Search for Disoriented Chiral Condensates in 158 A

arXiv:hep-ex/9710015v117Oct1997SearchForDisorientedChiralCondensatesIn158AGeVPb+PbCollisionsM.M.Aggarwala,A.Agnihotrib,Z.Ahammedc,A.L.S.Angelisd,V.Antonenkoe,V.Arefievf,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.Buijsℓ,E.-J.Buisℓ,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.Geurtsℓ,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.Kamermansℓ,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,I.Langbeink,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.Raevenℓ,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,PreprintsubmittedtoElsevierPreprint5February2008H.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¨ofelℓ,L.Tykarskiq,J.Urbahnk,N.v.Eijndhovenℓ,W.H.v.Heeringenℓ,G.J.v.Nieuwenhuizenr,A.Vinogradove,Y.P.Viyogic,A.Vodopianovf,S.V¨or¨osd,M.A.Vosℓ,B.Wyslouchr,K.Yagin,Y.Yokotan,G.R.YounggWA98CollaborationaUniversityofPanjab,Chandigarh160014,IndiabUniversityofRajasthan,Jaipur302004,Rajasthan,IndiacVariableEnergyCyclotronCentre,Calcutta700064,IndiadUniversityofGeneva,CH-1211Geneva4,SwitzerlandeRRC(Kurchatov),RU-123182Moscow,RussiafJointInstituteforNuclearResearch,RU-141980Dubna,RussiagOakRidgeNationalLaboratory,OakRidge,Tennessee37831-6372,USAhUniversityofJammu,Jammu180001,IndiaiUniversityofM¨unster,D-48149M¨unster,GermanyjSUBATECH,EcoledesMines,Nantes,FrancekGesellschaftf¨urSchwerionenforschung(GSI),D-64220Darmstadt,GermanyℓUniversiteitUtrecht/NIKHEF,NL-3508TAUtrecht,TheNetherlandsmUniversityofLund,SE-22100Lund,SwedennUniversityofTsukuba,Ibaraki305,JapanoNuclearPhysicsInstitute,CZ-25068Rez,CzechRep.pKVI,UniversityofGroningen,NL-9747AAGroningen,TheNetherlandsqInstituteforNuclearStudies,00-681Warsaw,PolandrMITCambridge,MA02139,USAsInstituteofPhysics,751-005Bhubaneswar,IndiatUniversityofTennessee,Knoxville,Tennessee37966,USA2AbstractTherestorationofchiralsymmetryanditssubsequentbreakingthroughaphasetransitionhasbeenpredictedtocreateregionsofDisorientedChiralCondensates(DCC).Thisphenomenonhasbeenpredictedtocauseanomalousfluctuationsintherelativeproductionofchargedandneutralpionsinhigh-energyhadronicandnuclearcollisions.TheWA98experimenthasbeenusedtomeasurechargedandphotonmultiplicitiesinthecentralregionof158AGeVPb+PbcollisionsattheCERNSPS.Inasampleof212646events,noclearDCCsignalcanbedistinguished.UsingasimpleDCCmodel,wehaveseta90%C.L.upperlimitonthemaximumDCCproductionallowedbythedata.1IntroductionTheapproximatechiralsymmetryoftheQCDvacuumisbelievedtobespon-taneouslybrokeninnaturebytheformationofanisoscalarquarkconden-sate.DisorientedChiralCondensates(DCC)mayforminlarge,hotregionsofhadronicmatterwherethissymmetryhasbeenbrieflyrestored[1].ADCChasanequalprobabilitytobeinanystaterelatedtothenormalvacuumbyachiralrotation.Byprojectingthespaceoftheseavailablestatesontoaba-sisofdefiniteisospin,ithasbeenfoundthatthechargedistributionofpionsemittedfromaDCChasacharacteristicform[2]:P(f)=12√f(1)wherefistheneutralfraction,f=NπoNπo+Nπ++Nπ−.(2)Thisallowsthepossibilityofhadronicinteractionswithanomalousfluctua-tionsbetweenchargedpionsandneutralpions,asseenthroughtheirtwo-photondecaychannel.ThephenomenologyofDCCswasfirstintroducedinthecontextofhadroniccollisionsbyBjorkenetal,whose“BakedAlaska”model[3]postulatedthatahotshell,expandingatthespeedoflight,couldshieldthecoolinteriorfromtheinfluenceofthenormalvacuumoutside,allowingalargeregionofDCCtoform.RajagopalandWilczek[4,5]studiedtheproductionofDCCsinnuclearcollisionsbystudyingthechiralphasetransitioninQCD,viaitssimilaritytotheO(4)Heisenbergmagnet[6].Throughnumericalsimulations,theyfound3thatasthesystemrapidlyexpandsandcoolsthroughthephasetransition,theequationsofmotioninduceanon-equilibriumrelaxationofthechiralfieldswhichamplifiestheproductionofsoftpionmodesinawell-definedchiraldirec-tion.Thiseffectivelycreatesclustersoflow-pTpions,withtheclustercharg