Search for Disoriented Chiral Condensates in 158 AGeV Pb+Pb Collisions

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

SearchForDisorientedChiralCondensatesIn

158AGeVPb+PbCollisions

M.M.Aggarwala,A.Agnihotrib,Z.Ahammedc,A.L.S.Angelisd,V.Antonenkoe,V.Are evf,V.Astakhovf,V.Avdeitchikovf,T.C.Awesg,P.V.K.S.Babah,S.K.Badyalh,A.Baldinef,L.Barabachf,C.Barlagi,S.Bathei,B.Batiouniaf,T.Bernierj,K.B.Bhallab,V.S.Bhatiaa,C.Blumei,R.Bockk,E.-M.Bohnei,

D.Bucheri,A.Buijs ,E.-J.Buis ,H.B¨uschingi,L.Carlenm,V.Chalyshevf,S.Chattopadhyayc,R.Cherbatcheve,T.Chujon,

A.Clausseni,A.C.Dasc,M.P.Decowskir,V.Djordjadzef,P.Donnid,I.Doubovike,M.R.DuttaMajumdarc,

K.ElChenawim,S.Eliseevo,K.Enosawan,P.Fokad,S.Fokine,V.Frolovf,M.S.Gantic,S.Garpmanm,O.Gavrishchukf,F.J.M.Geurts ,T.K.Ghoshp,R.Glasowi,S.K.Guptab,

B.Guskovf,H.A.Gustafssonm,H.H.Gutbrodj,R.Higuchin,I.Hrivnacovao,M.Ippolitove,H.Kalechofskyd,R.Kamermans ,K.-H.Kamperti,K.Karadjeve,K.Karpioq,S.Katon,S.Keesi,H.Kimg,B.W.Kolbk,I.Kosarevf,I.Koutcheryaeve,A.Kuglero,P.Kulinichr,V.Kumarb,M.Kuratan,K.Kuritan,N.Kuzminf,ngbeink,A.Lebedeve,Y.Y.Leek,H.L¨ohnerp,L.Luquinj,

D.P.Mahapatras,V.Mankoe,M.Martind,A.Maximovf,R.Mehdiyevf,G.Mgebrichvilie,Y.Miaken,D.Mikhalevf,

G.C.Mishras,Y.Miyamoton,D.Morrisont,

D.S.Mukhopadhyayc,V.Myalkovskif,H.Naefd,B.K.Nandis,S.K.Nayakj,T.K.Nayakc,S.Neumaierk,A.Nianinee,V.Nikitinef,S.Nikolaeve,S.Nishimuran,P.Nomokonovf,J.Nystrandm,F.E.Obenshaint,A.Oskarssonm,I.Otterlundm,

M.Pachro,A.Parfenovf,S.Pavlioukf,T.Peitzmanni,V.Petraceko,F.Plasilg,M.L.Purschkek,B.Raeven ,J.Rako,S.Raniwalab,V.S.Ramamurthys,N.K.Raoh,F.Retierej,K.Reygersi,G.Rolandr,L.Rosseletd,I.Roufanovf,C.Royj,J.M.Rubiod,H.Sakon,S.S.Sambyalh,R.Santoi,S.Saton,arXiv:hep-ex/9710015v1 17 Oct 1997

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

H.Schlaghecki,H.-R.Schmidtk,G.Shabratovaf,I.Sibiriake,T.Siemiarczukq,B.C.Sinhac,N.Slavinef,K.S¨oderstr¨omm,N.Solomeyd,S.P.Sørensent,P.Stankusg,G.Stefanekq,P.Steinbergr,E.Stenlundm,D.St¨ukeni,M.Sumberao,T.Svenssonm,M.D.Trivedic,A.Tsvetkove,C.Twenh¨ofel ,L.Tykarskiq,J.Urbahnk,N.v.Eijndhoven ,W.H.v.Heeringen ,

G.J.v.Nieuwenhuizenr,A.Vinogradove,Y.P.Viyogic,

A.Vodopianovf,S.V¨or¨osd,M.A.Vos ,B.Wys louchr,K.Yagin,

Y.Yokotan,G.R.Youngg

WA98Collaboration

aUniversity

bUniversity

cVariableofPanjab,Chandigarh160014,IndiaofRajasthan,Jaipur302004,Rajasthan,India

ofGeneva,CH-1211Geneva4,SwitzerlandEnergyCyclotronCentre,Calcutta700064,India

(Kurchatov),RU-123182Moscow,RussiadUniversityeRRC

fJoint

gOakInstituteforNuclearResearch,RU-141980Dubna,Russia

hUniversity

iUniversityRidgeNationalLaboratory,OakRidge,Tennessee37831-6372,USAofJammu,Jammu180001,India

EcoledesMines,Nantes,FranceofM¨unster,D-48149M¨unster,GermanyjSUBATECH,

kGesellschaftf¨urSchwerionenforschung(GSI),D-64220Darmstadt,Germany

Utrecht/NIKHEF,NL-3508TAUtrecht,TheNetherlands

ofLund,SE-22100Lund,Sweden

ofTsukuba,Ibaraki305,JapannUniversitymUniversity Universiteit

oNuclear

pKVI,PhysicsInstitute,CZ-25068Rez,CzechRep.

forNuclearStudies,00-681Warsaw,Poland

rMITUniversityofGroningen,NL-9747AAGroningen,TheNetherlandsqInstituteCambridge,MA02139,USA

sInstitute

tUniversityofPhysics,751-005Bhubaneswar,IndiaofTennessee,Knoxville,Tennessee37966,USA

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

1Introduction

TheapproximatechiralsymmetryoftheQCDvacuumisbelievedtobespon-taneouslybrokeninnaturebytheformationofanisoscalarquarkconden-sate.DisorientedChiralCondensates(DCC)mayforminlarge,hotregionsofhadronicmatterwherethissymmetryhasbeenbrie yrestored[1].ADCChasanequalprobabilitytobeinanystaterelatedtothenormalvacuumbyachiralrotation.Byprojectingthespaceoftheseavailablestatesontoaba-sisofde niteisospin,ithasbeenfoundthatthechargedistributionofpionsemittedfromaDCChasacharacteristicform[2]:

P(f)=1

f(1)

wherefistheneutralfraction,

f=Nπo

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

thatasthesystemrapidlyexpandsandcoolsthroughthephasetransition,theequationsofmotioninduceanon-equilibriumrelaxationofthechiral eldswhichampli estheproductionofsoftpionmodesinawell-de nedchiraldirec-tion.Thise ectivelycreatesclustersoflow-pTpions,withtheclusterchargedistributionfollowingequation(1).Itshouldbenotedthat,inbothstudies,thestrongestin uenceonthe nalstatecompositionisthesymmetryitselfratherthantheexactphysicsscenariostudied.Furtherworkcon rmedtheseinitialresults,evenafteraccountingforquantum uctuations,andproposedothermechanismswhichmightallowforlarge,long-livedDCCs[1].

Byallowingthepossibilityofeventswithalmostnoelectromagneticenergy,DCCsareanattractivehypothesistoexplainthe“Centauro”eventsseenincosmicrays[7].Theseeventshavealreadymotivatedsearchesforunusualcharge uctuationsattheS

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

determinationofthecentralityofeachcollision,weusethetransverseenergy(ET)measuredintheMidrapidityCalorimeter(MIRAC[13]).Forremovalofbackgroundevents,wealsousetheZero-DegreeCalorimeter(ZDC)andthePlasticBalldetector[14].

2.1Chargedparticlemultiplicity

WecountchargedparticlesusingacircularSiliconPadMultiplicityDetector(SPMD)[15]located32.8cmfromthetargetcovering2.35<η<3.75,thecentralrapidityregionatSPSenergies(whereηCMS=2.9),andfullazimuth.Thedetectorconsistsoffouroverlappingquadrants,eachfabricatedfromasingle300µmthicksiliconwafer.Theactiveareaofeachquadrantisdividedinto1012padsforming46azimuthalwedgesand22radialbinswithapadsizeincreasingwithradiustoprovideuniformpseudorapiditycoverage.Thee ciencyofdetectingachargedparticleintheactiveareahasbeendeterminedinatestbeamtobebetterthan99%.Conversely,thedetectoristransparenttohighenergyphotons,sinceonlyabout0.2%areexpectedtointeractinthesilicon.Duringthedatataking,95%ofthepadsworkedproperlyandareusedinthisanalysis.

Inacentralion-ioncollision,theoccupancycanbeashighas20%,imply-ingthat≈20%ofthepadscontaintwoormorehits.Anunbiasedwaytoestimatethetotalnumberofchargedparticlesinagiveneventundersuchconditionsistousethesumoftheenergydepositedinpadsexceeding1/2ofthemostprobableenergylossdividedbythemeanenergylossperparticleasdeterminedinlow-multiplicityevents:

Nch= dE/dxi

i=hits

N.For

typicalcentraleventswithamultiplicityof≈600,thisgivesanuncertaintyofabout2%.Tochecktheoverallscale,wecomparetheresultswiththemul-tiplicityobtainedbyassumingthattheparticlesaredistributeduniformlysothemulti-hitprobabilityisgivenbyPoissonstatistics.Asimplecalculation

′givesNch= Npadslog(1 Nhits/Npads),whereNpadsisthetotalnumberofpads,ingthisasacheck,weestimatethesystematicerroronNch,duetouncertaintiesinthegainsandbackgrounds,tobeabout4%.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

2.2Photonmultiplicity

WecountphotonsinthepreshowerPhotonMultiplicityDetector(PMD)sit-uated21.5mfromthetarget,coveringtheregion2.8<η<4.4.Thephotonsimpingingonthedetectorareconvertedin3.34X0thickleadandironandthesecondariesaredetectedin3mm-thicksquareplasticscintillatorpadsofvaryingsizes(15mm,20mmand23mm).Amatrixof50×38padsisplacedinonelight-tightboxmoduleandreadoutindividuallyviawavelengthshiftingoptical berscoupledtoanimageintensi erandCCDcamerasystemsimilartothatdescribedin[16].Themoduleswithsmallerpadsweremountedintheforwardangleregiontominimizeclusteroverlapatlargemultiplicitiesandtoprovidereasonablyuniformoccupancy.Outofatotalof28boxmodulesimplementedinthePMD,thedatapresentedherecorrespondto19boxmod-uleshaving35524pads.Theaverageoccupancyforthepartofthedetectorconsideredinthepresentcaseisaround15%forcentralevents.

Theprincipleofphotonidenti cationmakesuseofthefactthatphotonsaremorelikelytoshowerintheleadconverterandproducealargesignalinthescintillatorpads,whilenon-showeringhadronswillproduceasignalcorre-spondingtoasingleminimumionizingparticle(MIP).Signalsfromseveralneighbouringpadsarecombinedtoformclustersandthosewithenergydepo-sitionlargerthanthatcorrespondingto3MIPsareconsideredtobe”γ-like”clusters.Thisselectiongivesanaveragephotoncountinge ciencyofabout70%whichisalmostuniformovertherangeofcentralityandpseudorapidityconsidered.Italsocreatesane ectivelowerpTcuto of30MeV/c,atwhichpointthee ciencyfallsbelow35%.About15%oftheproducedhadronsim-pingingonthePMDinteractintheconverter,generatingsecondarieswhichalsodepositlargeenergyonthedetector.Thiscontaminationconstitutesabackgroundtophotoncounting.Inordertominimizee ectsduetovariationsintheangulardistributionsofchargedparticles,weonlyusedatawiththeGoliathmagnetturnedo .

Thephotoncountinge ciency,hadroncontaminationandtheassociateder-rorsarederivedusingtestbeamdataandGEANTsimulationusingamethodsimilartotheonesdescribedin[16,17].ThelevelofhadroncontaminationinthePMDwasveri edbycomparingtheazimuthaldistributionofhitsformagnet-onandmagnet-o data[18].Theazimuthaldistributionofchargedtracksbecomesverynon-uniforminthepresenceofthemagnetic eld,theamountofnon-uniformityindicatingthemagnitudeofthehadroncontamina-tion.

Itshouldbeemphasizedthatinthisanalysis,wedonotcorrectthedatausingtheseparameters.Insteadweaccountforallofthedetectore ectsbyfullysimulatingtheconversionofparticlesinthedetector,asdescribedbelow.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

2.3DataandEventSelection

Inthisanalysis,westudyreactionsinducedbya158AGeVPbbeamincidentupona213µmthick208Pbtarget.Thefundamental“beam”triggerconditionˇconsistsofasignalinagasCerenkovstartcounter[19]located3.5metersupstreamofthetargetandnocoincidentsignalinavetocounterwitha3mmcircularholelocated2.7metersupstreamfromthetarget.Abeamtriggerisconsideredtobeaminimum-biasinteractionifthetransverseenergysuminthefullMIRACacceptanceexceedsalowerthreshold.

ingthese,weremoveeventswhereasecondinteractionoccurredwithina±10µswindowbeforeandaftertherecordedevent.Still,ourTDCsystemcannotdistinguishtwoeventsthatarrivelessthan50nsapart.TheseareeliminatedbyrequiringthesumofenergydepositedintheMIRAC(3.5<η<5.5)andZDC(η>6)tobeconsistentwithasingleevent.Afterapplyingthesecuts,70%ofthedatasampleremains.

3GeneralFeaturesofDataandComparisonwithVENUS4.12Todescribethebulkofthedata,weusetheVENUS4.12[20]eventgeneratorwithitsdefaultsettings.TocompareVENUSwithourdata,wepropagatetherawgeneratoroutputthroughafullsimulationofourexperimentalsetupusingtheGEANT3.21[21]packagefromCERN.Thesimulationincorporatesthedetectorphysicse ectsandfoldsthemintothegenerateddata,whichisthenanalyzedusingthesamecodeusedfortherawexperimentaldata.Intherestofthispaper,theterm“VENUS”referstothecombinationofVENUS

4.12andthefullGEANT3.21detectorsimulation,nottotherawgeneratoroutput,unlessotherwisespeci ed.

TheSPMDsimulationincludesthee ectofLandau uctuationsintheenergylossofchargedparticlesinthesiliconandthepadgeometryofthedetector.Inadditiontothesecondariesfromtheion-ioncollisionitself,theSPMDisalsosensitivetotheδ-raysgeneratedbythe82+Pbionpassingthroughtheleadtarget.Wecangetaconservativeestimateoftheδ-raymultiplicityinphysicseventsbystudyingeventsthatsatisfytheconditionsforabeamtriggerbutnottheinteractiontrigger.These“beam”eventshaveameanmultiplicityintheSPMDof11.4±.5andawidthof5.9±.3.Theangulardistributionisconsistentwithaspatiallyuniformilluminationofthedetectorsurface.Toincludetheseion-inducedδ-raysinthesimulation,wesamplethemeasuredchargedmultiplicitydistributionforbeameventsandaddittothecharged

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

particlemultiplicityforeachsimulatedevent.WeestimatetheuncertaintyintheabsolutescaleofNchfromthesimulationtobelessthan3%andtherelativeuncertaintybetweendataandVENUStobelessthan2%.

ThePMDsimulationalsoincorporatesthee ectsofadditional uctuationstotheenergylossarisingduetothestatisticalnatureofthescintillationprocess;lighttransportthroughthewavelengthshifting bresandtheimageintensi erchains;andimperfectionsintheelectro-opticalimaging.Thewidthsduetothisextra uctuationwereobtainedbyacomparisonoftheGEANTandtestbeamresultsusingsinglepionsandelectronsatvariousenergies.Asallofthereadoutchainswerenotusedinthetestbeamexperiment,amethodofdetailedintercomparisonofthevariousfeaturesofdataandsimulationwasusedtoobtainthegainsoftheindividualreadoutunits.Weestimatetheuncertaintyontheabsolutemultiplicityscaleofsimulatedγ-likeclusters,duetouncertaintiesinvariousparametersofthesimulationanddataanalysis,tobe15%,andthattherelativeuncertaintybetweendataandVENUSis5%.InFigures2aand2bwepresenttheminimum-biasmultiplicitydistributionforchargedparticlesandγ-likeclusters.FortheDCCsearch,wewillconcentrateonthe10%mostcentralevents,de nedbyameasuredtransverseenergyofatleast300GeVin3.5<η<5.5.Thesecorrespondroughlytothetop620mbofthePb+Pbminimumbiascrosssectionσmb=6200mb.Afterallcutsareapplied,thereare212646eventsinthissample,whichwewillrefertoasthe“central”sampleintherestofthispaper.ThecentraldatasampleisshownbyclosedcirclesinFigs.2aand2bandacomparisonwithVENUSeventschosenbyidenticalcutsisshownbythehistogram.ThecorrelationbetweenthechargedandneutralmultiplicitiesispresentedinFigure3withtheminimumbiasdistributionoutlined,thecentralVENUSeventshatched,andthecentraldataeventsshownasscatteredpoints,eachpointcorrespondingtoasingleevent.

Themostdistinctivefeatureofthescatterplotisthestrongcorrelationbe-tweenthechargedandneutralmultiplicities.Areasonableexplanationofthiswouldbeifmostoftheproducedparticlesarepionswiththeirchargestatespartitionedbinomially,asmeasuredinppexperimentsatsimilarener-gies[22].Abinomialdistributionleadstoacorrelationwidthσ(Nch Nγ)∝

Nch+Nγ.Asthisisseeninbothdata

andVENUS,wecanstudythecontributionstothedi erentmultiplicitiestoverifythishypothesis.Infact,about80%ofthechargedparticlesproducedinVENUSarepions,therestbeingprotonsandkaons.Moreover,about85%ofproducedphotonscomefromπodecays.Thus,bysimplycountingthechargedparticlesandphotonsproducedinaheavyioncollision,wehaveareasonableestimateofthenumberofchargedandneutralpionscreated.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

Weverifythebinomialnatureofthecharge uctuationsinVENUSbystudy-ingits“binomiality”:

B=Nπch pchNπ(3)pch(1 pch)Nπ

whereNπchandNπarenumberofchargedpionsandthetotalnumberofpionsforeachevent,andpch=Nπch/Nπistheprobabilitythatapionischarged.Forapurebinomialdistribution,pch=2/3andBisGaussianwithameanatzeroandanRMSofone.ForVENUSwithoutGEANT,we ndanRMSofapproximately.95forpionsproducedinthecentralrapidityregionineventswithanimpactparameterlessthan6fm.ThisisconsistentwiththehypothesisthatthecorrelationarisesmainlyfromthebinomialpartitionofNπ,thetotalpionmultiplicity.

4Event-by-EventSearchforDCCs

DCCsshouldmodifythebinomialpartitioningofNπintochargedandneutralpions.EventsinwhichaDCCisproduced(henceforthreferredtoas“DCCevents”)willshowupasdeviationsfromthebinomialbehaviorandappearasoutlierswithrespecttothebulkofthedata.Wehavealreadydiscussedthatthechargedandneutralmultiplicitiesaredirectlysensitivetothechargedandneutralpionmultiplicitiesineachevent.Thus,DCCeventsshouldappearinthecorrelationofchargedandneutralmultiplicities,whiletheindividualdistributionswillbemainlyuna ected.

4.1DataAnalysis

Thestrongcorrelationbetweenchargedandneutralmultiplicitiesdescribedabovesuggestsamoreappropriatecoordinatesystemwithoneaxisbeingthemeasuredcorrelationaxisandtheotherperpendiculartoit.Ifalldetectedparticleswerepionsandthedetectorswereperfectandhadidenticalpseudo-rapidityacceptance,thenthecorrelationaxiswouldbeastraightline.Instead,wemustaccountforthefactthatathighmultiplicities,thepseudorapiditydistributionstendtonarrow,changingtherelativeacceptanceofchargedandneutralparticlesduetothenon-identicalaperturesoftheSPMDandPMD.Moreover,thelargeoccupanciesinthePMDleadtoaslightsaturatione ect.Itisthenusefultode neacoordinatesystemconsistingofacorrelationaxis(Z)describedbyasecond-orderpolynomial,andtheperpendiculardistance(DZ)fromit,whichisde nedtobepositiveforpointsbelowthisZaxis.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

TheseaxesareshownsuperimposedonFigure3andtheprojectionalongtheZ-axisisshowninFigure4a.ThefullprojectionalongtheDZ-axisisshowninFigure4b.Toaverygoodapproximation,thedataareGaussiandistributed,whichisconsistentwithbinomialpartition.TheVENUSresults,shownbythehistogram,arealsoGaussian,butwithaslightlysmallerwidth.Inbothcases,σDZ,thestandarddeviationofagaussian tintheDZdi-rection,increaseswithincreasingZ.WehavechosentoworkwiththescaledvariableSZ≡DZ/σDZinordertocomparerelative uctuationsatdi erent√multiplicities.Whilebinomialpartitionleadsto uctuationsthatgrowas

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

determineupperlimitsonthefrequencyofDCCproductionasafunctionofitssize,asrepresentedbyζ.

WehavecomputedSZdistributionsforseveralvaluesofζ,rangingfrom15%to90%.Tode neane ciencyfordetectingDCCs,westartfromtheobser-vationthatthedistributionassumingthenullhypothesisisGaussian.Withourstatistics,weexpectfeweventsfartherthan5to6σfromthemean.AneventcontainingaDCC,however,hasanenhancedprobabilityofbeingfoundinthisregion.Thecut|SZ|>Scutthende nesatwo-dimensionalregioninthescatterplotinwhichalleventsareconsideredtobe“DCCcandidates”.Oncethecutisset,theDCCe ciencyisde ned,forNMCVENUSevents,as

(Scut,ζ)=N(|SZ|>Scut,ζ)

NCentral(Scut,ζ)≤NU.L.

NData.(5)

Wehavecalculatedlimitsfortwoscenarios.The rstisbaseduponthecon-servativeassumptionthatVENUSshoulddescribethedataperfectlyintheabsenceofaDCCsignal.Undertheseassumptions,SZ=DZ/σDZasobtained

fromVENUS(asitwasinFigure5)andScut=6.,whichiswellawayfromthedatapointwiththelargestSZ.The90%C.L.limitispresentedinFigure6asasolidline.Theotherscenarioassumesthatthedi erencebetweenthedataandVENUSisduetodetectore ectsandthatthewidthsshouldbethesame.Inthiscase,SZ=DZ/σDZ,withσDZtakenfromthedata,andwe

chooseatightercutScut=5.Thislimitispresentedinthesame gureasadashedline.Thetwolimitsarequitedi erentatζ=15%butgetcloseratζ>30%.Inbothcases,theuncertaintyintheabsolutecomparisonsbetweenthedataandVENUShavenotbeenincludedintheupperlimitestimate.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

5Discussion

EarlierstudiesestimatedtheDCCradiustobearoundR≈3 4fm.Coupledwithavacuumenergydensityugivenbythechirale ectivepotentialtobe60-120MeV/fm3,andanassumedGaussianpTdistributionofwidth≈1/R,anaverageDCCwasthoughttogenerate4

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

jointlybytheGermanBMBFandDFG,theU.S.DOE,theSwedishNFR,theDutchStichtingFOM,theStiftungfuerDeutsch-PolnischeZusammenarbeit,theGrantAgencyoftheCzechRepublicundercontractNo.202/95/0217,theDepartmentofAtomicEnergy,theDepartmentofScienceandTechnology,theCouncilofScienti candIndustrialResearchandtheUniversityGrantsCommissionoftheGovernmentofIndia,theIndo-FRGExchangeProgramme,thePPEdivisionofCERN,theSwissNationalFund,theInternationalSci-enceFoundationunderContractN8Y000,theINTASunderContractINTAS-93-2773,ORISE,Research-in-AidforScienti cResearch(SpeciallyPromotedResearch&InternationalScienti cResearch)oftheMinistryofEducation,ScienceandCulture,theUniversityofTsukubaSpecialResearchProjects,andtheJSPSResearchFellowshipsforYoungScientists.ORNLismanagedbyLockheedMartinEnergyResearchCorporationundercontractDE-AC05-96OR22464withtheU.S.DepartmentofEnergy.TheMITgrouphasbeensupportedbytheUSDept.ofEnergyunderthecooperativeagreementDE-FC02-94ER40818.InadditionwewouldliketothankR.Birgeneau,H.Y.Chang,A.E.Chen,W.S.Edgerly,W.T.Lin,O.RunolfssonandB.Wadsworth.References

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The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

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The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

TOF2

2nd Arm

Plastic BallPMD

Start/Veto

Goliath

1st Arm

TOF1MIRACLEDAZDC

Fig.1.TheWA98ExperimentattheCERNSPS.ThisanalysisusestheSiliconPadMultiplicityDetector(SPMD)andthePhotonMultiplicityDetector(PMD)tomeasurethechargedandneutralmultiplicityforeachevent,andtheMid-RapidityCalorimeter(MIRAC)forthemeasurementofeventcentrality.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

Number of Events101010

10

10

15

432

a.)Nch

Number of Events10

1010

10

10

15432

b.)Nγ-like

Fig.2.Thechargedandneutralmultiplicitydistributionsareshownina)andb).Theopencirclesrepresenttheminimum-biasdistribution.The“central”sample(ET>300GeV)isrepresentedbyclosedcirclesforthedataandbyhistogramsforVENUS.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

Nch1000

900

800

700

600

500

400

300

200

100

0Nγ-like

Fig.3.ThisisthescatterplotshowingthecorrelationbetweenNchandNγ like.Thesolidoutlineshowsthetrendoftheminimumbiasdata.Thecentralsample(withET>300GeV)isshownaspointsforthedataandasahatchedregionforVENUS(withmuchlowerstatistics).OverlaidontheplotaretheZaxisandtheDZaxisataparticularvalueofZasexplainedinthetext.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

Number of Events101010

10

10

15

432

Z

a.)

Number of Events104103102

10

1

b.)

Z

Fig.4.a.)This gureshowsthedistributionofZ,withthesameconventionsasin gure2.b.)ThisshowsthedistributionofDZinthe“central”sampleforthedata(closedcircles)andforVENUS(histogram).Thedi erenceinthemeanbetweenthetwodistributionsarisesduetotheoverallscaledi erencesdiscussedinSection3.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

Number of Events

104103102

10

1

SZ

Fig.5.SZdistributionfortheexperimentaldataisshown,overlaidwithVENUSsimulationsincorporating0%,25%and60%DCCineveryevent.Allofthedistri-butionsarenormalizedtothetotalnumberofdataevents.

The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative produ

DCCs / Central Event

1-110101010

10

10-2-3-4-5-6

ζ(%)Fig.6.90%C.LupperlimitonDCCproductionpercentraleventasafunctionofthefractionofDCCpionsundertwoassumptions.ThethicklinegivestheupperlimitobtainedbyassumingtheσDZinSZiscompletelygivenbytheVENUScalculationrequiringtomakeacutat6σ.ThedashedlineshowsalessconservativelimitobtainedbyusingtheσDZmeasuredinthedataitself.Thisallowsustomake

atightercutat5σ,increasingtheDCCdetectione ciency.

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