Measurements of Six-Body Hadronic Decays of the D^0 Charmed

Measurements of Six-Body Hadronic Decays of the D^0 Charmed Meson

MeasurementsofSix-BodyHadronicDecays

oftheD0CharmedMeson

TheFOCUSCollaboration

J.M.LinkaP.M.YageraJ.C.AnjosbI.BediagabC.G¨obelb

A.A.MachadobJ.MagninbA.Massa errib

J.M.deMirandabI.M.PepebE.PolycarpobA.C.dosReisbS.CarrillocE.CasimirocE.CuautlecA.S´anchez-Hern´andezc

C.UribecF.V´azquezcL.AgostinodL.CinquinidJ.P.CumalatdB.O’ReillydI.SegonidJ.N.ButlereH.W.K.CheungeG.ChiodinieI.GaineseP.H.GarbinciuseL.A.GarreneE.GottschalkeP.H.KaspereA.E.KreymereR.KutschkeeM.WangeL.BenussifM.BertanifS.BiancofF.L.FabbrifA.ZallofM.ReyesgC.Cawl eldhD.Y.Kimh

A.RahimihJ.WisshR.GardneriA.KryemadhiiY.S.ChungjJ.S.KangjB.R.KojJ.W.KwakjK.B.LeejK.ChokH.ParkkG.Alimonti S.Barberis M.Boschini A.Cerutti P.D’Angelo M.DiCorato P.Dini L.Edera S.Erba M.Giammarchi P.Inzani F.Leveraro S.Malvezzi

D.Menasce M.Mezzadri L.Moroni D.Pedrini

C.Pontoglio F.Prelz M.Rovere S.Sala

T.F.DavenportIIImV.ArenanG.BocanG.BonominG.GianininG.LiguorinM.M.MerlonD.Pantean

D.LopesPegnanS.P.RattinC.RiccardinP.VitulonH.HernandezoA.M.LopezoE.LuiggioH.MendezoA.Pariso

J.E.RamirezoY.ZhangoJ.R.WilsonpT.HandlerqR.MitchellqA.D.BryantrD.EnghrM.Hosackr

W.E.JohnsrM.NehringrP.D.SheldonrK.Stensonr

E.W.VaanderingrM.WebsterrM.Shea s

aUniversity

bCentroarXiv:hep-ex/0401019v2 9 Feb 2004ofCalifornia,Davis,CA95616

07000M´exicoCity,DF,MexicoBrasileirodePesquisasF´ sicas,RiodeJaneiro,RJ,BrasilcCINVESTAV,

dUniversityofColorado,Boulder,CO80309

Measurements of Six-Body Hadronic Decays of the D^0 Charmed Meson

eFermi

fLaboratoriNationalAcceleratorLaboratory,Batavia,IL60510NazionalidiFrascatidell’INFN,Frascati,ItalyI-00044

ofGuanajuato,37150Leon,Guanajuato,Mexico

ofIllinois,Urbana-Champaign,IL61801

University,Bloomington,IN47405

University,Seoul,Korea136-701gUniversityhUniversityiIndianajKorea

kKyungpook

INFNNationalUniversity,Taegu,Korea702-701

ofNorthCarolina,Asheville,NC28804

ofPuertoRico,Mayaguez,PR00681

ofTennessee,Knoxville,TN37996

University,Nashville,TN37235

ofWisconsin,Madison,WI53706andUniversityofMilano,Milano,ItalymUniversitynDipartimentodiFisicaNucleareeTeoricaandINFN,Pavia,ItalyofSouthCarolina,Columbia,SC29208oUniversitypUniversityqUniversityrVanderbiltsUniversity

Seehttp://www-focus.fnal.gov/authors.htmlforadditionalauthorinformation1Introduction

Hadronicdecaysofcharmedmesonshavebeenextensivelystudiedinrecentyears.However,six-bodyhadronicdecaysoftheD0havenotbeenpreviouslyobserved;onlyanupperlimitexistsfortheD0→π+π+π+π π π branchingfraction[1].Inthispaper,wepresentthe rstbranchingratiomeasurements

Measurements of Six-Body Hadronic Decays of the D^0 Charmed Meson

oftheD0→K π+π+π+π π andD0→π+π+π+π π π decaymodes.ChargeconjugatestatesareimplicitlyincludedandweusetheabbreviationsD0→K5π,D0→6π,andD0→K3πforthefullychargedstates.

The xed-targetcharmphotoproductionexperimentFOCUScollecteddataduringthe1996–1997 xed-targetrunatFermilab.TheFOCUSdetectorisalargeaperturespectrometerwithexcellentvertexingandparticleidenti cationcapabilities.Aphotonbeamisderivedfromthebremsstrahlungofsecondaryelectronsandpositronsproducedfromthe800GeV/cTevatronprotonbeam.Thephotonbeaminteractswithasegmentedberyllium-oxidetarget.Theav-eragephotonenergyfortheinteractionscollectedforthemeasurementswereportis180GeV.Chargedparticlesaretrackedbytwosystemsofsiliconmicrovertexdetectors.Theupstreamsystem[2],consistingof4planes(twoviewsintwostations),isinterleavedwiththeexperimentaltarget,whiletheothersystemliesdownstreamofthetargetandconsistsoftwelveplanesofmicrostripsarrangedinfourstationsofthreeviews.Thesedetectorsprovidehighresolutionseparationofproductionanddecayvertices.Themomentumofachargedparticleisdeterminedbymeasuringitsde ectionsintwoanal-ysismagnetsofoppositepolaritywith vestationsofmultiwireproportionalˇchambers.ThreemulticellthresholdCerenkovcountersareusedtodiscrimi-natebetweenelectrons,pions,kaons,andprotons.

2Signalsandselectioncriteria

Acandidatedrivenvertexingalgorithm[3]isusedtoreconstructD0decaysintosix-body nalstates.AD0candidateconsistsofsixtracksinaneventthathavezerototalchargeandformavertexwithatleasta2%con dencelevel.ThemomentumvectoroftheD0candidate,formedfromthemomentaofthesixtracks,isthenintersectedwithatleastoneothertrackintheeventtoformtheD0productionvertex;thecon dencelevelofthisvertexisre-quiredtobeatleast1%.Additionalcutsareappliedbasedoneventgeometryandparticleidenti cation.Tominimizesystematicerrors,identicalcutsareusedonthetwosix-bodydecaymodesandonthenormalizingmode,exceptthattheD0→6πmodehasnokaonidenti cationcut.Ourmoste ectivecutforreducingnon-charmbackgroundsisasigni canceofdetachmentcutthatrequirestheseparation, ,betweentheD0productionanddecayver-ticespidedbyitserror,σ ,tobegreaterthansomethreshold,inourcase /σ >13.TheD0decayvertexisalsorequiredtobelocatedoutsideofma-terialinthetargetregionbyatleast2standarddeviations,whichservestoˇreducebackgroundsfromsecondaryinteractions.Cerenkovparticleidenti ca-tionisdoneusingaχ2-likevariableWi= 2lnLikelihood(i),whereirangesoverelectron,pion,kaon,andprotonhypotheses[4].Foreachpioncandidate,werequiremin{We,WK,Wp} Wπ> 4,whichrequiresthateachpioncan-

Measurements of Six-Body Hadronic Decays of the D^0 Charmed Meson

Events/(6 MeV/c)2520

15

10

5Events/(6 MeV/c2)Yield = 48 ± 105040302010(b)2Yield = 149 ± 17

01.7K5π Invariant Mass (GeV/c)1.81.9222.101.76π Invariant Mass (GeV/c)1.81.9222.1

Fig.1.Invariantmassdistributionsof(a)K5πand(b)6π.

didateisnothighlyfavoredtobeanelectron,kaon,orprotonratherthanapion.ForthekaoncandidateinD0→K5πandinthenormalizingmode,werequirethatthekaonhypothesisismorelikelythanthepionhypothesiswiththecutWπ WK>3.Finally,thelargestc …… 此处隐藏：8026字，全部文档内容请下载后查看。喜欢就下载吧 ……