The information from muon arrival time distributio

arXiv:astro-ph/0204266v116Apr2002Theinformationfrommuonarrivaltimedistributionsofhigh-energyEASasmeasuredwiththeKASCADEdetectorKASCADECollaborationT.Antonia,W.D.Apelb,A.F.Badeaa,1,2,K.Bekkb,A.Bercucib,2,H.Bl¨umerb,a,H.Bozdogb,I.M.Brancusc,C.B¨uttnerb,A.A.Chilingariand,K.Daumillera,P.Dollb,J.Englerb,F.Fesslera,H.J.Gilsb,R.Glasstettera,R.Haeuslera,A.Haungsb,D.Heckb,J.R.H¨orandela,A.Iwana,3,K.H.Kamperta,b,H.O.Klagesb,G.Maierb,H.J.Mathesb,H.J.Mayerb,J.Milkea,M.M¨ullerb,R.Obenlandb,J.Oehlschl¨agerb,S.Ostapchenkoa,4,M.Petcuc,H.Rebelb,M.Risseb,M.Rothb,G.Schatzb,H.Schielerb,J.Scholzb,T.Thouwb,H.Ulricha,J.H.Webera,A.Weindlb,J.Wentzb,J.Wocheleb,J.ZabierowskieaUniversityofKarlsruhe,Institutf¨urExperimentelleKernphysik,76021Karlsruhe,GermanybForschungszentrumKarlsruhe,Institutf¨urKernphysik,76021Karlsruhe,GermanycNationalInstituteofPhysicsandNuclearEngineering,7690Bucharest,RomaniadCosmicRayDivision,YerevanPhysicsInstitute,Yerevan36,ArmeniaeSoltanInstituteforNuclearStudies,90950Lodz,PolandAbstractUsingthefacilitiesoftheKASCADECentralDetectorEASmuonarrivaltimedistributions,observedwithreferencetothearrivaltimeofthefirstlocallyregisteredmuon,andtheircorrelationswithotherEASobservableshavebeenexperimentally1correspondingauthor:[e-mail]2onleaveofabsencefromNationalInstituteofPhysicsandNuclearEngineering,Bucharest,Romania3onleaveofabsencefromUniversityofLodz,Lodz,Poland4onleaveofabsencefromMoscowStateUniversity,Moscow,RussiaPreprintsubmittedtoElsevierPreprint1February2008investigated.Thevariationofadequatelydefinedtimeparameterswiththedis-tanceRμfromtheEASaxishasbeenmeasured.Theexperimentaldataenableastudyofthesensitivityofsuchlocalarrivaltimedistributions,whichcharacterisethestructureoftheshowerdisc,tothemasscompositionofcosmicraysintheenergyregionaroundtheknee.Forthatpurpose,nonparametricmultivariateeven-by-eventanalyseshavebeenperformedforanestimateofthemasscompositionspecifiedbythreedifferentmassgroups,invokingdetailedMonteCarlosimulationsoftheEASdevelopment.Itturnsoutthatlocalmuonarrivaltimedistributions,withoutinformationonthecurvatureoftheshowerdisc,displayaminorsensitivitytothemassoftheEASinducingparticle,atleastfordistancesfromtheshoweraxisRμ100m.ThemeasurementscompriseasubsetofallEASeventsregisteredbyKASCADEduetotheobservationconditionsofthearrivaltimedistributions,withathresholdofthemuonenergyEth=2.4GeVandaminimummultiplicitynthforbeingacceptedintheobserveddatasamples.ThissubsetissensitivetovariationsoftheintegralEASmuonenergyspectrum.BystudyingtheeventacceptanceintheregisteredsamplesonbasisofMonteCarlosimulationsatestoftheconsistencyoftheMonteCarlosimulationswiththedataisenabled,comparingtheresultsin-ferredfromobservationsatdifferentRμanddifferentnthvalues.Withinthepresentuncertaintiestheresultsofsuchatestshowaremarkableagreementoftheexpe-rimentalfindingswiththeMonteCarlosimulations,usingtheQGSJETmodelasgeneratorofthehigh-energyhadronicinteractions.Keywords:ExtensiveAirShowers,ArrivalTimeDistributions,PrimaryMassComposition,ModelTestPACS:98.70Sa,96.40Pq1IntroductionThetimedelayoftheparticlesinsidethefrontofExtensiveAirShowers(EAS)andthetemporalstructureofdifferentEAScomponentsareasubjectoflongstandinginterestofcosmicrayresearch.Infactthefirstexperimen-talstudieshavebeenperformedin1953byBassi,ClarkandRossi[1]andJellyandWhitehouse[2],followedbymanyothers[3]-[11].Therenewedin-terestarisesfromrecentmeasurementsusingadvanceddetectorfacilitiesliketheCOVERPLASTEXdetectorwithintheGREXarray[12]-[14],theEASTOParray[15]orthefacilitiesoftheKASCADEexperiment[16].Investi-gationsofthestructureoftheEASdiscbytheKASCADEexperimentarefocusedinparticularonthemuoncomponent[17]-[21].DuetothereducedinfluenceofmultipleCoulombscatteringofGeVmuonsandtheabsenceofabsorption,muonstravelnearlyinstraightlinesfromthelocusofproductiontotheobservingdetector.Thusmuonarrivaltimedistributions,observedatlargedistancesfromtheshoweraxis,areexpectedtomapthelongitudinalEASdevelopmentandtoreflectthedistributionofproductionheightsviathe2time-of-flightofthemuons.Withsomesimplifications,usingatriangulationprocedure,thedistributionoftheproductionheightscouldbeestimatedfromthetimedelayoftheobservedmuonsrelativetothearrivaltimeoftheshowercentre[17,22,23].Basicallythesameinformationcouldbealternativelyde-ducedfromthedistributionofanglesofmuonincidencerelativetotheshoweraxis[24].CorrespondingmeasurementsarealsoacurrentsubjectofKAS-CADEinvestigationsusingtheMuonTrackingDevice[25].Angle-of-incidenceobservationsorthecombinationwitharrivaltimemeasurements(asdiscussedwiththetermTimeTrackComplementary[22,26])donotrevealadditionalbasicinformation[23]thoughtheyprovideaninterestingpracticalalternative.Thebasicsensitivityofmuonarrivaltimedistributions(whosephenomeno-logicalfeaturesseenwiththeKASCADEexperimentarereportedinRef.[20])tolongitudinalEASdevelopmentandtotheelongationrate[27–29]putsthequestionwhichparticularparametersoftheobserveddistributionsprovideusefulsignaturesofthemassoftheEASprimaryandunderwhichconditionstheyarehelpfulforthedeterminationofthemasscompositio