Search for Disoriented Chiral Condensates in 158 AGeV Pb+Pb(8)

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.