Data taken by the Mark II detector at the SLAC e+e- storage ring PEP was used to search for exclusive decays of D and B mesons into two charged leptons plus a charged pion or kaon. All possible charge and lepton combinations consistent with charge conservation were considered and no evidence for any signals was found. We obtain upper limits for the various branching ratios ranging from 2.5×10-3 to 9.2×10-3, at a 90% confidence level. Some of these limits can be used to constrain leptoquark masses in various models. © 1990 The American Physical Society

Abrams, G

Adolphsen, CE

Akerlof, C

Alexander, JP

Alvarez, M

Amidei, D

Baden, AR

Ballam, J

Barish, BC

Barklow, T

Barnett, BA

Bartelt, J

Blockus, D

Bonvicini, G

Boyarski, A

Boyer, J

Brabson, B

Breakstone, A

Brom, JM

Bulos, F

Burchat, PR

Burke, DL

Butler, F

Calvino, F

Cence, RJ

Chapman, J

Cords, D

Coupal, DP

DeStaebler, HC

Dorfan, DE

Dorfan, JM

Drell, PS

Feldman, GJ

Fernandez, E

Field, RC

Ford, WT

Fordham, C

Frey, R

Fujino, D

Gan, KK

Gidal, G

Gladney, L

Glanzman, T

Gold, MS

Goldhaber, G

Green, A

Grosse-Wiesmann, P

Haggerty, J

Hanson, G

Harr, R

Harris, FA

Hawkes, CM

Hayes, K

Herrup, D

Heusch, CA

Himel, T

Hollebeek, RJ

Hutchinson, D

Hylen, J

Innes, WR

Jaffre, M

Jaros, JA

Klein, SR

Weir, AJ

Juricic, I

Kadyk, JA

Karlen, D

Kent, J

Koska, W

Kozanecki, W

Lankford, AJ

Larsen, RR

LeClaire, BW

Levi, ME

Litke, AM

Lockyer, NS

Lüth, V

Matthews, JAJ

Meyer, DI

Milliken, BD

Moffeit, KC

Müller, L

Nash, J

Nelson, ME

Nitz, D

Ogren, H

Ong, RA

O'Shaughnessy, KF

Parker, SI

Peck, C

Petersen, A

Petradza, M

Porter, FC

Rankin, P

Richter, B

Riles, K

Rowson, PC

Rust, DR

Sadrozinski, HFW

Schaad, T

eScholarship - University of California

UC IrvineUC Irvine Previously Published WorksTitleUpper limits on D± and B± decays to two leptons plus π± or K±Permalinkhttps://escholarship.org/uc/item/87n0z1krJournalPhysical Review D, 41(5)ISSN2470-0010AuthorsWeir, AJKlein, SRAbrams, Get al.Publication Date1990-03-01DOI10.1103/physrevd.41.1384Copyright InformationThis work is made available under the terms of a Creative Commons Attribution License, availalbe at https://creativecommons.org/licenses/by/4.0/ Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaPHYSICAL REVIEW D VOLUME 41, NUMBER 5 1 MARCH 1990Upper limits on D and 8*decays to two leptons plus n* or K*A. J. Weir, S. R. Klein, ~"' G. Abrams, C. E. Adolphsen, C. Akerlof, ' J. P. Alexander, ~' 'M. Alvarez, &"' D. Amidei, ~' ' A. R. Baden, "J. Ballam, ~ B.C. Barish, T. Barklow, ~B.A. Barnett, "J. Bartelt, ~ D. Blockus, G. Bonvicini, ' A. Boyarski, ~ J. Boyer, ~B.Brabson, A. Breakstone, ' J. M. Brom, ' ' F. Bulos, ~ P. R. Burchat, D. L. Burke, ~F. Butler, ~*'I' F. Calvino, ~'"' R. J. Cence, ' J. Chapman, ' D. Cords, ~ D. P. Coupal, ~H. C. DeStaebler, ~ D. E. Dorfan, J. M. Dorfan, ~ P. S. Drell, ~' ' G. J. Feldman, ~E. Fernandez, ~"' R. C. Field, ~ W. T. Ford, ~ C. Fordham, ~ R. Frey, ' D. Fujino, p K. K. Gan, ~G. Gidal, ~ L. Gladney, ~"T. Glanzman, ~ M. S. Gold, G. Goldhaber, ~ A. Green, ~'"'P. Grosse-Wiesmann, ~ J. Haggerty, ~'"' G. Hanson, ~ R. Harr, ~ F. A. Harris, ' C. M. Hawkes,K. Hayes, ~ D. Herrup, "'C. A. Heusch, T. Himel, ~ R. J. Hollebeek, ~"' D. Hutchinson, ~J. Hylen, "W. R. Innes, ~ M. Ja8're, ""J. A. Jaros, ~ I. Juricic, ' ' J. A. Kadyk,D. Karlen, ~'"' J. Kent, ~ W. Koska, ' W. Kozanecki, ~ A. J. Lankford, ~ R. R. Larsen, ~B.W. LeClaire, ~'"' M. E. Levi, ~ A. M. Litke, N. S. Lockyer, ~"V. Luth, ~J. A. J. Matthews, "D. I. Meyer, ' B.D. Milliken, K. C. Moff'eit, ~ L. Miiller, ~'~'J. Nash, ~ M. E. Nelson, ' D. Nitz, ' H. Ogren, e R. A. Ongg' ' K. F. O'Shaughnessy, ~S. I. Parker, ' C. Peck, A. Petersen, ~'q' M. Petradza, ' F. C. Porter, P. Rankin, &B.Richter, ~ K. Riles, ~ P. C. Rowson, ~' ' D. R. Rust, H. F. W. Sadrozinski, T. Schaad, ""T. L. Schalk, H. Schellman, ""W. B. Schmidke, ~ A. S. Schwarz, '"A. Seiden,P. D. Sheldon, ~'"' J. G. Smith, ~ A. Snyder, E. Soderstrom, D. P. Stoker, "R. Stroynowski, ' R. Thun, ' G. H. Trilling, r R. Tschirhart, ""'R. Van Kooten, ~H. Veltman, ""'P. Voruganti, ~ S. R. Wagner, ~ P. Weber, ~ A. J. Weinstein, S. Weisz, '"'S. L. White, ~'"' E. Wicklund, D. R. Wood, ~'"' D. Y. Wu, and J. M. Yelton~"California Institute of Technology, Pasadena, California 91125stanford Linear Accelerator Center, Stanford University, Stanford, California 94309Lawrence Berkeley Laboratory and Department ofPhysics, University of California, Berkeley, California 94720University of California, Santa Cruz, California 95064University ofMichigan, Ann Arbor, Michigan 48109tUniversity of Colorado, Boulder, Colorado 80309"Johns Hopkins University, Baltimore, Maryland 21218Indiana University, Bloomington, Indiana 47405University ofHawaii, Honolulu, Hawaii 96822"Harvard University, Cambridge, Massachusetts 02138(Received 10 July 1989)Data taken by the Mark II detector at the SLAC e+e storage ring PEP was used to search forexclusive decays of D —+ and B+ mesons into two charged leptons plus a charged pion or kaon. Allpossible charge and lepton combinations consistent with charge conservation were considered andno evidence for any signals was found. We obtain upper limits for the various branching ratiosranging from 2.5 X 10 ' to 9.2 X 10 ', at a 90/o confidenc level. Some of these limits can be usedto constrain leptoquark masses in various models.I. INTRODUCTIONMany extensions to the standard model allow for theexistence of leptoquarks, particles which can mediate thedecay of a quark into a lepton or vice versa. ' We havepreviously published results of a search for these lepto-quarks as mediators of the decay D ~ep. However, thisreaction is helicity suppressed by a factor of approxi-mately (rn„/rn~) . For this reason, reactions such asD*~epm are more likely to yield evidence of lepto-quarks. More generally, since reactions of this type lieoutside the standard model they would signal interestingnew physics and are therefore worth searching for, in-dependent of the leptoquark hypothesis.In addition to the potentially leptoquark-mediated de-cays, where the leptons have opposite charges, we alsosearch for final states where both leptons have the samecharge. Although these reactions have no obvioustheoretical motivation, and the simplest decay schemesdo not conserve charge at the quark level, it is possible toconstruct two-photon-like Feynman diagrams whichwould allow these decays to proceed, as in Fig. 1.We present here the results of a search for D —and 8—decays into 14 distinct final states. The D—+ and 8*wereproduced in 29-GeV e+e annihilation at the SLACstorage ring PEP. The search was based on data takenwith the Mark II detector in both the PEP5 and upgrad-ed configurations.41 1384 1990 The American Physical SocietyUPPER LIMITS ON D* AND 8+ DECAYS TO T%'0 LEPTONS. . . 1385w+w+IIFIG. 1. A possible diagram for the process D+~1+l+n.{the neutrino is required to be a Majorana particle).12VULQOJo 0GO~ 8—UJ0UJ 400i i[I II II II II II II III II II II II I~I II II II II II II II II II II II II Iii1 Ite+e x+IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII3-PARTICLE INVARIANT MASS( iIIIIIIIIIIIIII1IIIIIIIIIIIII i6(GeV/c )II. DETECTOR DESCRIPTIONFIG. 2. Representative invariant-mass distributions. Dashedlines indicate limits of B and D signal regions.The detectors have been described in detailelsewhere. In the PEP5 detector, charged particles weretracked in a 16-layer cylindrical drift chamber anda 7-layer precision vertex drift chamber in a 2.3-kGsolenoidal magnetic field. Charged-particle momentap (GeV/c) were measured with a resolution of5p/p=[(0. 010p) +(0.025) ]' . In the upgraded detec-tor, the PEP5 drift chambers were replaced with a 72-layer drift chamber and a 6-layer high-precision strawchamber in a 4.5-ko field giving a combined resolutionof 5p/p = [(0.003p) +(0.014) ]' . In both config-urations, electrons were identified by their energy deposi-tion in a lead-liquid-argon calorimeter, which covers64% of the 4m solid angle. Muons were identified over45% of the 4m solid angle in a planar, four-layer,iron/proportional tube system.The total accumulated luminosity was 209 pb ' in thePEP 5 configuration, and 28 pb ' in the upgradedconfiguration. Because of problems with the muon sys-tem early in the run, only 15 pb ' of the data with theupgraded detector was used for final states involving amuon.deposition in the liquid-argon calorimeter. Electronsfrom identifiable y conversions and Dalitz m decays wereremoved. Muons were required to have associated hitsin all four layers of the muon system. Because multiplescattering can be significant, it is possible for two tracksto share associated hits and both be identified as muons.Such cases are easily detected by a hand scan and wereremoved. To minimize backgrounds from pion and kaondecays and hadronic misidentification, the electrons andmuons were required to have mornenta of at least 2.0GeV/c. The third track was required to have a momen-tum of at least 500 MeV/c and, when assigned a pion orkaon mass, could be combined with the two leptons togive a charge and mass compatible with a D+—or B*.The three-particle combination was required to have amomentum of at least 4.0 GeV/c. The D+ candidateswere required to have a mass between 1.77 and 1.97GeV/c, and the 8* candidates were required to have amass between 4.0 and 6.5 GeV/c . No statisticallysignificant signal was observed in any channel. Tworepresentative mass distributions are shown in Fig. 2.III. EVENT SELECTION IV. MONTE CARLO SIMULATIONHadronic events were selected with a standard set ofcuts. We required at least five reconstructed chargedtracks which formed a vertex less than 4 crn radially, andwithin +7 cm axially from the expected e+e annihila-tion point. The scalar sum of the momenta of all chargedtracks was required to be at least 3.0 GeV, and the sum ofthe visible charged and neutral energy was required to beat least 7.5 GeV. Finally, in order for the event to be wellcontained in the detector, we required that the cosine ofthe angle between the beam line and the reconstructedthrust axis be smaller in magnitude than 0.7. A total of89 047 events passed these cuts.Events were divided into hemispheres on the basis ofthe event thrust axis. We searched for a hemisphere con-taining two identified leptons which combined with athird track to form a D —or 8 —candidate. Both leptoncharge combinations were allowed. Electrons wereidentified by an algorithm which looked at the energyThe detection efficiency was determined using a MonteCarlo simulation. The simulation is complicated by thepresence of a three-particle final state. Since the decaymechanism, and hence the matrix element, is unknown,several different decay schemes were tried. To simulatethe leptoquark-mediated decay we used a weak matrixelement with a neutral heavy propagator decaying to twoleptons. Schemes where the propagator decayed to a lep-ton plus a hadron were also considered. Finally, phasespace decays were studied. In practice, the exact schememade little difference; the maximum efficiency variationbetween the different schemes was less than 5%. For therest of the event generation we used the Lund model,with second-order QCD matrix element and the Petersonfragmentation function. Version 5.2 of the Lund Modelwas used, with the following parameters: AMs=0. 5 GeV(MS denotes the modified minimal-subtraction scheme),y;„=0.02, A =0.9, B =0.7, e, =0.05, eb =0.005,1386 A. J. WEIR et al.cr =0.265 GeV/c, P, =0.35, P =0.09.Using the Monte Carlo simulation, we estimated theone standard deviation widths of the D* and B—masspeaks in the PEP5 detector to be 100 MeV/c and 370MeV/c, respectively. Because the upgraded detectorhas substantially better mass resolution, narrower searchregions could have been used. However, none of thesearches yielded any candidate events in the upgradeddata and regions of the same width were used in bothdata samples.V. RESULTSThe numbers of candidate events for the channels ofinterest are shown in Table I. To be conservative, nobackground subtraction was attempted. However, thenumbers of observed events agree well with Monte Carlobackground predictions. Systematic errors come fromuncertainties in the tracking efficiency (3% per track),lepton identification efficiency (8%), overall D and 8 —+reconstruction efficiency (12%), D +—and 8* momentumspectra (7%), and luminosity (2%). A correction factorof 0.82 was applied to the Monte Carlo reconstructioneSciency to account for differences in track reconstruc-tion and lepton identification e%ciencies between theMonte Carlo simulation and the data.Calculation of upper limits on the cross section timesbranching ratios requires a knowledge of the D +—and B—+production rates. The inclusive D—+ production rate at&s =29 GeV has been measured by the High ResolutionSpectrometer (HRS) Collaboration to be 0.075+0.014nb. ' From this measurement, we included radiativecorrections to estimate that there are 22100+4100 D —+in our sample. Unfortunately, there are no measurementsof inclusive B—production at this energy, so we wereforced to rely on Monte Carlo predictions. Two hadroni-zation models were considered: the Lund parton showermodel and the Gottschalk model. "The predictions of theB+—production rate for the two models agreed to within7%%uo. We assigned a 10% systematic error for the uncer-tainty in the B*production rate and used the Lund esti-mate (which predicted fewer 8 ) to estimate that thereare 6850+690 B+—in our sample. The Gaussian distribu-tion associated with these systematic errors was convolut-ed with the Poisson distribution associated with the num-ber of observed events to find the 90%-confidence-levellimits shown in Table I.Many models predict that the branching ratios to lep-tons should be independent of the final-state leptons; inthis case, many channels may be combined to form moreinteresting limits. Several possible combinations areTABLE I. Results for individual channels. Charge-conjugate reactions implied. cr X BR (branchingratio) and BR are the 90%-C.L. Upper limits including the estimated systematic errors.ReactionD+~e+e n+D+ e+pD+ —+e p n.+D+~e+e K+D+~e+p E+D+ ~e p+K+D+~e+e+mD' p+p+~D+~e+e+KD+ ~p+p+KObservednumberReconstructionefficiency (%)4.3+0.43.5+0.43.5+0.43.3+0.33.9+0.43.3+0.33.3+0.33.0+0.33.9+0.43.0+0.32.9+0.33.6+0.42.8+0.32.6+0.3ET XBRlimit (pb)0.220.300.300.550.520.330.330.850.430.340.620.820.370.40BR limit(10 )2.53.33.35.94.83.43.49.24.83.76.89.14.04.3B+ e+e ~+B+ p+p m. +B+~e+e E+B ~e+p E+B+~e p+E+B+—+p+p K+B e+e+~B+ p+p n.B+~e+e+KB+ e+p+KB+~p+p+E8.6+0.95.6+0.65.6+0.63.9+0.48.6+0.95.6+0.65.6+0.63.9+0.48.6+0.95.6+0.63.9+0.48.6+0.95.6+0.63.9+0.40.110.160.160.240.190.130.130.240.110.160.240.110.160.243.96.46.49.16.86.46.46.43.96.49.13.96.49.141 UPPER LIMITS ON D+ AND B+ DECAYS TO TWO LEPTONS. . . 1387TABLE II. Combined results. cr X BR and BR are the 90%-C.L. upper limits including the estimat-ed systematic errors.ReactionD'-l+l- ~+D+ l+l E+D+-l+l+~-D+ ~l+ i+Se-a+ ~lie, llEObservednumber132511Averagereconstructionef5ciency (%)3.8+0.43.4+0.33.3+0.32.9+0.33.3+0.30. XBRlimit(pb)0.480.910.741.492.38BRlimit(10 ')5.210.18.216.826.9B+ I+l n.B+-l+l-Z+B+~l+I+-~B~1+l+EB+~lier, llE5.7+0.65.7+0.65.7+0.65.7+0.65.7+0.60.180.310.180.180.316.210.96.26.210.9shown in Table II.The opposite-sign lepton limits may be compared withthe results published by the CLEO Collaboration. ' Al-though our inclusive 8 limits are higher, we have present-ed previously unpublished limits on electron/muon andsame-sign dilepton final states. Also, our analysis is moreconservative in that we performed no background sub-traction.It is possible to turn these limits into limits on lepto-quark masses. However, this requires a considerableamount of model-dependent theoretical input, and it willnot be attempted here.VI. CONCLUSIONWe have presented limits on the production of eventsin which D—+ and B+—decay exclusively to two leptonsplus a charged pion or kaon.Note added After .the conclusion of this work, welearned of improved CLEO results on B-meson chan-nels. ''"Present address: Boston University, Boston, MA 02215.Present address: Cornell University, Ithaca, NY 14853."'Present address: Universidad Autonoma de Barcelona, Bella-terra, Spain.Present address: University of Chicago, Chicago, IL 60637."'Present address: Harvard University, Cambridge, MA 02138."Present address: Centre de Recherches Nucleaires, F-67037Strasbourg, France.&'Present address: University of Oklahoma, Norman, OK73019.'"'Present address: Universitat Politecnica de Catalunya,ETSEIB-DEN Barcelona, Spain.~')Present address: University of Pennsylvania, Philadelphia, PA19104.(j)Present address: O'Conner and Associates, Chicago, IL60604.'"Present address: Brookhaven National Laboratory, Upton,NY 11973."'Present address: Laboratoire de 1'Accelerateur Lineaire, F-91405 Orsay, France.Present address: Columbia University, New York, NY10027."Present address: Carleton University, Ottawa, Ontario, Cana-da, K1S 5B6.Present address: University of Wisconsin, Madison, WI53706.'~ Present address: Lab. fiir Hochenergie Physik Bern, CH-3012Bern, Switzerland.'q'Present address: SCS, Hamburg, F.R. Germany.'Present address: Universite de Geneve, CH-1211, Geneve 4,Switzerland."~Present address: Fermilab, Batavia, IL 60510.~'~Present address: Max-Planck Institut, Miinchen, F.R. Ger-many.'"'Present address: University of Illinois, Urbana, IL 61801.'"~Present address: Princeton University, Princeton, NJ 08544.' 'Present address: University of California, Berkeley, CA94720.'" Present address: CERN, CH-1211, Geneve 23, Switzerland.'&~Present address: University of Tennessee, Knoxville, TN37996."Present address: University of Florida, Gainesville, FL 32611.B. A. Campbell et al. , Int. J. Mod. Phys. A 2, 831 (1987); W.Buchmiiller and D. Wyler, Phys. Lett. B 177, 377 (1986).K. Riles et al. , Phys. Rev. D 35, 2914 (1987).I. I. Bigi, in Proceedings of the Sixteenth SLAC Summer Institute on Particle Physics, Stanford, California, 1988, edited byE. C. Brennan (SLAC Report No. 336, Stanford, 1989).4The PEP5 detector is described in R. H. Shindler et al. , Phys.Rev. D 24, 78 11981);J. Jaros, in Proceedings of the Internationa! Conference on Instrumentation for Colliding BeamPhysics, Stanford, California, 1982, edited by W. W. Ash(SLAC Report No. 0250, Stanford, 1982); the upgraded detec-tor is described in G. Abrams et al. , Nucl. Instrum. MethodsA281, 55 (1989).~W. T. Ford et al. , Nucl. Instrum. Methods A255, 486 (1987).R. Ong et al. , Phys. Rev. Lett. 60, 2587 (1988).7M. E. Nelson, Ph.D. thesis, Lawrence, Berkeley LaboratoryReport No. LBL-16724, 1983.We did not identify the pion or kaon as such, but associated1388 A. J. WEIR et al. 41with the track a pion (kaon) mass under the pion (kaon) hy-pothesis.B. Andersson, G. Gustafson, and T. Sjostrand, Nucl. Phys.B197,45 (1982); T. Sjostrand and M. Bengtsson, Comp. Phys.Commun. 43, 367 (1987).' P. Baringer et al. , Phys. Lett. B 206, 551 (1988).'T. D. Gottschalk and D. A. Morris, Nucl. Phys. B288, 729(1987).P. Avery et al. , Phys. Lett. B 183, 429 (1987); A. Bean et al. ,Phys. Rev. D 35, 3533 (1987); P. Haas et al. , Phys. Rev. Lett.60, 1614 (1988).' P. Avery et al. , Phys. Lett. 8 233, 471 (1989).

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Upper limits on D± and B± decays to two leptons plus π± or K±

Upper limits on D+/- and B+/- decays to two leptons plus pi +/- or K+/-

Upper limits on D+/- and B+/- decays to two leptons plus pi +/- or K+/-

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