质心系能量snnn=2000gev时的质心系产额比对碰撞心度的依赖性

质心系能量snnn=2000gev时的质心系产额比对碰撞心度的依赖性

椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、椰子糖苷元、，卡其色。接近发射阶段的区域，但报告是缓慢的。缓慢发射阶段的大多数区域都报告了接受微控制的微控制。p.pps。m.s.s。p.s。=s。=200年p.*200年p.s。新发射素p.pp。Thereexistmanymodelsinthemarkettodescribetherelativisticheavy-ioncollisions.HerewewanttouseanewmodelNEXUStodosomestudy.Thisnewparton-basedmodelisforhadron-hadroninteractionsandfortheinitialstageofnuclearcollisionsatveryhighenergies(RHIC,LHCandbeyond).Thisapproachiswantedtobeaself-consistenttreatment,usingthesameformalismforcalculatingcrosssectionsandparticleproduction.Tosomeextent,thisapproachprovidesalinkbetweentheGribov-Reggetheoryandthepartonmodel,soiscalled“Parton-basedGribov-ReggeTheory”.Inthisletter,wewilltrytousethenewmodelNEXUS(v2.0)togenerateMonteCarlodataforAu+Aucollisionsat√sΝΝ=200sNN−−−−√=200GeV.Theeventnumbergeneratedisabout66000.AnalyzingtheMonteCarlodata,wepresenttheˉp/pp¯/pratioindifferentregionsofcentrality,transversemomentumandrapidity,respectively.Centralityiscommonlyscaledbythemagnitudeofimpactparameterb.Inexperiment,however,itisnoteasytomeasurethisparameterdirectly,socentralityisusuallycharacterizedbytherelativechargedmultiplicitynch/nmax,i.e.theratioofeventchargedmultiplicitytomaximumchargedmultiplicity.ForMonteCarlodata,weregardtheimpactparameterasthecharacteristicquantityforcentrality.InFig.1(a)isshownthecorrelationbetweentheimpactparameterandrelativechargedmultiplicity.Withtheincreasingoftheimpactparameter,nch/nmaxdecreasesapproximatelylinearly.ThisresultisconsistentwiththeconclusionfromHIJINGmodelforAu+Auminimumbiascollisions.Therefore,wecanuseeitherimpactparameterorrelativechargedmultiplicityascharacteristicquantityforcentrality.Tocomparefurtherthecorrespondingrelationbetweenimpactparameterandrelativechargedmultiplicity,weplotˉp/pp¯/pratioasfunctionsofimpactparameterandrelativechargedmultiplicityinFig.1(b)andFig.1(c),respectively.Heretherapidityrangeis|y|<2andtherangeoftransversemomentumispt<2.Itcanbeseenfromthesetwofiguresthattheˉp/pp¯/pratiosarealmostconstant,exceptatthebeginningofFig.1(a)andatthetailofFig.1(b)wheretherearealittledropandasomewhatraise,respectively.TheresultisconsistentwithFig.1(a)thatimpactparameterandrelativechargedmultiplicityhaveanegtivecorrelation.So,whenwestudytheˉp/pp¯/pratio,bothimpactparameterandrelativechargedmultiplicitycanbeappliedtoscalecentralitybecausetheyareequivalent.Informationonbaryontransportmaybeobtainedbythetheˉp/pp¯/pratio.TheresultsfromSTARindicatethattostudythep-ˉpp−p¯pairproductionisimportantinmid-rapidity.Sowewilldothesystematicanddetailedstudyabouttheˉp/pp¯/pratioasfollows.Firstly,westudythecentralitydependenceofˉp/pp¯/pratiointhedifferentregionsoftransversemomentumandrapidity.Sinceimpactparameterandrelativechargedmultiplicityhavelinearcorrelation,wecanuseeitheroneofthemtostudy.Becausetherelativechargedmultiplicityiseasiertobeaccessedthanimpactparameterinexperiment,soherewechoosetheformerasthecharacteristicquantityforcentralitytostudytherelationbetweentheˉp/pp¯/pratioandcentrality.Fig.2(a)showstheˉp/pp¯/pratioasafunctionofcentrality.Here,wefixthetransversemomentumregionpt<2GeV,andrapidityisinthedifferentregions|y|<0.5,|y|<1,|y|<2,and|y|<3.Withtheenlargingofrapidityregion,theratiodecreases.Thisimpliesthatthemid-rapidityratiosarelargerthanthelargerapidityregionones.Namelyinlargerapidityregion,acertainfractionofthebaryonnumberistransportedfromtheincomingnucleus.For|y|<3,thereisadropfromperipheraltocentralcollisions.Thisresultisconsistentwithmorebaryonstoppingand/ornucleon-ˉpp¯annihilationincentralcollisionsrelativetoperipheralcollisions.InFig.2(b),fixingtherapidityregion|y|<2,weplotthreegroupsofsymbolsforthreedifferentptregions0.3<pt<0.6GeV,pt<1GeV,andpt<2GeV.Theratiosarealmostasameconstantforthesedifferentptregions.Fromabovetwofigures,wecanseethattheˉp/pp¯/pratiohasnostrongdependenceoncentralityintheconfinedrapidityregion.Then,wepresenttherelationbetweentheˉp/pp¯/pratioandtransversemomentum.InFig.3(a)theminimumbiasˉp/pp¯/pratio,asafunctionofptinthedifferentrapidityranges|y|<0.5,|y|<1,and|y|<2,isshown.Inthemid-rangesof|y|<0.5and|y|<1,theratiosarealmostconstantwithanidenticalconstant.Neverthelesswiththeincreasingof|y|theratioswilldecrease.ThereasonhasbeenmentionedintheexplanationfollowingFig.2(a)thatwiththerapidityregionenlarging,morebaryonnumberistransportedfromtheincomingnucleus.Finally,westudythedependenceofˉp/pp¯/pratioonrapidity.Fig.3(b)showstheˉp/pp¯/pratioasafunctionofrapidityintheranges0.3<pt<0.7GeV,pt<1GeV,pt<2GeV.Fordifferentrangesofpt,thereisnomuchdifferenceinˉp/pratios.Withintheregionof|y|<1,theratiosofˉp/pareapproximatelyconstant.Therefore,themid-rapidityˉp/pratioisalsoindependentofrapidity.Forcomparison,wedrawtheresultsonaverageˉp/pratiofromdifferentexperimentalgroupsandmodelsinFig.4.Thereisadramaticincreaseinthemid-rapidityˉp/pratioincentralheavyioncollisionsingoingfromAGStoSPSandtoRHIC.TheresultsfromHIJING(v2.0)modelandNEXUS(v2.0)modelarealsoplottedinthefigure.Insummary,weuseanewhadronicinteractionmodel——NEXUS,whichisaMonteCarloprocedurerelyingonaparton-basedGribov-Reggetheory.Withthisnewmodelwegenerateabout66000Au+AuminimumbiascollisionsMonteCarloeventsat√sΝΝ=200GeV.Wereporttheresultsaboutˉp/pratiointhemid-rapidity.Thereisnostrongcentralitydependenceinthemid-rapidityregion.Themid-rapidityˉp/pratioisessentiallyindependentofeithertransversemomentumorrapidity.Withintherapidityandtransversemomentumrangeof|y|<1.0andpt<1.0,theaverageˉp/