Search for Resonant Second Generation Slepton Production at the Fermilab Tevatron
V. M. Abazov,36B. Abbott,76M. Abolins,66B. S. Acharya,29M. Adams,52T. Adams,50M. Agelou,18J.-L. Agram,19 S. H. Ahn,31M. Ahsan,60G. D. Alexeev,36G. Alkhazov,40A. Alton,65G. Alverson,64G. A. Alves,2M. Anastasoaie,35T. Andeen,54S. Anderson,46B. Andrieu,17M. S. Anzelc,54Y. Arnoud,14M. Arov,53A. Askew,50B. A˚ sman,41 A. C. S. Assis Jesus,3O. Atramentov,58C. Autermann,21C. Avila,8C. Ay,24F. Badaud,13A. Baden,62L. Bagby,53 B. Baldin,51D. V. Bandurin,59P. Banerjee,29S. Banerjee,29E. Barberis,64P. Bargassa,81P. Baringer,59C. Barnes,44 J. Barreto,2J. F. Bartlett,51U. Bassler,17D. Bauer,44A. Bean,59M. Begalli,3M. Begel,72C. Belanger-Champagne,5 L. Bellantoni,51A. Bellavance,68J. A. Benitez,66S. B. Beri,27G. Bernardi,17R. Bernhard,42L. Berntzon,15I. Bertram,43 M. Besanc¸on,18R. Beuselinck,44V. A. Bezzubov,39P. C. Bhat,51V. Bhatnagar,27M. Binder,25C. Biscarat,43K. M. Black,63 I. Blackler,44G. Blazey,53F. Blekman,44S. Blessing,50D. Bloch,19K. Bloom,68U. Blumenschein,23A. Boehnlein,51
O. Boeriu,56T. A. Bolton,60F. Borcherding,51G. Borissov,43K. Bos,34T. Bose,78A. Brandt,79R. Brock,66 G. Brooijmans,71A. Bross,51D. Brown,79N. J. Buchanan,50D. Buchholz,54M. Buehler,82V. Buescher,23S. Burdin,51
S. Burke,46T. H. Burnett,83E. Busato,17C. P. Buszello,44J. M. Butler,63P. Calfayan,25S. Calvet,15J. Cammin,72 S. Caron,34W. Carvalho,3B. C. K. Casey,78N. M. Cason,56H. Castilla-Valdez,33S. Chakrabarti,29D. Chakraborty,53 K. M. Chan,72A. Chandra,49D. Chapin,78F. Charles,19E. Cheu,46F. Chevallier,14D. K. Cho,63S. Choi,32B. Choudhary,28
L. Christofek,59D. Claes,68B. Cle´ment,19C. Cle´ment,41Y. Coadou,5M. Cooke,81W. E. Cooper,51D. Coppage,59 M. Corcoran,81M.-C. Cousinou,15B. Cox,45S. Cre´pe´-Renaudin,14D. Cutts,78M. C´ wiok,30H. da Motta,2A. Das,63
M. Das,61B. Davies,43G. Davies,44G. A. Davis,54K. De,79P. de Jong,34S. J. de Jong,35E. De La Cruz-Burelo,65 C. De Oliveira Martins,3J. D. Degenhardt,65F. De´liot,18M. Demarteau,51R. Demina,72P. Demine,18D. Denisov,51 S. P. Denisov,39S. Desai,73H. T. Diehl,51M. Diesburg,51M. Doidge,43A. Dominguez,68H. Dong,73L. V. Dudko,38 L. Duflot,16S. R. Dugad,29A. Duperrin,15J. Dyer,66A. Dyshkant,53M. Eads,68D. Edmunds,66T. Edwards,45J. Ellison,49
J. Elmsheuser,25V. D. Elvira,51S. Eno,62P. Ermolov,38J. Estrada,51H. Evans,55A. Evdokimov,37V. N. Evdokimov,39 S. N. Fatakia,63L. Feligioni,63A. V. Ferapontov,60T. Ferbel,72F. Fiedler,25F. Filthaut,35W. Fisher,51H. E. Fisk,51 I. Fleck,23M. Ford,45M. Fortner,53H. Fox,23S. Fu,51S. Fuess,51T. Gadfort,83C. F. Galea,35E. Gallas,51E. Galyaev,56 C. Garcia,72A. Garcia-Bellido,83J. Gardner,59V. Gavrilov,37A. Gay,19P. Gay,13D. Gele´,19R. Gelhaus,49C. E. Gerber,52
Y. Gershtein,50D. Gillberg,5G. Ginther,72N. Gollub,41B. Go´mez,8K. Gounder,51A. Goussiou,56P. D. Grannis,73 H. Greenlee,51Z. D. Greenwood,61E. M. Gregores,4G. Grenier,20Ph. Gris,13J.-F. Grivaz,16S. Gru¨nendahl,51 M. W. Gru¨newald,30F. Guo,73J. Guo,73G. Gutierrez,51P. Gutierrez,76A. Haas,71N. J. Hadley,62P. Haefner,25 S. Hagopian,50J. Haley,69I. Hall,76R. E. Hall,48L. Han,7K. Hanagaki,51K. Harder,60A. Harel,72R. Harrington,64 J. M. Hauptman,58R. Hauser,66J. Hays,54T. Hebbeker,21D. Hedin,53J. G. Hegeman,34J. M. Heinmiller,52A. P. Heinson,49
U. Heintz,63C. Hensel,59G. Hesketh,64M. D. Hildreth,56R. Hirosky,82J. D. Hobbs,73B. Hoeneisen,12H. Hoeth,26 M. Hohlfeld,16S. J. Hong,31R. Hooper,78P. Houben,34Y. Hu,73Z. Hubacek,10V. Hynek,9I. Iashvili,70R. Illingworth,51 A. S. Ito,51S. Jabeen,63M. Jaffre´,16S. Jain,76K. Jakobs,23C. Jarvis,62A. Jenkins,44R. Jesik,44K. Johns,46C. Johnson,71 M. Johnson,51A. Jonckheere,51P. Jonsson,44A. Juste,51D. Ka¨fer,21S. Kahn,74E. Kajfasz,15A. M. Kalinin,36J. M. Kalk,61 J. R. Kalk,66S. Kappler,21D. Karmanov,38J. Kasper,63P. Kasper,51I. Katsanos,71D. Kau,50R. Kaur,27R. Kehoe,80 S. Kermiche,15S. Kesisoglou,78N. Khalatyan,63A. Khanov,77A. Kharchilava,70Y. M. Kharzheev,36D. Khatidze,71
H. Kim,79T. J. Kim,31M. H. Kirby,35B. Klima,51J. M. Kohli,27J.-P. Konrath,23M. Kopal,76V. M. Korablev,39 J. Kotcher,74B. Kothari,71A. Koubarovsky,38A. V. Kozelov,39J. Kozminski,66A. Kryemadhi,82S. Krzywdzinski,51 T. Kuhl,24A. Kumar,70S. Kunori,62A. Kupco,11 T. Kurcˇa,20,*J. Kvita,9S. Lager,41S. Lammers,71G. Landsberg,78 J. Lazoflores,50A.-C. Le Bihan,19P. Lebrun,20W. M. Lee,53A. Leflat,38F. Lehner,42V. Lesne,13J. Leveque,46P. Lewis,44
J. Li,79Q. Z. Li,51J. G. R. Lima,53D. Lincoln,51J. Linnemann,66V. V. Lipaev,39R. Lipton,51Z. Liu,5L. Lobo,44 A. Lobodenko,40M. Lokajicek,11A. Lounis,19P. Love,43H. J. Lubatti,83M. Lynker,56A. L. Lyon,51A. K. A. Maciel,2
R. J. Madaras,47P. Ma¨ttig,26C. Magass,21A. Magerkurth,65A.-M. Magnan,14N. Makovec,16P. K. Mal,56 H. B. Malbouisson,3S. Malik,68V. L. Malyshev,36H. S. Mao,6Y. Maravin,60M. Martens,51S. E. K. Mattingly,78 R. McCarthy,73R. McCroskey,46D. Meder,24A. Melnitchouk,67A. Mendes,15L. Mendoza,8M. Merkin,38K. W. Merritt,51 A. Meyer,21J. Meyer,22M. Michaut,18H. Miettinen,81T. Millet,20J. Mitrevski,71J. Molina,3N. K. Mondal,29J. Monk,45
R. W. Moore,5T. Moulik,59G. S. Muanza,16M. Mulders,51M. Mulhearn,71L. Mundim,3Y. D. Mutaf,73E. Nagy,15 M. Naimuddin,28M. Narain,63N. A. Naumann,35H. A. Neal,65J. P. Negret,8S. Nelson,50P. Neustroev,40C. Noeding,23
A. Nomerotski,51S. F. Novaes,4T. Nunnemann,25V. O’Dell,51D. C. O’Neil,5G. Obrant,40V. Oguri,3N. Oliveira,3
N. Oshima,51R. Otec,10G. J. Otero y Garzo´n,52M. Owen,45P. Padley,81N. Parashar,57S.-J. Park,72S. K. Park,31 J. Parsons,71R. Partridge,78N. Parua,73A. Patwa,74G. Pawloski,81P. M. Perea,49E. Perez,18K. Peters,45P. Pe´troff,16
M. Petteni,44R. Piegaia,1M.-A. Pleier,22P. L. M. Podesta-Lerma,33V. M. Podstavkov,51Y. Pogorelov,56M.-E. Pol,2 A. Pomposˇ,76B. G. Pope,66A. V. Popov,39W. L. Prado da Silva,3H. B. Prosper,50S. Protopopescu,74J. Qian,65A. Quadt,22
B. Quinn,67K. J. Rani,29K. Ranjan,28P. A. Rapidis,51P. N. Ratoff,43P. Renkel,80S. Reucroft,64M. Rijssenbeek,73 I. Ripp-Baudot,19F. Rizatdinova,77S. Robinson,44R. F. Rodrigues,3C. Royon,18P. Rubinov,51R. Ruchti,56V. I. Rud,38 G. Sajot,14A. Sa´nchez-Herna´ndez,33M. P. Sanders,62A. Santoro,3G. Savage,51L. Sawyer,61T. Scanlon,44D. Schaile,25
R. D. Schamberger,73Y. Scheglov,40H. Schellman,54P. Schieferdecker,25C. Schmitt,26C. Schwanenberger,45 A. Schwartzman,69R. Schwienhorst,66S. Sengupta,50H. Severini,76E. Shabalina,52M. Shamim,60V. Shary,18 A. A. Shchukin,39W. D. Shephard,56R. K. Shivpuri,28D. Shpakov,64V. Siccardi,19R. A. Sidwell,60V. Simak,10 V. Sirotenko,51P. Skubic,76P. Slattery,72R. P. Smith,51G. R. Snow,68J. Snow,75S. Snyder,74S. So¨ldner-Rembold,45
X. Song,53L. Sonnenschein,17A. Sopczak,43 M. Sosebee,79K. Soustruznik,9M. Souza,2B. Spurlock,79J. Stark,14 J. Steele,61K. Stevenson,55V. Stolin,37A. Stone,52D. A. Stoyanova,39J. Strandberg,41M. A. Strang,70M. Strauss,76 R. Stro¨hmer,25D. Strom,54M. Strovink,47L. Stutte,51S. Sumowidagdo,50A. Sznajder,3M. Talby,15P. Tamburello,46 W. Taylor,5P. Telford,45J. Temple,46B. Tiller,25M. Titov,23V. V. Tokmenin,36M. Tomoto,51T. Toole,62I. Torchiani,23 S. Towers,43T. Trefzger,24S. Trincaz-Duvoid,17D. Tsybychev,73B. Tuchming,18C. Tully,69A. S. Turcot,45P. M. Tuts,71
R. Unalan,66L. Uvarov,40S. Uvarov,40S. Uzunyan,53B. Vachon,5P. J. van den Berg,34R. Van Kooten,55 W. M. van Leeuwen,34N. Varelas,52E. W. Varnes,46A. Vartapetian,79I. A. Vasilyev,39M. Vaupel,26P. Verdier,20
L. S. Vertogradov,36M. Verzocchi,51F. Villeneuve-Seguier,44P. Vint,44J.-R. Vlimant,17E. Von Toerne,60 M. Voutilainen,68,†M. Vreeswijk,34H. D. Wahl,50L. Wang,62J. Warchol,56G. Watts,83M. Wayne,56M. Weber,51 H. Weerts,66N. Wermes,22M. Wetstein,62A. White,79D. Wicke,26G. W. Wilson,59S. J. Wimpenny,49M. Wobisch,51 J. Womersley,51D. R. Wood,64T. R. Wyatt,45Y. Xie,78N. Xuan,56S. Yacoob,54R. Yamada,51M. Yan,62T. Yasuda,51
Y. A. Yatsunenko,36K. Yip,74H. D. Yoo,78S. W. Youn,54C. Yu,14J. Yu,79A. Yurkewicz,73A. Zatserklyaniy,53 C. Zeitnitz,26D. Zhang,51T. Zhao,83Z. Zhao,65B. Zhou,65J. Zhu,73M. Zielinski,72D. Zieminska,55A. Zieminski,55
V. Zutshi,53and E. G. Zverev38
(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, Simon Fraser University, Burnaby, British Columbia, Canada,
York University, Toronto, Ontario, Canada, and McGill University, Montreal, Quebec, Canada
6Institute of High Energy Physics, Beijing, People’s Republic of China 7University of Science and Technology of China, Hefei, People’s Republic of China
8Universidad de los Andes, Bogota´, Colombia
9Center for Particle Physics, Charles University, Prague, Czech Republic 10Czech Technical University, 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
13Laboratoire de Physique Corpusculaire, IN2P3-CNRS, Universite´ Blaise Pascal, Clermont-Ferrand, France 14Laboratoire de Physique Subatomique et de Cosmologie, IN2P3-CNRS, Universite de Grenoble 1, Grenoble, France
15CPPM, IN2P3-CNRS, Universite´ de la Me´diterrane´e, Marseille, France 16IN2P3-CNRS, Laboratoire de l’Acce´le´rateur Line´aire, Orsay, France
17LPNHE, IN2P3-CNRS, Universite´s Paris VI and VII, Paris, France 18DAPNIA/Service de Physique des Particules, CEA, Saclay, France
19IReS, IN2P3-CNRS, Universite´ Louis Pasteur, Strasbourg, France, and Universite´ de Haute Alsace, Mulhouse, France 20Institut de Physique Nucle´aire de Lyon, IN2P3-CNRS, Universite´ Claude Bernard, Villeurbanne, France
21III. Physikalisches Institut A, RWTH Aachen, Aachen, Germany 22Physikalisches Institut, Universita¨t Bonn, Bonn, Germany 23Physikalisches Institut, Universita¨t Freiburg, Freiburg, Germany
24Institut fu¨r Physik, Universita¨t Mainz, Mainz, Germany 25Ludwig-Maximilians-Universita¨t Mu¨nchen, Mu¨nchen, Germany 26Fachbereich Physik, University of 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
32SungKyunKwan University, Suwon, Korea 33CINVESTAV, Mexico City, Mexico
34FOM-Institute NIKHEF and University of Amsterdam/NIKHEF, Amsterdam, The Netherlands 35Radboud University Nijmegen/NIKHEF, Nijmegen, The Netherlands
36Joint Institute for Nuclear Research, Dubna, Russia 37Institute for Theoretical and Experimental Physics, Moscow, Russia
38Moscow State University, Moscow, Russia 39Institute for High Energy Physics, Protvino, Russia 40Petersburg Nuclear Physics Institute, St. Petersburg, Russia
41Lund University, Lund, Sweden, Royal Institute of Technology and Stockholm University, Stockholm, Sweden,
and Uppsala University, Uppsala, Sweden
42Physik Institut der Universita¨t Zu¨rich, Zu¨rich, Switzerland 43Lancaster University, Lancaster, United Kingdom
44Imperial College, London, United Kingdom 45University of Manchester, Manchester, United Kingdom
46University of Arizona, Tucson, Arizona 85721, USA
47Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA 48California State University, Fresno, California 93740, USA
49University of California, Riverside, California 92521, USA 50Florida State University, Tallahassee, Florida 32306, USA 51Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
52University of Illinois at Chicago, Chicago, Illinois 60607, USA 53Northern Illinois University, DeKalb, Illinois 60115, USA
54Northwestern University, Evanston, Illinois 60208, USA 55Indiana University, Bloomington, Indiana 47405, USA 56University of Notre Dame, Notre Dame, Indiana 46556, USA
57Purdue University Calumet, Hammond, Indiana 46323, USA 58Iowa State University, Ames, Iowa 50011, USA 59University of Kansas, Lawrence, Kansas 66045, USA 60Kansas State University, Manhattan, Kansas 66506, USA 61Louisiana Tech University, Ruston, Louisiana 71272, USA 62University of Maryland, College Park, Maryland 20742, USA
63Boston University, Boston, Massachusetts 02215, USA 64Northeastern University, Boston, Massachusetts 02115, USA
65University of Michigan, Ann Arbor, Michigan 48109, USA 66Michigan State University, East Lansing, Michigan 48824, USA
67University of Mississippi, University, Mississippi 38677, USA 68University of Nebraska, Lincoln, Nebraska 68588, USA 69Princeton University, Princeton, New Jersey 08544, USA 70State University of New York, Buffalo, New York 14260, USA
71Columbia University, New York, New York 10027, USA 72University of Rochester, Rochester, New York 14627, USA 73State University of New York, Stony Brook, New York 11794, USA
74Brookhaven National Laboratory, Upton, New York 11973, USA 75Langston University, Langston, Oklahoma 73050, USA 76University of Oklahoma, Norman, Oklahoma 73019, USA 77Oklahoma State University, Stillwater, Oklahoma 74078, USA
78Brown University, Providence, Rhode Island 02912, USA 79University of Texas, Arlington, Texas 76019, USA 80Southern Methodist University, Dallas, Texas 75275, USA
81Rice University, Houston, Texas 77005, USA 82University of Virginia, Charlottesville, Virginia 22901, USA
83University of Washington, Seattle, Washington 98195, USA
(Received 3 May 2006; published 15 September 2006)
We present a search for supersymmetry in the R-parity violating resonant production and decay of smuons and muon sneutrinos in the channels ~ !~0
1, ~ !~02;3;4, and ~! ~1;2. We analyzed
the Fermilab Tevatron Collider. The observed number of events is in agreement with the standard model expectation, and we calculate 95% C.L. limits on the slepton production cross section times branching fraction to gaugino plus muon, as a function of slepton and gaugino masses. In the framework of minimal supergravity, we set limits on the coupling parameter 0211, extending significantly previous results obtained in Run I of the Tevatron and at the CERN LEP collider.
DOI:10.1103/PhysRevLett.97.111801 PACS numbers: 14.80.Ly, 04.65.+e, 12.60.Jv, 13.85.Rm
Supersymmetry (SUSY) predicts the existence of a new particle for every standard model (SM) particle, differing by half a unit in spin. The quantum number R parity [1], defined as R 13BL2S, where B, L, and S are the baryon, lepton, and spin quantum numbers, is 1 for SM and 1 for SUSY particles. Often R parity is assumed to be conserved, which leaves the lightest supersymmetric par-ticle (LSP) stable. However, SUSY does not require R-parity conservation.
If R-parity violation (6Rp) is allowed, the following
tri-linear and bitri-linear terms appear in the superpotential [2]: W6Rp1 2ijkLiL jEk 0ijkLiQ jDk 1 2 00 ijkU iDjD k iLiH1; (1) where L and Q are the lepton and quark SU(2) doublet superfields and E, U, D denote the singlet fields. The indices have the following meaning: i; j; k 1; 2; 3 family index; ; 1;2 weak isospin index; ; ; 1; 2; 3 color index. The coupling strengths are given by the Yukawa coupling constants , 0, and 00. The last term, iLiH1, mixes the lepton and the Higgs superfields. The and 0 couplings give rise to final states with multiple leptons, which provide excellent signatures at the Tevatron. A detailed review of 6Rp SUSY is given in [3].
In the following, we assume that all 6Rp couplings ex-cept 0211 are zero. This implies (muon) lepton number violation. The 6Rp coupling constants are already
con-strained by low-energy experiments, in particular 0211< 0:059mq~=100 GeV [4]. For the squark masses mq~ kine-matically accessible at the Tevatron, this limit on 0211 is significantly improved by the present analysis.
The D0 Collaboration searched for resonant slepton production in Run I [5]. The H1 experiment at DESY searched for resonant squark production [6] in the frame-work of R-parity violating supersymmetry and published limits on the couplings 01jk. The combined limits from the LEP collider at CERN are reviewed by [5]. Assuming R-parity violating decay via LQ D couplings, the limits are m~01 39 GeV, m~1 103 GeV, m~
78 GeV, and m ~ 90 GeV.
At p pcolliders, an initial q qpair can produce a single slepton [7]. Assuming a nonzero 0211 coupling, smuons or muon sneutrinos are produced. The s channel production is dominant and depends on the value of this coupling 0211. The contributions of the t and u channels are negligible compared to the resonant s channel [8]. The value of 0211 influences the lifetime of the neutralino, but the signal
cross sections corresponding to an observable ~0 1 decay length are not (yet) accessible.
The slepton can then decay into a lepton and a gaugino without violating R parity. The 0
211 coupling allows neu-tralino decays in the detector via virtual sparticles (such as muon sneutrinos, smuons, and squarks) into two 1st gen-eration quarks and one 2nd gengen-eration lepton [9]. The ~0 1 decay branching fractions as predicted by mSUGRA, with the ratio of the Higgs expectation values tan 5, the sign of the Higgsino mass parameter < 0, and the common trilinear scalar coupling A0 0, are assumed, leading to BR ~0
1! q1q01 BR ~01 ! q1q1. The dominant slepton intermediate decays as well as the corresponding final states are indicated in TableI.
Because of the challenging multijet QCD environment and the advantage of the ability to reconstruct the neu-tralino and smuon masses, at least two muons were re-quired in the final state. This leaves the three channels (i) ~ !~0
1, (ii) ~ !~02;3;4, and (iii) ~ ! ~1;2which are analyzed independently. The analyses are insensitive to events where the ~0
1 decays into qq 0 and where no
second muon is created in the cascade.
The data for this analysis were recorded by the D0 detector between April 2002 and August 2004 at a center-of-mass energy of 1.96 TeV. The integrated lumi-nosity corresponds to 380 25 pb1.
The D0 detector [10] has a central tracking system consisting of a silicon microstrip tracker and a central fiber tracker, both located within a 2 T superconducting sole-noidal magnet, with designs optimized for tracking and vertexing at pseudorapidities j j < 3 and j j < 2:5, re-spectively. A liquid-argon and uranium calorimeter has a central section covering pseudorapidities j j & 1:1, and two end calorimeters that extend coverage to j j 4:2. The muon system covering j j < 2:0 consists of a layer of tracking detectors and scintillation trigger counters in front of 1.8 T iron toroids, followed by two similar layers behind the toroids. The first level of the trigger (level 1) is based on fast information from the tracking, calorimetry, and muon
TABLE I. Smuon and muon-sneutrino decay channels: the
final states correspond to ~0
1! q1q01 and ~ 1 ! qq 0~0 1. ~
ldecay channel Dominant final states
~ !~0 2, 2 jets ~ !~ 1, 6ET, 4 jets ~ ! ~0 1, 6ET, 2 jets ~ ! ~ 2, 4 jets PRL 97, 111801 (2006) P H Y S I C A L R E V I E W L E T T E R S 15 SEPTEMBER 2006
systems. At the next trigger stage (level 2), the rate is re-duced further. These first two levels of triggering rely mainly on hardware and firmware. The final level of the trigger, level 3, with access to the full event information, uses software algorithms to reduce the rate to tape to 50 Hz.
The signal was simulated with SUSYGEN [11]. The leading-order SUSYGEN signal cross sections have been multiplied by higher order, slepton-mass dependent QCD-correction factors [12] of size 1.4 –1.5 calculated with the CTEQ6M [13] parton distribution functions (PDFs). The influence of the PDF uncertainty on the cross section is 3% – 6%, estimated from the CTEQ6M error functions. The influence of the renormalization scale and the factorization scale F is less than 5% for all slepton masses below 500 GeV, if m~l=2 F 2m~l[14].
The dominant background is inclusive production of Z=! . It was simulated with the PYTHIA [15] Monte Carlo (MC) generator and normalized using the pre-dicted next-to-next-to-leading-order cross section [16], calculated with the CTEQ6 PDFs. All other SM processes contribute only slightly to the total background as seen in Fig. 1. These contributions were simulated using the
PYTHIA generator and normalized using
next-to-leading-order cross section predictions calculated using CTEQ6M PDFs. All MC events were passed through a detailed detector simulation based on GEANT [17], followed by the reconstruction program used for data.
Events were collected with di-muon triggers requiring at least two muons at level 1. At level 3 at least one track or one muon with a varying transverse momentum pT
thresh-old of typically 5–15 GeV was required. To account for the trigger effects, simulated events were weighted using effi-ciencies determined from the data.
All events were required to contain two muons. One of the muons was required to have pT > 15 GeV, and the
second muon was required to have pT> 8 GeV. A central
track match was required for both muons. The muons in the signal are expected to be isolated. We define muons as ‘‘loose’’ (‘‘tight’’) isolated, if the sum of the pT of the tracks in a cone with radius Rconep 2 2 0:5, where ln tan
2 is the pseudorapidity and is the azimuthal angle, around the muon direction is less than 10 GeV (2.5 GeV), and the sum of the transverse energies of the calorimeter cells in a hollow cone (0:1 Rcone 0:4) is less than 10 GeV (2.5 GeV). Both selected muons were required to pass the tight isolation requirement. The invariant di-muon mass distribution of this di-muon sample Invariant di-muon mass [GeV]
(a) 0 20 40 60 80 100 120 140 160 180 Events / 3.6 GeV 0 500 1000 1500 2000 2500 3000 0 20 40 60 80 100 120 140 160 180 0 500 1000 1500 2000 2500 3000 -1 , 0.38 fb O D Data 100 × µ 1 0 χ ∼ → µ ∼ 100 × µ 2,3,4 0 χ ∼ → µ ∼ 100 × µ 1,2± χ ∼ → µ ν ∼ µ µ → * γ Z/ QCD from Data other SM SM uncertainty σ 1 ±
Invariant di-muon di-jet mass [GeV]
(b) 0 100 200 300 400 500 600 Events / 20.0 GeV 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 0 10 20 30 40 50 60 70 80 -1 , 0.38 fb O D Data 5 × µ 1 0 χ ∼ → µ ∼ 5 × µ 2,3,4 0 χ ∼ → µ ∼ 5 × µ 1,2 ± χ ∼ → µ ν ∼ µ µ → * γ Z/ QCD from Data other SM SM uncertainty σ 1 ±
FIG. 1 (color online). Invariant di-muon mass in the two-muon sample (a) and reconstructed 4-body mass of two muons and two jets (b). The cascade decays in channels (ii) and (iii) lead to less energy per particle, thus lower invariant masses. The signal expectation for the point with m~l 260 GeV and m~0
1 100 GeV is scaled in plot (a) by a factor of 100 and in plot (b) by a factor of 5. The dominant
SM background is Z=! ; other SM backgrounds are Z=! ; WW, WZ, ZZ, tt, and production. The total SM 1
uncertainty is shown as dashed black lines. The data are in good agreement with the SM expectation.
TABLE II. Expected and observed events at different stages of the event selection. The signal efficiency is given for the point with m~l 260 GeV and m~0
1 100 GeV with respect to the total slepton production. The first uncertainty on the SM expectation is statistical; the second is due to systematics.
Cut Data SM expectation Signal efficiency
2 selection 23 206 22 700 70 2900 5:5% 0:7%
pT jet1> 15 GeV 3852 3760 40 560 4:8% 0:6%
is shown in Fig. 1(a). At least two jets with transverse momentum pT 15 GeV and reconstructed with a cone
algorithm (Rcone 0:5) [18] were required. Only jets within j j < 2:0 were used. The reconstructed slepton mass with two muons and two jets is shown in Fig. 1(b). The event selection is summarized in TableII.
Background from multijet QCD events was extracted from data using loose muon isolation requirements. This QCD enriched data sample was scaled to match the data in a signal free region. At least one isolation criterion with respect to other energy depositions in the calorimeter or to other tracks must not be tight for at least one muon to create an orthogonal sample utilized to model the QCD background.
Two-dimensional selection requirements in planes spanned by the reconstructed ~l and ~ candidate masses, the invariant di-muon and di-jet masses, and the sums of muon momenta and jet momenta were used to separate the signal s from SM backgrounds b. The selection require-ments were chosen so that the signal efficiency signal purity / s
sb
p of a specific cut, applied on a training sample, was maximized. The selection requirements were
optimized for each (slepton mass, gaugino mass) combi-nation (117 in total).
In the ~ !~01 analysis (i), the slepton mass was reconstructed with the two leading muons and the two jets. In the signal MC calculation, the leading muon usually originates from the slepton decay vertex. The neutralino mass was therefore reconstructed with both jets and the next-to-leading muon.
Hadronic decays of vector bosons from the gaugino cascade to ~0
1 can lead to additional jets in channels (ii) and (iii). A simple likelihood was calculated for each combination to reconstruct a vector boson and the neutra-lino candidate mass. The slepton mass was reconstructed from all jets with ET> 15 GeV and the two leading muons.
After the optimization, for the point with m~l 260 GeV and m~0
1 100 GeV, we find 14=28=8 events in the data
while 11:9 2:11:51:6=25:4 3:26:74:2=6:5 1:62:01:2 events are expected from SM backgrounds for the three channels, respectively, with a typical signal efficiency of up to 2%. For all 117 mass combinations, the data are in agreement with the SM expectation throughout the entire event selec-tion range.
The systematic uncertainties from different sources were added in quadrature. For the limit calculation, the total systematic uncertainties of the background and signal samples were taken to be 100% correlated. A summary of the uncertainties is given in TableIIIwith their contri-butions to the two-muon and two-jet sample.
In the absence of an excess in the data, we set cross section limits on resonant slepton production. To be as model independent as possible, we calculated 95% C.L. with respect to the slepton production cross section times branching fraction to gaugino plus muon using the C:L:s method [19]. The limit is then given in the slepton-mass and gaugino-mass plane, as shown in Fig. 2. In addition, our results are shown in Fig.3as 0211 exclusion contours interpreted within the mSUGRA framework, with tan 5, < 0, and A0 0. The slepton-mass and gaugino-mass pair define the universal scalar and fermion masses m0and
) [GeV] 1 0 χ ∼ Mass ( 0 50 100 150 200 250 ) [GeV]µ ∼ Mass ( 50 100 150 200 250 300 350 400 450 500 ) [pb] µ1 0 χ ∼ →µ ∼ BR(× ) µ ∼ → p (pσ Limit 2 4 6 8 10 12 14 16 18 ) [pb] µ1 0 χ ∼ →µ ∼ BR(× ) µ ∼ → p (pσ Limit 2 4 6 8 10 12 14 16 18 LEP <2pb <4pb <6pb <20pb -1 , 0.38 fb O D (a) ) [GeV] 2 0 χ ∼ Mass ( 0 50 100 150 200 250 ) [GeV]µ ∼ Mass ( 50 100 150 200 250 300 350 400 450 500 ) [pb] µ 2,3,4 0 χ ∼ →µ ∼ BR(× ) µ ∼ → p (pσ Limit 2 4 6 8 10 12 14 16 18 ) [pb] µ 2,3,4 0 χ ∼ →µ ∼ BR(× ) µ ∼ → p (pσ Limit 2 4 6 8 10 12 14 16 18 LEP <2pb <4pb <6pb <20pb -1 , 0.38 fb O D (b) ) [GeV] 1 ± χ ∼ Mass ( 0 50 100 150 200 250 ) [GeV]µ ν ∼ Mass ( 50 100 150 200 250 300 350 400 ) [pb] µ1 ± χ ∼ →µ ν ∼ BR(× ) µ ν ∼ → p (pσ Limit 2 4 6 8 10 12 14 16 18 ) [pb] µ1 ± χ ∼ →µ ν ∼ BR(× ) µ ν ∼ → p (pσ Limit 2 4 6 8 10 12 14 16 18 LEP <2pb <4pb <6pb -1 , 0.38 fb O D (c)
FIG. 2 (color online). 95% C.L. on slepton production cross section times branching fraction to gaugino plus muon for the channels (i) ~ !~0
1(a), (ii) ~ !~02;3;4(b), and (iii) ~! ~1;2(c) as a function of slepton and gaugino masses. The darkest region
corresponds to a cross section of less that 2 pb. Successively lighter regions have successively higher limits. TABLE III. Effect of the systematic uncertainties in the
two-muon and two-jet sample on background and signal cross sections. The muon ID contribution comprises the uncertainties due to muon reconstruction, isolation, track finding and match-ing, and resolution for the two muons. The systematic uncer-tainties on the signal strongly depend on the neutralino mass, so a typical range is given.
Uncertainty Background Signal
Jet energy scale 13.7% 2% – 26%
Muon ID 7.8% 8% –14%
Luminosity (does not apply to QCD) 5.5% 6.5%
Trigger efficiency 5.2% 4% – 9%
MC , K-factor, PDF 3.7% 5%
QCD background estimation 3.1% —
MC statistics 2.2% 3% – 24%
m1=2. All three channels were combined to form one limit for q q ! ~l, with ~l ~; ~.
A lower limit on the slepton mass for a given LQ D coupling 0211 can be extracted from Fig. 3. These limits do not depend on other masses. They are indicated by arrows and summarized in TableIV. Similarly, the exclu-sion contour can be translated within mSUGRA into con-straints on other masses and parameters.
In summary, we have searched for R-parity violating supersymmetry via a nonzero LQ Dcoupling 0211 in final states with at least two muons and two jets. No excess in comparison with SM expectation was found and we set model independent cross section limits, improved com-pared to D0 Run I by 1 order of magnitude. The limits are interpreted within the mSUGRA framework and trans-lated into the best constraints to date on the coupling strength 0211. D0 Run I excluded slepton masses up to 280 GeV for 0211 0:09 and m ~0
1 200 GeV. Now, slepton masses up to 358 GeV can be excluded, for 0211 0:09 independent of other masses.
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); CAPES, 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); PPARC (United Kingdom); MSMT (Czech Republic); CRC Program, CFI, NSERC, and WestGrid Project (Canada); BMBF and DFG (Germany); SFI (Ireland); The Swedish Research Council (Sweden); Research Corporation; Alexander von Humboldt Foundation; and the Marie Curie Program.
*On leave from IEP SAS Kosice, Slovakia.
†Visitor from Helsinki Institute of Physics, Helsinki, Finland.
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TABLE IV. Limits on the slepton mass ~l for a given LQ D
coupling 0211and tan 5, < 0 from Fig.3.
Excluded slepton-mass range Coupling strength
m~l 210 GeV for 0 211 0:04 m~l 340 GeV for 0211 0:06 m~l 363 GeV for 0211 0:10 ) [GeV] 1 0 χ∼ Mass ( 0 50 100 150 200 250 300 350 ) [GeV]l ~ Mass ( 100 200 300 400 500 600 LEP
Not allowed region in mSUGRA
<0.04 <0.06 <0.08 <0.12 <0.16 >0.04 >0.06 >0.10 <0 µ )=5, β tan( 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 211 λ
Exclusion contour for a given
211
′λ
Exclusion contour for a given
-1
, 0.38 fb O D
FIG. 3 (color online). 95% C.L. exclusion contour on 0211 couplings within the mSUGRA framework for tan 5 and
< 0. The arrows indicate limits on the slepton mass ~l, for a given coupling 0
