相对论重离子碰撞试验的现状及展望

Evidenceofself-affinetargetfragmentationprocessin197Au-AgBrinteractionsat10.7AGeVD.H.Zhang,F.Wang,J.X.Cheng,B.Cheng,Q.Wang,H.Q.Zhang,R.XuInstituteofModernPhysics,ShanxiNormalUniversityLinfen041004,ChinaSept.2,20081、Introduction2、Experimentaldetails3、MethodofStudy4、ExperimentalResults5、Conclusions1.IntroductionInhighenergyinteractions,thestudyofnon-statisticalfluctuationshaveenteredintoanewerasinceBialasandPeschanski(NPB273(1986)703)introducedanattractivemethodologytostudynon-statisticalfluctuationsinmultiparticleproduction.TheysuggestedthatthescaledfactorialmomentFqhasagrowthfollowingapowerlawwithdecreasingphasespaceintervalsizeandthisfeaturesignalstheonsetofintermittencyinthecontextofhighenergyinteractions.Thisscaledfactorialmomentmethodhasthefeaturethatitcanmeasurethenon-statisticalfluctuationsavoidingthestatisticalnoise.Uptonow,mostoftheanalysishavebeencarriedoutintherelativisticproducedparticleswiththecommonbeliefthattheseparticlesarethemostinformativeaboutthereactiondynamicsandthuscouldbeeffectiveinrevealingtheunderlyingphysicsofrelativisticnucleus-nucleuscollisions.However,thephysicsofnucleus-nucleuscollisionsathighenergiesisnotyetconclusiveandthereforealltheavailableprobesneedtothoroughlyexploitedtowardsmeaningfulanalysisofexperimentaldata.1.IntroductionInrelativisticheavyioninducednuclearemulsioninteractions,thetargetfragmentationproduceshighlyionizingparticlesresponsibleforheavytrackswhicharesubdividedintograyandblacktracks.Thegraytracksarethemedium-energy(30-400MeV)knocked-outtargetprotons(orrecoiledprotons)withrange3mmandvelocity0.3β0.7.Theyaresupposedtocarrysomeinformationabouttheinteractiondynamicsbecausethetimescaleoftheemissionoftheseparticlesisofthesameorder(10-22s)asthatoftheproducedparticles.Thegeneralbeliefabouttheserecoiledprotonsisthattheyarethelowenergypartoftheinternuclearcascadeformedinhighenergyinteractions.Theblacktrackswithrange3mmandvelocityβ0.3areattributedtoevaporationfromhighlyexcitednucleiinthethermodynamicallyequilibriumstate.Intherestsystemofthetargetnucleus,theemissiondirectionoftheevaporatedparticlesisdistributedisotropically.1.IntroductionIntheanalysisofintermittencymostofthestudiesareperformedintheone-dimensionalspaceonly,buttherealprocessoccursinthreedimensions.Soone-dimensionalanalysisisnotsufficientenoughtomakeanycommentonthecompletedynamicalfluctuationspattern.AccordingtoOchs(PLB247(1990)101),inalower-dimensionalprojectionthefluctuationswillbereducedbytheaveragingprocess.Intwo-dimensionalanalysisgenerallythephasespacearedividedequallyinbothdirectionsassumingthatthephasespacesareisotropicinnature.Consequentlyself-similarfluctuationsareexpected.Itmayhappenthatthefluctuationsareanisotropicandthescalingbehaviorisdifferentindifferentdirectionsgivingrisetoself-affinescaling.Sofaronlyafewworkshavebeenreportedwheretheevidenceofself-affinemultiparticleproductionisindicatedbythedata(Ghoshetal.,EPJA14(2002)77,PRC66(2002)047901,JPG29(2003)983,IJMPE13(2004)1179,MPLA22(2007)1759,Wangetal.,PLB410(1997)323,WuandLiu,PRL70(1993)3197).1.IntroductionInmostoftheearlierworksonintermittency,bestlinearfitsweredrawninthetotalbinrangefromsomepre-conceivedideas.Actually,theplotsarenotperfectlylinearinthewholebinrange,rathernicelinearbehaviorisapparentinselectivebinranges.Soitwouldbebettertoinvestigateintermittencyinthosebinranges.Theintermittencypatterncannotonlysuggestthedynamicalnatureoffluctuationbutalsorevealstheinnerfractalstructureofthefluctuationcodimensionsdq(Ochs,PLB247(1990)101,BialasandGazdzicki,PLB252(1990)483),whicharerelatedtotheintermittencyindicesaqasdq=aq/(q-1).Uniquedqforadifferentorderofmomentssuggestsmonofractalitywhereasorderdependenceofdqsignalsthepresenceofmultifractality.Multifractalitymaybeduetoself-similarcascading,whereasmonofractalityisassociatedwiththermaltransitions.Now,thereisafeelingthatself-similarcascadingisnotconsistentwithparticlecreationduringonephasebutinsteadrequiresanon-thermalphasetransition.1.IntroductionAccordingtoPeschanski(PLB410(1991)323)ifthedynamicsofintermittencyisduetoself-similarcascading,thenthereisapossibilityofobservinganon-thermalphasetransition.Thesignalsofnon-thermalphasetransitioncanbestudiedwiththehelpoftheparameterλq=(aq+1)/q.Theconditionfornon-thermalphasetransitionmayoccurwhenthefunctionλqhasaminimumvalueatq=qc(Peschanski,NPB327(1989)144,PLB410(1991)323,BialasandZaeeswski,PLB238(1990)413).Amongthetwodifferentregionsqqcandqqc,numeroussmallfluctuationsdominatetheregionqqc,butintheregionqqc,dominanceofsmallnumberofverylargefluctuationsoccur.Thissituationresemblesamixtureofaliquidofmanysmallfluctuationsandadust“consistingofafewgrainsofverylargedensity.Theminimumofthefunctionλqmaybeamanifestationofthefactthattheliquidandthedustphasecoexist.2.ExperimentaldetailsStacksofNIKFIBR-2nuclearemulsionplateswerehorizontallyexposedtoa197Aubeamat10.7AGeVatBNLAGS.BA2000microscopeswitha100oilimmersionobjectiveand10ocularlenseswereusedtoscantheplates.Thetracksarepickedupatadistanceof5mmfromtheedgeoftheplatesandarecarefullyfolloweduntilthey