Search for Diphoton Events with Large Missing Transverse Energy in 6:3 fb�1 of p �p Collisions at ffiffiffi s p ¼ 1:96 TeV V.M. Abazov,35 B. Abbott,73 M. Abolins,62 B. S. Acharya,29 M. Adams,48 T. Adams,46 G.D. Alexeev,35 G. Alkhazov,39 A. Alton,61,* G. Alverson,60 G.A. Alves,2 L. S. Ancu,34 M. Aoki,47 Y. Arnoud,14 M. Arov,57 A. Askew,46 B. Åsman,40 O. Atramentov,65 C. Avila,8 J. BackusMayes,80 F. Badaud,13 L. Bagby,47 B. Baldin,47 D. V. Bandurin,46 S. Banerjee,29 E. Barberis,60 P. Baringer,55 J. Barreto,2 J. F. Bartlett,47 U. Bassler,18 S. Beale,6 A. Bean,55 M. Begalli,3 M. Begel,71 C. Belanger-Champagne,40 L. Bellantoni,47 J. A. Benitez,62 S. B. Beri,27 G. Bernardi,17 R. Bernhard,22 I. Bertram,41 M. Besançon,18 R. Beuselinck,42 V.A. Bezzubov,38 P. C. Bhat,47 V. Bhatnagar,27 G. Blazey,49 S. Blessing,46 K. Bloom,64 A. Boehnlein,47 D. Boline,70 T. A. Bolton,56 E. E. Boos,37 G. Borissov,41 T. Bose,59 A. Brandt,76 O. Brandt,23 R. Brock,62 G. Brooijmans,68 A. Bross,47 D. Brown,17 J. Brown,17 X. B. Bu,7 D. Buchholz,50 M. Buehler,79 V. Buescher,24 V. Bunichev,37 S. Burdin,41,† T. H. Burnett,80 C. P. Buszello,42 B. Calpas,15 S. Calvet,16 E. Camacho-Pérez,32 M.A. Carrasco-Lizarraga,32 E. Carrera,46 B. C.K. Casey,47 H. Castilla-Valdez,32 S. Chakrabarti,70 D. Chakraborty,49 K.M. Chan,53 A. Chandra,78 G. Chen,55 S. Chevalier-Théry,18 D.K. Cho,75 S.W. Cho,31 S. Choi,31 B. Choudhary,28 T. Christoudias,42 S. Cihangir,47 D. Claes,64 J. Clutter,55 M. S. Cooke,68 M. Cooke,47 W. E. Cooper,47 M. Corcoran,78 F. Couderc,18 M.-C. Cousinou,15 A. Croc,18 D. Cutts,75 M. Ćwiok,30 A. Das,44 G. Davies,42 K. De,76 S. J. de Jong,34 E. De La Cruz-Burelo,32 F. Déliot,18 M. Demarteau,47 R. Demina,69 D. Denisov,47 S. P. Denisov,38 S. Desai,47 K. DeVaughan,64 H. T. Diehl,47 M. Diesburg,47 A. Dominguez,64 T. Dorland,80 A. Dubey,28 L. V. Dudko,37 D. Duggan,65 A. Duperrin,15 S. Dutt,27 A. Dyshkant,49 M. Eads,64 D. Edmunds,62 J. Ellison,45 V.D. Elvira,47 Y. Enari,17 S. Eno,58 H. Evans,51 A. Evdokimov,71 V.N. Evdokimov,38 G. Facini,60 A. V. Ferapontov,75 T. Ferbel,58,69 F. Fiedler,24 F. Filthaut,34 W. Fisher,62 H. E. Fisk,47 M. Fortner,49 H. Fox,41 S. Fuess,47 T. Gadfort,71 A. Garcia-Bellido,69 V. Gavrilov,36 P. Gay,13 W. Geist,19 W. Geng,15,62 D. Gerbaudo,66 C. E. Gerber,48 Y. Gershtein,65 G. Ginther,47,69 G. Golovanov,35 A. Goussiou,80 P. D. Grannis,70 S. Greder,19 H. Greenlee,47 Z. D. Greenwood,57 E.M. Gregores,4 G. Grenier,20 Ph. Gris,13 J.-F. Grivaz,16 A. Grohsjean,18 S. Grünendahl,47 M.W. Grünewald,30 F. Guo,70 J. Guo,70 G. Gutierrez,47 P. Gutierrez,73 A. Haas,68,‡ S. Hagopian,46 J. Haley,60 L. Han,7 K. Harder,43 A. Harel,69 J.M. Hauptman,54 J. Hays,42 T. Hebbeker,21 D. Hedin,49 H. Hegab,74 A. P. Heinson,45 U. Heintz,75 C. Hensel,23 I. Heredia-De La Cruz,32 K. Herner,61 G. Hesketh,60 M.D. Hildreth,53 R. Hirosky,79 T. Hoang,46 J. D. Hobbs,70 B. Hoeneisen,12 M. Hohlfeld,24 S. Hossain,73 Z. Hubacek,10 N. Huske,17 V. Hynek,10 I. Iashvili,67 R. Illingworth,47 A. S. Ito,47 S. Jabeen,75 M. Jaffré,16 S. Jain,67 D. Jamin,15 R. Jesik,42 K. Johns,44 M. Johnson,47 D. Johnston,64 A. Jonckheere,47 P. Jonsson,42 J. Joshi,27 A. Juste,47,x K. Kaadze,56 E. Kajfasz,15 D. Karmanov,37 P. A. Kasper,47 I. Katsanos,64 R. Kehoe,77 S. Kermiche,15 N. Khalatyan,47 A. Khanov,74 A. Kharchilava,67 Y. N. Kharzheev,35 D. Khatidze,75 M.H. Kirby,50 J.M. Kohli,27 A.V. Kozelov,38 J. Kraus,62 A. Kumar,67 A. Kupco,11 T. Kurča,20 V. A. Kuzmin,37 J. Kvita,9 S. Lammers,51 G. Landsberg,75 P. Lebrun,20 H. S. Lee,31 S.W. Lee,54 W.M. Lee,47 J. Lellouch,17 L. Li,45 Q. Z. Li,47 S.M. Lietti,5 J. K. Lim,31 D. Lincoln,47 J. Linnemann,62 V.V. Lipaev,38 R. Lipton,47 Y. Liu,7 Z. Liu,6 A. Lobodenko,39 M. Lokajicek,11 P. Love,41 H. J. Lubatti,80 R. Luna-Garcia,32,k A. L. Lyon,47 A.K.A. Maciel,2 D. Mackin,78 R. Madar,18 R. Magaña-Villalba,32 S. Malik,64 V. L. Malyshev,35 Y. Maravin,56 J. Martı́nez-Ortega,32 R. McCarthy,70 C. L. McGivern,55 M.M. Meijer,34 A. Melnitchouk,63 D. Menezes,49 P. G. Mercadante,4 M. Merkin,37 A. Meyer,21 J. Meyer,23 N. K. Mondal,29 G. S. Muanza,15 M. Mulhearn,79 E. Nagy,15 M. Naimuddin,28 M. Narain,75 R. Nayyar,28 H.A. Neal,61 J. P. Negret,8 P. Neustroev,39 H. Nilsen,22 S. F. Novaes,5 T. Nunnemann,25 G. Obrant,39 D. Onoprienko,56 J. Orduna,32 N. Osman,42 J. Osta,53 G. J. Otero y Garzón,1 M. Owen,43 M. Padilla,45 M. Pangilinan,75 N. Parashar,52 V. Parihar,75 S. K. Park,31 J. Parsons,68 R. Partridge,75,‡ N. Parua,51 A. Patwa,71 B. Penning,47 M. Perfilov,37 K. Peters,43 Y. Peters,43 G. Petrillo,69 P. Pétroff,16 R. Piegaia,1 J. Piper,62 M.-A. Pleier,71 P. L.M. Podesta-Lerma,32,{ V.M. Podstavkov,47 M.-E. Pol,2 P. Polozov,36 A.V. Popov,38 M. Prewitt,78 D. Price,51 S. Protopopescu,71 J. Qian,61 A. Quadt,23 B. Quinn,63 M. S. Rangel,16 K. Ranjan,28 P. N. Ratoff,41 I. Razumov,38 P. Renkel,77 P. Rich,43 M. Rijssenbeek,70 I. Ripp-Baudot,19 F. Rizatdinova,74 M. Rominsky,47 C. Royon,18 P. Rubinov,47 R. Ruchti,53 G. Safronov,36 G. Sajot,14 A. Sánchez-Hernández,32 M. P. Sanders,25 B. Sanghi,47 A. S. Santos,5 G. Savage,47 L. Sawyer,57 T. Scanlon,42 R.D. Schamberger,70 Y. Scheglov,39 H. Schellman,50 T. Schliephake,26 S. Schlobohm,80 C. Schwanenberger,43 R. Schwienhorst,62 J. Sekaric,55 H. Severini,73 E. Shabalina,23 V. Shary,18 A. A. Shchukin,38 R. K. Shivpuri,28 V. Simak,10 V. Sirotenko,47 P. Skubic,73 P. Slattery,69 D. Smirnov,53 K. J. Smith,67 G. R. Snow,64 J. Snow,72 S. Snyder,71 S. Söldner-Rembold,43 L. Sonnenschein,21 A. Sopczak,41 M. Sosebee,76 K. Soustruznik,9 B. Spurlock,76 J. Stark,14 V. Stolin,36 D.A. Stoyanova,38 E. Strauss,70 M. Strauss,73 D. Strom,48 L. Stutte,47 P. Svoisky,34 PRL 105, 221802 (2010) P HY S I CA L R EV I EW LE T T E R S week ending 26 NOVEMBER 2010 0031-9007=10=105(22)=221802(8) 221802-1 � 2010 The American Physical Society M. Takahashi,43 A. Tanasijczuk,1 W. Taylor,6 M. Titov,18 V. V. Tokmenin,35 D. Tsybychev,70 B. Tuchming,18 C. Tully,66 P.M. Tuts,68 L. Uvarov,39 S. Uvarov,39 S. Uzunyan,49 R. Van Kooten,51 W.M. van Leeuwen,33 N. Varelas,48 E.W. Varnes,44 I. A. Vasilyev,38 P. Verdier,20 L. S. Vertogradov,35 M. Verzocchi,47 M. Vesterinen,43 D. Vilanova,18 P. Vint,42 P. Vokac,10 H.D. Wahl,46 M.H. L. S. Wang,69 J. Warchol,53 G. Watts,80 M. Wayne,53 M. Weber,47,** M. Wetstein,58 A. White,76 D. Wicke,24 M.R. J. Williams,41 G.W. Wilson,55 S. J. Wimpenny,45 M. Wobisch,57 D. R. Wood,60 T. R. Wyatt,43 Y. Xie,47 C. Xu,61 S. Yacoob,50 R. Yamada,47 W.-C. Yang,43 T. Yasuda,47 Y.A. Yatsunenko,35 Z. Ye,47 H. Yin,7 K. Yip,71 H.D. Yoo,75 S.W. Youn,47 J. Yu,76 S. Zelitch,79 T. Zhao,80 B. Zhou,61 N. Zhou,68 J. Zhu,61 M. Zielinski,69 D. Zieminska,51 and L. Zivkovic68 (D0 Collaboration) 1Universidad de Buenos Aires, Buenos Aires, Argentina 2LAFEX, Centro Brasileiro de Pesquisas Fı́sicas, Rio de Janeiro, Brazil 3Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil 4Universidade Federal do ABC, Santo André, Brazil 5Instituto de Fı́sica Teórica, Universidade Estadual Paulista, São Paulo, Brazil 6Simon Fraser University, Vancouver, British Columbia, Canada, and York University, Toronto, Ontario, Canada 7University of Science and Technology of China, Hefei, People’s Republic of China 8Universidad de los Andes, Bogotá, Colombia 9Charles University, Faculty of Mathematics and Physics, Center for Particle Physics, Prague, Czech Republic 10Czech Technical University in Prague, Prague, Czech Republic 11Center for Particle Physics, Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic 12Universidad San Francisco de Quito, Quito, Ecuador 13LPC, Université Blaise Pascal, CNRS/IN2P3, Clermont, France 14LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, Grenoble, France 15CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France 16LAL, Université Paris-Sud, CNRS/IN2P3, Orsay, France 17LPNHE, Universités Paris VI and VII, CNRS/IN2P3, Paris, France 18CEA, Irfu, SPP, Saclay, France 19IPHC, Université de Strasbourg, CNRS/IN2P3, Strasbourg, France 20IPNL, Université Lyon 1, CNRS/IN2P3, Villeurbanne, France and Université de Lyon, Lyon, France 21III. Physikalisches Institut A, RWTH Aachen University, Aachen, Germany 22Physikalisches Institut, Universität Freiburg, Freiburg, Germany 23II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany 24Institut für Physik, Universität Mainz, Mainz, Germany 25Ludwig-Maximilians-Universität München, München, Germany 26Fachbereich Physik, Bergische Universität Wuppertal, Wuppertal, Germany 27Panjab University, Chandigarh, India 28Delhi University, Delhi, India 29Tata Institute of Fundamental Research, Mumbai, India 30University College Dublin, Dublin, Ireland 31Korea Detector Laboratory, Korea University, Seoul, Korea 32CINVESTAV, Mexico City, Mexico 33FOM-Institute NIKHEF and University of Amsterdam/NIKHEF, Amsterdam, The Netherlands 34Radboud University Nijmegen/NIKHEF, Nijmegen, The Netherlands 35Joint Institute for Nuclear Research, Dubna, Russia 36Institute for Theoretical and Experimental Physics, Moscow, Russia 37Moscow State University, Moscow, Russia 38Institute for High Energy Physics, Protvino, Russia 39Petersburg Nuclear Physics Institute, St. Petersburg, Russia 40Stockholm University, Stockholm and Uppsala University, Uppsala, Sweden 41Lancaster University, Lancaster LA1 4YB, United Kingdom 42Imperial College London, London SW7 2AZ, United Kingdom 43The University of Manchester, Manchester M13 9PL, United Kingdom 44University of Arizona, Tucson, Arizona 85721, USA 45University of California Riverside, Riverside, California 92521, USA 46Florida State University, Tallahassee, Florida 32306, USA 47Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA 48University of Illinois at Chicago, Chicago, Illinois 60607, USA PRL 105, 221802 (2010) P HY S I CA L R EV I EW LE T T E R S week ending 26 NOVEMBER 2010 221802-2 49Northern Illinois University, DeKalb, Illinois 60115, USA 50Northwestern University, Evanston, Illinois 60208, USA 51Indiana University, Bloomington, Indiana 47405, USA 52Purdue University Calumet, Hammond, Indiana 46323, USA 53University of Notre Dame, Notre Dame, Indiana 46556, USA 54Iowa State University, Ames, Iowa 50011, USA 55University of Kansas, Lawrence, Kansas 66045, USA 56Kansas State University, Manhattan, Kansas 66506, USA 57Louisiana Tech University, Ruston, Louisiana 71272, USA 58University of Maryland, College Park, Maryland 20742, USA 59Boston University, Boston, Massachusetts 02215, USA 60Northeastern University, Boston, Massachusetts 02115, USA 61University of Michigan, Ann Arbor, Michigan 48109, USA 62Michigan State University, East Lansing, Michigan 48824, USA 63University of Mississippi, University, Mississippi 38677, USA 64University of Nebraska, Lincoln, Nebraska 68588, USA 65Rutgers University, Piscataway, New Jersey 08855, USA 66Princeton University, Princeton, New Jersey 08544, USA 67State University of New York, Buffalo, New York 14260, USA 68Columbia University, New York, New York 10027, USA 69University of Rochester, Rochester, New York 14627, USA 70State University of New York, Stony Brook, New York 11794, USA 71Brookhaven National Laboratory, Upton, New York 11973, USA 72Langston University, Langston, Oklahoma 73050, USA 73University of Oklahoma, Norman, Oklahoma 73019, USA 74Oklahoma State University, Stillwater, Oklahoma 74078, USA 75Brown University, Providence, Rhode Island 02912, USA 76University of Texas, Arlington, Texas 76019, USA 77Southern Methodist University, Dallas, Texas 75275, USA 78Rice University, Houston, Texas 77005, USA 79University of Virginia, Charlottesville, Virginia 22901, USA 80University of Washington, Seattle, Washington 98195, USA (Received 14 August 2010; published 24 November 2010) We report a search for diphoton events with large missing transverse energy produced in p �p collisions at ffiffiffi s p ¼ 1:96 TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider and correspond to 6:3 fb�1 of integrated luminosity. The observed missing transverse energy distribution is well described by the standard model prediction, and 95% C.L. limits are derived on two realizations of theories beyond the standard model. In a gauge-mediated supersymmetry breaking scenario, the breaking scale � is excluded for �< 124 TeV. In a universal extra dimension model including gravitational decays, the compactification radius Rc is excluded for R�1 c < 477 GeV. DOI: 10.1103/PhysRevLett.105.221802 PACS numbers: 14.80.Ly, 12.60.Jv, 13.85.Rm, 14.80.Rt In the standard model (SM), events with two high trans- verse momentum photons (��) and large missing trans- verse energy [1] (ET) are produced at a small rate in p �p collisions. This final state is therefore sensitive to contri- butions from processes beyond the SM (BSM). We report a search for �� events with large ET produced in p �p colli- sions recorded by using the D0 detector at the Fermilab Tevatron Collider. The sensitivity is assessed for two benchmark BSM models, gauge-mediated supersymmetry (SUSY) breaking (GMSB) [2] and universal extra dimen- sions (UED) [3]. In GMSB models, the masses of the SUSY partners to SM particles arise from SM gauge interactions and are proportional to the effective SUSY breaking scale �. As the gravitino ( ~G) does not participate in SM gauge interactions, it has a small mass [4] and is the lightest SUSY particle. Assuming R parity conservation [5], the SUSY process with the largest cross section at the Tevatron would be chargino and neutralino pair production (�� 1 � 0 2, �� 1 � � 1 ) [6], followed by decay chains to the next-to- lightest SUSY particle. We consider the case when the lightest neutralino (�0 1) is the next-to-lightest SUSY parti- cle [7] and decays promptly with the dominant branching fraction yielding a photon and an essentially massless gravitino (�0 1 ! ~G�) [8]. The two gravitinos escape detec- tion, resulting in the final state ��þ ET þ X, where X denotes leptons and jets produced in the decay chains [9]. In UED models, extra spatial dimensions are predicted that are accessible to all SM fields. We consider the case of a single UED that is compactified with radius Rc, resulting PRL 105, 221802 (2010) P HY S I CA L R EV I EW LE T T E R S week ending 26 NOVEMBER 2010 221802-3 http://dx.doi.org/10.1103/PhysRevLett.105.221802 in a tower of states for each SM field, called Kaluza-Klein (KK) excitations, with the masses of these states separated by R�1 c . At the Tevatron, the UED process with the largest cross section would be the production of pairs of first-level KK quarks [10], followed by decay chains to the lightest KK particle, the KK photon (��). If additional larger extra dimensions also exist that are only accessible to gravity, the lightest KK particle is able to decay promptly through gravitational interactions to a photon and a graviton (�� ! G�) [11,12]. The two gravitons escape detection, resulting in the final state ��þ ET þ X. Searches for BSM physics in ��þET þ X events have been performed at the CERN eþe� Collider (LEP) [13] and at the Tevatron in run I [14] and run II [15–18]. This analysis uses similar search methods to those adopted in Ref. [18] and employs a 6 times larger data set and im- proved photon identification criteria utilizing a neural net- work (NN) discriminant. The photon NN discriminant has been recently used in a measurement [19] by D0 of differ- ential cross sections and kinematic properties of �� events produced at the Tevatron. The larger data set has substan- tially increased the search sensitivity and has allowed an improved formulation of the data-derived SM background prediction. The background prediction, including the as- sessment of systematic uncertainties, was developed by using only the ET � 50 GeV region of the �� sample. Once finalized, the events with ET > 50 GeV were in- cluded in evaluating the consistency with the SM predic- tion and the sensitivity to the signal models. In addition to substantially improved limits on the GMSB model, this Letter also presents the first limits on the UED model with gravitational decays. The D0 detector [20] consists of an inner tracker, a liquid-argon–uranium calorimeter, and a muon spectrome- ter. The tracking system is comprised of a silicon micro- strip tracker and a central fiber tracker, both located within a 2 T superconducting solenoidal magnet. A central calo- rimeter covers pseudorapidities j�j< 1:1, and two end-cap calorimeters extend the coverage to j�j< 4:2, where � ¼ � ln½tanð�=2Þ�, and � is the polar angle with respect to the proton beam direction. The electromagnetic (EM) section of the calorimeter is segmented in four longitudinal layers (EMi, i ¼ 1; 4) with transverse segmentation����� ¼ 0:1� 0:1 (� is the azimuthal angle), except in EM3 where it is 0:05� 0:05. A central preshower detector utilizing several layers of scintillating strips, positioned between the solenoid coil and central calorimeter, provides a precise measurement of EM shower position. The trajectory of photon candidates is reconstructed by combining the four EM-layer and central preshower detector measure- ments [18]. The data analyzed correspond to an integrated luminos- ity of 6:3� 0:4 fb�1 [21] and were selected by using a collection of EM calorimeter-based single electron and photon triggers that are close to 100% efficient for signal events from the benchmark models satisfying the accep- tance requirements of this analysis. Events containing identified calorimeter noise patterns which could bias the ET distribution are removed. Diphoton candidate events are selected by requiring at least two photon candidates with transverse energy ET > 25 GeV identified in the central calorimeter. Photon candidates are selected from EM clusters reconstructed within a cone of radius R � ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið��Þ2 þ ð��Þ2p ¼ 0:2 by requiring (i) 95% of the cluster energy be deposited in the EM layers, (ii) the calorimeter isolation variable I � ½Etotð0:4Þ � EEMð0:2Þ�= EEMð0:2Þ be less than 0.10, where EtotðRÞ ½EEMðRÞ� is the total [EM] energy in a cone of radius R about the cluster centroid, (iii) the shower width in EM3 be consistent with an EM shower, (iv) the scalar sum of the transverse mo- mentum (pT) of tracks originating from the p �p collision vertex (PV) in a 0:05 35 GeV, and the data-only and MC-only extremes are used to define a systematic uncer- tainty on this shape. The ET shape in misID-jet events is modeled with a data sample satisfying the same requirements as the �� sample with the exception that at least one of the photon candi- dates fails the NN requirement. Additionally, photon iden- tification requirements (iii) and (iv) are loosened to reduce the statistical uncertainty on the ET shape. A systematic uncertainty on the ET shape in events with misidentified jets is obtained by varying the photon identification criteria. The instrumental ET background estimate is normalized such that the number of events with ET < 10 GeV is equal to that in the �� sample. The relative contribution of SM �� and misID-jet background events is determined by a fit to the �� sample ET distribution for ET < 20 GeV. The fit accounts for the small contribution of SM background with genuine ET in the fit region and is verified to be insensitive to signal contributions for benchmark model cross sections relevant to this analysis. The SM �� contribution to the �� sample over the full ET range is ð41� 17Þ%. A systematic uncertainty accounts for changes in the shape of the predicted instrumental ET distribution arising from the uncertainty in the determination of the SM �� contribution. SM background with genuine ET arises from real SM ��þ ET þ X events and from events with an electron misidentified as a photon (misID-ele.). The misID-ele. contribution is derived by using an e� data sample, com- posed primarily of instrumental ET sources for ET < 20 GeV and Wð! e�Þ� and Wð! e�Þ þ jet events at higher ET values. The instrumental ET sources are mod- eled with the previously introduced ee and misID-jet ET shapes, respectively. The Z ! ee normalization is deter- mined by fitting the Z boson peak in the e� invariant mass distribution, and the multijet ET shape is normalized to provide the remaining contribution in the ET < 10 GeV region. The presence of real ET contributions in the e� sample is seen as an excess of events with high ET values above the predicted contributions from instrumental sources. This excess is well described by W� and W þ jet events. The expected W boson peak is observed in the transverse mass distribution of e� sample events with ET > 30 GeV. The normalization of theW þ jet contribu- tion is determined from a comparison of the data photon NN shape with MC real and fake photon NN shapes [19] in this ET region. The remaining contribution is in good agreement with PYTHIA W� production after applying a next-to-leading order (NLO) QCD correction [25] and an additional þ15% scaling factor accounting for QED final state radiation in inclusive W production. The final state [GeV] T Missing E 0 50 100 150 200 250 300 E ve n ts / 2. 5 G eV -310 -210 -110 1 10 210 310 -1 6.3 fb∅D sample dataγγ = 120 TeV)ΛSM + GMSB ( = 460 GeV)-1 c SM + UED (R γγSM γγW/Z + misidentified electrons misidentified jets FIG. 1 (color online). ET distribution in the �� sample shown with statistical uncertainty and expected SM background from events with a misidentified jet, a misidentified electron, W=Zþ �� events, and SM �� events. The expected ET distribution in the presence of GMSB and UED events is also displayed for example values of � and R�1 c , respectively. PRL 105, 221802 (2010) P HY S I CA L R EV I EW LE T T E R S week ending 26 NOVEMBER 2010 221802-5 radiation component [26] is determined with data using the �Rðe; �Þ distribution. The predicted misID-ele. contribu- tion to the �� sample equals the excess of high ET events in the e� sample, scaled by fe!�=ð1� fe!�Þ, where fe!� ¼ 0:020� 0:005 denotes the rate at which an elec- tron fakes a photon satisfying the selection criteria, as measured with Z ! ee data. Real SM diphoton events with large genuine ET origi- nate from W=Zþ �� processes. This background contri- bution is estimated with MC by using MADGRAPH [27]. Events with inclusive W and Z boson decay modes are simulated, with W ! l�ðl ¼ e;�; �Þ and Z ! � �� pro- viding the largest genuine ET contribution. A total of 1:6� 0:1 W þ �� events and 3:8� 0:3 Zþ �� events are estimated to be present in the �� sample. Figure 1 displays the �� sample ET distribution, which is in good agreement with the SM prediction over the full ET range. Table I provides the observed number of �� sample events and the SM prediction in three ET regions. We determine the sensitivity to the GMSB scenario by using a set of values, termed SPS8 [28], for the model parameters. In this set the scale � is unconstrained, Mmes ¼ 2�, Nmes ¼ 1, tan ¼ 15, and �> 0 [28]. The masses and decay widths of SUSY particles are calculated with SUSYHIT 1.3 [29] and used to generate PYTHIA MC events. The event selection efficiency is 0:17� 0:02 at � ¼ 120 TeV and does not differ significantly for other � values studied. The NLO production cross section is calculated with PROSPINO 2.1 [6]. The expected ET distribution for the SM and GMSB at � ¼ 120 TeV is depicted in Fig. 1. The number of expected GMSB events in three ET regions is listed in Table I for � ¼ 100 and 120 TeV. We consider the UED model as implemented in PYTHIA 6.421 [30], leaving R�1 c unconstrained and setting ~�Rc ¼ 20, where ~� is the cutoff scale for radiative corrections to KK masses. This UED model is implemented in a higher (4þ N)-dimensional space, where R�1 c is much larger than that of the N compact extra dimensions accessible only to gravity, inducing KK particle decays through gravitational interactions. We choose N ¼ 6 and a fundamental Planck scale MD ¼ 5 TeV, such that only the �� ! G� decay occurs with appreciable branching fraction [12]. The event selection efficiency is 0:19� 0:02 at R�1 c ¼ 460 GeV and TABLE I. Observed number of �� events, predicted background from instrumental ET sources (SM ��, �þ jet, QCD multijet) and genuine ET sources (W�, W þ jet, W=Zþ ��), and total predicted SM background, in three ET intervals. The expected number of GMSB and UED signal events is listed for two � and R�1 c values. The total uncertainty on the SM background and expected signal is given. SM background events Expected signal events ET interval Observed GMSB GMSB UED UED (GeV) events Instr. ET Genuine ET Total � ¼ 100 TeV � ¼ 120 TeV R�1 c ¼ 420 GeV R�1 c ¼ 460 GeV 35–50 18 9:6� 1:9 2:3� 0:5 11:9� 2:0 1:8� 0:1 0:3� 0:1 1:4� 0:1 0:3� 0:1 50–75 3 3:5� 0:8 1:5� 0:3 5:0� 0:9 4:1� 0:3 0:8� 0:1 2:9� 0:2 0:6� 0:1 >75 1 1:1� 0:4 0:8� 0:1 1:9� 0:4 14:3� 1:1 4:4� 0:4 24:7� 2:0 6:4� 0:5 [TeV]Λ 80 90 100 110 120 130 140 [ fb ] σ 1 10 210 [GeV]0 1 χm 120 140 160 180 [GeV]± 1 χm 220 240 260 280 300 320 340 360 NLO cross section observed limit expected limit σ 1 ±expected limit σ 2 ±expected limit -1 6.3 fb∅D SPS8 GMSB SUSY (Prospino 2.1) [GeV]-1 cR 380 400 420 440 460 480 500 [ fb ] σ 1 10 210 [GeV] D q*m 460 480 500 520 540 560 580 [GeV]g*m 480 500 520 540 560 580 600 620 LO cross section observed limit expected limit σ 1 ±expected limit σ 2 ±expected limit -1 6.3 fb∅D c=20RΛ∼=1 UED (PYTHIA 6.421), δ FIG. 2 (color online). The predicted cross section for the benchmark GMSB and UED models, and 95% C.L. expected and observed exclusion limits, as a function of � and R�1 c , respectively. For the GMSB model, corresponding masses are shown for the lightest chargino �� 1 and neutralino �0 1. For the UED model, corresponding masses are shown for the KK quark q�D and KK gluon g�. The mass of the KK photon �� is approximately equal to R�1 c . PRL 105, 221802 (2010) P HY S I CA L R EV I EW LE T T E R S week ending 26 NOVEMBER 2010 221802-6 does not differ significantly for other R�1 c values studied. The expected ET distribution for the SM and UED at R�1 c ¼ 460 TeV is depicted in Fig. 1. The number of expected UED events in three ET regions is listed in Table I for R�1 c ¼ 420 and 460 GeV. Systematic uncertainties for sources of instrumental ET are attributed to the uncertainty of the ET shape in SM �� and misID-jet events and their relative normalization. An uncertainty in the shape of the ET distribution for the misID-ele. contribution arises from the uncertainty in the Z ! ee contribution to the e� sample, and a 25% misID- ele. normalization uncertainty results from the fe!� uncertainty. Systematic uncertainties in the contributions estimated with MC arise from the integrated luminosity (6.1%), trigger efficiency (2%), and photon identification (3% per photon) and trajectory (3%) efficiencies. Uncertainty in parton distribution functions [31] yield systematic uncertainties of up to 5% and 20% in the production rate of GMSB and UED events, respectively. No evidence for BSM physics is observed in the �� sample ET distribution, and limits on the benchmark models are derived by using a Poisson log-likelihood ratio test [32] incorporating the full ET distribution. Pseudoexperiments are generated according to the background-only and signal plus background hypotheses and account for statistical uncertainty on the expected number of events and systematic uncertainties. The cross section limit is evaluated by using the CLs modified fre- quentist approach [32]. Figure 2 shows the predicted GMSB and UED cross section with parton distribution function uncertainty and 95% C.L. cross section exclusion limit, as functions of � and R�1 c , respectively. For GMSB, the NLO cross section uncertainty is small compared to the parton distribution function uncertainty. The UED NLO cross section has not yet been computed. In conclusion, we have presented a search for physics beyond the standard model in the ��þ ET þ X final state at the Tevatron. The observed ET distribution is consistent with the SM expectation, and limits on two benchmark models are derived. In the SPS8 GMSB model, values of the effective SUSY breaking scale �< 124 TeV are ex- cluded at 95% C.L. The limit excludes m�0 1 < 175 GeV, representing improvements of 50 [18] and 26 GeV [16] with respect to previous measurements. Additionally, the first assessment is made of the sensitivity to the UED model with KK particle decays induced by gravitational interactions, excluding values of the compactification ra- dius R�1 c < 477 GeV at 95% C.L. We thank the staffs at Fermilab and collaborating insti- tutions and acknowledge support from the DOE and NSF (USA); CEA and CNRS/IN2P3 (France); FASI, Rosatom, and RFBR (Russia); CNPq, FAPERJ, FAPESP, and FUNDUNESP (Brazil); DAE and DST (India); Colciencias (Colombia); CONACyT (Mexico); KRF and KOSEF (Korea); CONICET and UBACyT (Argentina); FOM (The Netherlands); STFC and the Royal Society (United Kingdom); MSMT and GACR (Czech Republic); CRC Program and NSERC (Canada); BMBF and DFG (Germany); SFI (Ireland); The Swedish Research Council (Sweden); and CAS and CNSF (China). *Visitor from Augustana College, Sioux Falls, SD, USA. †Visitor from The University of Liverpool, Liverpool, United Kingdom. ‡Visitor from SLAC, Menlo Park, CA, USA. xVisitor from ICREA/IFAE, Barcelona, Spain. kVisitor from Centro de Investigacion en Computacion— IPN, Mexico City, Mexico. {Visitor from ECFM, Universidad Autonoma de Sinaloa, Culiacán, Mexico. **Visitor from Universität Bern, Bern, Switzerland. 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