Search for Doubly Charged Higgs Bosons with Lepton-Flavor-Violating Decays involving Tau Leptons
aa r X i v : . [ h e p - e x ] A ug Search for Doubly Charged Higgs Bosons with Lepton-Flavor-Violating Decaysinvolving Tau Leptons
T. Aaltonen, J. Adelman, T. Akimoto, M.G. Albrow, B. ´Alvarez Gonz´alez, S. Amerio, D. Amidei, A. Anastassov, A. Annovi, J. Antos, M. Aoki, G. Apollinari, A. Apresyan, T. Arisawa, A. Artikov, W. Ashmanskas, A. Attal, A. Aurisano, F. Azfar, P. Azzi-Bacchetta, P. Azzurri, N. Bacchetta, W. Badgett, A. Barbaro-Galtieri, V.E. Barnes, B.A. Barnett, S. Baroiant, V. Bartsch, G. Bauer, P.-H. Beauchemin, F. Bedeschi, P. Bednar, S. Behari, G. Bellettini, J. Bellinger, A. Belloni, D. Benjamin, A. Beretvas, J. Beringer, T. Berry, A. Bhatti, M. Binkley, D. Bisello, I. Bizjak, R.E. Blair, C. Blocker, B. Blumenfeld, A. Bocci, A. Bodek, V. Boisvert, G. Bolla, A. Bolshov, D. Bortoletto, J. Boudreau, A. Boveia, B. Brau, A. Bridgeman, L. Brigliadori, C. Bromberg, E. Brubaker, J. Budagov, H.S. Budd, S. Budd, K. Burkett, G. Busetto, P. Bussey, A. Buzatu, K. L. Byrum, S. Cabrera r , M. Campanelli, M. Campbell, F. Canelli, A. Canepa, D. Carlsmith, R. Carosi, S. Carrillo l , S. Carron, B. Casal, M. Casarsa, A. Castro, P. Catastini, D. Cauz, M. Cavalli-Sforza, A. Cerri, L. Cerrito p , S.H. Chang, Y.C. Chen, M. Chertok, G. Chiarelli, G. Chlachidze, F. Chlebana, K. Cho, D. Chokheli, J.P. Chou, G. Choudalakis, S.H. Chuang, K. Chung, W.H. Chung, Y.S. Chung, C.I. Ciobanu, M.A. Ciocci, A. Clark, D. Clark, G. Compostella, M.E. Convery, J. Conway, B. Cooper, K. Copic, M. Cordelli, G. Cortiana, F. Crescioli, C. Cuenca Almenar r , J. Cuevas o , R. Culbertson, J.C. Cully, D. Dagenhart, M. Datta, T. Davies, P. de Barbaro, S. De Cecco, A. Deisher, G. De Lentdecker d , G. De Lorenzo, M. Dell’Orso, L. Demortier, J. Deng, M. Deninno, D. De Pedis, P.F. Derwent, G.P. Di Giovanni, C. Dionisi, B. Di Ruzza, J.R. Dittmann, M. D’Onofrio, S. Donati, P. Dong, J. Donini, T. Dorigo, S. Dube, J. Efron, R. Erbacher, D. Errede, S. Errede, R. Eusebi, H.C. Fang, S. Farrington, W.T. Fedorko, R.G. Feild, M. Feindt, J.P. Fernandez, C. Ferrazza, R. Field, G. Flanagan, R. Forrest, S. Forrester, M. Franklin, J.C. Freeman, I. Furic, M. Gallinaro, J. Galyardt, F. Garberson, J.E. Garcia, A.F. Garfinkel, K. Genser, H. Gerberich, D. Gerdes, S. Giagu, V. Giakoumopolou a , P. Giannetti, K. Gibson, J.L. Gimmell, C.M. Ginsburg, N. Giokaris a , M. Giordani, P. Giromini, M. Giunta, V. Glagolev, D. Glenzinski, M. Gold, N. Goldschmidt, A. Golossanov, G. Gomez, G. Gomez-Ceballos, M. Goncharov, O. Gonz´alez, I. Gorelov, A.T. Goshaw, K. Goulianos, A. Gresele, S. Grinstein, C. Grosso-Pilcher, R.C. Group, U. Grundler, J. Guimaraes da Costa, Z. Gunay-Unalan, C. Haber, K. Hahn, S.R. Hahn, E. Halkiadakis, A. Hamilton, B.-Y. Han, J.Y. Han, R. Handler, F. Happacher, K. Hara, D. Hare, M. Hare, S. Harper, R.F. Harr, R.M. Harris, M. Hartz, K. Hatakeyama, J. Hauser, C. Hays, M. Heck, A. Heijboer, B. Heinemann, J. Heinrich, C. Henderson, M. Herndon, J. Heuser, S. Hewamanage, D. Hidas, C.S. Hill c , D. Hirschbuehl, A. Hocker, S. Hou, M. Houlden, S.-C. Hsu, B.T. Huffman, R.E. Hughes, U. Husemann, J. Huston, J. Incandela, G. Introzzi, M. Iori, A. Ivanov, B. Iyutin, E. James, B. Jayatilaka, D. Jeans, E.J. Jeon, S. Jindariani, W. Johnson, M. Jones, K.K. Joo, S.Y. Jun, J.E. Jung, T.R. Junk, T. Kamon, D. Kar, P.E. Karchin, Y. Kato, R. Kephart, U. Kerzel, V. Khotilovich, B. Kilminster, D.H. Kim, H.S. Kim, J.E. Kim, M.J. Kim, S.B. Kim, S.H. Kim, Y.K. Kim, N. Kimura, L. Kirsch, S. Klimenko, M. Klute, B. Knuteson, B.R. Ko, S.A. Koay, K. Kondo, D.J. Kong, J. Konigsberg, A. Korytov, A.V. Kotwal, J. Kraus, M. Kreps, J. Kroll, N. Krumnack, M. Kruse, V. Krutelyov, T. Kubo, S. E. Kuhlmann, T. Kuhr, N.P. Kulkarni, Y. Kusakabe, S. Kwang, A.T. Laasanen, S. Lai, S. Lami, S. Lammel, M. Lancaster, R.L. Lander, K. Lannon, A. Lath, G. Latino, I. Lazzizzera, T. LeCompte, J. Lee, J. Lee, Y.J. Lee, S.W. Lee q , R. Lef`evre, N. Leonardo, S. Leone, S. Levy, J.D. Lewis, C. Lin, C.S. Lin, J. Linacre, M. Lindgren, E. Lipeles, A. Lister, D.O. Litvintsev, T. Liu, N.S. Lockyer, A. Loginov, M. Loreti, L. Lovas, R.-S. Lu, D. Lucchesi, J. Lueck, C. Luci, P. Lujan, P. Lukens, G. Lungu, L. Lyons, J. Lys, R. Lysak, E. Lytken, P. Mack, D. MacQueen, R. Madrak, K. Maeshima, K. Makhoul, T. Maki, P. Maksimovic, S. Malde, S. Malik, G. Manca, A. Manousakis a , F. Margaroli, C. Marino, C.P. Marino, A. Martin, M. Martin, V. Martin j , M. Mart´ınez, R. Mart´ınez-Ballar´ın, T. Maruyama, P. Mastrandrea, T. Masubuchi, M.E. Mattson, P. Mazzanti, K.S. McFarland, P. McIntyre, R. McNulty i , A. Mehta, P. Mehtala, S. Menzemer k , A. Menzione, P. Merkel, C. Mesropian, A. Messina, T. Miao, N. Miladinovic, J. Miles, R. Miller, C. Mills, M. Milnik, A. Mitra, G. Mitselmakher, H. Miyake, S. Moed, N. Moggi, C.S. Moon, R. Moore, M. Morello, P. Movilla Fernandez, J. M¨ulmenst¨adt, A. Mukherjee, Th. Muller, R. Mumford, P. Murat, M. Mussini, J. Nachtman, Y. Nagai, A. Nagano, J. Naganoma, K. Nakamura, I. Nakano, A. Napier, V. Necula, C. Neu, M.S. Neubauer, J. Nielsen f , L. Nodulman, M. Norman, O. Norniella, E. Nurse, S.H. Oh, Y.D. Oh, I. Oksuzian, T. Okusawa, R. Oldeman, R. Orava, K. Osterberg, S. Pagan Griso, C. Pagliarone, E. Palencia, V. Papadimitriou, A. Papaikonomou, A.A. Paramonov, B. Parks, S. Pashapour, J. Patrick, G. Pauletta, M. Paulini, C. Paus, D.E. Pellett, A. Penzo, T.J. Phillips, G. Piacentino, J. Piedra, L. Pinera, K. Pitts, C. Plager, L. Pondrom, X. Portell, O. Poukhov, N. Pounder, F. Prakoshyn, A. Pronko, J. Proudfoot, F. Ptohos h , G. Punzi, J. Pursley, J. Rademacker c , A. Rahaman, V. Ramakrishnan, N. Ranjan, I. Redondo, B. Reisert, V. Rekovic, P. Renton, M. Rescigno, S. Richter, F. Rimondi, L. Ristori, A. Robson, T. Rodrigo, E. Rogers, S. Rolli, R. Roser, M. Rossi, R. Rossin, P. Roy, A. Ruiz, J. Russ, V. Rusu, H. Saarikko, A. Safonov, W.K. Sakumoto, G. Salamanna, O. Salt´o, L. Santi, S. Sarkar, L. Sartori, K. Sato, A. Savoy-Navarro, T. Scheidle, P. Schlabach, E.E. Schmidt, M.A. Schmidt, M.P. Schmidt, M. Schmitt, T. Schwarz, L. Scodellaro, A.L. Scott, A. Scribano, F. Scuri, A. Sedov, S. Seidel, Y. Seiya, A. Semenov, L. Sexton-Kennedy, A. Sfyria, S.Z. Shalhout, M.D. Shapiro, T. Shears, P.F. Shepard, D. Sherman, M. Shimojima n , M. Shochet, Y. Shon, I. Shreyber, A. Sidoti, P. Sinervo, A. Sisakyan, A.J. Slaughter, J. Slaunwhite, K. Sliwa, J.R. Smith, F.D. Snider, R. Snihur, M. Soderberg, A. Soha, S. Somalwar, V. Sorin, J. Spalding, F. Spinella, T. Spreitzer, P. Squillacioti, M. Stanitzki, R. St. Denis, B. Stelzer, O. Stelzer-Chilton, D. Stentz, J. Strologas, D. Stuart, J.S. Suh, A. Sukhanov, H. Sun, I. Suslov, T. Suzuki, A. Taffard e , R. Takashima, Y. Takeuchi, R. Tanaka, M. Tecchio, P.K. Teng, K. Terashi, J. Thom g , A.S. Thompson, G.A. Thompson, E. Thomson, P. Tipton, V. Tiwari, S. Tkaczyk, D. Toback, S. Tokar, K. Tollefson, T. Tomura, D. Tonelli, S. Torre, D. Torretta, S. Tourneur, W. Trischuk, Y. Tu, N. Turini, F. Ukegawa, S. Uozumi, S. Vallecorsa, N. van Remortel, A. Varganov, E. Vataga, F. V´azquez l , G. Velev, C. Vellidis a , V. Veszpremi, M. Vidal, R. Vidal, I. Vila, R. Vilar, T. Vine, M. Vogel, I. Volobouev q , G. Volpi, F. W¨urthwein, P. Wagner, R.G. Wagner, R.L. Wagner, J. Wagner-Kuhr, W. Wagner, T. Wakisaka, R. Wallny, S.M. Wang, A. Warburton, D. Waters, M. Weinberger, W.C. Wester III, B. Whitehouse, D. Whiteson e , A.B. Wicklund, E. Wicklund, G. Williams, H.H. Williams, P. Wilson, B.L. Winer, P. Wittich g , S. Wolbers, C. Wolfe, T. Wright, X. Wu, S.M. Wynne, A. Yagil, K. Yamamoto, J. Yamaoka, T. Yamashita, C. Yang, U.K. Yang m , Y.C. Yang, W.M. Yao, G.P. Yeh, J. Yoh, K. Yorita, T. Yoshida, G.B. Yu, I. Yu, S.S. Yu, J.C. Yun, L. Zanello, A. Zanetti, I. Zaw, X. Zhang, Y. Zheng b , and S. Zucchelli (CDF Collaboration ∗ ) Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China Argonne National Laboratory, Argonne, Illinois 60439 Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain Baylor University, Waco, Texas 76798 Istituto Nazionale di Fisica Nucleare, University of Bologna, I-40127 Bologna, Italy Brandeis University, Waltham, Massachusetts 02254 University of California, Davis, Davis, California 95616 University of California, Los Angeles, Los Angeles, California 90024 University of California, San Diego, La Jolla, California 92093 University of California, Santa Barbara, Santa Barbara, California 93106 Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain Carnegie Mellon University, Pittsburgh, PA 15213 Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia Joint Institute for Nuclear Research, RU-141980 Dubna, Russia Duke University, Durham, North Carolina 27708 Fermi National Accelerator Laboratory, Batavia, Illinois 60510 University of Florida, Gainesville, Florida 32611 Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy University of Geneva, CH-1211 Geneva 4, Switzerland Glasgow University, Glasgow G12 8QQ, United Kingdom Harvard University, Cambridge, Massachusetts 02138 Division of High Energy Physics, Department of Physics,University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland University of Illinois, Urbana, Illinois 61801 The Johns Hopkins University, Baltimore, Maryland 21218 Institut f¨ur Experimentelle Kernphysik, Universit¨at Karlsruhe, 76128 Karlsruhe, Germany Center for High Energy Physics: Kyungpook National University,Daegu 702-701, Korea; Seoul National University, Seoul 151-742,Korea; Sungkyunkwan University, Suwon 440-746,Korea; Korea Institute of Science and Technology Information, Daejeon,305-806, Korea; Chonnam National University, Gwangju, 500-757, Korea Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720 University of Liverpool, Liverpool L69 7ZE, United Kingdom University College London, London WC1E 6BT, United Kingdom Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Institute of Particle Physics: McGill University, Montr´eal,Canada H3A 2T8; and University of Toronto, Toronto, Canada M5S 1A7 University of Michigan, Ann Arbor, Michigan 48109 Michigan State University, East Lansing, Michigan 48824 University of New Mexico, Albuquerque, New Mexico 87131 Northwestern University, Evanston, Illinois 60208 The Ohio State University, Columbus, Ohio 43210 Okayama University, Okayama 700-8530, Japan Osaka City University, Osaka 588, Japan University of Oxford, Oxford OX1 3RH, United Kingdom University of Padova, Istituto Nazionale di Fisica Nucleare,Sezione di Padova-Trento, I-35131 Padova, Italy LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France University of Pennsylvania, Philadelphia, Pennsylvania 19104 Istituto Nazionale di Fisica Nucleare Pisa, Universities of Pisa,Siena and Scuola Normale Superiore, I-56127 Pisa, Italy University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Purdue University, West Lafayette, Indiana 47907 University of Rochester, Rochester, New York 14627 The Rockefeller University, New York, New York 10021 Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1,University of Rome “La Sapienza,” I-00185 Roma, Italy Rutgers University, Piscataway, New Jersey 08855 Texas A&M University, College Station, Texas 77843 Istituto Nazionale di Fisica Nucleare, University of Trieste/ Udine, Italy University of Tsukuba, Tsukuba, Ibaraki 305, Japan Tufts University, Medford, Massachusetts 02155 Waseda University, Tokyo 169, Japan Wayne State University, Detroit, Michigan 48201 University of Wisconsin, Madison, Wisconsin 53706 Yale University, New Haven, Connecticut 06520 (Dated: October 30, 2018)We search for pair production of doubly charged Higgs particles ( H ±± ) followed by decays intoelectron-tau ( eτ ) and muon-tau ( µτ ) pairs using data (350 pb − ) collected from ¯ pp collisions at √ s = 1 .
96 TeV by the CDF II experiment. We search separately for cases where three or fourfinal-state leptons are detected, and combine results for exclusive decays to left-handed eτ ( µτ )pairs. We set an H ±± lower mass limit of 114 (112) GeV /c at the 95% confidence level. ∗ With visitors from a University of Athens, 15784 Athens, Greece, b Chinese Academy of Sciences, Beijing 100864, China, c Universityof Bristol, Bristol BS8 1TL, United Kingdom, d University Librede Bruxelles, B-1050 Brussels, Belgium, e University of CaliforniaIrvine, Irvine, CA 92697, f University of California Santa Cruz, Santa Cruz, CA 95064, g Cornell University, Ithaca, NY 14853, h University of Cyprus, Nicosia CY-1678, Cyprus, i University Col-lege Dublin, Dublin 4, Ireland, j University of Edinburgh, Edin-burgh EH9 3JZ, United Kingdom, k University of Heidelberg, D-69120 Heidelberg, Germany, l Universidad Iberoamericana, Mexico
The Standard Model (SM) Higgs mechanism providesa framework in which particles can acquire mass whilepreserving local gauge invariance. The complex scalarHiggs doublet of the SM is just one of many viable im-plementations, and many extensions to the SM containHiggs triplets [1, 2, 3]. For example the left-right sym-metric ( SU (2) L × SU (2) R × U (1) B − L ) extension of theelectroweak force [2] casts parity violation as a low-energyphenomenon by invoking a right-handed weak interac-tion broken above the electroweak scale. This model pre-dicts small but nonzero neutrino masses (consistent withrecent experiments [4, 5]) related to the suppression ofthe right-handed weak current [2]. Another model withan extended Higgs sector is the Higgs triplet model [3],which predicts a massive left-handed Majorana neutrinowithout requiring a right-handed neutrino. An importantphenomenological feature of the above models is the pre-diction of doubly charged Higgs bosons ( H ±± ) as partof a Higgs triplet. Doubly charged Higgs bosons cou-ple to Higgs and electroweak gauge bosons and eitherleft-handed or right-handed charged leptons ( ℓ ), and arerespectively denoted H ±± L or H ±± R [6].The only significant production mode at the FermilabTevatron is predicted to be q ¯ q → γ ∗ /Z → H ++ H −− , andthe leptonic decay modes dominate for H ±± in the massrange m ( H ±± ) < ( m ( W ± ) + m ( H ± ))[7]. Lepton-flavor-violating (LFV) decay modes are allowed, and may beparticularly large (e.g., the branching fraction for the µτ mode may be near 1/3) in the Higgs triplet model if themass hierarchy of the quarks and charged leptons alsoholds for the neutrino sector[8].The H ±± L ( H ±± R ) is excluded below 99 GeV /c (97 GeV /c ) at the 95% C.L. by previous searches at LEP[9], assuming production cross sections according to theleft-right symmetric models [2] and 100% branching ratioto any one dilepton decay channel. Recent searches fromthe Fermilab Tevatron have resulted in 95% C.L. lowermass limits of 136, 133, and 115 GeV /c for H ±± L in the µµ , ee , and eµ channels, respectively, and a lower masslimit of 113 GeV /c for the H ±± R in the µµ channel [10].We present the first results from hadron colliders on H ++ L H −− L pair production and subsequent decay throughLFV channels involving taus. We use data correspondingto an integrated proton-antiproton luminosity of ≈ − [11] collected at √ s = 1 .
96 TeV by the CDF IIexperiment at the Fermilab Tevatron, and set mass lim-its in the left-right symmetric model [2, 7] for exclusivedecays in the eτ and µτ channels. We present limits on D.F., Mexico, m University of Manchester, Manchester M13 9PL,England, n Nagasaki Institute of Applied Science, Nagasaki, Japan, o University de Oviedo, E-33007 Oviedo, Spain, p Queen Mary, Uni-versity of London, London, E1 4NS, England, q Texas Tech Univer-sity, Lubbock, TX 79409, r IFIC(CSIC-Universitat de Valencia),46071 Valencia, Spain, the cross section times branching ratio squared, σ × B ,which can be interpreted in the context of various models[7].CDF II [12, 13], a cylindrical detector with concen-tric layers, has inner silicon strip detectors (SVX) and awire drift chamber (COT) for tracking inside a solenoidalcoil. The COT provides tracking in the pseudorapidityregion | η | < ∼ | η | < ∼ | η | < | η |≤ ≈ ≤| η |≤ | η | < | η | < /c .Identification of hadronically decaying taus ( τ h ) is fullydescribed elsewhere [14]. In tau reconstruction, all tracksare assumed to correspond to charged pions, and alltrackless CES/CEM clusters are assumed to correspondto π mesons. A tight τ h must have 1 or 3 localizedtracks, and can have additional localized π candidates.The localization is defined by a variable size “signal cone”(between 3 ◦ and 10 ◦ , depending on the tau’s momen-tum) around the highest p T track associated with the τ h .The region between the signal cone and a larger 30 ◦ coneserves as an isolation annulus in which the summed p T of all tracks must be less than 2 GeV /c and the summed E T of all π mesons must be less than 0.5 GeV. The4-momentum of a τ h is taken to be the vector sum ofthe 4-momenta of the tau’s tracks and π candidates inthe signal cone. The charge of a τ h is the sum of thecharges of its tracks, and must equal ±
1. A loose τ h isthe same as a tight τ h in the region | η | < < | η | < π related cuts are dropped,and the energy of a loose τ h is estimated from the plugcalorimeters.To increase signal acceptance, systems of one or threeisolated, localized tracks in the region | η | < ◦ and30 ◦ respectively. These “isolated track systems” (ITSs)have acceptance for e , µ , and τ leptons. The efficien-cies of lepton reconstruction, identification, and isolationrequirements are measured in data using electrons fromdecays of Υ mesons, electrons and muons from decays of Z bosons, and taus from W bosons.We require at least three reconstructed isolatedcharged leptons to suppress large cross-section back-grounds such as dijets, γ + jets, and W ( → ℓν ℓ )+ jets.Events are classified according to the number of isolatedhigh p T leptons detected, and separate selections are usedfor the 3- ℓ and 4- ℓ signatures. The data are collected bylepton plus isolated track triggers [15]. These triggersrequire one central lepton ( e or µ ) and a second cen-tral isolated track. The integrated luminosities of the eτ and µτ samples are 350 pb − and 322 pb − , respec-tively. Trigger efficiencies for electrons (muons) are es-timated from events with photon conversions and Z → ee ( J/ψ → µµ and Z → µµ ) decays. The efficiency for theisolated track is measured from a jet sample. The over-all trigger efficiencies are ≈
95% for H ±± masses in therange 80-130 GeV /c . The specific lepton requirementsfor the eτ and µτ searches are summarized in Table I.We use CTEQ5L parton density functions (PDFs) inthe pythia generator [16] and a geant -based [17] de-tector simulation, scaled to next-to-leading order (NLO)cross sections [7], to estimate the signal and backgroundprocesses. Our signal MC samples scan the H ±± massrange 80-130 GeV /c at 10 GeV /c intervals. The poten-tial SM backgrounds for both the 3- ℓ and 4- ℓ searches are: Z / γ ∗ → leptons produced in association with ≥ ZZ and W Z with both bosons decay-ing leptonically; t ¯ t with leptonically decaying W bosons; W bosons decaying leptonically produced in associationwith ≥ ≥ eτ signature, γ + hadronicjets events are also a potential background, while cosmicray muons are a potential background in the µτ channel.The backgrounds with the larger production cross sec-tions (e.g., QCD, W ) are suppressed by multiple powersof the lepton misidentification rates ( ≈ − for jet → τ ,and ≈ − for jet → e, µ ).Event selection for the 3- ℓ events begins with theremoval of events that are consistent with cosmicray muons [18] or low-mass Drell-Yan lepton pairs( M ( e + e − ) <
30 GeV /c ; M ( µ + µ − ) <
30 GeV /c ). Also, events consistent with Z + γ production with the photonmisidentified as an electron are efficiently removed by re-quiring at least 20 GeV of missing transverse energy ( E/ T )[13]. Signal events with at least one τ decaying to an elec-tron typically have E/ T >
20 GeV, due to the significantfraction of the τ ’s energy carried off by the two neutrinos,while Z + γ events are typically well measured, and thushave small E/ T . Similarly, in the 4- ℓ search, events consis-tent with having four final-state electrons must have atleast 20 GeV of E/ T . No attempt is made to reconstructthe full H ±± mass, but we do require the presence of alike-sign eτ or µτ pair with an invariant mass in the range30-125 GeV /c . This selection is nearly 100% efficient forsignal but reduces diboson and top backgrounds.To further reduce backgrounds, in particular Z + jets,we impose a requirement on the scalar sum of the leptontransverse energies and E/ T ( Y T ). The Y T requirement de-pends on whether an event is tagged as a Z boson decay.It is more efficient to remove events consistent with Z boson decays by Y T than by a direct mass cut, becausesome of the signal has oppositely charged leptons in the Z mass range, but large Y T values compared to Z +jets events. The Y T cut values for tagged and untaggedevents, as well as the mass window used in Z boson tag-ging, are optimized by running pseudoexperiments andchoosing the sets of cut values that result in the bestexpected limits on H ++ . The eτ search uses Y T cutsof 190 GeV for untagged events and 300 GeV for eventstagged as Z boson candidates, defined as an e + e − pair inthe mass range 71-111 GeV /c . The µτ search uses Y T cuts of 190 GeV for untagged events, and 350 GeV forevents tagged as Z boson candidates, defined as a µ + µ − pair in the mass range 76-116 GeV /c . In the µτ analy-sis, a muon with a severely mismeasured p T may lead tospuriously high Y T . We minimize the mismeasurementrisk by imposing additional cuts on the highest p T tracksin the events.Events with four isolated leptons have less backgroundthan trilepton events, so less restrictive cuts are applied.We first require Y T >
120 GeV. Events tagged as Z bosonsare required to have E/ T >
20 GeV in the eτ search and Y T >
150 GeV in the µτ search. As with Y T and Z -veto for the 3- ℓ channels, pseudoexperiments were con-ducted with various values of both cuts, and the cutsthat resulted in the best expected limits were chosenfor each analysis. The acceptances for the 3- ℓ and 4- ℓ channels are roughly equal, and the combined accep-tance grows approximately linearly with H ±± mass from8% at 85 GeV /c to 14% at 135 GeV /c . Observed andexpected event yields for signal and background for the3- ℓ and 4- ℓ searches are shown in Table II. The signalevent yields assume σ × B = 89 . f b , corresponding toexclusive decays of 110 GeV /c H ±± to eτ ( µτ ) pairs inmodels [2] and [3]. The Z + jets process is the most sig-nificant single background, with 0.15 + . − . ( stat ) expectedevents for each of the combined (3- ℓ + 4- ℓ ) µτ and eτ searches. The combined background from W Z and ZZ production amounts to 0.12 ± ± eτ ( µτ ) search. t ¯ t background is 0.01 +0 . − . (0.06 +0 . − . )events in the eτ ( µτ ) search. Cosmic ray, γ + jets, andQCD backgrounds are negligible and determined fromdata.Systematic uncertainties on backgrounds from NLOcross section uncertainties are 4% for Z and W bosonproduction processes and 8% for diboson and top quarkproduction processes [19]. A 6% uncertainty applies tothe integrated luminosity of our dataset. A 28% (21%)systematic uncertainty is used for the W → ℓν ℓ ( Z → ℓℓ )background predictions to account for imperfect knowl-edge of the jet → τ h misidentification rate. Imperfect sim-ulation of the track curvature resolution is accounted forby a 0.1 event systematic uncertainty on the combinedbackgrounds for the µτ search. The combined systematicuncertainty for all backgrounds amounts to 0.04 (0.11)events for the eτ ( µτ ) search. The total uncertainties onbackgrounds, shown in Table II, are statistically domi-nated. Systematic uncertainties on the signal cross sec-tion include NLO cross section uncertainties (7.5%) [7],luminosity (6%) [11], and parton density function (PDF)uncertainty (5%) [20]. The uncertainty on signal accep-tance (6.1%) is driven by uncertainties on track isolationefficiency (4.5% and 6% for 3- ℓ and 4- ℓ channels, respec-tively), and π isolation efficiencies (1.5% and 2% for 3- ℓ and 4- ℓ channels, respectively).We find that the background predictions agree withdata in all control samples, including samples in the kine-matic region Y T <
150 GeV enriched with QCD, Z boson,and W boson events. To check our predictions in thehigh- Y T regime while keeping the analysis “blind,” wecheck the number of events that pass all analysis se-lections except track isolation for the second tight lep-ton (Table I). After finalizing all selection requirementsand our limit setting procedure, we search the signalregions in both the 3- ℓ and 4- ℓ channels. We observeno events in either the 3- ℓ or 4- ℓ channels for both the µτ and eτ searches, which is consistent with the SMbackgrounds of 0.24 +0 . − . eτ events and 0.39 ± µτ events. Limits are set using a Bayesian method basedon a Poisson likelihood, with a flat prior for signal crosssection and Gaussian priors for uncertainties on signal,background acceptance, and integrated luminosity. The3- ℓ and 4- ℓ channels are treated as separate measure-ments, taking into account correlated systematic uncer-tainties [14]. We set an upper σ × B limit for the pro-cess p ¯ p → H ++ L H −− L → e + τ + e − τ − of 74 fb at the 95% C.L.,which corresponds in models [2] and [3] to a mass limit of114 GeV /c . The process p ¯ p → H ++ L H −− L → µ + τ + µ − τ − isexcluded above a cross section of 78 fb at the 95% C.L.,corresponding to a mass limit of 112 GeV /c in the samemodels. The exclusion curves are shown in Fig. 1.We thank the Fermilab staff and the technical staffs ofthe participating institutions for their vital contributions. This CDF work was supported by the U.S. Departmentof Energy and National Science Foundation; the ItalianIstituto Nazionale di Fisica Nucleare; the Ministry ofEducation, Culture, Sports, Science and Technology ofJapan; the Natural Sciences and Engineering ResearchCouncil of Canada; the National Science Council of theRepublic of China; the Swiss National Science Founda-tion; the A.P. Sloan Foundation; the Bundesministeriumf¨ur Bildung und Forschung, Germany; the Korean Sci-ence and Engineering Foundation and the Korean Re-search Foundation; the Science and Technology FacilitiesCouncil and the Royal Society, UK; the Institut Nationalde Physique Nucleaire et Physique des Particules/CNRS;the Russian Foundation for Basic Research; the Comisi´onInterministerial de Ciencia y Tecnolog´ıa, Spain; the Eu-ropean Community’s Human Potential Programme un-der contract HPRN-CT-2002-00292; and the Academyof Finland. Signature Lepton Flavor E T ( P T ) | η | ℓ st (tight) e >
20 GeV < . nd (tight) τ h or e >
15 GeV < . rd (loose) τ h or e >
10 GeV < . ℓ th (loose) Isolated Track >
10 GeV /c < . eτ search. For the µτ search, the first leptonchanges from e to µ , and the third lepton changes from τ h or e to isolated track. eτ Selection Exp. Signal Background Data3- ℓ Lepton ID 2.94 ± ± M LS , M OS ± ± Y T / Z veto 2.4 ± ± Y T ± +0 . − . ℓ Lepton ID 1.61 ± ± Y T / Z veto 1.60 ± +0 . − . µτ Selection Exp. Signal Background Data3- ℓ Lepton ID 3.06 ± ± . M LS , M OS ± ± Y T / Z veto 2.35 ± ± Y T ± ± ℓ Lepton ID 1.65 ± ± Y T / Z veto 1.64 ± ± /c , σ × B = 89 . fb ) and background in the3- ℓ and 4- ℓ searches. M LS ( M OS ) represent the invariantmass requirements on the like (opposite) sign leptons. The Z veto refers to the additional Y T requirement on Z bosontagged events. The uncertainties are combined statistical andsystematic. FIG. 1: Theoretical production cross sections for the pairproduction of left-handed H ±± , and 95% C.L. limit curvesfor σ ( p ¯ p → H ++ H −− → ) × B ( ℓ + τ + ℓ − τ − ), for ℓ = e (solid), µ (dashed). The vertical dashed line corresponds to limitsfrom experiments at LEP2 for exclusive H ±± L decays to anyone dilepton channel [9].[1] T. P. Cheng and L.-F. Li, Phys. Rev. D , 2860 (1980).[2] R. N. Mohapatra and G. Senjanovic, Phys. Rev. Lett. , 912 (1980).[3] A. Akeroyd and M. Aoki, Phys. Rev. D , 35011 (2005).[4] Y. Fukuda et al. (Super-Kamiokande), Phys. Rev. Lett. , 1562 (1998), hep-ex/9807003.[5] Q. R. Ahmad et al. (SNO), Phys. Rev. Lett. , 11301(2002), nucl-ex/0204008.[6] With the present dataset, expected mass limits for H ±± R are much lower than the LEP2 limits because the H ±± R pair production cross section is about half as large as thatfor H ±± L .[7] M. Muhlleitner and M. Spira, Phys. Rev. D , 117701(2003).[8] E. Ma, M. Raidal, and U. Sarkar, Phys. Rev. Lett. ,3769 (2000).[9] R. Barate et al. (Aleph, Delphi, L3, and Opal), Phys.Lett. B , 61 (2003).[10] D. Acosta et al. (CDF), Phys. Rev. Lett. , 221802(2004).[11] S. Klimenko, J. Konigsberg, and T. M. Liss, Fermilab-Pub FN/0741 (2003).[12] D. Acosta et al. (CDF), Phys. Rev. D , 32001 (2005).[13] CDF uses a cylindrical coordinate system in which φ isthe azimuthal angle, θ is the polar angle, r is the ra-dius from the nominal beamline, and + z points from thenominal interaction point along the proton beam. Thepseudorapidity is defined η = − ln[ tan ( θ/ E T ( p T ), and the total calorimetrictransverse energy imbalance is denoted as E/ T .[14] A. Abulencia et al. (CDF), Phys. Rev. D , 92004(2007).[15] A. Anastassov et al. , Nucl. Instrum. Methods A , 609–611 (2004).[16] S. Mrenna, L. Lonnblad, and T. Sjostrand, pythia W5013 (1994), we used version 3.15.[18] A. V. Kotwal, H. K. Gerberich, and C. Hays, Nucl. In-strum. Methods A , 113006 (1999).[20] We calculate this uncertainty from the changes in crosssection due to 1 σσ