净质子、重子和电荷多重性非统计波动的比较研究

0Comparativestudyfornon-statisticalfluctuationofnet-proton,baryon,andchargemultiplicities净质子、重子和电荷多重性非统计波动的比较研究May9-May141234

OutlineIntroductionNon-statisticalmomentsofconservedquantitiesResultsformomentsandtheproductsofconservedquantitiesSummary12Introduction1AttemptswerethenmadetolocatetheQCDcriticalpoint(CP),wherethefirstorderphasetransitiongivesovertothe‘crossover’intheQCDphasediagram3Skewness:Inastaticandinfinitemedium,variousmomentsofconservedquantitiesarerelatedtothecorrelationlengthM.Asakawa,U.Heinz,B.Muller,PRL85(2000)2072Kurtosis:4TheproductsofhighermomentsrelatedtotheratioofconservedquantitynumbersusceptibilitiesConservedquantityeventdistributionbecomesnon-GaussianandthesusceptibilitydivergeswhenQCPisapproached.Thiscausesproductstochangesignificantly5M.Asakawaetal.,PRL103(2009)262301M.A.Stephanov,PRL102(2009)032301AcrossingofthePhaseboundarymayresultsinachangeofsignofskewnessofnet-protondistributionasafunctionoftheenergydensity.6M.A.Stephanov,PRL107(2011)052301Thesignofthekurtosisofnet-protondistributioncouldbenegativeasthecriticalpointisapproachedfromthecrossoversideoftheQCDphasetransition.7net-proton,net-baryon,andnet-chargeexcitationfunctionsinPb+Pbcollisionsbehaveratherdifferently:Thenet-protonandnet-chargeκσ2areslightlynegativebutthenet-baryonκσ2keepslargenegativevaluesNahrgangM,SchusterT,StockR,MitrovskiMandBleicherM2012Eur.Phys.J.C722143(UrQMD)8asafunctionoftherapiditywindowsizewasalsodifferent:boththenet-protonandnet-chargearedifferentlyfluctuatedaroundzero,butthenet-baryonreachesalargenegativevalueatthelargewindow9Theopinionin“KitazawaMandAsakawaM2012Phys.Rev.C86024904”isquiteopposite:Theyanalyticallyderivedarelationbetweenthebaryonnumbercumulantandtheprotonnumbercumulantwiththeassumptionsthattheconservedobservablenumberdistributionisabinomialfunctionandthatthestrangebaryonisconsideredapproximately.Thusthenet-baryonandnet-protoncumulantshaveasimilarbehavior.10Distributionofconservedquantity

Momentsaboutmean

Momentsaboutzero

2Non-statisticalmomentsofconservedquantities11Keymoments:A.VarianceB.SkewnessC.KurtosisD.Products12ThephasetransitionandtheapproachoftheCPisamatterofdynamicseliminatethefinitesizeandlimitedstatisticseffectsTopronouncetheeffectofdynamicfluctuation,oneshouldstudynon-statisticalmomentexcitationfunctions:insteadofstudyingonly,where

iscalculatedfrom

mixedevents13Realevents:

measuredorgeneratedevents,withdynamicalconservationssuchasmomentumconservationetc.Mixedevents:

constructedrandomlyfromrealevents,bykeepingtherealeventmultiplicity.Inmixedeventsdynamicalconservationsandcorrelationsaregone,but<x>isnotchanged.

ThePACIAEmodelisusedtogeneratetheevents143ResultsDai-meiZhou,etal.,PRC85(2012)064916STAR,X.F.Luo,arXiv:1106.292615Dai-meiZhou,etal.,PRC85(2012)064916;STARPRL105,(2010)02230216Dai-meiZhou,etal.,PRC85(2012)064916STARPRL105,(2010)02230217Athigherbeamenergiestheskewnessisnegative,indicatingmoredominanceofthehadronicsideofthephasetransition.Thekurtosisbecomessignificantlynegative,althoughsmallathigherbeamenergies,indicatingthatthefreeze-outisindeedinthephasetransitiondomain.18

Theeffectoffinitewindowsdramaticallyinfluencesthecnmulantofconservedobservables.

Net-chargecumulantmaybemoreadvantageousfortheinvestigationoftheCPsingularityBzdakandV.Koch,Phys.ReV.C86,044904(2012)arxiV:1206.4286v1[nucl-th]19Dai-MeiZhou,Zeng-ZengLuo,Yuncheng,AyutLimphirat,Yu-LiangYan,Yu-PengYan,XuCaiandBen-haoSa,J.Phys.G:Nucl.Part.Phys.41(2014)06510320XiaofengLuoforSTARCollaboration,arxiV:1210.5573[nucl-ex]J.Phys.G:Nucl.Part.Phys.41(2014)0651032122STARCollaboration,2013ActaPhys.Pol.Suppl.6437Thenet-protonandthenet-chargetheoreticalrealexcitationfunctionofSσandinwindowIarecomparablewiththecorrespondingSTARdata23Thenet-proton,net-baryon,andnet-chargerealeventhighermomentexcitationfunctionofMandσappeartohaveasimilardependenceonthewindowsize.ButthedependenceofS,κ,Sσ,andonthewindowsizeisrathercomplicated24Thedependenceofthenon-statisticalSkewnessandonthecollisionsenergybecomestrongerwithincreasingthewindowsize.25Suddendroptoanegativevalue(oraturningpoint)mayindicatesomekindofdynamicalchangesandhavetobestudiedfurtherthenet-baryonSandSσcalculatedinwindowIIIaswellasκinwindowIandIIvarydramaticallyatthesame√sNN26Onecannotseeanydramaticchangeofthenet-chargenon-statisticalmoments274SummaryWehavecalculatedtherealandnon-statisticalexcitationfunctionsofhighermomentofthenet-proton,net-baryonandnet-chargenumbereventdistributions(2)PACIAEmodelisusedto