Search for Supersymmetry with Gauge-Mediated Breaking in Diphoton Events at D0
V. M. Abazov,32B. Abbott,69M. Abolins,60B. S. Acharya,26D. L. Adams,67M. Adams,47T. Adams,45M. Agelou,16 J.-L. Agram,17S. N. Ahmed,31S. H. Ahn,28G. D. Alexeev,32G. Alkhazov,36A. Alton,59G. Alverson,58G. A. Alves,2 S. Anderson,41B. Andrieu,15Y. Arnoud,12A. Askew,72B. A˚ sman,37O. Atramentov,52C. Autermann,19C. Avila,7 L. Babukhadia,66T. C. Bacon,39A. Baden,56S. Baffioni,13B. Baldin,46P. W. Balm,30S. Banerjee,26E. Barberis,58 P. Bargassa,72P. Baringer,53C. Barnes,39J. Barreto,2J. F. Bartlett,46U. Bassler,15D. Bauer,50A. Bean,53S. Beauceron,15 F. Beaudette,14M. Begel,65A. Bellavance,62S. B. Beri,25G. Bernardi,15R. Bernhard,46,* I. Bertram,38M. Besanc¸on,16A. Besson,17R. Beuselinck,39V. A. Bezzubov,35P. C. Bhat,46V. Bhatnagar,25M. Bhattacharjee,66M. Binder,23 A. Bischoff,44K. M. Black,57I. Blackler,39G. Blazey,48F. Blekman,30D. Bloch,17U. Blumenschein,21A. Boehnlein,46 O. Boeriu,51T. A. Bolton,54P. Bonamy,16F. Borcherding,46G. Borissov,38K. Bos,30T. Bose,64C. Boswell,44A. Brandt,71 G. Briskin,70R. Brock,60G. Brooijmans,64A. Bross,46N. J. Buchanan,45D. Buchholz,49M. Buehler,47V. Buescher,21
S. Burdin,46T. H. Burnett,74E. Busato,15J. M. Butler,57J. Bystricky,16F. Canelli,65W. Carvalho,3B. C. K. Casey,70 D. Casey,60N. M. Cason,51H. Castilla-Valdez,29S. Chakrabarti,26D. Chakraborty,48K. M. Chan,65A. Chandra,26
D. Chapin,70F. Charles,17E. Cheu,41L. Chevalier,16D. K. Cho,65S. Choi,44S. Chopra,67T. Christiansen,23 L. Christofek,53D. Claes,62A. R. Clark,42B. Cle´ment,17C. Cle´ment,37Y. Coadou,5D. J. Colling,39L. Coney,51 B. Connolly,45M. Cooke,72W. E. Cooper,46D. Coppage,53M. Corcoran,72J. Coss,18A. Cothenet,13M.-C. Cousinou,13
S. Cre´pe´-Renaudin,12M. Cristetiu,44M. A. C. Cummings,48D. Cutts,70H. da Motta,2B. Davies,38G. Davies,39 G. A. Davis,65K. De,71P. de Jong,30S. J. de Jong,31E. De La Cruz-Burelo,29C. De Oliveira Martins,3S. Dean,40 K. Del Signore,59F. De´liot,16P. A. Delsart,18M. Demarteau,46R. Demina,65P. Demine,16D. Denisov,46S. P. Denisov,35 S. Desai,66H. T. Diehl,46M. Diesburg,46M. Doidge,38H. Dong,66S. Doulas,58L. Duflot,14S. R. Dugad,26A. Duperrin,13
J. Dyer,60A. Dyshkant,48M. Eads,48D. Edmunds,60T. Edwards,40J. Ellison,44J. Elmsheuser,23J. T. Eltzroth,71 V. D. Elvira,46S. Eno,56P. Ermolov,34O. V. Eroshin,35J. Estrada,46D. Evans,39H. Evans,64A. Evdokimov,33 V. N. Evdokimov,35J. Fast,46S. N. Fatakia,57D. Fein,41L. Feligioni,57T. Ferbel,65F. Fiedler,23F. Filthaut,31W. Fisher,63
H. E. Fisk,46F. Fleuret,15M. Fortner,48H. Fox,21W. Freeman,46S. Fu,46S. Fuess,46C. F. Galea,31E. Gallas,46 E. Galyaev,51M. Gao,64C. Garcia,65A. Garcia-Bellido,74J. Gardner,53V. Gavrilov,33D. Gele´,17R. Gelhaus,44 K. Genser,46C. E. Gerber,47Y. Gershtein,70G. Geurkov,70G. Ginther,65K. Goldmann,24T. Golling,20B. Go´mez,7 K. Gounder,46A. Goussiou,51G. Graham,56P. D. Grannis,66S. Greder,17J. A. Green,52H. Greenlee,46Z. D. Greenwood,55 E. M. Gregores,4S. Grinstein,1J.-F. Grivaz,14L. Groer,64S. Gru¨nendahl,46M. W. Gru¨newald,27W. Gu,6S. N. Gurzhiev,35 G. Gutierrez,46P. Gutierrez,69A. Haas,64N. J. Hadley,56H. Haggerty,46S. Hagopian,45I. Hall,69R. E. Hall,43C. Han,59 L. Han,40K. Hanagaki,46P. Hanlet,71K. Harder,54R. Harrington,58J. M. Hauptman,52R. Hauser,60C. Hays,64J. Hays,49 T. Hebbeker,19C. Hebert,53D. Hedin,48J. M. Heinmiller,47A. P. Heinson,44U. Heintz,57C. Hensel,53G. Hesketh,58 M. D. Hildreth,51R. Hirosky,73J. D. Hobbs,66B. Hoeneisen,11M. Hohlfeld,22S. J. Hong,28R. Hooper,51S. Hou,59Y. Hu,66 J. Huang,50 Y. Huang,59I. Iashvili,44R. Illingworth,46A. S. Ito,46S. Jabeen,53M. Jaffre´,14S. Jain,69V. Jain,67K. Jakobs,21 A. Jenkins,39R. Jesik,39Y. Jiang,59K. Johns,41M. Johnson,46P. Johnson,41A. Jonckheere,46P. Jonsson,39H. Jo¨stlein,46 A. Juste,46M. M. Kado,42D. Ka¨fer,19W. Kahl,54S. Kahn,67E. Kajfasz,13A. M. Kalinin,32J. Kalk,60D. Karmanov,34
J. Kasper,57D. Kau,45Z. Ke,6R. Kehoe,60S. Kermiche,13S. Kesisoglou,70A. Khanov,65A. Kharchilava,51 Y. M. Kharzheev,32K. H. Kim,28B. Klima,46M. Klute,20J. M. Kohli,25M. Kopal,69V. M. Korablev,35J. Kotcher,67 B. Kothari,64A. V. Kotwal,64A. Koubarovsky,34A. Kouchner,16O. Kouznetsov,12A. V. Kozelov,35J. Kozminski,60
J. Krane,52M. R. Krishnaswamy,26S. Krzywdzinski,46M. Kubantsev,54S. Kuleshov,33Y. Kulik,46S. Kunori,56 A. Kupco,16T. Kurcˇa,18V. E. Kuznetsov,44S. Lager,37N. Lahrichi,16G. Landsberg,70J. Lazoflores,45A.-C. Le Bihan,17 P. Lebrun,18S. W. Lee,28W. M. Lee,45A. Leflat,34C. Leggett,42F. Lehner,46,* C. Leonidopoulos,64P. Lewis,39J. Li,71 Q. Z. Li,46X. Li,6J. G. R. Lima,48D. Lincoln,46S. L. Linn,45J. Linnemann,60V. V. Lipaev,35R. Lipton,46L. Lobo,39 A. Lobodenko,36M. Lokajicek,10A. Lounis,17J. Lu,6H. J. Lubatti,74A. Lucotte,12L. Lueking,46C. Luo,50M. Lynker,51 A. L. Lyon,46 A. K. A. Maciel,48R. J. Madaras,42P. Ma¨ttig,24A. Magerkurth,59A.-M. Magnan,12M. Maity,57P. K. Mal,26 S. Malik,55V. L. Malyshev,32V. Manankov,34H. S. Mao,6Y. Maravin,46T. Marshall,50M. Martens,46M. I. Martin,48 S. E. K. Mattingly,70A. A. Mayorov,35R. McCarthy,66R. McCroskey,41T. McMahon,68D. Meder,22H. L. Melanson,46
A. Melnitchouk,70X. Meng,6M. Merkin,34K. W. Merritt,46A. Meyer,19C. Miao,70H. Miettinen,72D. Mihalcea,48 C. S. Mishra,46J. Mitrevski,64N. Mokhov,46J. Molina,3N. K. Mondal,26H. E. Montgomery,46R. W. Moore,5M. Mostafa,1 G. S. Muanza,18M. Mulders,46Y. D. Mutaf,66E. Nagy,13F. Nang,41M. Narain,57V. S. Narasimham,26N. A. Naumann,31
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P. M. Perea,44E. Perez,16O. Peters,30P. Pe´troff,14M. Petteni,39L. Phaf,30R. Piegaia,1P. L. M. Podesta-Lerma,29 V. M. Podstavkov,46B. G. Pope,60E. Popkov,57W. L. Prado da Silva,3H. B. Prosper,45S. Protopopescu,67 M. B. Przybycien,49,†J. Qian,59A. Quadt,20B. Quinn,61K. J. Rani,26P. A. Rapidis,46P. N. Ratoff,38N. W. Reay,54 J.-F. Renardy,16S. Reucroft,58J. Rha,44M. Ridel,14M. Rijssenbeek,66I. Ripp-Baudot,17F. Rizatdinova,54C. Royon,16 P. Rubinov,46R. Ruchti,51B. M. Sabirov,32G. Sajot,12A. Sa´nchez-Herna´ndez,29M. P. Sanders,40A. Santoro,3G. Savage,46
L. Sawyer,55T. Scanlon,39R. D. Schamberger,66H. Schellman,49P. Schieferdecker,23C. Schmitt,24A. A. Schukin,35 A. Schwartzman,63R. Schwienhorst,60S. Sengupta,45H. Severini,69E. Shabalina,47V. Shary,14W. D. Shephard,51 D. Shpakov,58R. A. Sidwell,54V. Simak,9V. Sirotenko,46D. Skow,46P. Skubic,69P. Slattery,65R. P. Smith,46K. Smolek,9
G. R. Snow,62J. Snow,68S. Snyder,67S. So¨ldner-Rembold,40X. Song,48Y. Song,71L. Sonnenschein,57A. Sopczak,38 V. Sorı´n,1M. Sosebee,71K. Soustruznik,8M. Souza,2B. Spurlock,71N. R. Stanton,54J. Stark,12J. Steele,55 G. Steinbru¨ck,64K. Stevenson,50V. Stolin,33A. Stone,47D. A. Stoyanova,35J. Strandberg,37M. A. Strang,71M. Strauss,69 R. Stro¨hmer,23M. Strovink,42L. Stutte,46A. Sznajder,3M. Talby,13P. Tamburello,41W. Taylor,66P. Telford,40J. Temple,41 S. Tentindo-Repond,45E. Thomas,13B. Thooris,16M. Tomoto,46T. Toole,56J. Torborg,51S. Towers,66T. Trefzger,22 S. Trincaz-Duvoid,15T. G. Trippe,42B. Tuchming,16C. Tully,63A. S. Turcot,67P. M. Tuts,64L. Uvarov,36S. Uvarov,36
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Y. Yen,24K. Yip,67S. W. Youn,49J. Yu,71A. Yurkewicz,60A. Zabi,14A. Zatserklyaniy,48M. Zdrazil,66C. Zeitnitz,22 B. Zhang,6D. Zhang,46X. Zhang,69T. Zhao,74Z. Zhao,59H. Zheng,51B. Zhou,59Z. Zhou,52J. Zhu,56M. Zielinski,65
D. Zieminska,50A. Zieminski,50R. Zitoun,66V. Zutshi,48E. G. Zverev,34and A. Zylberstejn16
(D0 Collaboration)
1Universidad de Buenos Aires, Buenos Aires, Argentina 2LAFEX, Centro Brasileiro de Pesquisas Fı´sicas, Rio de Janeiro, Brazil
3Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil 4Instituto de Fı´sica Teo´rica, Universidade Estadual Paulista, Sa˜o Paulo, Brazil
5University of Alberta, Edmonton, Alberta, Canada
and Simon Fraser University, Burnaby, British Columbia, Canada
6Institute of High Energy Physics, Beijing, People’s Republic of China 7Universidad de los Andes, Bogota´, Colombia
8Center for Particle Physics, Charles University, Prague, Czech Republic 9Czech Technical University, Prague, Czech Republic
10Institute of Physics, Academy of Sciences, Center for Particle Physics, Prague, Czech Republic 11Universidad San Francisco de Quito, Quito, Ecuador
12Laboratoire de Physique Subatomique et de Cosmologie, IN2P3-CNRS, Universite de Grenoble 1, Grenoble, France 13CPPM, IN2P3-CNRS, Universite´ de la Me´diterrane´e, Marseille, France
14Laboratoire de l’Acce´le´rateur Line´aire, IN2P3-CNRS, Orsay, France 15LPNHE, Universite´s Paris VI and VII, IN2P3-CNRS, Paris, France
16DAPNIA/Service de Physique des Particules, CEA, Saclay, France 17IReS, IN2P3-CNRS, Universite´ Louis Pasteur Strasbourg, Strasbourg, France
and Universite´ de Haute Alsace, Alsace, France
18Institut de Physique Nucle´aire de Lyon, IN2P3-CNRS, Universite´ Claude Bernard, Villeurbanne, France 19RWTH Aachen, III. Physikalisches Institut A, Aachen, Germany
20Physikalisches Institut, Universita¨t Bonn, Bonn, Germany 21Physikalisches Institut, Universita¨t Freiburg, Freiburg, Germany
22Institut fu¨r Physik, Universita¨t Mainz, Mainz, Germany 23Ludwig-Maximilians-Universita¨t Mu¨nchen, Mu¨nchen, Germany 24Fachbereich Physik, University of Wuppertal, Wuppertal, Germany
25Panjab University, Chandigarh, India
26Tata Institute of Fundamental Research, Mumbai, India 27University College Dublin, Dublin, Ireland 28Korea Detector Laboratory, Korea University, Seoul, Korea
29CINVESTAV, Mexico City, Mexico
30FOM-Institute NIKHEF and University of Amsterdam/NIKHEF, Amsterdam, The Netherlands 31University of Nijmegen/NIKHEF, Nijmegen, The Netherlands
32Joint Institute for Nuclear Research, Dubna, Russia 33Institute for Theoretical and Experimental Physics, Moscow, Russia
34Moscow State University, Moscow, Russia 35Institute for High Energy Physics, Protvino, Russia 36Petersburg Nuclear Physics Institute, St. Petersburg, Russia
37Lund University, Lund, Sweden, Royal Institute of Technology, Stockholm University, Stockholm, Sweden,
and Uppsala University, Uppsala, Sweden
38Lancaster University, Lancaster, United Kingdom 39Imperial College, London, United Kingdom 40University of Manchester, Manchester, United Kingdom
41University of Arizona, Tucson, Arizona 85721, USA
42Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA 43California State University, Fresno, California 93740, USA
44University of California, Riverside, California 92521, USA 45Florida State University, Tallahassee, Florida 32306, USA 46Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
47University of Illinois at Chicago, Chicago, Illinois 60607, USA 48Northern Illinois University, DeKalb, Illinois 60115, USA
49Northwestern University, Evanston, Illinois 60208, USA 50Indiana University, Bloomington, Indiana 47405, USA 51University of Notre Dame, Notre Dame, Indiana 46556, USA
52Iowa State University, Ames, Iowa 50011, USA 53University of Kansas, Lawrence, Kansas 66045, USA 54Kansas State University, Manhattan, Kansas 66506, USA 55Louisiana Tech University, Ruston, Louisiana 71272, USA 56University of Maryland, College Park, Maryland 20742, USA
57Boston University, Boston, Massachusetts 02215, USA 58Northeastern University, Boston, Massachusetts 02115, USA
59University of Michigan, Ann Arbor, Michigan 48109, USA 60Michigan State University, East Lansing, Michigan 48824, USA
61University of Mississippi, University, Mississippi 38677, USA 62University of Nebraska, Lincoln, Nebraska 68588, USA 63Princeton University, Princeton, New Jersey 08544, USA
64Columbia University, New York, New York 10027, USA 65University of Rochester, Rochester, New York 146274, USA 66State University of New York, Stony Brook, New York 1179, USA
67Brookhaven National Laboratory, Upton, New York 11973, USA 68Langston University, Langston, Oklahoma 73050, USA 69University of Oklahoma, Norman, Oklahoma 73019, USA
70Brown University, Providence, Rhode Island 02912, USA 71University of Texas, Arlington, Texas 76019, USA
72Rice University, Houston, Texas 77005, USA 73University of Virginia, Charlottesville, Virginia 22901, USA
74University of Washington, Seattle, Washington 98195, USA
(Received 30 August 2004; published 31 January 2005)
We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb1of data collected by the D0 experiment at the Fermilab Tevatron Collider in 2002 – 2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-to-lightest SUSY particle.
DOI: 10.1103/PhysRevLett.94.041801 PACS numbers: 14.80.Ly, 12.60.Jv, 13.85.Rm
Low-scale supersymmetry (SUSY) is one of the most promising solutions to the hierarchy problem associated with the large disparity between electroweak and Planck scales. It stabilizes the Higgs boson mass and postulates that for each known particle there exists a superpartner. Bosons have fermion superpartners and vice versa. None of the superpartners have been observed so far, so superpart-ner masses must be much larger than that of their partsuperpart-ners; i.e., SUSY is a broken symmetry.
Experimental signatures of supersymmetry are deter-mined by the manner and scale of its breaking. In models with gauge-mediated supersymmetry breaking (GMSB) [1,2] it is achieved by the introduction of new chiral super-multiplets, called messengers, which couple to the ultimate source of supersymmetry breaking, and also to the SUSY particles. At colliders, assuming R-parity conservation [3], superpartners are produced in pairs, and then each decays to the next-to-lightest SUSY particle (NLSP), which can be either a neutralino or a slepton. In the former case, which is considered in this Letter, the NLSP decays into a photon and a gravitino (the lightest superpartner in GMSB SUSY models, with mass less than 1 keV) which is stable and escapes detection, creating an imbalance of the transverse energy in the event. Therefore the signal we are looking for is a final state with two energetic photons and large missing transverse energy (E6 T).
The differences in event kinematics between particular GMSB SUSY models result in different experimental sen-sitivities, so in order to obtain quantitative results we consider a model referred to as Snowmass Slope SPS 8 [4]. This model has only one dimensioned parameter that determines the effective scale of SUSY breaking. The minimal GMSB parameters correspond to a messenger mass Mm 2, the number of messengers N5 1, the ratio of the vacuum expectation values of the two Higgs fields tan 15, and the sign of the Higgsino mass term > 0. The lifetime of the neutralino is not fixed by this model line and is assumed to be sufficiently short to result in decays with prompt photons. Current lower limits on the GMSB neutralino mass for somewhat similar model pa-rameters are 65, 75, and 100 GeV, from the CDF [5], D0 [6], and CERN LEP Collaborations [7], respectively.
We search for SUSY production in p p collisions at
s p
1:96 TeV at the Fermilab Tevatron Collider. The D0 detector comprises a central tracking system in a 2 T superconducting solenoidal magnet, a liquid argon/ura-nium calorimeter, and a muon spectrometer [8]. The track-ing system consists of a silicon microstrip tracker and a scintillating fiber tracker and provides coverage for charged particles in the pseudorapidity range jj < 3, where lntan
2 and is the polar angle with re-spect to the proton beam direction (z). The calorimeters are finely segmented and consist of a central section (CC)
covering jj 1:1, and two end calorimeters (EC) extend-ing coverage to jj 4, all housed in separate cryostats [9]. Scintillators installed between the CC and EC cryostats provide sampling of developing showers for 1:1 < jj < 1:4. The electromagnetic (EM) section of the calorimeter has four longitudinal layers and transverse segmentation of 0:1 0:1 in space (where is the azimuthal angle), except in the third layer, corresponding to EM shower maximum, where it is 0:05 0:05. The data sam-ple was collected between April 2002 and March 2004, using triggers requiring at least one energetic cluster or two less energetic ones in the electromagnetic layers of the calorimeter. The integrated luminosity of the sample is 263 17 pb1.
Photons and electrons are identified in two steps: first, selection of the EM clusters, and then their separation into photons or electrons. EM clusters are selected from calorimeter clusters by requiring that (i) at least 90% of the energy be deposited in the EM section of the calorime-ter, (ii) the calorimeter isolation variable (I) be less than 0.15, where I Etot0:4 EEM0:2 =EEM0:2 , where Etot0:4 is the total shower energy in a cone of radius R
2 2 p
0:4, and EEM0:2 is the EM energy in a cone R 0:2, (iii) the transverse and longitudinal shower profiles be consistent with those expected for an EM shower, and (iv) the scalar sum of the pT of all tracks originating from the primary vertex in an annulus of 0:05 <R < 0:4 around the cluster be less than 2 GeV. The cluster is then defined as an electron if there is a reconstructed track pointing to it and a photon otherwise. Jets are reconstructed using the iterative, midpoint cone algorithm [10] with a cone size of 0.5. E6 T is determined
from the energy deposited in the calorimeter for jj < 4 and is corrected for jet and EM energy scales.
We select candidates by requiring events to have two photons each with ET> 20 GeV and pseudorapidity jj <
1:1. To suppress events with mismeasured E6 T, we apply the following requirements. We reject any event when the difference in azimuth () between the highest ET jet (if jets are present) and the direction of the E6 T is more than 2.5 rad, or if the between the direction of the E6 T and either photon is less than 0.5 rad. These selections yield 1909 events ( sample), out of which 1800 have E6 T< 15 GeV and two have E6 T> 40 GeV. The two events con-stitute the E6 T sample.
The main backgrounds arise from standard model pro-cesses with misidentified photons and/or mismeasured E6 T.
The background from processes with no inherent E6 T
(mul-tijet events, direct photon production, Z ! ee, etc.) is estimated using events with two EM clusters that satisfy photon-identification criteria (i) and (ii) but fail the shower-shape requirement (iii). These events, called the QCD sample, must pass the same trigger and other
selec-tions that define the sample. They have characteristics similar to the background in the sample and, in par-ticular, are expected to have similar E6 T resolution. This assumption was checked by varying the selection criteria and comparing the E6 T distribution in the QCD sample to that in Z ! ee events. The QCD sample comprises 18 437 events, with 17 379 events having E6 T< 15 GeV, and 27 events with E6 T> 40 GeV. We estimate the background in the E6 T sample resulting from mismeasurement of E6 T by normalizing the number of QCD events to that of the sample for E6 T< 15 GeV. This yields 2:8 0:5 events
with E6 T> 40 GeV, with uncertainty dominated by the
statistics of the QCD sample.
The other sources of background correspond to events with genuine E6 T in which an electron is misidentified as a photon, for example, from W “” events (where “”
denotes both true photons and jets misidentified as pho-tons), and from Z ! ! ee X and tt ! ee jets production. We estimate this contribution us-ing the e sample which has the same trigger, kinematic, and EM identification requirements as the sample. This sample contains 889 events, 782 events with E6 T< 15 GeV
and 15 events with E6 T> 40 GeV. To estimate the
contri-bution of such events to the E6 Tsample, we first subtract
the QCD background component of the e sample. This is done by normalizing the QCD sample to the e sample for E6 T< 15 GeV. Then, using the probability for an electron to be misidentified as a photon (measured using Z ! ee events to be 0:064 0:004), we estimate this background to be 0:9 0:2 events with statistically dominated uncer-tainty. Therefore the total expected background to the E6 T sample is 3:7 0:6 events. The E6 T distributions for the sample, background without genuine E6 T, and the total background are shown in Fig. 1, together with an expected distribution from the Snowmass Slope model with 80 TeV, the latter multiplied by a factor of 10 for clarity.
To estimate the expected signal, we generated Monte Carlo (MC) events for several points on the Snowmass Slope (see Table I), covering the neutralino mass range from 72 GeV, somewhat below the existing limits [6,7], to 116 GeV. We used ISAJET 7.58 [11] to determine SUSY interaction eigenstate masses and cou-plings. PYTHIA 6.202[12] was used to generate the events after determining the sparticle masses, branching fractions, and leading-order (LO) production cross sections using the CTEQ5L [13] parton distribution functions (PDF). MC events were processed through full detector simulation and reconstruction and processed with the analysis pro-gram used for the data.
The dominant contributions to the cross section are from the production of lightest charginos ( ~1~1) and chargino-second neutralino pairs ( ~0
2~
1). The total cross section in Table I is calculated to leading order inPYTHIAfor GMSB SUSY production. The ‘‘K factor’’ used to account for higher-order corrections is applied to estimate the next-to-leading-order cross section. The values of the K factor in Table I are taken from Ref. [14]. The sources of error on signal efficiency include uncertainty on photon
(GeV)
TMissing E
0 50 100 150 200Events / 5 GeV
1 10 102 103 data γ γ Background with no T genuine missing E Total background SUSY signal x10DØ
FIG. 1. The E6 T distribution for the diphoton and background
samples. Also shown is the expected distribution for the GMSB point with 80 TeV, multiplied by a factor of 10.
TABLE I. Points on the Snowmass Slope: their cross sections, efficiencies, and cross-section limits. , TeV m~0
1;GeV m~
1;GeV
LO
tot, pb Kfactor Efficiency 95% C.L. Limit, pb
55 71.8 126.3 0.735 1.236 0:092 0:009 0.184 60 79.1 140.2 0.468 1.227 0:100 0:009 0.170 65 86.4 154.3 0.301 1.217 0:111 0:011 0.153 70 93.7 168.2 0.204 1.207 0:124 0:012 0.137 75 101.0 182.3 0.138 1.197 0:137 0:013 0.124 80 108.2 196.0 0.094 1.187 0:149 0:014 0.114 85 115.5 209.9 0.066 1.177 0:154 0:015 0.110
tion (4% per photon), MC statistics (5%), and choice of PDF (5%).
Since the observed number of events is in good agree-ment with that expected from the standard model, we conclude that there is no evidence for GMSB SUSY in our data. To calculate the upper limit on the production cross section for each sampled point on the Snowmass Slope, we use a Bayesian approach [15] with a flat prior for the signal cross section. The calculation takes into account uncertainties on the expected number of back-ground events, efficiency, and luminosity. The selection E
6 T> 40 GeV for the signal sample leads to the best
ex-pected limit, given the predicted background and exex-pected signal distributions. Our limits are shown in Table I, and plotted in Fig. 2, together with the expected signal cross section. The upper limit on the cross section is below the
expected value for < 79:6 TeV, corresponding to lower limits on gaugino masses of m~
1 > 194:9 GeV and m~01>
107:7 GeV. The expected limit, given the predicted num-ber of background events, is < 74:5 TeV. We find that the gaugino mass limits depend only slightly on the pa-rameters of the minimal GMSB. We have considered mod-els with values of tan and N5 different from the Snowmass Slope and arrive at very similar results as de-tailed by Table II.
To summarize, we searched for inclusive high-ET di-photon events with large missing transverse energy. Such events are predicted in supersymmetric models with low-scale gauge-mediated supersymmetry breaking. We find no excess of such events and interpret the result as a lower limit on gaugino masses. For a representative point in the parameter space, we determine that at a 95% confidence level, the masses of the lightest chargino and neutralino are larger than 195 and 108 GeV, respectively. These are the most restrictive limits to date for the Snowmass Slope model.
We thank S. Martin for valuable discussions and S. Mrenna for his help with the event generators. We thank the staffs at Fermilab and collaborating institutions and acknowledge support from the Department of Energy and National Science Foundation (USA), Commissariat a` l’Energie Atomique and CNRS/Institut National de Physique Nucle´aire et de Physique des Particules (France), Ministry of Education and Science, Agency for Atomic Energy, and RF President Grants Program (Russia), CAPES, CNPq, FAPERJ, FAPESP, and FUNDUNESP (Brazil), Departments of Atomic Energy and Science and Technology (India), Colciencias (Colombia), CONACyT (Mexico), KRF (Korea), CONICET and UBACyT (Argentina), The Foundation for Fundamental Research on Matter (The Netherlands), PPARC (United Kingdom), Ministry of Education (Czech Republic), Natural Sciences and Engineering Research Council and WestGrid Project (Canada), BMBF and DFG (Germany), A. P. Sloan Foundation, Civilian Research and Development Foundation, Research Corporation, Texas Advanced Research Program, and the Alexander von Humboldt Foundation.
*Visitor from University of Zurich, Zurich, Switzerland.
†Visitor from Institute of Nuclear Physics, Krakow,
Poland.
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Fixed parameters 95% C.L. lower limits
Mm= tan N5 sgn( ) m~0 1 m~ 1 m~02 2 15 1 79.6 107.7 194.9 195.9 2 5 1 79.5 106.0 191.6 193.3 10 5 2 44.0 111.4 196.0 198.7
(TeV)
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55 60 65 70 75 80 85(pb)σ
10-2 10-1 1 (GeV) 1 0 χ ∼ m 80 90 100 110 (GeV) 1 + χ ∼ m 140 160 180 200 = 15 β tan = 1 5 N Λ = 2 m M > 0 µ GMSB:DØ
FIG. 2. Predicted cross sections for the Snowmass Slope model vs in leading order (thin solid line with crosses), multiplied by the K factor (thin dashed line), and the 95% C.L. limits (solid line).
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