Article
Reference
Search for new physics in lepton + photon + X events with 929 pb
−1of pp collisions at s√=1.96 TeV
CDF Collaboration
CAMPANELLI, Mario (Collab.), et al.
Abstract
We present results of a search at CDF in 929±56 pb−1 of pp collisions at 1.96 TeV for the anomalous production of events containing a high-transverse momentum charged lepton (ℓ, either e or μ) and photon (γ), accompanied by missing transverse energy (E̸T), and/or additional leptons and photons, and jets (X). We use the same selection criteria as in a previous CDF Run I search, but with an order-magnitude larger data set, a higher pp collision energy, and the CDF II detector. We find 163 ℓγE̸T+X events, compared to an expectation of 150.6±13.0 events. We observe 74 ℓℓγ+X events, compared to an expectation of 65.1±7.7 events. We find no events similar to the Run I eeγγE̸T event.
CDF Collaboration, CAMPANELLI, Mario (Collab.), et al . Search for new physics in lepton + photon + X events with 929 pb
−1of pp collisions at s√=1.96 TeV. Physical Review. D , 2007, vol. 75, no. 11, p. 112001
DOI : 10.1103/PhysRevD.75.112001
Available at:
http://archive-ouverte.unige.ch/unige:38441
Disclaimer: layout of this document may differ from the published version.
Search for new physics in lepton photon X events with 929 pb
1of p p collisions
at
p s
1:96 TeV
A. Abulencia,24J. Adelman,13T. Affolder,10T. Akimoto,56M. G. Albrow,17D. Ambrose,17S. Amerio,44D. Amidei,35 A. Anastassov,53K. Anikeev,17A. Annovi,19J. Antos,14M. Aoki,56G. Apollinari,17J.-F. Arguin,34T. Arisawa,58 A. Artikov,15W. Ashmanskas,17A. Attal,8F. Azfar,43P. Azzi-Bacchetta,44P. Azzurri,47N. Bacchetta,44W. Badgett,17 A. Barbaro-Galtieri,29V. E. Barnes,49B. A. Barnett,25S. Baroiant,7V. Bartsch,31G. Bauer,33F. Bedeschi,47S. Behari,25
S. Belforte,55G. Bellettini,47J. Bellinger,60A. Belloni,33D. Benjamin,16A. Beretvas,17J. Beringer,29T. Berry,30 A. Bhatti,51M. Binkley,17D. Bisello,44R. E. Blair,2C. Blocker,6B. Blumenfeld,25A. Bocci,16A. Bodek,50V. Boisvert,50
G. Bolla,49A. Bolshov,33D. Bortoletto,49J. Boudreau,48A. Boveia,10B. Brau,10L. Brigliadori,5C. Bromberg,36 E. Brubaker,13J. Budagov,15H. S. Budd,50S. Budd,24S. Budroni,47K. Burkett,17G. Busetto,44P. Bussey,21K. L. Byrum,2
S. Cabrera,16,qM. Campanelli,20M. Campbell,35F. Canelli,17A. Canepa,49S. Carillo,18,iD. Carlsmith,60R. Carosi,47 S. Carron,34M. Casarsa,55A. Castro,5P. Catastini,47D. Cauz,55M. Cavalli-Sforza,3A. Cerri,29L. Cerrito,43,m S. H. Chang,28Y. C. Chen,1M. Chertok,7G. Chiarelli,47G. Chlachidze,15F. Chlebana,17I. Cho,28K. Cho,28D. Chokheli,15 J. P. Chou,22G. Choudalakis,33S. H. Chuang,60K. Chung,12W. H. Chung,60Y. S. Chung,50M. Ciljak,47C. I. Ciobanu,24
M. A. Ciocci,47A. Clark,20D. Clark,6M. Coca,16G. Compostella,44M. E. Convery,51J. Conway,7B. Cooper,36 K. Copic,35M. Cordelli,19G. Cortiana,44F. Crescioli,47C. Cuenca Almenar,7,oJ. Cuevas,11,lR. Culbertson,17J. C. Cully,35
D. Cyr,60S. DaRonco,44M. Datta,17S. D’Auria,21T. Davies,21M. D’Onofrio,3D. Dagenhart,6P. de Barbaro,50 S. De Cecco,52A. Deisher,29G. De Lentdecker,50,cM. Dell’Orso,47F. Delli Paoli,44L. Demortier,51J. Deng,16 M. Deninno,5D. De Pedis,52P. F. Derwent,17G. P. Di Giovanni,45C. Dionisi,52B. Di Ruzza,55J. R. Dittmann,4 P. DiTuro,53C. Do¨rr,26S. Donati,47M. Donega,20P. Dong,8J. Donini,44T. Dorigo,44S. Dube,53J. Efron,40R. Erbacher,7
D. Errede,24S. Errede,24R. Eusebi,17H. C. Fang,29S. Farrington,30I. Fedorko,47W. T. Fedorko,13R. G. Feild,61 M. Feindt,26J. P. Fernandez,32R. Field,18G. Flanagan,49A. Foland,22S. Forrester,7G. W. Foster,17M. Franklin,22 J. C. Freeman,29H. Frisch,13I. Furic,13M. Gallinaro,51J. Galyardt,12J. E. Garcia,47F. Garberson,10A. F. Garfinkel,49
C. Gay,61H. Gerberich,24D. Gerdes,35S. Giagu,52P. Giannetti,47A. Gibson,29K. Gibson,48J. L. Gimmell,50 C. Ginsburg,17N. Giokaris,15,aM. Giordani,55P. Giromini,19M. Giunta,47G. Giurgiu,12V. Glagolev,15D. Glenzinski,17
M. Gold,38N. Goldschmidt,18J. Goldstein,43,bA. Golossanov,17G. Gomez,11G. Gomez-Ceballos,11M. Goncharov,54 O. Gonza´lez,32I. Gorelov,38A. T. Goshaw,16K. Goulianos,51A. Gresele,44M. Griffiths,30S. Grinstein,22 C. Grosso-Pilcher,13R. C. Group,18U. Grundler,24J. Guimaraes da Costa,22Z. Gunay-Unalan,36C. Haber,29K. Hahn,33
S. R. Hahn,17E. Halkiadakis,53A. Hamilton,34B.-Y. Han,50J. Y. Han,50R. Handler,60F. Happacher,19K. Hara,56 M. Hare,57S. Harper,43R. F. Harr,59R. M. Harris,17M. Hartz,48K. Hatakeyama,51J. Hauser,8A. Heijboer,46 B. Heinemann,30J. Heinrich,46C. Henderson,33M. Herndon,60J. Heuser,26D. Hidas,16C. S. Hill,10,bD. Hirschbuehl,26
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T. R. Junk,24T. Kamon,54P. E. Karchin,59Y. Kato,42Y. Kemp,26R. Kephart,17U. Kerzel,26V. Khotilovich,54 B. Kilminster,40D. H. Kim,28H. S. Kim,28J. E. Kim,28M. J. Kim,12S. B. Kim,28S. H. Kim,56Y. K. Kim,13N. Kimura,56
L. Kirsch,6S. Klimenko,18M. Klute,33B. Knuteson,33B. R. Ko,16K. Kondo,58D. J. Kong,28J. Konigsberg,18 A. Korytov,18A. V. Kotwal,16A. Kovalev,46A. C. Kraan,46J. Kraus,24I. Kravchenko,33M. Kreps,26J. Kroll,46 N. Krumnack,4M. Kruse,16V. Krutelyov,10T. Kubo,56S. E. Kuhlmann,2T. Kuhr,26Y. Kusakabe,58S. Kwang,13 A. T. Laasanen,49S. Lai,34S. Lami,47S. Lammel,17M. Lancaster,31R. L. Lander,7K. Lannon,40A. Lath,53G. Latino,47
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T. Maki,23P. Maksimovic,25S. Malde,43G. Manca,30F. Margaroli,5R. Marginean,17C. Marino,26C. P. Marino,24 A. Martin,61M. Martin,25V. Martin,21,gM. Martı´nez,3T. Maruyama,56P. Mastrandrea,52T. Masubuchi,56H. Matsunaga,56 M. E. Mattson,59R. Mazini,34P. Mazzanti,5K. S. McFarland,50P. McIntyre,54R. McNulty,30,fA. Mehta,30P. Mehtala,23 S. Menzemer,11,hA. Menzione,47P. Merkel,49C. Mesropian,51A. Messina,36T. Miao,17N. Miladinovic,6J. Miles,33 R. Miller,36C. Mills,10M. Milnik,26A. Mitra,1G. Mitselmakher,18A. Miyamoto,27S. Moed,20N. Moggi,5B. Mohr,8
R. Moore,17M. Morello,47P. Movilla Fernandez,29J. Mu¨lmensta¨dt,29A. Mukherjee,17Th. Muller,26R. Mumford,25
P. Murat,17J. Nachtman,17A. Nagano,56J. Naganoma,58I. Nakano,41A. Napier,57V. Necula,18C. Neu,46M. S. Neubauer,9 J. Nielsen,29,pT. Nigmanov,48L. Nodulman,2O. Norniella,3E. Nurse,31S. H. Oh,16Y. D. Oh,28I. Oksuzian,18
T. Okusawa,42R. Oldeman,30R. Orava,23K. Osterberg,23C. Pagliarone,47E. Palencia,11V. Papadimitriou,17 A. A. Paramonov,13B. Parks,40S. Pashapour,34J. Patrick,17G. Pauletta,55M. Paulini,12C. Paus,33D. E. Pellett,7 A. Penzo,55T. J. Phillips,16G. Piacentino,47J. Piedra,45L. Pinera,18K. Pitts,24C. Plager,8L. Pondrom,60X. Portell,3
O. Poukhov,15N. Pounder,43F. Prakoshyn,15A. Pronko,17J. Proudfoot,2F. Ptohos,19,eG. Punzi,47J. Pursley,25 J. Rademacker,43,bA. Rahaman,48N. Ranjan,49S. Rappoccio,22B. Reisert,17V. Rekovic,38P. Renton,43M. Rescigno,52
S. Richter,26F. Rimondi,5L. Ristori,47A. Robson,21T. Rodrigo,11E. Rogers,24S. Rolli,57R. Roser,17M. Rossi,55 R. Rossin,18A. Ruiz,11J. Russ,12V. Rusu,13H. Saarikko,23S. Sabik,34A. Safonov,54W. K. Sakumoto,50G. Salamanna,52
O. Salto´,3D. Saltzberg,8C. Sa´nchez,3L. Santi,55S. Sarkar,52L. Sartori,47K. Sato,17P. Savard,34A. Savoy-Navarro,45 T. Scheidle,26P. Schlabach,17E. E. Schmidt,17M. P. Schmidt,61M. Schmitt,39T. Schwarz,7L. Scodellaro,11A. L. Scott,10
A. Scribano,47F. Scuri,47A. Sedov,49S. Seidel,38Y. Seiya,42A. Semenov,15L. Sexton-Kennedy,17A. Sfyrla,20 M. D. Shapiro,29T. Shears,30P. F. Shepard,48D. Sherman,22M. Shimojima,56,lM. Shochet,13Y. Shon,60I. Shreyber,37
A. Sidoti,47P. Sinervo,34A. Sisakyan,15J. Sjolin,43A. J. Slaughter,17J. Slaunwhite,40K. Sliwa,57J. R. Smith,7 F. D. Snider,17R. Snihur,34M. Soderberg,35A. Soha,7S. Somalwar,53V. Sorin,36J. Spalding,17F. Spinella,47T. Spreitzer,34
P. Squillacioti,47M. Stanitzki,61A. Staveris-Polykalas,47R. St. Denis,21B. Stelzer,8O. Stelzer-Chilton,43D. Stentz,39 J. Strologas,38D. Stuart,10J. S. Suh,28A. Sukhanov,18H. Sun,57T. Suzuki,56A. Taffard,24,nR. Takashima,41Y. Takeuchi,56
K. Takikawa,56M. Tanaka,2R. Tanaka,41M. Tecchio,35P. K. Teng,1K. Terashi,51J. Thom,17,dA. S. Thompson,21 E. Thomson,46P. Tipton,61V. Tiwari,12S. Tkaczyk,17D. Toback,54S. Tokar,14K. Tollefson,36T. Tomura,56D. Tonelli,47
S. Torre,19D. Torretta,17S. Tourneur,45W. Trischuk,34R. Tsuchiya,58S. Tsuno,41N. Turini,47F. Ukegawa,56 T. Unverhau,21S. Uozumi,56D. Usynin,46S. Vallecorsa,20N. van Remortel,23A. Varganov,35E. Vataga,38F. Va´zquez,18,i
G. Velev,17G. Veramendi,24V. Veszpremi,49R. Vidal,17I. Vila,11R. Vilar,11T. Vine,31I. Vollrath,34I. Volobouev,29,o G. Volpi,47F. Wu¨rthwein,9P. Wagner,54R. G. Wagner,2R. L. Wagner,17J. Wagner,26W. Wagner,26R. Wallny,8 S. M. Wang,1A. Warburton,34S. Waschke,21D. Waters,31M. Weinberger,54W. C. Wester III,17B. Whitehouse,57
D. Whiteson,46A. B. Wicklund,2E. Wicklund,17G. Williams,34H. H. Williams,46P. Wilson,17B. L. Winer,40 P. Wittich,17,dS. Wolbers,17C. Wolfe,13T. Wright,35X. Wu,20S. M. Wynne,30A. Yagil,17K. Yamamoto,42J. Yamaoka,53
T. Yamashita,41C. Yang,61U. K. Yang,13,jY. C. Yang,28W. M. Yao,29G. P. Yeh,17J. Yoh,17K. Yorita,13T. Yoshida,42 G. B. Yu,50I. Yu,28S. S. Yu,17J. C. Yun,17L. Zanello,52A. Zanetti,55I. Zaw,22X. Zhang,24J. Zhou,53and S. Zucchelli5
(CDF Collaboration)
1Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China
2Argonne National Laboratory, Argonne, Illinois 60439, USA
3Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain
4Baylor University, Waco, Texas 76798, USA
5Istituto Nazionale di Fisica Nucleare, University of Bologna, I-40127 Bologna, Italy
6Brandeis University, Waltham, Massachusetts 02254, USA
7University of California, Davis, Davis, California 95616, USA
8University of California, Los Angeles, Los Angeles, California 90024, USA
9University of California, San Diego, La Jolla, California 92093, USA
10University of California, Santa Barbara, Santa Barbara, California 93106, USA
11Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain
12Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
13Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
14Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia
15Joint Institute for Nuclear Research, RU-141980 Dubna, Russia
16Duke University, Durham, North Carolina 27708
17Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
18University of Florida, Gainesville, Florida 32611, USA
19Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy
20University of Geneva, CH-1211 Geneva 4, Switzerland
21Glasgow University, Glasgow G12 8QQ, United Kingdom
22Harvard University, Cambridge, Massachusetts 02138, USA
23Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland
24University of Illinois, Urbana, Illinois 61801, USA
25The Johns Hopkins University, Baltimore, Maryland 21218, USA
26Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany
27High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, Japan
28Center for High Energy Physics: Kyungpook National University, Taegu 702-701, Korea;
Seoul National University, Seoul 151-742, Korea;
and SungKyunKwan University, Suwon 440-746, Korea
29Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
30University of Liverpool, Liverpool L69 7ZE, United Kingdom
31University College London, London WC1E 6BT, United Kingdom
32Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain
33Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
34Institute of Particle Physics: McGill University, Montre´al, Canada H3A 2T8;
and University of Toronto, Toronto, Canada M5S 1A7
35University of Michigan, Ann Arbor, Michigan 48109, USA
36Michigan State University, East Lansing, Michigan 48824, USA
37Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia
38University of New Mexico, Albuquerque, New Mexico 87131, USA
39Northwestern University, Evanston, Illinois 60208, USA
40The Ohio State University, Columbus, Ohio 43210, USA
41Okayama University, Okayama 700-8530, Japan
42Osaka City University, Osaka 588, Japan
43University of Oxford, Oxford OX1 3RH, United Kingdom
44University of Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy
45LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France
46University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
47Istituto Nazionale di Fisica Nucleare Pisa, Universities of Pisa, Siena and Scuola Normale Superiore, I-56127 Pisa, Italy
48University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
49Purdue University, West Lafayette, Indiana 47907, USA
50University of Rochester, Rochester, New York 14627, USA
51The Rockefeller University, New York, New York 10021, USA
52Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, University of Rome ‘‘La Sapienza,’’ I-00185 Roma, Italy
53Rutgers University, Piscataway, New Jersey 08855, USA
54Texas A&M University, College Station, Texas 77843, USA
55Istituto Nazionale di Fisica Nucleare, University of Trieste/Udine, Italy
56University of Tsukuba, Tsukuba, Ibaraki 305, Japan
57Tufts University, Medford, Massachusetts 02155, USA
58Waseda University, Tokyo 169, Japan
59Wayne State University, Detroit, Michigan 48201, USA
oVisiting scientist from Texas Tech University, Lubbock, TX 79409, USA.
nVisiting scientist from University of California Santa Cruz, Santa Cruz, CA 95064, USA.
mVisiting scientist from University of London, Queen Mary College, London, E1 4NS, England.
lVisiting scientist from University de Oviedo, E-33007 Oviedo, Spain.
kVisiting scientist from Nagasaki Institute of Applied Science, Nagasaki, Japan.
jVisiting scientist from University of Manchester, Manchester M13 9PL, England.
iVisiting scientist from Universidad Iberoamericana, Mexico D.F., Mexico.
hVisiting scientist from University of Heidelberg, D-69120 Heidelberg, Germany.
gVisiting scientist from University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
fVisiting scientist from University of Dublin, University College Dublin, Dublin 4, Ireland.
eVisiting scientist from University of Cyprus, Nicosia CY-1678, Cyprus.
dVisiting scientist from Cornell University, Ithaca, NY 14853.
cVisiting scientist from University Libre de Bruxelles, B-1050 Brussels, Belgium.
bVisiting scientist from University of Bristol, Bristol BS8 1TL, United Kingdom.
aVisiting scientist from University of Athens, University of Athens, 15784 Athens, Greece.
pVisiting scientist from University of California, Irvine, Irvine, CA 92697, USA.
qVisiting scientist from IFIC (CSIC-Universitat de Valencia), 46071 Valencia, Spain.
. . .
60University of Wisconsin, Madison, Wisconsin 53706, USA
61Yale University, New Haven, Connecticut 06520, USA (Received 21 February 2007; published 28 June 2007)
We present results of a search at CDF in92956 pb1ofppcollisions at 1.96 TeV for the anomalous production of events containing a high-transverse momentum charged lepton (‘, eithereor) and photon (), accompanied by missing transverse energy (E6 T), and/or additional leptons and photons, and jets (X).
We use the same selection criteria as in a previous CDF Run I search, but with an order-magnitude larger data set, a higherppcollision energy, and the CDF II detector. We find 163‘E6 TXevents, compared to an expectation of150:613:0events. We observe 74‘‘Xevents, compared to an expectation of 65:17:7events. We find no events similar to the Run IeeE6 Tevent.
DOI:10.1103/PhysRevD.75.112001 PACS numbers: 13.85.Rm, 12.60.Jv, 13.85.Qk, 14.80.Ly
I. INTRODUCTION
An important test of the standard model (SM) of particle physics [1] is to measure and understand the properties of the highest momentum-transfer particle collisions, which correspond to measurements at the shortest distances. The chief predictions of the SM for these collisions are the numbers and types of the fundamental fermions and gauge bosons that are produced, and their associated kinematic distributions. The predicted high-energy behavior of the SM, however, becomes unphysical at an interaction energy on the order of several TeV. New physical phenomena are required to ameliorate this high-energy behavior. These unknown phenomena may involve new elementary parti- cles, new fundamental forces, and/or a modification of space-time geometry. These new phenomena are likely to show up as an anomalous production rate of a combination of the known fundamental particles, including those detector-based signatures such as missing transverse en- ergy (E6 T) or penetrating particle tracks that within the confines of the SM are associated with neutrinos and muons, respectively.
The unknown nature of possible new phenomena in the energy range accessible at the Tevatron is the motivation for a search strategy that does not focus on a single model or class of models of new physics, but presents a wide net for new phenomena. In this paper we present the results of a comparison of standard model predictions with the rates measured at the Tevatron with the CDF detector for final states containing at least one high-pT lepton (eor) and photon, plus other detected objects (leptons, photons, jets, E6 T).
The initial motivation for such an inclusive search (‘‘signature-based search’’) came from the observation in 1995 by the CDF experiment [2] of an event consistent with the production of two energetic photons, two ener- getic electrons, and large missing transverse energyE6 T[3].
This signature is predicted to be very rare in the SM, with the dominant contribution being from the production of four gauge bosons: twoW bosons and two photons. The event raised theoretical interest, however, as it had, in addition to large missing transverse momentum, very high total transverse energy, and a pattern of widely-
separated leptons and photons that was consistent with the decay of a pair of new heavy particles.
There are many models of new physics that could pro- duce such a signature [4]. Gauge-mediated models of supersymmetry [5], in which the lightest superpartner (LSP) is a light gravitino, provide a model in which each partner of a pair of supersymmetric particles produced in a pp interaction decays in a chain that leads to a produced gravitino, visible as E6 T. If the next-to-lightest neutralino (NLSP) has a photino component, each chain also can result in a photon. Models of supersymmetry in which the symmetry breaking is due to gravity also can produce decay chains with photons [6]. For example, if the NLSP is largely photinolike, and the lightest is largely Higgsino, decays of the former to the latter will involve the emission of a photon [7]. More generally, pair-production of selec- trons or gauginos can result in final-states with large E6 T, two photons and two leptons. Models with additional space dimensions [8] predict excited states of the known standard model particles. The production of a pair of excited elec- trons [9] would provide a natural source for two photons and two electrons (although not E6 T unless the pair were produced with some other, undetected, particle). As in the case of supersymmetry, there are many parameters in such models, with a resulting broad range of possible signatures with multiple gauge bosons [10].
Rather than search the huge parameter space of the models current at that time, the CDF Run I analyses that followed up on the eeE6 T event used a strategy of
‘‘signature-based’’ inclusive searches to cast a wider net for new phenomena: in this case one search for two photonsXX [2], and a second for one leptonone photonX‘X [11–13], whereX can bee,,, orE6 T, plus any number of jets. In particular the latter signature, the subject of this present paper, would be sensitive to decay chains in which only one chain produces a photon, a broader set of models.
The Run I ‘X search found good agreement with SM predictions in 86 pb1 of data at a center-of-mass energy of 1.8 TeV, except in the‘E6 T channel, in which 16 events were observed with an expectation of7:60:7, corresponding to a 2:7 excess. The Run I paper con- cluded: ‘‘However, an excess of events with 0.7% like-
lihood (equivalent to 2.7 standard deviations for a Gaussian distribution) in one subsample among the five studied is an interesting result, but it is not a compelling observation of new physics. We look forward to more data in the upcom- ing run of the Fermilab Tevatron’’ [12].
Here we present the results from Run II with more than 10 times the statistics of the Run I measurement. We have repeated the ‘X search with the same kinematic se- lection criteria in a data set corresponding to an exposure of92956 pb1, a higherppcollision energy, 1.96 TeV, and the CDF II detector [14]. The results correspond to the full data set taken during the period March, 2002 through February, 2006, and include data from the first third of this sample which have already been presented [15]. We give a detailed description of the selection criteria, background calculations, and kinematic distributions for the‘E6 T and
‘‘channels. We also present results for the first time for theeXand‘signatures.
This paper is organized as follows. Section II gives a brief description of the CDF II detector, emphasizing the changes from Run I. Section III presents the electron, muon, photon, andE6 T identification criteria, and the kine- matic event selection criteria. The data flow as additional selection criteria are added, resulting in the measured number of events in each signature, is also described.
The standard model W and Z samples, used as control samples, are described in Sec. IV. Section V gives an introduction to the selection of the Inclusive‘Xevent sample. Section VI describes the selection of the ‘E6 T signal sample, and presents the measured kinematic dis- tributions. Similarly, the‘‘signal sample selection and kinematic distributions are presented in Sec. VII. A search for the ‘ signature is briefly described in Sec. VIII.
Section IX summarizes the SM expectations from W, W, Z, Z production, and backgrounds from mis- identified photons,E6 T, and/or leptons. Sections X and XI summarize the results and present the conclusions, respectively.
II. THE CDF II DETECTOR
The CDF II detector is a cylindrically symmetric spec- trometer designed to study pp collisions at the Fermilab Tevatron based on the same solenoidal magnet and central calorimeters as the CDF I detector [16]. Because the analysis described here is intended to repeat the Run I search as closely as possible, we note especially the dif- ferences from the CDF I detector relevant to the detection of leptons, photons, andE6 T. The tracking systems used to measure the momenta of charged particles have been re- placed with a central outer tracker (COT) with smaller drift cells [17], and an enhanced system of silicon strip detectors [18]. The calorimeters in the regions [19] with pseudora- pidity jj>1 have been replaced with a more compact scintillator-based design, retaining the projective geometry [20]. The coverage in ’ of the central upgrade muon
detector (CMP) and central extension muon detector (CMX) systems [21] has been extended; the central muon detector (CMU) system is unchanged.
III. SELECTION OF‘XEVENTS
In order to make the present search statisticallya priori, the identification of leptons and photons is essentially the same as in the Run I search [11], with only minor technical changes due to the differences in detector details between the upgraded CDF II detector and CDF I.
The scope and strategy of the Run I analysis were designed to reflect the motivating principles. Categories of photon-lepton events were defineda prioriin a way that characterized the different possibilities for new physics.
For each category, the inclusive event total and basic kine- matic distributions can be compared with standard model expectations. The decay products of massive particles are typically isolated from other particles, and possess large transverse momentum and low rapidity. The search is therefore limited to those events with at least one isolated, central (jj<1:0) photon withE6 T>25 GeV, and at least one isolated, central electron or muon withE6 T>25 GeV.
These photon-lepton candidates are further partitioned by angular separation. Events where exactly one photon and one lepton are detected nearly opposite in azimuth (’‘>150) are characteristic of a two-particle final- state (two-body photon-lepton events), and the remaining photon-lepton events are characteristic of three or more particles in the final-state (multibody photon-lepton events). The multibody photon-lepton events are then fur- ther studied for the presence of additional particles: pho- tons, leptons, or the missing transverse energy associated with weakly interacting neutral particles.
In the subsections below we describe the real-time (‘‘on- line’’) event selection criteria by the trigger system, and the subsequent event selection ‘‘offline,’’ including the selec- tion of electrons, muons, and photons, the rejection of jet background for leptons and photons by track and calorime- ter ‘‘isolation’’ requirements, and the construction of the missing transverse energy E6 T and total transverse energy HT.
A. The online selection by the trigger system A three-level trigger system [14] selects events with a high-transverse momentum (pT) [3] lepton (pT>
18 GeV) or photon (ET>25 GeV) in the central region,
jj&1:0. The trigger system selects photon and electron
candidates from clusters of energy in the central electro- magnetic calorimeter. Electrons are distinguished from photons by the presence of a COT track pointing at the cluster. The muon trigger requires a COT track that ex- trapolates to a track segment (‘‘stub’’) in the muon cham- bers [22]. At each trigger level all transverse momenta are calculated using the nominal center of the interaction region along the beam line,z0[19].
. . .
B. Overview of event selection
Inclusive‘events (Fig.1) are selected by requiring a centralcandidate withET>25 GeVand a centraleor withE‘T >25 GeVoriginating less than 60 cm along the beam line from the detector center and passing the ‘‘tight’’
criteria listed below. All transverse momenta, including that of the photon, are calculated using the vertex within 5 cmof the lepton origin that has the largest scalar sum of transverse momentum from tracks associated to that vertex. Both signal and control samples are drawn from this‘sample (Fig.1).
Considering the control samples first, from the‘sam- ple we select back-to-back events with exactly one photon and one lepton (i.e. E6 T<25 GeV); this is the dominant contribution to the‘ sample, and has a large Drell-Yan component. A subset of this sample is the ‘‘Z-like’’ sample, which provides the calibration for the probability that an electron radiates and is detected as a photon, as discussed in Sec. IX B 1. The remaining back-to-back events are called the two-body events and were not used in this analysis.
All events which either have more than one lepton or photon, or in which the lepton and photon are not back-to- back (and hence the event cannot be a Two-Body event), are classified as ‘‘inclusive multibody‘X.’’ These are further subdivided into three categories: ‘E6 T (Sec. V) (‘‘multibody ‘E6 T Events’’), for which the E6 T (Sec. III B 5) is greater than 25 GeV, ‘‘(Sec. VII) and
‘(Sec. VIII) (‘‘multiphoton and multilepton events’’), and events with exactly one lepton and exactly one photon,
which are not back-to-back. The events with exactly one lepton and exactly one photon, which are not back-to-back were not used in the analysis.
1. Electron selection
An electron candidate passing the tight selection must have: (a) a high-quality track in the COT withpT>0:5E6 T, unless E6 T >100 GeV, in which case thepT threshold is set to 25 GeV; (b) a good transverse shower profile at shower maximum [23] that matches the extrapolated track position; (c) a lateral sharing of energy in the two calo- rimeter towers containing the electron shower consistent with that expected; and (d) minimal leakage into the had- ron calorimeter [24].
Additional central electrons are required to haveET>
20 GeVand to satisfy the tight central electron criteria but with a track requirement of onlypT>10 GeV(rather than 0:5ET), and no requirement on a shower maximum measurement or lateral energy sharing between calorime- ter towers. Electrons in the end-plug calorimeters (1:2<
jj<2:0) are required to have ET>15 GeV, minimal leakage into the hadron calorimeter, a ‘‘track’’ containing at least 3 hits in the silicon tracking system, and a shower transverse shape consistent with that expected, with a centroid close to the extrapolated position of the track [25].
2. Muon selection
A muon candidate passing the tight cuts must have: (a) a well-measured track in the COT with pT >25 GeV;
(b) energy deposited in the calorimeter consistent with expectations [26]; (c) a muon stub [22] in both the CMU and CMP, or in the CMX, consistent with the extrapolated COT track [27]; and (d) COT timing consistent with a track from app collision [28].
Additional muons are required to have pT>20 GeV and to satisfy the same criteria as for tight muons but with fewer hits required on the track, or, alternatively, for muons outside the muon system fiducial volume, a more stringent cut on track quality but no requirement that there be a matching stub in the muon systems [29].
3. Photon selection
Photon candidates are required to have: no associated track with pT>1 GeV; at most one track with pT<
1 GeV, pointing at the calorimeter cluster; good profiles in both transverse dimensions at shower maximum; and minimal leakage into the hadron calorimeter [24].
4. ‘‘Isolated’’ leptons and photons
To reduce background from photons or leptons from the decays of hadrons produced in jets, both the photon and the lepton in each event are required to be ‘‘isolated’’ [30]. The ET deposited in the calorimeter towers in a cone in’ space [19] of radius R0:4around the photon or lepton lγ+X Sample
EγT > 25 GeV, ElT > 25 GeV 1678 (199 and 1479)
Exactly 1l, 1γ
∆φlγ > 150°,E
E
E E
T < 25 GeV 1214 (84 and 1130)
Inclusiv e Multi-Body lγ+X 464 (115 and 349)
Z-Likelγ
81 GeV< Meγ <101 GeV 648 (28 and 620)
Exactly 1l, 1γ,
∆φlγ < 150°,
T <25 GeV 227 (27 and 200)
Tw o-Bo dy Ev ents 566 (56 and 510)
lγ T,
T >25 GeV 163 (67 and 96)
llγ Ev ents 74 (21 and 53)
lγγ Ev ents none observed
FIG. 1. ‘XSample: the subsets of inclusive lepton-photon events analyzed. The number of events in each subcategory is given as a sum of muons and electrons. The first term in paren- thesis refers toXwhile the latter refers to theeX.
position is summed, and theETdue to the photon or lepton is subtracted. The remainingET is required to be less than 2:0 GeV0:02 ET 20 GeV for a photon, or less than 10% of the ET for electrons or pT for muons. In addition, for photons the scalar sum of thepT of all tracks in the cone must be less than2:0 GeV0:005ET.
5. Missing transverse energy andHT
Missing transverse energy E6 T is calculated from the calorimeter tower energies in the region jj<3:6.
Corrections are then made to theE6 T for nonuniform calo- rimeter response [31] for jets with uncorrected ET >
15 GeVand <2:0, and for muons withpT>20 GeV.
The variableHT is defined for each event as the sum of the transverse energies of the leptons, photons, jets, andE6 T that pass the above selection criteria.
IV. CONTROL SAMPLES
Because we are looking for processes with small cross sections, and hence small numbers of measured events, we use larger control samples to validate our understanding of the detector performance and to measure efficiencies and backgrounds.
We useW andZevents reconstructed from the same inclusive lepton datasets as control samples to ensure that the efficiencies for high-pT electrons and muons are well understood. In addition, theWsamples provide the con- trol samples for the understanding of E6 T. The selection criteria for theW samples require a tight lepton andE6 T >
25 GeV. We find 571 194 W!e events and 381 727 W !events. For theZsamples we require two leptons, at least one of which satisfies the tight criteria. We find 30 808Z!ee events and 30 086Z! events.
The photon control sample is constructed fromZ!ee events in which one of the electrons radiates a high-ET such that theeinvariant mass is within 10 GeV of theZ mass.
V. THE INCLUSIVE‘XEVENT SAMPLE A total of 1678 events, 1479 inclusive e and 199 inclusive candidates, pass the ‘ selection criteria.
Of the 1479 inclusive eevents, 1130 have the electron and photon within 30 of back-to-back in ’, E6 T<
25 GeV, and no additional leptons or photons. These are dominated by Z!ee decays in which one of the electrons radiates a high-ET photon while traversing ma- terial before entering the COT active volume, leading to the observation of an electron and a photon approximately back-to-back in’, with aneinvariant mass close to the Zmass.
VI. THE INCLUSIVE‘E6 T EVENT SAMPLE The first search we perform is in the ‘E6 TX sub- sample, defined by requiring that an event contain E6 T>
25 GeVin addition to theand tight lepton. Of the 1678
‘events, 96 eE6 T events and 67E6 T events pass the E6 T requirement.
A. Kinematic distributions in the electron and muon samples
The muon and electron signatures have different back- grounds and detector resolutions, among other differences.
While these are corrected for, it is useful to plot the observed distributions separately before combining them.
We show both the individual sample distributions as well as the final combined plot [32].
FIG. 2 (color online). The distributions for events in theeE6 T sample (points in the left-hand four plots) and theE6 T sample (points in the right-hand four plots) for (a) theE6 Tof the photon; (b) theE6 Tof the lepton; (c) the missing transverse energy,E6 T; and (d) the transverse mass of the‘E6 T system. The histograms show the expected SM contributions, including estimated backgrounds from misidentified photons and leptons.
. . .
1. Distributions in photonET, leptonET,E6 T, and 3-body transverse mass
Figure 2 shows the observed distributions in (a) the ET of the photon; (b) the ET of the lepton; (c) E6 T; and (d) the transverse mass of the ‘E6 T system, where MT E‘TETE6 T2—E~‘T E~T6E~T21=2. The left-hand set of four plots shows the distributions for electrons; the right-hand set shows the distributions for muons.
2. Distributions inHT,‘,‘E6 T,Me Figure 3 shows the distributions for the eE6 T sample (left) and E6 T sample (right) in (a) HT, the sum of the transverse energies of the lepton, photon, jets, and E6 T; (b) the distance in - space between the photon and lepton; (c) the angular separation inbetween the lepton and the missing transverse energy,E6 T; and (d) the invariant mass of the‘system. The histograms show the expected
FIG. 4 (color online). The distributions for events in the‘E6 T sample (points) in (a) the E6 T of the photon; (b) the E6 T of the lepton (eor); (c) the missing transverse energy,E6 T; and (d) the transverse mass of the‘E6 T system. The histograms show the expected SM contributions, including estimated backgrounds from misidentified photons and leptons.
FIG. 3 (color online). The distributions for events in theeE6 T sample (points in the left-hand four plots) and theE6 T sample (points in the right-hand four plots) in (a)HT, the sum of the transverse energies of the lepton, photon, jets andE6 T; (b) the distance in -space between the photon and lepton; (c) the angular separation inbetween the lepton and the missing transverse energy,E6 T; and (d) the invariant mass of the‘system. The histograms show the expected SM contributions, including estimated backgrounds from misidentified photons and leptons.
FIG. 5 (color online). The distributions for events in the‘E6 T sample (points) in (a)HT, the sum of the transverse energies of the lepton, photon, jets and E6 T; (b) the distance in -space between the photon and lepton; (c) the angular separation in between the lepton andE6 T; and (d) the invariant mass of the‘ system. The histograms show the expected SM contributions, including estimated backgrounds from misidentified photons and leptons.
SM contributions, including estimated backgrounds from misidentified photons and leptons.
The electron and muon kinematic distributions are com- bined in Fig.4and5. There is very good agreement with the expected standard model shapes.
VII. THE INCLUSIVE‘‘EVENT SAMPLE A second search, for the ‘‘X signature, is con- structed by requiring anothereorin addition to the tight lepton and the.
The‘‘search criteria select 74 events (53eeand 21 ) of the 1678‘events. Noeevents are observed.
A. Distributions in photonET, leptonET, dilepton invariant mass, and‘‘mass
Figure6shows the observed distributions in the signa- ture ee (left-hand plots) and channels (right-hand plots) for: (a) the ET of the photon; (b) the ET of the electrons; (c) the 2-body mass of the dilepton system;
and (d) the 3-body massMeeorM. For theZprocess occurring via initial-state radiation, the dilepton invariant massM‘‘distribution is peaked around theZ0pole. For the final-state radiation, the three body invariant mass M‘‘
distribution is peaked about theZ0pole.
The combined distributions for electrons and muons are shown in Fig.7.
B. Distributions inHTandR‘
Figure8shows the distributions for theeesample (left- hand plots) andsample (right-hand plots) for: (a)HT, the sum of the transverse energies of the electron, photon, jets andE6 T; (b) and the distance in-space between the photon and each of the two leptons. The histograms show the expected SM contributions, including estimated back- grounds from misidentified photons and leptons. The dis- tributions for electrons and muons are combined in Fig.9.
C. The distributions inE6 T
We do not expect SM events with largeE6 T in the‘‘
sample; the Run IeeE6 T event was of special interest in the context of supersymmetry [33] due to the large value of E6 T (557 GeV). Figure10shows the distributions inE6 T for the andeesubsamples of the ‘‘sample. We observe 3‘‘events withE6 T>25 GeV, compared to an expectation of0:60:1events.
FIG. 6 (color online). The distributions for events in theeesample (points in the left-hand four plots) and thesample (points in the right-hand four plots) in (a) theETof the photon; (b) theET(pT) of the electrons (muons) (two entries per event); (c) the 2-body mass of the dilepton system; and (d) the 3-body massM‘‘. The histograms show the expected SM contributions.
FIG. 7 (color online). The distributions for events in the‘‘
sample (points) in (a) the ET of the photon; (b) the ET of the leptons (two entries per event); (c) the 2-body mass of the dilepton system; and (d) the 3-body massM‘‘. The histograms show the expected SM contributions.
. . .
VIII. SEARCH FOR THE‘SIGNATURE In some models of new phenomena the decay chain of each of a pair of new heavy particles ends in a photon plus other particles [33]. One such signature that contains two photons and is a subset of the‘Xselection is‘.
The selection for the ‘ search starts with a tight lepton and a photon, each with ET>25 GeV, from the same ‘X sample as the‘E6 T and‘‘searches. An additional photon with ET>25 GeV, passing the same selection criteria as the first, is then required. We observe
no ‘ events, compared to the expectation of 0:62 0:15.
IX. STANDARD MODEL EXPECTATIONS A.W,Z,W,Z
The dominant SM source of‘events is electroweakW andZ= production along with aradiated from one of the charged particles involved in the process [34]. The number of such events is estimated using leading-order (LO) event generators [35–37]. Initial-state radiation is simulated by the PYTHIA Monte Carlo (MC) program [38] tuned to reproduce the underlying event. The gener- ated particles are then passed through a full detector simu- lation, and these events are then reconstructed with the same code used for the data.
The expected contributions from W and Z=
production to the ‘E6 T and ‘‘ searches are given in Tables I and II, respectively. The expected contributions to the esearch are given in Table IV. A correction for higher-order processes (Kfactor) that depends on both the dilepton mass and photonET has been applied [39]. In the
‘E6 T signature we expect71:5010:01events fromW and17:753:65fromZ=. In the‘‘signature, we expect63:407:48events fromZ=; the contribu- tion from W is negligible. The uncertainties on the SM contributions include those from parton distribution func- tions (5%), factorization scale (2%), K factor (3%), a comparison of different MC generators (5%), and the luminosity (6%).
We have used bothMADGRAPH[35] andCOMPHEP[37]
to simulate the triboson channels W and Z. The expected contributions are small,0:970:12and1:14 0:13events in the‘E6 T and‘‘signatures, respectively.
The expected contributions from W and Z=
production to the‘search are given in TablesIandII.
B. Backgrounds from misidentifications 1. ‘‘Fake’’ photons
High pT photons are copiously created from hadron decays in jets initiated by a scattered quark or gluon. In FIG. 8 (color online). The distributions for events in theeesample (points in the left-hand two plots) and thesample (points in the right-hand two plots) in (a)HT, the sum of the transverse energies of the lepton, photon, jets andE6 T; (b) the distance in- space between the photon and each of the two leptons (two entries per event). The histograms show the expected SM contributions, including estimated backgrounds from misidentified photons and leptons.
FIG. 9 (color online). The distributions for events in the‘‘
sample (points) in (a)HT, the sum of the transverse energies of the lepton, photon, jets andE6 T; (b) the distance in-space between the photon and each of the two leptons (two entries per event). The histograms show the expected SM contributions, including estimated backgrounds from misidentified photons and leptons.
FIG. 10 (color online). The distributions in missing transverse energyE6 T observed in the inclusive search for (a)events and (b) ee events. The histograms show the expected SM contributions.
