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January 26, 2010 10:17 WSPC/INSTRUCTION FILE meson2008biegun International JournalofModernPhysicsA 0 (cid:13)c WorldScientificPublishingCompany 1 0 2 n a J EMC studies using the simulation framework of PANDA 6 2 ] AleksandraBiegunforthePANDAcollaboration∗† h p KernfysischVersnellerInstituut, Universityof Groningen, Zernikelaan 25, 9747 AAGroningen, - The Netherlands p m ReceivedDayMonthYear o RevisedDayMonthYear c . s c The Anti-Proton ANnihilation at DArmstadt (PANDA) experiment proposed at the i FacilityforAntiprotonandIonResearch(FAIR)inDarmstadt(Germany)willperform s y ahigh-precisionspectroscopyofcharmoniumandexotichadrons,suchashybrids,glue- h balls andhypernuclei. A highlyintense beam of anti-protons providedby HighEnergy p Storage Ring(HESR) withan unprecedented resolutionwillscan amass range of2 to [ 5.5GeV/c2. InpreparationforexperimentswithPANDA,carefulandlarge-scalesimulationstu- 1 diesneedtobeperformedinthecomingyearstodetermineanalysisstrategies,toprovide v feedbackforthedesign,constructionandperformanceoptimisationofindividualdetector 0 components and to design methods for the calibration and interpretation of the exper- 3 imental results. Results of a simulation for the ElectroMagnetic Calorimeter (EMC), 6 built from lead tungstate (PWO) crystals and placed inside the Target Spectrometer 4 (TS), arepresented. ThesimulationswerecarriedoutusingthePandaRootframework, . whichisbasedonROOTandbeingdeveloped bythePANDAcollaboration. 1 0 Keywords: Antiproton,charmedhybrid,PANDA. 0 1 PACSnumbers:13.25.Ft,87.64.Aa,01.50.hv : v i X 1. Motivation r With the PANDA experiment at FAIR in Darmstadt1, a high resolution hadron a spectroscopy will be performed. The charmonium states partly discovered with e- xisting e+e− experiments will be measuredwith the PANDA with much higher resolution,whichcouldnotbe achievedbye+e− machines,butonlyviap¯p processes. The exotic hybrid and glueball states, predicted by lattice QCD, as well as p¯A collisions will be also investigated. The experimental setup of the PANDA project needs to be able to reconstruct predicted states and their decay channels with high precision.Both,chargedandneutral decay products of resonances,have to be detected with very good spatial and energy resolutions. For this purpose, detailed simulationsandacorrespondinganalysisofvariousphysicschannelsareperformed. ∗Onleaveofabsence fromtheINP,PolishAcademyofScience, Kraków,Poland. †E-mailaddress:[email protected]. 1 January 26, 2010 10:17 WSPC/INSTRUCTION FILE meson2008biegun 2 Aleksandra Biegunfor the PANDA collaboration In this paper, the decay of the the hc charmonium state via the following reaction is discussed: p+p→hc →ηc+γ →(π0+π0+η)+γ →7γ. (1) This is an example of a neutral decay, which can be studied with PANDA. The PANDA detection system will be the perfect instrument for this, since it is highly compact, versatile and has a 4π coverage. 2. PANDA detection system and PandaRoot framework ThePANDAdetectionsystemispresentedintheleftpictureinFig.1.Itdepictsthe MicroVertexDetector(MVD),TimeProjectionChamber(TPC)and,alternatively, StrawTubeTracker(STT),ElectroMagneticCalorimeter(EMC),Cherenkovdetec- tor (DIRC), Muon detector (MUO), Time-Of-Flight (TOF), Drift Chambers (DC) and the Forward Calorimeter (FC). The EMC detector, placed inside the Target Spectrometer (TS), consists of the forward end-cap (FwEndCap), barrel (Barrel) and the backward end-cap (BwEndCap) and is shown in more detail on the right hand side in Fig. 1. This highly granulated calorimeter, built from ∼16000 PWO crystalswith the size of about2x2x20cm3 and 22Xo radiationlength,was usedto reconstructthepresentedcharmoniumhc (1)fromsevenphotonsinthefinalstate. Fig. 1. Left: The PANDA detection system. Right: The forward end-cap (FwEndCap), barrel (Barrel) and the backward end-cap (BwEndCap) of the EMC together with a beam pipe. Both picturesaremodelledusingthePandaRootsimulationandanalysisframework. Reaction (1) has been simulated by using the EvtGen2 event generator which has been included inside the simulation and analysis framework of the PANDA, called PandaRoot3. EvtGen,adaptedfor PANDA, was designedby BaBar4 and originally usedforthesimulationofthephysicsoftheBmesondecays.TheRhopackage5 was applied to reconstruct invariant masses of final-state and intermediate particles of 6 Eq. (1). The simulation framework is based on the Virtual Monte Carlo concept, January 26, 2010 10:17 WSPC/INSTRUCTION FILE meson2008biegun EMCstudies using the simulation framework of PANDA 3 whichallowstoperformsimulationsfordifferenttransportmodelswithoutchanging the usercodeorgeometrydescription.Theelectronicresponseofthe EMCcrystals wassimulatedtogetherwithanoptimisedclusterreconstructionanalysis.TheEMC response has been compared and tuned to experimental data. 3. Analysis of the hc state The two-photon invariant mass spectrum, as presented in the top panels in Fig. 2. shows a clear signals from π0 and η particles on top of a continuous combinatorial background. ThespectrumwasfittedusingaGaussianfunctionrepresentingsignal Ν10000 Ν4000 π0 η 9000 3500 8000 3000 7000 6000 2500 5000 2000 4000 1500 3000 1000 2000 1000 500 00 0.05 0.1 0.15 0.2 0.25 0.3 00.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 M γ γ M (πG0 (GeeVV//cc22 )) M γ γ M(ηG (GeeVV//cc22 )) Ν60000 η Ν800 η c 700 c 50000 600 40000 500 30000 400 300 20000 200 10000 100 00 0.5 1 1.5 2 2.5 3 3.5 00 0.5 1 1.5 2 2.5 3 3.5 M π 0 π 0 η M (ηGc (GeeVV//cc 22 )) M π 0 π 0 η M(Gηc (eGVeV/c/ c 2 2)) Fig. 2. The invariant masses of π0, η and ηc obtained from decay channel (1). Lower left plot showsηc masswithacombinatorialbackgroundwhilethelowerrightonepresentsaverycleanηc massspectrum aftercuts imposedatπ0 andη massesshowedinupperplotsinthisfigure. together with the second order polynomial function, representing the background. Astandarddeviation,σ,of6 MeVand15MeVwasfoundforthe π0 andη,respec- tively. Pions and etas were selected by applying a windows of 3σ around the two peaks as indicated by the arrows in both panels. The 3σ cuts have been applied to reduce the huge combinatorial background. The bottom-left panel in Fig. 2. depicts the invariantmass of the (π0π0η) systemfor which alltwo-photoncandidates were used to identify π0 and η particles. The bottom-right panel depicts the same analysis with the cuts applied to identify π0 and η mesons. Note that the peak to backgroundratiodrasticallyimprovedby a factor2500,as expected. The combina- tionofthereconstructedηc mass,togetherwiththeremainingphoton,providesthe January 26, 2010 10:17 WSPC/INSTRUCTION FILE meson2008biegun 4 Aleksandra Biegunfor the PANDA collaboration Fig.3. Theinvariantmassofthecharmonium hc state, reconstructed from seven photons in thefinalstatefromthedecaychannel(1).The solidlinerepresentsthespectrumobtainedus- ing GEANT3 while the dashed line represents asimulationusingGEANT4. identification of the hc particle, as shown in Fig. 3. In this analysis, only cuts for π0 and η masses have been applied. The simulated spectrum representing the hc, yields to a peak-to-background of 30, a mass resolution (FWHM) of 70 MeV, and an efficiency of the hc reconstructionof about 30%. The distributions predicted by the two transport models, GEANT3 and GEANT4, are comparable. A small shift of25MeVcanbeobserved,whichcanoriginatefromsmalldifferencesintheenergy response between GEANT3 and GEANT4. A further study is in progress. 4. Summary The analysisofthe charmoniumhc state via the neutralchannelhas been done for two different transportmodels within the PandaRootframework.A more extensive simulation for other channels, including charged particles, will be studied in the near future. Acknowledgements This research is supported by Veni-grant 680-47-120 from the Netherlands Or- ganisation for Scientific Research (NWO), the University of Groningen and the Gesellschaft fu¨r SchwerionenforschungmbH (GSI), Darmstadt. References 1. TPR for PANDA,Strong Interaction Studieswith Antiprotons(2005). http://fairroot.gsi.de, http://www-panda.gsi.de 2. http://www.slac.stanford.edu/∼lange/EvtGen/ 3. Stefano Spataro for the PANDAcollaboration, InternationalConferenceonComputinginHighEnergyandNuclearPhysics,inJournal of Physics: Conference Series 119, 032035 (2008), and references therein. 4. http://www.slac.stanford.edu/BFROOT/ 5. Klaus Götzen, InternationalConferenceonComputinginHighEnergyandNuclearPhysics,inJournal of Physics: Conference Series 119, 032020 (2008), and references therein. January 26, 2010 10:17 WSPC/INSTRUCTION FILE meson2008biegun EMCstudies using the simulation framework of PANDA 5 6. R.Brun, F. Carminati, I. Hrivnacova,A. Morsch The Virtual Monte Carlo Computing in High Energy and Nuclear Physics,La Jolla, California, 24-28 March 2003