Study of hadronic five-body decays of charmed mesons involving KS0

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  • Physics Letters B 586 (2004) 191197





    K.BP. D


    D. L

    Study of hadronic five-body decays ofcharmed mesons involving K0S

    FOCUS Collaboration.M. Link a, P.M. Yager a, J.C. Anjos b, I. Bediaga b, C. Gbel b, A.A. Machado b,J. Magnin b, A. Massafferri b, J.M. de Miranda b, I.M. Pepe b, E. Polycarpo b,

    .C. dos Reis b, S. Carrillo c, E. Casimiro c, E. Cuautle c, A. Snchez-Hernndez c,C. Uribe c, F. Vzquez c, L. Agostino d, L. Cinquini d, J.P. Cumalat d, J. Jacobs d,. OReilly d, I. Segoni d, M. Wahl d, J.N. Butler e, H.W.K. Cheung e, G. Chiodini e,

    I. Gaines e, P.H. Garbincius e, L.A. Garren e, E. Gottschalk e, P.H. Kasper e,.E. Kreymer e, R. Kutschke e, M. Wang e, L. Benussi f, M. Bertani f, S. Bianco f,

    . Fabbri f, A. Zallo f, M. Reyes g, C. Cawlfield h, D.Y. Kim h, A. Rahimi h, J. Wiss h,R. Gardner i, A. Kryemadhi i, Y.S. Chung j, J.S. Kang j, B.R. Ko j, J.W. Kwak j,. Lee j, K. Cho k, H. Park k, G. Alimonti l, S. Barberis l, M. Boschini l, A. Cerutti l,

    Angelo l, M. DiCorato l, P. Dini l, L. Edera l, S. Erba l, M. Giammarchi l, P. Inzani l,. Leveraro l, S. Malvezzi l, D. Menasce l, M. Mezzadri l, L. Moroni l, D. Pedrini l,C. Pontoglio l, F. Prelz l, M. Rovere l, S. Sala l, T.F. Davenport III m, V. Arena n,G. Boca n, G. Bonomi n, G. Gianini n, G. Liguori n, M.M. Merlo n, D. Pantea n,opes Pegna n, S.P. Ratti n, C. Riccardi n, P. Vitulo n, H. Hernandez o, A.M. Lopez o,E. Luiggi o, H. Mendez o, A. Paris o, J.E. Ramirez o, Y. Zhang o, J.R. Wilson p,T. Handler q, R. Mitchell q, D. Engh r, M. Hosack r, W.E. Johns r, M. Nehring r,

    P.D. Sheldon r, K. Stenson r, E.W. Vaandering r, M. Webster r, M. Sheaff s

    a University of California, Davis, CA 95616, USAb Centro Brasileiro de Pesquisas Fsicas, Rio de Janeiro, RJ, Brazil

    c CINVESTAV, 07000 Mxico City, DF, Mexicod University of Colorado, Boulder, CO 80309, USA

    e Fermi National Accelerator Laboratory, Batavia, IL 60510, USAf Laboratori Nazionali di Frascati dellINFN, I-00044 Frascati, Italy

    g University of Guanajuato, 37150 Leon, Guanajuato, Mexicoh University of Illinois, Urbana-Champaign, IL 61801, USA

    i Indiana University, Bloomington, IN 47405, USAj Korea University, Seoul 136-701, South Korea

    k Kyungpook National University, Taegu 702-701, South Koreal INFN and University of Milano, Milano, Italy

    m University of North Carolina, Asheville, NC 28804, USAn Dipartimento di Fisica Nucleare e Teorica and INFN, Pavia, Italy

    693/$ see front matter 2004 Elsevier B.V. All rights reserved.1016/j.physletb.2003.11.078

  • 192 FOCUS Collaboration / Physics Letters B 586 (2004) 191197

    o University of Puerto Rico, Mayaguez, PR 00681, USAp University of South Carolina, Columbia, SC 29208, USA

    q University of Tennessee, Knoxville, TN 37996, USAr lle, T

    son, W

    ted 28



    We ates

    mode ode

    We al = 0. (D0 (D0 sonaperfor 200


    Mocharmto mostandiThis ia subnot idon focays isults oCollamodebrancrelativon thpresendecay



    ractucer evhargnd aipoleentified. In this Letter we extend our work [1]ur-body decays involving a K0S to five-body de-nvolving a K0S . We have already published re-n all charged five-body modes [2]. The FOCUS

    boration presents the first evidence of the decayD+s K0SK0S++, measures an inclusive

    hing ratio for the mode D0 K0S++e to D0 K0S+ and places an upper limite mode D0 K0SK++. Finally wet the first resonant substructure analysis of themode D0 K0S++.

    e data were collected during the 19961997target run at Fermilab. Bremsstrahlung of elec-and photons with an endpoint energy of ap-ately 300 GeV produces photons which in-

    mail address: (J.P. Cumalat).RL:

    of silicon vertex detectors [3] in the target region andby multi-wire proportional chambers downstream ofthe interaction. Particle identification is performed bythree threshold Cerenkov counters, two electromag-netic calorimeters, a hadronic calorimeter, and twomuon systems.

    Five-body D0 and D+s decays are reconstructedusing a candidate driven vertex algorithm [4]. A de-cay vertex is formed from the reconstructed chargedtracks. The K0S is also reconstructed using techniquesdescribed elsewhere [5]. The momentum informationfrom the K0S and the charged tracks is used to forma candidate D momentum vector, which is intersectedwith other tracks to find the production vertex. Eventsare selected based on several criteria. The confidencelevel for the production vertex and for the charm de-cay vertex must be greater than 1%. The reconstructedmass of the K0S must be within four standard devia-tions of the nominal K0S mass. The typical K

    0S massVanderbilt University, Nashvis University of Wisconsin, Madi

    Received 29 October 2003; accep

    Editor: M. Do


    study the decay of D0 and D+s mesons into five-body final stD+s K0SK0S++. The branching ratio for the new m

    so determine the branching ratio of (D0K0S++)



    ++) < 0.054 (90% CL). An analysis of the remed.4 Elsevier B.V. All rights reserved.

    13.25.Ft; 14.40.Lb

    re information on multibody final states in thesector is an essential ingredient for our ability

    del decay rates and to further increase our under-ng of the decay process in heavy quark systems.s particularly important for the D+s decays wherestantial part of its hadronic decay rate is still


    dN 37235, USAI 53706, USA

    November 2003

    including a K0S

    and report the discovery of the decay

    is (D+s K0SK0S++)

    (D+s K0SK++)= 0.102 0.029 0.029.

    095 0.005 0.007 as well as an upper limit for

    nt substructure for D0 K0S++ is also

    in a segmented beryllium-oxide target to pro-charmed particles. The average photon energyents which satisfy our trigger is 180 GeV.ed decay particles with a momentum of 1 GeV/cbove are analyzed by two oppositely polarized

    magnets. Tracking is performed by a system

  • FOCUS Collaboration / Physics Letters B 586 (2004) 191197 193

    Fig. 1.K0SK

    resolufor eaor eleis usecandihypotthan 6kaonkaonfavoreW betweby itsordertionsquiretarget

    Fosis cufor DInvariant mass distributions for (a) K0S++, (b) K0

    S++ for D tagged events, (c) K0

    SK0S+, and (d)

    ++. The fits are described in the text.

    tion is approximately 6 MeV/c2. The likelihoodch charged particle to be a proton, kaon, pion,ctron based on Cerenkov particle identificationd to make additional requirements [6]. For piondates we require a loose cut that no alternativehesis is favored over the pion hypothesis by more

    units of log-likelihood. In addition, for eachcandidate we require the negative log-likelihoodhypothesis, WK =2 ln(kaon likelihood), to bed over the corresponding pion hypothesisW byWK > 2. We also require the distance ( 5 mm)en the primary and secondary vertices dividederror ( 500 m) to be at least 10. Finally, in

    to reduce background due to secondary interac-of particles from the production vertex, we re-the secondary vertex to be located outside thematerial.

    r individual modes we apply additional analy-ts. Due to the large combinatoric background0 K0S++, we increase the separa-

    tion requirement of the secondary vertex from beingjust outside the target material to two standard devi-ations from the edge of the target material. Fig. 1(a)shows the K0S

    ++ invariant mass plot forevents that satisfy these cuts. The distribution is fittedwith a Gaussian for the D0 signal (1283 57 events)with the width and mass floated and a first degreepolynomial for the background. Fig. 1(b) shows theK0S

    ++ invariant mass plot for events origi-nating from a D+ D0+ decay.

    The D+s K0SK0S++ mode is difficult todetect due to the relative inefficiency of K0S recon-struction and that most of the time only the three pi-ons define the secondary vertex. The confidence levelthat a pion track from the decay vertex intersects theproduction vertex must be less than 2%. We also re-quire a reconstructed D+s momentum of greater than25 GeV/c. Fig. 1(c) shows the K0SK0S++ massplot for events which satisfy these cuts. This is thefirst observation of this mode. We fit with a Gaussian

  • 194 FOCUS Collaboration / Physics Letters B 586 (2004) 191197

    Table 1Branching ratios, event yields, and efficiency ratios for modes involving a K0

    S. All branching ratios are inclusive of subresonant modes

    Decay mode Ratio of events Efficiency ratio Branching ratio (D0


    (D+s (D+s

    (D0 (D0

    Table 2Compato prev


    E831 (tPDG avARGUCLEOE691 [

    (37and a

    ThpresseThusquantMontnumbdata.structWe alis 0.1Fig. 1ant man up


    +The rsimulnels aonantanalythe DK0SKtion iThe re


    g raWethe

    ant srmin


    od olits

    f chauringe de

    ariannd thtter.

    dditient sf theon ve sp

    ant se br


    n difre ev

    nce o


    ertainbody decays using studies of D K anddecays based on PDG information [7] and oursis described below, respectively. We measure+s K0SK0S++ mode relative to D+s ++. We test for dependency on cut selec-n both modes by individually varying each cut.sults are shown in Table 1, and we compare our

    D0 K+ decays. The systematic effects are thenall added in quadrature to obtain the final systematicerror. Table 3 summarizes the contributions to the sys-tematic errors for the two branching ratios.

    We do not observe a signal in the decay D0 K0SK

    ++ and we calculate an upper limitK0S++)








  • FOCUS Collaboration / Physics Letters B 586 (2004) 191197 195

    Table 3Summary of the systematic error contributions


    +) (D+s K0SK0S++)

    D mom

    Fit variMonteKS rec

    Abs. trResonaTotal

    for thK0S

    +the msignalmass,

    and bsignalspond

    Wecut vathesemethothe syvaryinand tameasu

    systemsubstrstatesusedas ou

    are thsystem

    WeeventsThe inof Co

    U =

    wherethe penumbs is thlimit

    r the



    e haay Dinnedbora

    nt sug ve

    ifficuecaynd (hann


    red ahann


    +e sidencrsec

    lso r0.1ord

    eenuishumb12U2 2sys

    U + b sU + b ,

    U is the original upper limit of events, sys isrcent systematic error determined above, b is theer of events observed in the sideband region, ande number of signal events. We calculate an upperof 5.64 events, corresponding to an upper limit

    quirement the KS would need to be paired with eachpion when searching for a K and the real com-bination could not be identified given our statistics.Fig. 1(b) shows the K0S++ invariant massplot for events which satisfy these cuts. We then de-termine the acceptance corrected yield into each sub-resonant mode using a weighting technique wherebyeach event is weighted by its kinematic values in three (D0K0S

    entum and run period 0.003ance 0.004Carlo statistics 0.001onstruction 0.002acking efficiency 0.004nt substructure 0.002


    e branching ratio with the respect to D0 +. We evaluate the upper limit using

    ethod of Rolke and Lopez [12]. We define theregion as being within 2 of the nominal D0and the two sideband regions as (48) above

    elow the D0 mass. We observe 3 events in theregion and 6 events in the sidebands, corre-

    ing to an upper limit of 5.02 events (@90% CL).study systematic effects for this channel from

    riation and resonant substructure, and includein our determination of the upper limit using thed of Cousins and Highland [13]. We determinestematic error from cut variation by individuallyg each cut, fitting the resulting distribution,king the variance between each branching ratiorement as our systematic error. We also studyatic effects from our uncertainty in the resonant

    ucture of the mode by varying the subresonantincluded in the Monte Carlo simulation, and

    the variance in the resulting branching ratiosr systematic error. These two systematic effectsen added in quadrature to give a final relativeatic error of 26%.then determine the increase in our upper limit of, U , taking into account the systematic error.crease in the upper limit is based on the equation

    usins and Highland:











    isintwgn (D+s K0SK++)0.0200.0090.0020.0130.0040.0120.029

    branching ratio of:


    < 0.054 (@90% CL).

    ve studied the resonance substructure in the de-0 K0S++. We use an incoherentfit method [14] developed by the E687 Col-

    tion which assumes the final state is an incoher-perposition of subresonant decay modes contain-ctor resonances. A coherent analysis would belt given our limited statistics. For subresonantmodes we consider the lowest mass (K0S)+) resonances, as well as a nonresonantel: K++, K0S0+, K0+ and++)NR. All states not explicitly consid-re assumed to be included in the nonresonantel.r the resonant substructure analysis of D0 + we place additional cuts to enhance

    gnal to background ratio. We require the con-e level that a track from the decay vertex in-ts the production vertex be less than 8%. Weequire the D0 to come from a D+ decay, that44 GeV/c2 < MD+ MD0 < 0.148 GeV/c2,er to reduce background and distinguish be-D0 and D0. Requiring the pion tag to distin-

    between D0 and D0 is crucial in reducing theer of combinations per event. Without this re-

  • 196 FOCUS Collaboration / Physics Letters B 586 (2004) 191197

    Fig. 2. )N(e) inclusive sum of all four modes.


    it in ofit. Eiwhethexpecsplit iCarlobins itweenand th

    ni =

    The ethe ef


    The Mcreatebin poasses: (K0S), (+), and (++). No reso-in the (++) submass exists, but we include

    rder to compute a meaningful 2 estimate of theght population bins are constructed depending oner each of the three submasses falls within theted resonance (in the case of ++, the bin isnto high and low mass regions). For each Montesimulation the bin population, ni , in the eight

    s determined and a matrix, Ti , is calculated be-the generated states, , Monte Carlo yields, Y ,e eight bins i:


    lements of the matrix, T , can be summed to giveficiency for each mode, :



    onte Carlo determined matrix is inverted toa new weighting matrix which multiplies the

    pulations to produce efficiency corrected yields.

    Table 4Fractions relative to the inclusive mode for the resonance substruc-ture of the D0 K0S++ decay mode. These values arenot corrected for unseen decay modes

    Subresonant mode Fraction of K0S++

    (K0S++)NR < 0.46 @90% CL

    K++ 0.17 0.28 0.02K0S0+ 0.40 0.24 0.07

    K0+ 0.60 0.21 0.09

    The weight includes the contributions from the fourcombinations we have for each event. Each data eventcan then be weighted according to its values in the sub-mass bins. Once the weighted distributions for eachof the four modes are generated, we determine theacceptance corrected yield by fitting the distributionswith a Gaussian signal and a linear background. Us-ing incoherent Monte Carlo mixtures of the four sub-resonant modes we verify our procedure is able tocorrectly recover the generated mixtures of the fourmodes.K0S++ weighted invariant mass for (a) (K0

    S++ R, (b) K++, (c) K0S0+, (d) K0+,

  • FOCUS Collaboration / Physics Letters B 586 (2004) 191197 197

    The results for K0S++ are summarized

    in Table 4. The four weighted histograms with fitsare shown in Fig. 2, where Fig. 2(e) is the weighteddistribution for the sum of all subresonant modes.The goodness of fit is evaluated by calculating a 2for the hypothesis of consistency between...


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