. Dhaliwal159, R. Dhullipudi24,l, A. Di Ciaccio134a,134b, L. Di Ciaccio4, A. Di Girolamo29, B. Di Girolamo29, S. Di Luise135a,135b, A. Di Mattia174, B. Di Micco29, R. Di Nardo47, A. Di Simone134a,134b, R. Di Sipio19a,19b, M.A. Diaz31a, F. Diblen18c, E.B. Diehl88, J. Dietrich41, T.A. Dietzsch58a, S. Diglio87,
K. Dindar Yagci39, J. Dingfelder20, C. Dionisi133a,133b, P. Dita25a, S. Dita25a, F. Dittus29, F. Djama84, T. Djobava51b, M.A.B. do Vale23c, A. Do Valle Wemans125a, T.K.O. Doan4, M. Dobbs86, R. Dobinson29,∗, D. Dobos29,
E. Dobson29,m, J. Dodd34, C. Doglioni49, T. Doherty53, Y. Doi66,∗, J. Dolejsi127, I. Dolenc75, Z. Dolezal127, B.A. Dolgoshein97,∗, T. Dohmae156, M. Donadelli23d, M. Donega121, J. Donini33, J. Dopke29, A. Doria103a, A. Dos Anjos174, M. Dosil11, A. Dotti123a,123b, M.T. Dova71, A.D. Doxiadis106, A.T. Doyle53, Z. Drasal127,
J. Drees176, N. Dressnandt121, H. Drevermann29, C. Driouichi35, M. Dris9, J. Dubbert100, S. Dube14, E. Duchovni173, G. Duckeck99, A. Dudarev29, F. Dudziak64, M. D¨uhrssen29, I.P. Duerdoth83, L. Duflot116, M-A. Dufour86,
M. Dunford29, H. Duran Yildiz3a, R. Duxfield140, M. Dwuznik37, F. Dydak29, M. D¨uren52, W.L. Ebenstein44, J. Ebke99, S. Eckweiler82, K. Edmonds82, C.A. Edwards77, N.C. Edwards53, W. Ehrenfeld41, T. Ehrich100,
T. Eifert144, G. Eigen13, K. Einsweiler14, E. Eisenhandler76, T. Ekelof167, M. El Kacimi136c, M. Ellert167, S. Elles4, F. Ellinghaus82, K. Ellis76, N. Ellis29, J. Elmsheuser99, M. Elsing29, D. Emeliyanov130, R. Engelmann149, A. Engl99, B. Epp62, A. Eppig88, J. Erdmann54, A. Ereditato16, D. Eriksson147a, J. Ernst1, M. Ernst24, J. Ernwein137,
D. Errede166, S. Errede166, E. Ertel82, M. Escalier116, C. Escobar124, X. Espinal Curull11, B. Esposito47, F. Etienne84, A.I. Etienvre137, E. Etzion154, D. Evangelakou54, H. Evans61, L. Fabbri19a,19b, C. Fabre29, R.M. Fakhrutdinov129, S. Falciano133a, Y. Fang174, M. Fanti90a,90b, A. Farbin7, A. Farilla135a, J. Farley149, T. Farooque159, S. Farrell164, S.M. Farrington119, P. Farthouat29, P. Fassnacht29, D. Fassouliotis8, B. Fatholahzadeh159, A. Favareto90a,90b, L. Fayard116, S. Fazio36a,36b, R. Febbraro33, P. Federic145a, O.L. Fedin122, W. Fedorko89, M. Fehling-Kaschek48, L. Feligioni84, D. Fellmann5, C. Feng32d, E.J. Feng30, A.B. Fenyuk129, J. Ferencei145b, J. Ferland94, W. Fernando110, S. Ferrag53, J. Ferrando53, V. Ferrara41, A. Ferrari167, P. Ferrari106, R. Ferrari120a, D.E. Ferreira de Lima53,
A. Ferrer168, M.L. Ferrer47, D. Ferrere49, C. Ferretti88, A. Ferretto Parodi50a,50b, M. Fiascaris30, F. Fiedler82, A. Filipˇciˇc75, A. Filippas9, F. Filthaut105, M. Fincke-Keeler170, M.C.N. Fiolhais125a,h, L. Fiorini168, A. Firan39, G. Fischer41, P. Fischer20, M.J. Fisher110, M. Flechl48, I. Fleck142, J. Fleckner82, P. Fleischmann175,
S. Fleischmann176, T. Flick176, A. Floderus80, L.R. Flores Castillo174, M.J. Flowerdew100, M. Fokitis9, T. Fonseca Martin16, D.A. Forbush139, A. Formica137, A. Forti83, D. Fortin160a, J.M. Foster83, D. Fournier116, A. Foussat29, A.J. Fowler44, K. Fowler138, H. Fox72, P. Francavilla11, S. Franchino120a,120b, D. Francis29, T. Frank173, M. Franklin57, S. Franz29, M. Fraternali120a,120b, S. Fratina121, S.T. French27, C. Friedrich41, F. Friedrich43,
R. Froeschl29, D. Froidevaux29, J.A. Frost27, C. Fukunaga157, E. Fullana Torregrosa29, B.G. Fulsom144, J. Fuster168, C. Gabaldon29, O. Gabizon173, T. Gadfort24, S. Gadomski49, G. Gagliardi50a,50b, P. Gagnon61, C. Galea99,
E.J. Gallas119, V. Gallo16, B.J. Gallop130, P. Gallus126, K.K. Gan110, Y.S. Gao144,e, V.A. Gapienko129,
A. Gaponenko14, F. Garberson177, M. Garcia-Sciveres14, C. Garc´ıa168, J.E. Garc´ıa Navarro168, R.W. Gardner30, N. Garelli29, H. Garitaonandia106, V. Garonne29, J. Garvey17, C. Gatti47, G. Gaudio120a, B. Gaur142, L. Gauthier137, P. Gauzzi133a,133b, I.L. Gavrilenko95, C. Gay169, G. Gaycken20, J-C. Gayde29, E.N. Gazis9, P. Ge32d, Z. Gecse169, C.N.P. Gee130, D.A.A. Geerts106, Ch. Geich-Gimbel20, K. Gellerstedt147a,147b, C. Gemme50a, A. Gemmell53, M.H. Genest55, S. Gentile133a,133b, M. George54, S. George77, P. Gerlach176, A. Gershon154, C. Geweniger58a, H. Ghazlane136b, N. Ghodbane33, B. Giacobbe19a, S. Giagu133a,133b, V. Giakoumopoulou8, V. Giangiobbe11, F. Gianotti29, B. Gibbard24, A. Gibson159, S.M. Gibson29, L.M. Gilbert119, V. Gilewsky92, D. Gillberg28, A.R. Gillman130, D.M. Gingrich2,d, J. Ginzburg154, N. Giokaris8, M.P. Giordani165c, R. Giordano103a,103b, F.M. Giorgi15, P. Giovannini100, P.F. Giraud137, D. Giugni90a, M. Giunta94, P. Giusti19a, B.K. Gjelsten118, L.K. Gladilin98, C. Glasman81, J. Glatzer48, A. Glazov41, K.W. Glitza176, G.L. Glonti65, J.R. Goddard76, J. Godfrey143, J. Godlewski29, M. Goebel41, T. G¨opfert43, C. Goeringer82, C. G¨ossling42, T. G¨ottfert100, S. Goldfarb88, T. Golling177, A. Gomes125a,b, L.S. Gomez Fajardo41, R. Gonc¸alo77,
J. Goncalves Pinto Firmino Da Costa41, L. Gonella20, A. Gonidec29, S. Gonzalez174, S. Gonz´alez de la Hoz168, G. Gonzalez Parra11, M.L. Gonzalez Silva26, S. Gonzalez-Sevilla49, J.J. Goodson149, L. Goossens29,
P.A. Gorbounov96, H.A. Gordon24, I. Gorelov104, G. Gorfine176, B. Gorini29, E. Gorini73a,73b, A. Goriˇsek75, E. Gornicki38, V.N. Goryachev129, B. Gosdzik41, A.T. Goshaw5, M. Gosselink106, M.I. Gostkin65,
I. Gough Eschrich164, M. Gouighri136a, D. Goujdami136c, M.P. Goulette49, A.G. Goussiou139, C. Goy4, S. Gozpinar22, I. Grabowska-Bold37, P. Grafstr¨om29, K-J. Grahn41, F. Grancagnolo73a, S. Grancagnolo15, V. Grassi149,
V. Gratchev122, N. Grau34, H.M. Gray29, J.A. Gray149, E. Graziani135a, O.G. Grebenyuk122, T. Greenshaw74, Z.D. Greenwood24,l, K. Gregersen35, I.M. Gregor41, P. Grenier144, J. Griffiths139, N. Grigalashvili65, A.A. Grillo138, S. Grinstein11, Y.V. Grishkevich98, J.-F. Grivaz116, E. Gross173, J. Grosse-Knetter54, J. Groth-Jensen173, K. Grybel142, V.J. Guarino5, D. Guest177, C. Guicheney33, A. Guida73a,73b, S. Guindon54, H. Guler86,n, J. Gunther126, B. Guo159, J. Guo34, A. Gupta30, Y. Gusakov65, V.N. Gushchin129, P. Gutierrez112, N. Guttman154, O. Gutzwiller174, C. Guyot137, C. Gwenlan119, C.B. Gwilliam74, A. Haas144, S. Haas29, C. Haber14, H.K. Hadavand39, D.R. Hadley17, P. Haefner100, F. Hahn29, S. Haider29, Z. Hajduk38, H. Hakobyan178, D. Hall119, J. Haller54, K. Hamacher176, P. Hamal114,
M. Hamer54, A. Hamilton146b,o, S. Hamilton162, H. Han32a, L. Han32b, K. Hanagaki117, K. Hanawa161, M. Hance14, C. Handel82, P. Hanke58a, J.R. Hansen35, J.B. Hansen35, J.D. Hansen35, P.H. Hansen35, P. Hansson144, K. Hara161, G.A. Hare138, T. Harenberg176, S. Harkusha91, D. Harper88, R.D. Harrington45, O.M. Harris139, K. Harrison17,
J. Hartert48, F. Hartjes106, T. Haruyama66, A. Harvey56, S. Hasegawa102, Y. Hasegawa141, S. Hassani137, M. Hatch29, D. Hauff100, S. Haug16, M. Hauschild29, R. Hauser89, M. Havranek20, B.M. Hawes119, C.M. Hawkes17,
R.J. Hawkings29, A.D. Hawkins80, D. Hawkins164, T. Hayakawa67, T. Hayashi161, D. Hayden77, C.P. Hays119, H.S. Hayward74, S.J. Haywood130, E. Hazen21, M. He32d, S.J. Head17, V. Hedberg80, L. Heelan7, S. Heim89, B. Heinemann14, S. Heisterkamp35, L. Helary4, C. Heller99, M. Heller29, S. Hellman147a,147b, D. Hellmich20, C. Helsens11, R.C.W. Henderson72, M. Henke58a, A. Henrichs54, A.M. Henriques Correia29, S. Henrot-Versille116, F. Henry-Couannier84, C. Hensel54, T. Henß176, C.M. Hernandez7, Y. Hern´andez Jim´enez168, R. Herrberg15, G. Herten48, R. Hertenberger99, L. Hervas29, G.G. Hesketh78, N.P. Hessey106, E. Hig´on-Rodriguez168, D. Hill5,∗, J.C. Hill27, N. Hill5, K.H. Hiller41, S. Hillert20, S.J. Hillier17, I. Hinchliffe14, E. Hines121, M. Hirose117, F. Hirsch42, D. Hirschbuehl176, J. Hobbs149, N. Hod154, M.C. Hodgkinson140, P. Hodgson140, A. Hoecker29, M.R. Hoeferkamp104, J. Hoffman39, D. Hoffmann84, M. Hohlfeld82, M. Holder142, S.O. Holmgren147a, T. Holy128, J.L. Holzbauer89, Y. Homma67, T.M. Hong121, L. Hooft van Huysduynen109, T. Horazdovsky128, C. Horn144, S. Horner48, J-Y. Hostachy55, S. Hou152, M.A. Houlden74, A. Hoummada136a, J. Howarth83, D.F. Howell119, I. Hristova15, J. Hrivnac116, I. Hruska126, T. Hryn’ova4, P.J. Hsu82, S.-C. Hsu14, G.S. Huang112, Z. Hubacek128, F. Hubaut84, F. Huegging20, A. Huettmann41, T.B. Huffman119, E.W. Hughes34, G. Hughes72, R.E. Hughes-Jones83,
M. Huhtinen29, P. Hurst57, M. Hurwitz14, U. Husemann41, N. Huseynov65,p, J. Huston89, J. Huth57, G. Iacobucci49, G. Iakovidis9, M. Ibbotson83, I. Ibragimov142, R. Ichimiya67, L. Iconomidou-Fayard116, J. Idarraga116, P. Iengo103a, O. Igonkina106, Y. Ikegami66, M. Ikeno66, Y. Ilchenko39, D. Iliadis155, N. Ilic159, M. Imori156, T. Ince20,
J. Inigo-Golfin29, P. Ioannou8, M. Iodice135a, K. Iordanidou8, V. Ippolito133a,133b, A. Irles Quiles168, C. Isaksson167, A. Ishikawa67, M. Ishino68, R. Ishmukhametov39, C. Issever119, S. Istin18a, A.V. Ivashin129, W. Iwanski38,
H. Iwasaki66, J.M. Izen40, V. Izzo103a, B. Jackson121, J.N. Jackson74, P. Jackson144, M.R. Jaekel29, V. Jain61, K. Jakobs48, S. Jakobsen35, J. Jakubek128, D.K. Jana112, E. Jansen78, H. Jansen29, A. Jantsch100, M. Janus48, G. Jarlskog80, L. Jeanty57, K. Jelen37, I. Jen-La Plante30, P. Jenni29, A. Jeremie4, P. Jeˇz35, S. J´ez´equel4, M.K. Jha19a, H. Ji174, W. Ji82, J. Jia149, Y. Jiang32b, M. Jimenez Belenguer41, G. Jin32b, S. Jin32a, O. Jinnouchi158,
M.D. Joergensen35, D. Joffe39, L.G. Johansen13, M. Johansen147a,147b, K.E. Johansson147a, P. Johansson140,
S. Johnert41, K.A. Johns6, K. Jon-And147a,147b, G. Jones119, R.W.L. Jones72, T.W. Jones78, T.J. Jones74, O. Jonsson29, C. Joram29, P.M. Jorge125a, J. Joseph14, K.D. Joshi83, J. Jovicevic148, T. Jovin12b, X. Ju174, C.A. Jung42,
R.M. Jungst29, V. Juranek126, P. Jussel62, A. Juste Rozas11, V.V. Kabachenko129, S. Kabana16, M. Kaci168, A. Kaczmarska38, P. Kadlecik35, M. Kado116, H. Kagan110, M. Kagan57, S. Kaiser100, E. Kajomovitz153, S. Kalinin176, L.V. Kalinovskaya65, S. Kama39, N. Kanaya156, M. Kaneda29, S. Kaneti27, T. Kanno158,
V.A. Kantserov97, J. Kanzaki66, B. Kaplan177, A. Kapliy30, J. Kaplon29, D. Kar53, M. Karagounis20, M. Karagoz119, M. Karnevskiy41, V. Kartvelishvili72, A.N. Karyukhin129, L. Kashif174, G. Kasieczka58b, R.D. Kass110,
A. Kastanas13, M. Kataoka4, Y. Kataoka156, E. Katsoufis9, J. Katzy41, V. Kaushik6, K. Kawagoe70, T. Kawamoto156, G. Kawamura82, M.S. Kayl106, V.A. Kazanin108, M.Y. Kazarinov65, R. Keeler170, R. Kehoe39, M. Keil54,
G.D. Kekelidze65, J.S. Keller139, J. Kennedy99, M. Kenyon53, O. Kepka126, N. Kerschen29, B.P. Kerˇsevan75, S. Kersten176, K. Kessoku156, J. Keung159, F. Khalil-zada10, H. Khandanyan166, A. Khanov113, D. Kharchenko65, A. Khodinov97, A.G. Kholodenko129, A. Khomich58a, T.J. Khoo27, G. Khoriauli20, A. Khoroshilov176,
N. Khovanskiy65, V. Khovanskiy96, E. Khramov65, J. Khubua51b, H. Kim147a,147b, M.S. Kim2, S.H. Kim161, N. Kimura172, O. Kind15, B.T. King74, M. King67, R.S.B. King119, J. Kirk130, L.E. Kirsch22, A.E. Kiryunin100, T. Kishimoto67, D. Kisielewska37, T. Kittelmann124, A.M. Kiver129, E. Kladiva145b, M. Klein74, U. Klein74, K. Kleinknecht82, M. Klemetti86, A. Klier173, P. Klimek147a,147b, A. Klimentov24, R. Klingenberg42, J.A. Klinger83, E.B. Klinkby35, T. Klioutchnikova29, P.F. Klok105, S. Klous106, E.-E. Kluge58a, T. Kluge74, P. Kluit106, S. Kluth100, N.S. Knecht159, E. Kneringer62, J. Knobloch29, E.B.F.G. Knoops84, A. Knue54, B.R. Ko44, T. Kobayashi156, M. Kobel43, M. Kocian144, P. Kodys127, K. K¨oneke29, A.C. K¨onig105, S. Koenig82, L. K¨opke82, F. Koetsveld105, P. Koevesarki20, T. Koffas28, E. Koffeman106, L.A. Kogan119, S. Kohlmann176, F. Kohn54, Z. Kohout128, T. Kohriki66, T. Koi144, T. Kokott20, G.M. Kolachev108, H. Kolanoski15, V. Kolesnikov65, I. Koletsou90a, J. Koll89, M. Kollefrath48, S.D. Kolya83, A.A. Komar95, Y. Komori156, T. Kondo66, T. Kono41,q, A.I. Kononov48, R. Konoplich109,r,
N. Konstantinidis78, A. Kootz176, S. Koperny37, K. Korcyl38, K. Kordas155, V. Koreshev129, A. Korn119, A. Korol108, I. Korolkov11, E.V. Korolkova140, V.A. Korotkov129, O. Kortner100, S. Kortner100, V.V. Kostyukhin20,
M.J. Kotam¨aki29, S. Kotov100, V.M. Kotov65, A. Kotwal44, C. Kourkoumelis8, V. Kouskoura155, A. Koutsman160a, R. Kowalewski170, T.Z. Kowalski37, W. Kozanecki137, A.S. Kozhin129, V. Kral128, V.A. Kramarenko98,
