Search for Disoriented Chiral Condensates in 158 AGeV Pb+Pb(7)

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