BABAR-PUB-01/19 SLAC-PUB-9102 Search for the Rare Decays B → Kℓ+ℓ− and B → K∗ℓ+ℓ− B. Aubert,1 D. Boutigny,1 J.-M. Gaillard,1 A. Hicheur,1 Y. Karyotakis,1 J. P. Lees,1 P. Robbe,1 V. Tisserand,1 A. Palano,2 A. Pompili,2 G. P. Chen,3 J. C. Chen,3 N. D. Qi,3 G. Rong,3 P. Wang,3 Y. S. Zhu,3 G. Eigen,4 B. Stugu,4 G. S. Abrams,5 A. W. Borgland,5 A. B. Breon,5 D. N. Brown,5 J. Button-Shafer,5 R. N. Cahn,5 A. R. Clark,5 M. S. Gill,5 A. V. Gritsan,5 Y. Groysman,5 R. G. Jacobsen,5 R. W. Kadel,5 J. Kadyk,5 L. T. Kerth,5 Yu. G. Kolomensky,5 J. F. Kral,5 C. LeClerc,5 M. E. Levi,5 G. Lynch,5 P. J. Oddone,5 M. Pripstein,5 N. A. Roe,5 A. Romosan,5 M. T. Ronan,5 V. G. Shelkov,5 A. V. Telnov,5 W. A. Wenzel,5 T. J. Harrison,6 C. M. Hawkes,6 2 D. J. Knowles,6 S. W. O’Neale,6 R. C. Penny,6 A. T. Watson,6 N. K. Watson,6 T. Deppermann,7 K. Goetzen,7 0 H. Koch,7 M. Kunze,7 B. Lewandowski,7 K. Peters,7 H. Schmuecker,7 M. Steinke,7 N. R. Barlow,8 W. Bhimji,8 0 2 N. Chevalier,8 P. J. Clark,8 W. N. Cottingham,8 B. Foster,8 C. Mackay,8 F. F. Wilson,8 K. Abe,9 C. Hearty,9 T. S. Mattison,9 J. A. McKenna,9 D. Thiessen,9 S. Jolly,10 A. K. McKemey,10 V. E. Blinov,11 A. D. Bukin,11 n a D. A. Bukin,11 A. R. Buzykaev,11 V. B. Golubev,11 V. N. Ivanchenko,11 A. A. Korol,11 E. A. Kravchenko,11 J A. P. Onuchin,11 S. I. Serednyakov,11 Yu. I. Skovpen,11 V. I. Telnov,11 A. N. Yushkov,11 D. Best,12 M. Chao,12 4 D. Kirkby,12 A. J. Lankford,12 M. Mandelkern,12 S. McMahon,12 D. P. Stoker,12 K. Arisaka,13 C. Buchanan,13 S. Chun,13 D. B. MacFarlane,14 S. Prell,14 Sh. Rahatlou,14 G. Raven,14 V. Sharma,14 C. Campagnari,15 1 v B. Dahmes,15 P. A. Hart,15 N. Kuznetsova,15 S. L. Levy,15 O. Long,15 A. Lu,15 J. D. Richman,15 W. Verkerke,15 8 J. Beringer,16 A. M. Eisner,16 M. Grothe,16 C. A. Heusch,16 W. S. Lockman,16 T. Pulliam,16 T. Schalk,16 0 R. E. Schmitz,16 B. A. Schumm,16 A. Seiden,16 M. Turri,16 W. Walkowiak,16 D. C. Williams,16 M. G. Wilson,16 0 1 E. Chen,17 G. P. Dubois-Felsmann,17 A. Dvoretskii,17 D. G. Hitlin,17 S. Metzler,17 J. Oyang,17 F. C. Porter,17 0 A. Ryd,17 A. Samuel,17 M. Weaver,17 S. Yang,17 R. Y. Zhu,17 S. Devmal,18 T. L. Geld,18 S. Jayatilleke,18 2 G. Mancinelli,18 B. T. Meadows,18 M. D. Sokoloff,18 T. Barillari,19 P. Bloom,19 M. O. Dima,19 W. T. Ford,19 0 U. Nauenberg,19 A. Olivas,19 P. Rankin,19 J. Roy,19 J. G. Smith,19 W. C. van Hoek,19 J. Blouw,20 J. L. Harton,20 / x M. Krishnamurthy,20 A. Soffer,20 W. H. Toki,20 R. J. Wilson,20 J. Zhang,20 T. Brandt,21 J. Brose,21 e - T. Colberg,21 M. Dickopp,21 R. S. Dubitzky,21 A. Hauke,21 E. Maly,21 R. Mu¨ller-Pfefferkorn,21 S. Otto,21 p K. R. Schubert,21 R. Schwierz,21 B. Spaan,21 L. Wilden,21 D. Bernard,22 G. R. Bonneaud,22 F. Brochard,22 e h J. Cohen-Tanugi,22 S. Ferrag,22 S. T’Jampens,22 Ch. Thiebaux,22 G. Vasileiadis,22 M. Verderi,22 A. Anjomshoaa,23 : R. Bernet,23 A. Khan,23 D. Lavin,23 F. Muheim,23 S. Playfer,23 J. E. Swain,23 J. Tinslay,23 M. Falbo,24 v i C. Borean,25 C. Bozzi,25 S. Dittongo,25 L. Piemontese,25 E. Treadwell,26 F. Anulli,27,∗ R. Baldini-Ferroli,27 X A. Calcaterra,27 R. de Sangro,27 D. Falciai,27 G. Finocchiaro,27 P. Patteri,27 I. M. Peruzzi,27,∗ M. Piccolo,27 ar Y. Xie,27 A. Zallo,27 S. Bagnasco,28 A. Buzzo,28 R. Contri,28 G. Crosetti,28 M. Lo Vetere,28 M. Macri,28 M. R. Monge,28 S. Passaggio,28 F. C. Pastore,28 C. Patrignani,28 M. G. Pia,28 E. Robutti,28 A. Santroni,28 S. Tosi,28 M. Morii,29 R. Bartoldus,30 R. Hamilton,30 U. Mallik,30 J. Cochran,31 H. B. Crawley,31 P.-A. Fischer,31 J. Lamsa,31 W. T. Meyer,31 E. I. Rosenberg,31 G. Grosdidier,32 C. Hast,32 A. Ho¨cker,32 H. M. Lacker,32 S. Laplace,32 V. Lepeltier,32 A. M. Lutz,32 S. Plaszczynski,32 M. H. Schune,32 S. Trincaz-Duvoid,32 G. Wormser,32 R. M. Bionta,33 V. Brigljevi´c,33 D. J. Lange,33 M. Mugge,33 K. van Bibber,33 D. M. Wright,33 A. J. Bevan,34 J. R. Fry,34 E. Gabathuler,34 R. Gamet,34 M. George,34 M. Kay,34 D. J. Payne,34 R. J. Sloane,34 C. Touramanis,34 M. L. Aspinwall,35 D. A. Bowerman,35 P. D. Dauncey,35 U. Egede,35 I. Eschrich,35 N. J. W. Gunawardane,35 J. A. Nash,35 P. Sanders,35 D. Smith,35 D. E. Azzopardi,36 J. J. Back,36 G. Bellodi,36 P. Dixon,36 P. F. Harrison,36 R. J. L. Potter,36 H. W. Shorthouse,36 P. Strother,36 P. B. Vidal,36 G. Cowan,37 S. George,37 M. G. Green,37 A. Kurup,37 C. E. Marker,37 P. McGrath,37 T. R. McMahon,37 S. Ricciardi,37 F. Salvatore,37 G. Vaitsas,37 D. Brown,38 C. L. Davis,38 J. Allison,39 R. J. Barlow,39 J. T. Boyd,39 A. C. Forti,39 J. Fullwood,39 F. Jackson,39 G. D. Lafferty,39 N. Savvas,39 J. H. Weatherall,39 J. C. Williams,39 A. Farbin,40 A. Jawahery,40 V. Lillard,40 J. Olsen,40 D. A. Roberts,40 J. R. Schieck,40 G. Blaylock,41 C. Dallapiccola,41 K. T. Flood,41 S. S. Hertzbach,41 R. Kofler,41 V. B. Koptchev,41 T. B. Moore,41 H. Staengle,41 S. Willocq,41 B. Brau,42 R. Cowan,42 G. Sciolla,42 F. Taylor,42 R. K. Yamamoto,42 M. Milek,43 P. M. Patel,43 F. Palombo,44 J. M. Bauer,45 L. Cremaldi,45 V. Eschenburg,45 R. Kroeger,45 J. Reidy,45 D. A. Sanders,45 D. J. Summers,45 J. Y. Nief,46 P. Taras,46 2 H. Nicholson,47 C. Cartaro,48 N. Cavallo,48,† G. De Nardo,48 F. Fabozzi,48 C. Gatto,48 L. Lista,48 P. Paolucci,48 D. Piccolo,48 C. Sciacca,48 J. M. LoSecco,49 J. R. G. Alsmiller,50 T. A. Gabriel,50 J. Brau,51 R. Frey,51 E. Grauges,51 M. Iwasaki,51 N. B. Sinev,51 D. Strom,51 F. Colecchia,52 F. Dal Corso,52 A. Dorigo,52 F. Galeazzi,52 M. Margoni,52 G. Michelon,52 M. Morandin,52 M. Posocco,52 M. Rotondo,52 F. Simonetto,52 R. Stroili,52 E. Torassa,52 C. Voci,52 M. Benayoun,53 H. Briand,53 J. Chauveau,53 P. David,53 Ch. de la Vaissi`ere,53 L. Del Buono,53 O. Hamon,53 F. Le Diberder,53 Ph. Leruste,53 J. Ocariz,53 L. Roos,53 J. Stark,53 P. F. Manfredi,54 V. Re,54 V. Speziali,54 E. D. Frank,55 L. Gladney,55 Q. H. Guo,55 J. Panetta,55 C. Angelini,56 G. Batignani,56 S. Bettarini,56 M. Bondioli,56 F. Bucci,56 E. Campagna,56 M. Carpinelli,56 F. Forti,56 M. A. Giorgi,56 A. Lusiani,56 G. Marchiori,56 F. Martinez-Vidal,56 M. Morganti,56 N. Neri,56 E. Paoloni,56 M. Rama,56 G. Rizzo,56 F. Sandrelli,56 G. Simi,56 G. Triggiani,56 J. Walsh,56 M. Haire,57 D. Judd,57 K. Paick,57 L. Turnbull,57 D. E. Wagoner,57 J. Albert,58 P. Elmer,58 C. Lu,58 V. Miftakov,58 S. F. Schaffner,58 A. J. S. Smith,58 A. Tumanov,58 E. W. Varnes,58 G. Cavoto,59 D. del Re,59 R. Faccini,14,59 F. Ferrarotto,59 F. Ferroni,59 E. Lamanna,59 M. A. Mazzoni,59 S. Morganti,59 G. Piredda,59 F. Safai Tehrani,59 M. Serra,59 C. Voena,59 S. Christ,60 R. Waldi,60 T. Adye,61 N. De Groot,61 B. Franek,61 N. I. Geddes,61 G. P. Gopal,61 S. M. Xella,61 R. Aleksan,62 S. Emery,62 A. Gaidot,62 S. F. Ganzhur,62 P.-F. Giraud,62 G. Hamel de Monchenault,62 W. Kozanecki,62 M. Langer,62 G. W. London,62 B. Mayer,62 B. Serfass,62 G. Vasseur,62 Ch. Y`eche,62 M. Zito,62 M. V. Purohit,63 H. Singh,63 A. W. Weidemann,63 F. X. Yumiceva,63 I. Adam,64 D. Aston,64 N. Berger,64 A. M. Boyarski,64 G. Calderini,64 M. R. Convery,64 D. P. Coupal,64 D. Dong,64 J. Dorfan,64 W. Dunwoodie,64 R. C. Field,64 T. Glanzman,64 S. J. Gowdy,64 T. Haas,64 T. Himel,64 T. Hryn’ova,64 M. E. Huffer,64 W. R. Innes,64 C. P. Jessop,64 M. H. Kelsey,64 P. Kim,64 M. L. Kocian,64 U. Langenegger,64 D. W. G. S. Leith,64 S. Luitz,64 V. Luth,64 H. L. Lynch,64 H. Marsiske,64 S. Menke,64 R. Messner,64 D. R. Muller,64 C. P. O’Grady,64 V. E. Ozcan,64 A. Perazzo,64 M. Perl,64 S. Petrak,64 H. Quinn,64 B. N. Ratcliff,64 S. H. Robertson,64 A. Roodman,64 A. A. Salnikov,64 T. Schietinger,64 R. H. Schindler,64 J. Schwiening,64 A. Snyder,64 A. Soha,64 S. M. Spanier,64 J. Stelzer,64 D. Su,64 M. K. Sullivan,64 H. A. Tanaka,64 J. Va’vra,64 S. R. Wagner,64 A. J. R. Weinstein,64 W. J. Wisniewski,64 D. H. Wright,64 C. C. Young,64 P. R. Burchat,65 C. H. Cheng,65 T. I. Meyer,65 C. Roat,65 R. Henderson,66 W. Bugg,67 H. Cohn,67 J. M. Izen,68 I. Kitayama,68 X. C. Lou,68 F. Bianchi,69 M. Bona,69 D. Gamba,69 L. Bosisio,70 G. Della Ricca,70 L. Lanceri,70 P. Poropat,70 G. Vuagnin,70 R. S. Panvini,71 C. M. Brown,72 P. D. Jackson,72 R. Kowalewski,72 J. M. Roney,72 H. R. Band,73 E. Charles,73 S. Dasu,73 A. M. Eichenbaum,73 H. Hu,73 J. R. Johnson,73 R. Liu,73 F. Di Lodovico,73 Y. Pan,73 R. Prepost,73 I. J. Scott,73 S. J. Sekula,73 J. H. von Wimmersperg-Toeller,73 S. L. Wu,73 Z. Yu,73 T. M. B. Kordich,74 and H. Neal74 (The BABAR Collaboration) 1Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France 2Universit`a di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy 3Institute of High Energy Physics, Beijing 100039, China 4University of Bergen, Inst. of Physics, N-5007 Bergen, Norway 5Lawrence Berkeley National Laboratory and University of California, Berkeley, CA 94720, USA 6University of Birmingham, Birmingham, B15 2TT, United Kingdom 7Ruhr Universit¨at Bochum, Institut fu¨r Experimentalphysik 1, D-44780 Bochum, Germany 8University of Bristol, Bristol BS8 1TL, United Kingdom 9University of British Columbia, Vancouver, BC, Canada V6T 1Z1 10Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom 11Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia 12University of California at Irvine, Irvine, CA 92697, USA 13University of California at Los Angeles, Los Angeles, CA 90024, USA 14University of California at San Diego, La Jolla, CA 92093, USA 15University of California at Santa Barbara, Santa Barbara, CA 93106, USA 16University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, CA 95064, USA 17California Institute of Technology, Pasadena, CA 91125, USA 18University of Cincinnati, Cincinnati, OH 45221, USA 19University of Colorado, Boulder, CO 80309, USA 20Colorado State University, Fort Collins, CO 80523, USA 21Technische Universit¨at Dresden, Institut fu¨r Kern- und Teilchenphysik, D-01062 Dresden, Germany 22Ecole Polytechnique, F-91128 Palaiseau, France 23University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom 24Elon University, Elon University, NC 27244-2010, USA 25Universit`a di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy 3 26Florida A&M University, Tallahassee, FL 32307, USA 27Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy 28Universit`a di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy 29Harvard University, Cambridge, MA 02138, USA 30University of Iowa, Iowa City, IA 52242, USA 31Iowa State University, Ames, IA 50011-3160, USA 32Laboratoire de l’Acc´el´erateur Lin´eaire, F-91898 Orsay, France 33Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 34University of Liverpool, Liverpool L69 3BX, United Kingdom 35University of London, Imperial College, London, SW7 2BW, United Kingdom 36Queen Mary, University of London, E1 4NS, United Kingdom 37University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom 38University of Louisville, Louisville, KY 40292, USA 39University of Manchester, Manchester M13 9PL, United Kingdom 40University of Maryland, College Park, MD 20742, USA 41University of Massachusetts, Amherst, MA 01003, USA 42Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, MA 02139, USA 43McGill University, Montr´eal, QC, Canada H3A 2T8 44Universit`a di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy 45University of Mississippi, University, MS 38677, USA 46Universit´e de Montr´eal, Laboratoire Ren´e J. A. L´evesque, Montr´eal, QC, Canada H3C 3J7 47Mount Holyoke College, South Hadley, MA 01075, USA 48Universit`a di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy 49University of Notre Dame, Notre Dame, IN 46556, USA 50Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 51University of Oregon, Eugene, OR 97403, USA 52Universit`a di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy 53Universit´es Paris VI et VII, Lab de Physique Nucl´eaire H. E., F-75252 Paris, France 54Universit`a di Pavia, Dipartimento di Elettronica and INFN, I-27100 Pavia, Italy 55University of Pennsylvania, Philadelphia, PA 19104, USA 56Universit`a di Pisa, Scuola Normale Superiore and INFN, I-56010 Pisa, Italy 57Prairie View A&M University, Prairie View, TX 77446, USA 58Princeton University, Princeton, NJ 08544, USA 59Universit`a di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy 60Universit¨at Rostock, D-18051 Rostock, Germany 61Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom 62DAPNIA, Commissariat `a l’Energie Atomique/Saclay, F-91191 Gif-sur-Yvette, France 63University of South Carolina, Columbia, SC 29208, USA 64Stanford Linear Accelerator Center, Stanford, CA 94309, USA 65Stanford University, Stanford, CA 94305-4060, USA 66TRIUMF, Vancouver, BC, Canada V6T 2A3 67University of Tennessee, Knoxville, TN 37996, USA 68University of Texas at Dallas, Richardson, TX 75083, USA 69Universit`a di Torino, Dipartimento di Fiscia Sperimentale and INFN, I-10125 Torino, Italy 70Universit`a di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy 71Vanderbilt University, Nashville, TN 37235, USA 72University of Victoria, Victoria, BC, Canada V8W 3P6 73University of Wisconsin, Madison, WI 53706, USA 74Yale University, New Haven, CT 06511, USA (Dated: January 4, 2002) Wepresent results from a search for theflavor-changingneutral currentdecays B→Kℓ+ℓ− and B →K∗ℓ+ℓ−, where ℓ+ℓ− is either an e+e− or µ+µ− pair. The data sample comprises 22.7×106 Υ(4S) → BB decays collected with the BABAR detector at the PEP-II B Factory. We obtain the 90% C.L. upper limits B(B → Kℓ+ℓ−) < 0.50×10−6 and B(B → K∗ℓ+ℓ−) < 2.9×10−6, close to Standard Model predictions for these branching fractions. We have also obtained limits on the lepton-family-violating decaysB →Ke±µ∓ and B→K∗e±µ∓. PACSnumbers: 13.25.Hw,13.20.He The flavor-changing neutral current decays B → with branching fractions predictedto be of order 10−7− Kℓ+ℓ− and B → K∗(892)ℓ+ℓ−, where ℓ± is a charged 10−6 [1, 2]. The dominant contributions arise at the lepton, are highly suppressed in the Standard Model, one-loop level and are known as electroweak penguins. 4 Besides probing Standard Model loop effects, these rare To prevent bias in the analysis, we optimized the event- decays are important because their rates and kinematic selection criteria using Monte Carlo samples: we did not distributions are sensitive to new, heavy particles—such look at the data in the signal region or in the sidebands as those predicted by supersymmetric models—that can that were used to measure the background until these appear virtually in the loop [1, 2]. criteria were fixed. Signal efficiencies were determined The Standard Model predictions for B → K(∗)ℓ+ℓ− using the Ali et al. model [1]. include three main contributions: the electromagnetic Weselecteventsthathaveatleastfourchargedtracks, (EM) penguin, the Z penguin, and the W+W− box dia- the ratio R2 of the second and zeroth Fox-Wolfram mo- gram. Evidence for the EMpenguin amplitude has been ments [6] less than 0.5, and two oppositely charged lep- obtained from the observation of B → K∗γ and inclu- tons with momentum p>0.5 (1.0) GeV/c for e (µ) can- sive B → Xsγ, where Xs is any hadronic system with didates. Electron-positron pairs consistent with photon strangeness [3, 4]. conversions in the detector material are vetoed. We re- Calculations of decay rates for B → K(∗)ℓ+ℓ− based quire charged kaon candidates to be identified as kaons andthechargedpioninK∗ →Kπ nottobeidentifiedas ontheStandardModelhavesignificantuncertaintiesdue to strong interactions. For example, Ali et al. [1] predict akaon. ForB →K∗ℓ+ℓ−,werequirethemassoftheK∗ B(B →Kℓ+ℓ−)=(0.57+0.17)×10−6 for both e+e− and candidate to be within 75 MeV/c2 of the mean K∗(892) µ+µ− final states, B(B−→0.1K0∗e+e−) = (2.3+0.7)×10−6, mass. KS0 candidates are reconstructed from two oppo- and B(B → K∗µ+µ−) = (1.9+0.5)×10−6.−0T.5he contri- sitely charged tracks that form a good vertex displaced −0.4 from the primary vertex by at least 1 mm. bution of the EM penguin amplitude to B →K∗ℓ+ℓ− is The decays B →J/ψ(→ℓ+ℓ−)K(∗) and particularlystrongatlowvaluesofmℓ+ℓ−,givingalarger B →ψ(2S)(→ℓ+ℓ−)K(∗) have identical topologies rate for B →K∗e+e− than for B →K∗µ+µ−. to signal events. These backgrounds are suppressed by We search for the following decays: B+ → K+ℓ+ℓ−, B0 → K0ℓ+ℓ−, B+ → K∗+ℓ+ℓ−, and B0 → K∗0ℓ+ℓ−, applying a veto in the ∆E vs. mℓ+ℓ− plane (Fig. 1). S This veto removes charmonium events not only with re- whereK∗0 →K+π−,K∗+ →K0π+,K0 →π+π−,andℓ S S constructed mℓ+ℓ− values near the nominal charmonium is either an e or µ. We also search for the lepton-family- violating decays B → K(∗)e±µ∓. Throughout this pa- masses, but also events that lie further away in mℓ+ℓ− due to photon radiation (more pronounced in electron per, charge-conjugatemodes are implied. channels) or track mismeasurement. Removing all of The data used in the analysis were collected with the these events simplifies the description of the background BABAR detector at the PEP-II storage ring at the Stan- shape. Charmonium events can, however, pass this ford Linear Accelerator Center during 1999-2000. We veto if one of the leptons (typically a muon) and the analyzed a 20.7 fb−1 data sample taken on the Υ(4S) kaon are misidentified as each other. If reassignment resonance consisting of (22.7±0.4)×106 Υ(4S) → BB of particle types results in a dilepton mass consistent events. with the J/ψ or ψ(2S) mass, the candidate is vetoed. This search relies primarily on the charged-particle There is also significant feed-up from B →J/ψK and tracking and particle-identification capabilities of the B →ψ(2S)K into B →K∗ℓ+ℓ−, since energy lost due BABARdetector[5]. Chargedparticletrackingisprovided to bremsstrahlung in B → J/ψK can be compensated by a five-layer silicon vertex tracker (SVT) and a 40- for by including a random pion. If the Kℓ+ℓ− system layerdriftchamber(DCH).TheDIRC,aCherenkovring- in a B → K∗ℓ+ℓ− candidate is kinematically consistent imagingparticle-identificationsystem,isusedforcharged with B → J/ψ(→ ℓ+ℓ−γ)K, assuming that the photon hadron identification. Electrons are identified using (which is not directly observed) was radiated along the theelectromagneticcalorimeter(EMC),whichcomprises direction of either lepton, then the candidate is vetoed. 6580 thallium-doped CsI crystals. These systems are Apart from the charmonium vetoes, we analyze the full mounted inside a 1.5 T solenoidalsuperconducting mag- mℓ+ℓ− range. net. Muonsareidentifiedintheinstrumentedfluxreturn Continuumbackgroundfromnon-resonante+e− →qq (IFR), in which resistive plate chambers are interleaved production is suppressed using a Fisher discriminant[7], with the iron plates of the magnet flux return. a linear combination of the input variables with opti- We extract the signal using the kinematic variables mized coefficients. The variables are R2; cosθB, the m = E∗2−( p∗)2 and ∆E = m2+p∗2 − cosine of the angle between the B candidate and the ES b i i i i i Eb∗,whepreEb∗ isthPe beamenergyinthePe+pe− rest(c.m.) beam axis in the c.m. frame; cosθT, the cosine of the frame,p∗ isthec.m.momentumofdaughterparticleiin angle between the thrust axis of the candidate B meson i the B mesoncandidate, and mi is the mass of particle i. daughter particles and that of the rest of the particles Forsignalevents,mES peaksattheB mesonmasswitha in the c.m. frame; and mKℓ, the invariant mass of the resolutionofabout2.5MeV/c2 and∆E peaksnearzero, K-lepton system, where the lepton is selected according indicatingthatthecandidatesystemofparticleshastotal to its chargerelativeto the strangenessofthe K(∗). The energyconsistentwiththebeamenergyinthec.m.frame. variablemKℓhelpsdiscriminateagainstbackgroundfrom 5 00..44 yields, we generate and fit a series of toy Monte Carlo samples in which the background probability density 00..22 function is taken from our fit to the data, but the mean ) V number of signalevents is varied. We generateten thou- e G 00 sand samples for each mean value, increasing the mean ( E until90%ofthefitstoasetofsamplesgiveasignalyield D --00..22 greaterthan that obtainedby fitting the data. To give a measureofthesensitivityoftheanalysiswelistinTableI --00..44 aneffectivebackgroundyield. Thisquantityisdefinedas 22 33 44 22 33 44 the square of the error on the signal yield from a fit to me+e- (GeV/c2) mm +m - (GeV/c2) a toy Monte Carlo sample drawn from the background probability function, with no signal contribution. FIG.1: Charmoniumvetointhe∆Evs.mℓ+ℓ− planefor(a) Table I lists the systematic uncertainties from the fit, B→K(∗)e+e− and(b)B→K(∗)µ+µ−. Hatchedregionsare (∆B/B) ,expressedaccordingtotheireffectonthelim- vetoed. The dots correspond to a Monte Carlo simulation of fit B →J/ψ(→ℓ+ℓ−)K and B →ψ(2S)(→ℓ+ℓ−)K. Most sig- its. The sensitivity of the limits to the values used for naleventswouldlie inthe∆E region betweenthehorizontal signal-shape parameters is determined by performing al- lines. ternative fits using parameters from the B → J/ψK(∗) controlsamples. Formodeswithelectrons,wealsovaried thefractionofsignaleventsinthetailofthe∆Edistribu- semileptonic D decays, for which mKℓ <mD. tion. To determine whether a more general background Combinatorial background from BB events is sup- shapewouldleadtodifferentresults,weintroducedaddi- pressed using a signal-to-BB likelihood ratio that com- tional parameters and allowed for a correlation between bines candidate B and dilepton vertex probabilities; the m and ∆E. This procedure shifted the upper lim- ES significance of the dilepton separation along the beam its by 2% to 5%, depending on the mode. Most of the direction; cosθB; and the missing energy, Emiss, of the uncertainty associated with the background shape is in- event in the c.m. frame. The variableEmiss provides the corporated in the statistical error on the yield because strongest discrimination against BB background, since the backgroundshape is determined from the fit. events with semileptonic decays usually have significant unobservedenergyduetoneutrinos. Foreachfinalstate, we select at most one combination of particles per event 50 B → J/y K B → J/y K as a B signal candidate. If multiple candidates occur, J/y → e+e- J/y → m +m - V 40 weselectthe candidatewiththe greatestnumberofdrift e G chamber and SVT hits on the charged tracks. 1 30 0 We use the known charmonium decays B → J/ψK(∗) s/0. 20 andB →ψ(2S)K(∗) to checkthe efficiency ofour analy- ntrie sis cuts. Figure 2 compares the ∆E distributions (ab- E 10 solutely normalized) of these charmonium samples in 0 MonteCarlowithdata. We findgoodagreementinboth B → J/y K*0 B → J/y K*0 30 J/y → e+e- J/y → m +m - the normalization and the shape. V e We extract the signal and background yields in G each channel using a two-dimensional extended un- 0.01 20 binned maximum likelihood fit in the region defined by es/ mES > 5.2 GeV/c2 and |∆E| < 0.25 GeV. The signal Entri 10 shapes, including the effects of radiation on the ∆E dis- tribution and the correlation between m and ∆E, are 0 ES -0.1 -0.05 0 0.05-0.05 0 0.05 obtained by parametrizing the GEANT3 Monte Carlo [8] simulationofthe signal. Thebackgroundis describedby D E (GeV) D E (GeV) a function [9] with two parameters that are determined in our fits to the data. Backgroundsfrom BB that peak FIG.2: Comparison ofeventyieldsand∆E shapesbetween data and Monte Carlo for the charmonium control samples. inthesignalregionaresuppressedtolessthan0.2events The points with error bars show the data, and the solid his- in each mode. Although we allow the signal yield to be togramsshowthepredictionofthecharmoniumMonteCarlo. negative, we have imposed a lower cut-off such that the Alloftheanalysis selection criteriahavebeenapplied except total fit function is positive. The fit results are shown for the charmonium veto, which is reversed. The large tails in Fig. 3 and summarized in Table I. We observe no in the e+e− modes are dueto photon radiation. Small shifts significant signals. betweendataandMonteCarloaretakenintoaccountassys- To determine 90% C.L. upper limits on the signal tematic uncertainties on thesignal yields. 6 TABLEI: Resultsfrom thefitstoB→K(∗)ℓ+ℓ− andB→K(∗)e±µ∓ modes. Thecolumnsfrom left toright arefittedsignal yield [10]; upper limit on the signal yield; the contribution of the background to the error on the signal yield, expressed as an effectivebackgroundyield(seetext);thesignalefficiency,ǫ(notincludingthebranchingfractionsforK∗,K0,andK0 decays); S the systematic error on the selection efficiency, (∆B/B)ǫ; the systematic error from the fit, (∆B/B)fit; the branching fraction central value(B); and theupperlimit on the branchingfraction, including systematic errors. Mode Signal 90% C.L. Effective ǫ (∆B/B)ǫ (∆B/B)fit B/10−6 B/10−6 yield yield background (%) (%) (%) 90% C.L. B+ →K+e+e− −0.2+1.5 3.1 0.7 17.5 ±7.6 ±4.0 0.0+0.4 0.8 −0.0 −0.0 B+ →K+µ+µ− −0.3+1.3 2.6 0.6 10.5 ±7.5 ±4.0 −0.1+0.5 1.2 −0.0 −0.0 B0 →K∗0e+e− 3.8+3.8 8.8 1.4 10.2 ±8.8 ±11.9 2.5+2.5 6.6 −2.1 −1.4 B0 →K∗0µ+µ− −0.3+1.7 3.5 0.7 8.0 ±10.8 ±3.0 −0.2+1.4 3.2 −0.0 −0.0 B0 →K0e+e− 1.1+2.7 4.2 0.2 15.7 ±8.8 ±9.5 0.9+2.2 3.9 −0.9 −0.8 B0 →K0µ+µ− 0.0+1.2 2.5 0.1 9.6 ±8.8 ±3.0 0.0+1.6 3.7 −0.0 −0.0 B+ →K∗+e+e− −0.4+1.9 3.8 1.6 8.5 ±11.0 ±5.0 −0.8+4.3 9.6 −0.0 −0.0 B+ →K∗+µ+µ− 1.2+2.4 4.5 0.3 5.8 ±13.0 ±7.6 3.9+8.1 17.3 −1.0 −3.2 B+ →K+e±µ∓ −0.4+1.4 2.9 1.3 16.8 ±5.7 ±4.0 −0.1+0.4 0.8 −0.0 −0.0 B0 →K∗0e±µ∓ 1.1+3.3 5.3 2.7 11.9 ±7.1 ±10.4 0.6+1.8 3.3 −1.6 −0.9 B0 →K0e±µ∓ 1.1+2.1 4.1 0.5 14.6 ±7.3 ±11.2 0.9+1.9 4.1 −0.9 −0.8 B+ →K∗+e±µ∓ −0.4+1.8 3.5 1.1 9.3 ±9.6 ±3.0 −0.8+3.8 8.0 −0.0 −0.0 (a) K+e+e- (b) K+m +m - pression cut (±2.0%), the BB suppression cut (±3.0%), 4 K0 selection (±4.0%), Monte Carlo signal statistics S (±3.0% to ±5.0%), the theoretical model dependence of 2 theefficiency(±4.0%to±7.0%,dependingonthemode), 0 and the number of BB events (±1.6%). The uncertain- 2 4 (c) K*0e+e- (d) K*0m +m - ties on the efficiencies due to model-dependence of form c V/ factors are taken to be the full range of variation ob- Me 2 tained from different theoretical models [1]. In setting 3 an upper limit, the systematic uncertainties from the ef- ntries/ 20 (e) KS0 e+e- (f) KS0 m +m - fiinciqeunacyd,ra(∆tuBre/,Ba)nǫ,datnhdeflriommittihseinfictr,e(a∆seBd/Bby)fitth,iasrefaacdtodre.d E Table I also includes the results for the lepton-family- 1 violating decays B → K(∗)eµ, where the signal efficien- ciesweredeterminedfromphase-spaceMonteCarlosim- 0 4 (g) K*+e+e- (h) K*+m +m - ulations. We observe no evidence for these decays. We determine the branchingfractionsB(B →Kℓ+ℓ−) and B(B → K∗ℓ+ℓ−) averaged over both B meson 2 charge and lepton type (e+e− and µ+µ−) by perform- ing a simultaneous maximum likelihood fit to the four 0 5.2 5.22 5.24 5.26 5.285.2 5.22 5.24 5.26 5.28 contributing channels in each case. In combining the mES (GeV/ c 2) mES (GeV/ c 2) B → K∗ℓ+ℓ− modes, the ratio of branching fractions B(B → K∗e+e−)/B(B → K∗µ+µ−) = 1.2 from the FIG.3: Projectionsfromindividualmaximumlikelihoodfits model of Ali et al. [1] is used to weight the yield in the ontom forthe∆Esignalregions: −0.11<∆E <0.05GeV ES muon channel relative to that in the electron channel. (electrons) and −0.07<∆E <0.05 GeV (muons). The dot- The extracted yield corresponds to the electron mode. tedlinesshowthebackgroundcomponent,andthesolidlines The combined fits give show the sum of background and signal components. B(B →Kℓ+ℓ−) = (−0.06+0.24±0.03)×10−6, −0.00 B(B →K∗ℓ+ℓ−) = (0.9+1.3±0.1)×10−6, −0.9 The systematic uncertainties on the efficiency, where the first error is statistical and the second is sys- (∆B/B)ǫ, are listed in Table I and arise from charged- tematic. Weevaluatetheupperlimitsonthesecombined particletracking(±1.2%/lepton,±2.0%forthepionfrom modes and obtain K∗ →Kπ,and±1.3%/trackforotherchargedhadrons), particle identification (±1.4%/electron, ±1.0%/muon, B(B →Kℓ+ℓ−) < 0.50×10−6 at 90% C.L. ±2.0%/track for kaons and pions), the continuum sup- B(B →K∗ℓ+ℓ−) < 2.9×10−6 at 90% C.L. 7 Theselimitsrepresentanimprovementoverpreviously 6400 (1995); C. Greub, A. Ioannissian, and D. Wyler, published results from CDF [11] and CLEO [12]. The Phys. Lett. B 346, 149 (1995); J.L. Hewett and Belle [13] experiment has also recently obtained results J.D. Wells, Phys. Rev. D 55, 5549 (1997); C.Q. Geng and C.P. Kao, Phys. Rev. D 54, 5636 (1996); and refer- on these modes. We see no evidence for a signal, and ences therein. our limits are close to many of the predictions based on [3] CLEO Collaboration, R. Ammar et al., the Standard Model. With the rapidly increasing size of Phys. Rev.Lett. 71, 674 (1993). our data sample, we expect to have significantly better [4] CLEO Collaboration, M.S. Alam et al., sensitivity to these modes in the future. Phys. Rev.Lett. 74, 2885 (1995). We are grateful for the excellent luminosity and ma- [5] BABAR Collaboration, B. Aubertet al.,hep-ex/0105044, chineconditionsprovidedbyourPEP-IIcolleagues. The to appear in Nucl. Instrum.Methods (2001). [6] G.C. Fox and S. Wolfram, Phys. Rev. Lett. 41, 1581 collaborating institutions wish to thank SLAC for its (1978). support and kind hospitality. This work is supported [7] R.A. Fisher, Ann.Eugenics 7, 179 (1936). by DOE and NSF (USA), NSERC (Canada), IHEP [8] “GEANT–Detector Description and Simulation Tool”, (China), CEA and CNRS-IN2P3 (France), BMBF (Ger- CERN Program Library Long WriteupW5013 (1995). many), INFN (Italy), NFR (Norway), MIST (Russia), [9] We parametrize the background shape using and PPARC (United Kingdom). Individuals have re- m2 ceived support from the Swiss NSF, A. P. Sloan Foun- f(mES,∆E) = Ne−s∆EmESr1− mEb2E∗2Se−ξ(cid:16)1−EbE∗2S(cid:17), dation, Research Corporation, and Alexander von Hum- where N is a normalization factor and s and ξ are free boldt Foundation. parameters determined from thefit to thedata. [10] Wheneverpossible,wereporttwo-sided68%centralcon- fidenceintervals.Forchannelsconstrainedbytherequire- mentthatthetotalfitfunctionbenon-negative,wequote a single-sided 68% confidence interval and set the lower ∗ Also with Universit`adi Perugia, Perugia, Italy statistical error to zero. † Also with Universit`adella Basilicata, Potenza, Italy [11] CDF Collaboration, T. Affolder et al., Phys. Rev. Lett. [1] A.Ali et al.,Phys. Rev. D 61, 074024 (2000); P. Colan- 83, 3378 (1999). gelo et al., Phys. Rev. D 53, 3672 (1996); D. Melikhov, [12] CLEO Collaboration, S. Anderson et al., N.Nikitin,andS.Simula,Phys.Rev.D57,6814(1998). Phys. Rev.Lett. 87, 181803 (2001). [2] T.M. Aliev et al., Phys. Lett. B 400, 194 (1997); [13] Belle Collaboration, K.Abeet al.,hep-ex/0109026, sub- T.M. Aliev, M. Savci, and A. O¨zpineci, Phys. Rev. D mitted to Phys.Rev.Lett. 56, 4260 (1997); G. Burdman, Phys. Rev. D 52,