PANDA, the detector to study AntiProton ANnihilations at DArmstadt, will be
installed at the future international Facility for Anti-proton and Ion Research
(FAIR) in Darmstadt, Germany. The PANDA physics program is oriented towards the
studies of the strong interaction and hadron structure performed with the
highest quality beam of anti-protons [1]. In the preparation for PANDA
experiments, large-scale simulation studies are being performed to validate the
performance of all individual detector components and to advice on detector
optimisation. The feasibility of the analysis strategies together with the
calibration methods are being studied. Simulations were carried out using the
framework called PandaROOT [2], based on ROOT and the Virtual Monte Carlo
concept [3].
  [1] http://www-panda.gsi.de; Technical Progress Report (2005); Physics
Performance Report (2009), arXiv:0903.3905v1.
  [2] [PANDA Collaboration] S. Spataro, J. Phys. 119, 032035 (2008).
  [3] http://root.cern.chComment: Proceeding of the XXXI Mazurian Lakes Conference on Physics, Piaski,
  30.08-6.09, 200

Biegun, A.

English

arXiv

PANDA, the detector to study AntiProton ANnihilations at DArmstadt, will be installed at the future international Facility for Anti-proton and Ion Research (FAIR) in Darmstadt, Germany. The PANDA physics program is oriented towards the studies of the strong interaction and hadron structure performed with the highest quality beam of anti-protons [1]. In the, preparation for PANDA experiments, large-scale simulation studies are being performed to validate the performance of all individual detector components and to advice on detector optimisation. The feasibility of the analysis strategies together with the calibration methods are being studied. Simulations were carried out using the framework called PandaROOT [2], based on ROOT and the Virtual Monte Carlo concept [3].</p

ARTS repository - University of Groningen

   University of GroningenFeasibility Studies for the PANDA Experiment at FAIRBiegun, A.; PANDA CollaborationPublished in:Acta Physica Polonica BIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2010Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Biegun, A., & PANDA Collaboration (2010). Feasibility Studies for the PANDA Experiment at FAIR. ActaPhysica Polonica B, 41(2), 277-283.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 30-10-2023Vol. 41 (2010) ACTA PHYSICA POLONICA B No 2FEASIBILITY STUDIES FOR THE PANDAEXPERIMENT AT FAIR∗A. Biegunfor the PANDA CollaborationKVI/University of Groningen, 9747 AA Groningen, The Netherlands(Received January 14, 2010)PANDA, the detector to study AntiProton ANnihilations at DArmstadt,will be installed at the future international Facility for Anti-proton and IonResearch (FAIR) in Darmstadt, Germany. The PANDA physics program isoriented towards the studies of the strong interaction and hadron struc-ture performed with the highest quality beam of anti-protons [1]. In thepreparation for PANDA experiments, large-scale simulation studies are beingperformed to validate the performance of all individual detector compo-nents and to advice on detector optimisation. The feasibility of the analysisstrategies together with the calibration methods are being studied. Simu-lations were carried out using the framework called PandaROOT [2], basedon ROOT and the Virtual Monte Carlo concept [3].PACS numbers: 13.25.Ft, 87.64.Aa, 01.50.hv, 29.40.Mc1. IntroductionWith the PANDA physics program various questions related to the prop-erties of the strong interaction will be answered. This experiment operatesin the transition region between the perturbative and the non-perturbativeQCD regimes and, thereby, will gain insight into the mechanism of hadronmass generation and quark confinement.The highest quality beam of anti-protons, in terms of intensity and reso-lution, is the key ingredient for the PANDA project. The momentum range ofanti-protons of 1.5–15 GeV/c gives access to a center-of-mass energy rangefrom 2.2–5.5 GeV/c2 in pp annihilations. The PANDA detector will measureprecisely momenta and scattering angles of both charged and neutral parti-cles of the reaction products to detect the complete spectrum of final statesrelevant for the PANDA physics cases.∗ Presented at the XXXI Mazurian Lakes Conference on Physics, Piaski, Poland,August 30–September 6, 2009.(277)278 A. Biegun2. The PandaROOT frameworkThe offline software for PANDA, PandaROOT, is an extension of theFairROOT [4] framework being designed for the FAIR project. The PandaROOTframework, being developed by the PANDA Collaboration, is being used forboth simulation and data analysis of the PANDA physics studies. It containstools adapted from high energy physics experiments, such as event gener-ators, to produce the reaction of interest and its decay chain, to generatethe background from pp annihilation or to study the pA collision. Also, var-ious tools allowing to test the reconstruction algorithm, and the completedigitization and reconstruction chain, and allowing to perform a detailedanalysis together with the full geometry model are included in this frame-work. PandaROOT is highly versatile and enables a user-friendly interface tovarious transport engines, like GEANT3, GEANT4 and Fluka [5].3. The PANDA setupTo enable a rich physics program with the PANDA detector, all componentshave to be carefully designed and tuned.The PANDA detector, with its compo-nents, is presented in Fig. 1 and consists of two parts, a Target Spectrometer(TS) and a Forward Spectrometer (FS). Precise tracking and Particle IDen-tification (PID) are crucial to measure momenta of particles with a gooddetection efficiency. This is achieved by exploiting a Micro-Vertex-Detector(MVD), Straw Tube Tracker (STT) or, alternatively Time Projection Cham-ber (TPC), six Drift Chambers (DC), a muon and Cherenkov (DIRC De-tection of Internally Reflected Cherenkov) detectors, marked in Fig. 1. Thehigh resolution Electro Magnetic Calorimeter (EMC) in the TS and the FS isFig. 1. The PANDA detection system.Feasibility Studies for the PANDA Experiment at FAIR 279particular important to detect photons in a very broad energy range, startingfrom a few tens of MeV up to several GeV, as expected in the reactions aimedfor PANDA. All sub-detectors together will cover nearly the full solid angle.A very high precision anti-proton beam, ∆p/p ∼ 10−4–10−5, together witha high luminosity, L ∼ 1031–1032 cm−2s−1, allow to measure very narrow,50–100 keV, mass states of charmonium and reactions with cross-sectionsdown to in the order of pb. The main requirements addressed to the track-ing devices are a good momentum resolution at the percent level and theability to handle high count rates. The MVD is the detector closest to theinteraction point. This tracking device for charged particles is essential fora very precise determination of secondary decay vertices of short-lived par-ticles. A spatial resolution below 100 µm is required and simulations showthat 11 µm can be achieved [1]. The MVD is surrounded by the STT or theTPC, which will be used for a main track reconstruction. The position reso-lution in x and y coordinates of about 150 µm and the resolution of 3mm inz direction is expected. The TPC or the STT will be combined with the sub-system consisting of Gas Electron Multiplier (GEM) detectors to performtracking in the FS at angles below 22◦. The GEMs have rate capabilitiesthousand times larger than achievable with drift chambers, therefore theycan handle a higher flux of particles. The generator for background reac-tions (DPM [6]) was used to generate events at the momentum of 3.6GeV/cand the reconstructed paths from the MVD combined with the TPC tracksare presented in Fig. 2(a). This graph shows a very good matching of tracksegments coming from these two detectors. One of the systems used for PIDin PANDA is the DIRC detector, used for identifying particles with momentaabove 1 GeV/c. The velocity information determined from the CherenkovFig. 2. (a) Reconstructed tracks of charged particles from track segments in MVD(dots in the middle) and TPC (outer curves) detectors. (b) Identification of chargedparticles with different momenta and charge using the MVD, TPC and DIRC de-tectors. The Y axis represents the Cherenkov angle Θ. Plots are taken fromS. Spataro, INFN Torino.280 A. Biegunangle Θ = arccos(1/nβ) of a charged particle, propagating in the mediumwith the refractive index n, is combined with the momentum informationfrom the tracking detectors. Fig. 2(b) presents the identification of 104 par-ticles generated with the DPM and reconstructed by the MVD, TPC andDIRC detectors. A very good separation of charged particles, π+, π− andprotons, has been shown. The EMC detector, Fig. 3(a), is mainly used forphoton detection, but it also measures the deposited energy of electrons,positrons, muons and hadrons. Muons and hadrons lose only a certain frac-tion of their kinetic energy by ionisation processes, while e− and e+ deposittheir complete energy in the electromagnetic shower. This information canbe used for PID as illustrated in Fig. 3(b). The PANDA physics program reliesheavily on the capability to measure photons with high energy, position and,partly, time resolutions over a wide dynamic range. Thus, a highly granularEMC detector will be employed with fast PWO scintillators having a shortradiation length, X0 = 0.89 cm, a high energy resolution for photons andelectrons, 1.5%/√E(GeV) + 1.3%, and a very good time resolution, < 1 nsfor deposited energy above 80 MeV, obtained from a measurement with a re-alistic prototype equipped with a 1 cm2 Avalanche Photo Diode (APD) andSampling ADC readout [7]. In the final configuration the PWO crystals willbe equipped with two APDs of 1 cm2 size each, thus gaining an improvementfactor up to√2 for the energy and time resolution. Such photon detectorsare needed to cope with high count rates and with the proposed compactdesign of the TS.Fig. 3. (a) A 3D view of the electromagnetic calorimeter in the target spectrometerof PANDA. The barrel EMC (Barrel) and both, forward (FwEndCap) and back-ward (BwEndCap) EMC end-caps are shown. (b) E/p versus track momentum forelectrons and pions in the momentum range between 0.3GeV/c and 5GeV/c.Feasibility Studies for the PANDA Experiment at FAIR 2814. The charmonium hc (11P1) reconstructionThe invariant mass reconstruction requires a precise determination of theenergy deposited by photons and the opening angle between them, which canbe achieved only by a highly granulated calorimeter; the PANDA EMC fulfilsthis requirement. The EMC plays a crucial role in the reconstruction ofthe singlet (11P1) state of charmonium, hc, presented below. The followingdecay mode of the hc:p+ p→ hc → ηc + γ →(π0 + π0 + η)+ γ → 7γ (1)has been studied in this work. The chain (1) was generated with the Evt-Gen generator and the invariant mass analysis was done using the Rhopackage [1]. The two-photon invariant-mass spectra, reconstructed fromcombinations of seven photons in the final state are presented in Fig. 4.Peaks which stem from π0 and η masses are found on top of a combinatorialbackground. A Gaussian function, describing the signal convoluted with asecond-order polynomial, describing the background, was fitted. Cuts witha window of 3σ around the π0 and η mass peaks were applied in a fur-ther analysis and the background was reduced significantly. With thesecuts, a clean ηc invariant mass spectrum was extracted to finally identifythe hc state, as demonstrated in Fig. 5. The hc reconstruction efficiency,εReco, obtained from the presented analysis was found to be 26%. The ex-pected number of events to be measured during the PANDA experiment wasestimated taking into account the production cross-section, σp, which wascalculated from the Breit–Wigner formula at the resonance energy for theprocess: pp→ hc → ηc+γ [1]. Also, the total branching ratio for the processηc → π0π0η, BRηc→π0π0ηtot , was used. In the table on the right hand site ofFig. 4. The two-photon invariant mass spectra reconstructed in the EMC detectorfrom combinations of seven photons in the final state from chain (1). A Gaussianfit combined with a second-order polynomial is shown.282 A. BiegunParameters Eventsper dayσp 33 [nb]BRηc→π0π0ηtot 6.153× 10−3εReco 26 [%]t 1 [day]LHL 2×1032 [cm−2s−1] 931LHR 1031 [cm−2s−1] 47Fig. 5. Left: ηcγ invariant mass reconstructed after 3σ window cuts on π0, η andηc masses. Right: Parameters used to calculate the collected number of events perday, expected to reveal the signal of charmonium hc. The calculated numbers ofmeasured events/day are presented in the lower part of the table.Fig. 5 the most important ingredients, which were used in the analysis, aresummarized. The calculation was done for two modes available for PANDA:the high luminosity mode, LHL, with σp/p ∼ 10−4, and the high resolutionmode, LHR, with σp/p ≤ 4 × 10−5 and the estimated numbers of collectedevents/day are presented in that table. The obtained numbers are by factorsof 5 and 10 larger for LHR and LHL, respectively, than for other decay modesof the charmonium hc state, such as hc → ηcγ → ΦΦγ (2), described in [1].This is mainly due to the total branching ratio BRηc→π0π0ηtot = 6.153× 10−3,which is one order of magnitude larger than the total branching ratio ofBRηc→ΦΦtot = 6.24 × 10−4. The disadvantage might be an insufficient back-ground suppression of the decay channel (1) compared to the channel (2).A complete background analysis of the competing channels as pp→ π0π0π0and pp→ π0π0η is ongoing.5. Summary and conclusionsWith the PANDA detector a broad range of physics studies will be covered.The precise measurement of the momentum and position of a particle willbe possible using highly tuned tracking, PID and EMC sub-detectors. The11P1 state of charmonium is one of several benchmark channels studied forPANDA, where masses and widths will be measured precisely. Recently, thehc was studied in e+e− experiments (CLEO-c [8], BES3 [9]), but so-far onlyan upper limit for the total width, Γ < 1MeV, has been published. Inthe pp annihilation experiment, such as PANDA, the exact value of Γ will bemeasured. In this work we analysed the decay of the hc → ηcγ → π0π0η.Preliminary studies show that the observation of this channel is feasible andfurther investigations of its background are under way.Feasibility Studies for the PANDA Experiment at FAIR 283This work is supported by Veni-grant 680-47-120 from the NetherlandsOrganisation for Scientific Research (NWO), the University of Groningenand the Helmholtzzentrum für Schwerionenforschung GmbH (GSI), Darm-stadt.REFERENCES[1] http://www-panda.gsi.de; Technical Progress Report (2005); Physics Per-formance Report (2009) [arXiv:0903.3905v1].[2] [PANDA Collaboration] S. Spataro, J. Phys. 119, 032035 (2008).[3] http://root.cern.ch[4] http://fairroot.gsi.de[5] http://www.fluka.org[6] A. Capella et al., Phys. Rep. 236, 225 (1994).[7] M. Kavatsyuk et al., IEEE Nuclear Science Symposium and Medical ImagingConference, 25–31 Oct. 2009, Orlando, USA.[8] S. Dobbs et al., Phys. Rev. Lett. 101, 182003 (2008) [arXiv:0805.4599v1].[9] http://bes3.ihep.ac.cn

Feasibility Studies for the PANDA Experiment at FAIR

University of Groningen

   University of GroningenFeasibility Studies for the PANDA Experiment at FAIRBiegun, A.; PANDA CollaborationPublished in:Acta Physica Polonica BIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2010Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Biegun, A., & PANDA Collaboration (2010). Feasibility Studies for the PANDA Experiment at FAIR. ActaPhysica Polonica B, 41(2), 277-283.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019Vol. 41 (2010) ACTA PHYSICA POLONICA B No 2FEASIBILITY STUDIES FOR THE PANDAEXPERIMENT AT FAIR∗A. Biegunfor the PANDA CollaborationKVI/University of Groningen, 9747 AA Groningen, The Netherlands(Received January 14, 2010)PANDA, the detector to study AntiProton ANnihilations at DArmstadt,will be installed at the future international Facility for Anti-proton and IonResearch (FAIR) in Darmstadt, Germany. The PANDA physics program isoriented towards the studies of the strong interaction and hadron struc-ture performed with the highest quality beam of anti-protons [1]. In thepreparation for PANDA experiments, large-scale simulation studies are beingperformed to validate the performance of all individual detector compo-nents and to advice on detector optimisation. The feasibility of the analysisstrategies together with the calibration methods are being studied. Simu-lations were carried out using the framework called PandaROOT [2], basedon ROOT and the Virtual Monte Carlo concept [3].PACS numbers: 13.25.Ft, 87.64.Aa, 01.50.hv, 29.40.Mc1. IntroductionWith the PANDA physics program various questions related to the prop-erties of the strong interaction will be answered. This experiment operatesin the transition region between the perturbative and the non-perturbativeQCD regimes and, thereby, will gain insight into the mechanism of hadronmass generation and quark confinement.The highest quality beam of anti-protons, in terms of intensity and reso-lution, is the key ingredient for the PANDA project. The momentum range ofanti-protons of 1.5–15 GeV/c gives access to a center-of-mass energy rangefrom 2.2–5.5 GeV/c2 in pp annihilations. The PANDA detector will measureprecisely momenta and scattering angles of both charged and neutral parti-cles of the reaction products to detect the complete spectrum of final statesrelevant for the PANDA physics cases.∗ Presented at the XXXI Mazurian Lakes Conference on Physics, Piaski, Poland,August 30–September 6, 2009.(277)278 A. Biegun2. The PandaROOT frameworkThe oﬄine software for PANDA, PandaROOT, is an extension of theFairROOT [4] framework being designed for the FAIR project. The PandaROOTframework, being developed by the PANDA Collaboration, is being used forboth simulation and data analysis of the PANDA physics studies. It containstools adapted from high energy physics experiments, such as event gener-ators, to produce the reaction of interest and its decay chain, to generatethe background from pp annihilation or to study the pA collision. Also, var-ious tools allowing to test the reconstruction algorithm, and the completedigitization and reconstruction chain, and allowing to perform a detailedanalysis together with the full geometry model are included in this frame-work. PandaROOT is highly versatile and enables a user-friendly interface tovarious transport engines, like GEANT3, GEANT4 and Fluka [5].3. The PANDA setupTo enable a rich physics program with the PANDA detector, all componentshave to be carefully designed and tuned.The PANDA detector, with its compo-nents, is presented in Fig. 1 and consists of two parts, a Target Spectrometer(TS) and a Forward Spectrometer (FS). Precise tracking and Particle IDen-tification (PID) are crucial to measure momenta of particles with a gooddetection efficiency. This is achieved by exploiting a Micro-Vertex-Detector(MVD), Straw Tube Tracker (STT) or, alternatively Time Projection Cham-ber (TPC), six Drift Chambers (DC), a muon and Cherenkov (DIRC De-tection of Internally Reflected Cherenkov) detectors, marked in Fig. 1. Thehigh resolution Electro Magnetic Calorimeter (EMC) in the TS and the FS isFig. 1. The PANDA detection system.Feasibility Studies for the PANDA Experiment at FAIR 279particular important to detect photons in a very broad energy range, startingfrom a few tens of MeV up to several GeV, as expected in the reactions aimedfor PANDA. All sub-detectors together will cover nearly the full solid angle.A very high precision anti-proton beam, ∆p/p ∼ 10−4–10−5, together witha high luminosity, L ∼ 1031–1032 cm−2s−1, allow to measure very narrow,50–100 keV, mass states of charmonium and reactions with cross-sectionsdown to in the order of pb. The main requirements addressed to the track-ing devices are a good momentum resolution at the percent level and theability to handle high count rates. The MVD is the detector closest to theinteraction point. This tracking device for charged particles is essential fora very precise determination of secondary decay vertices of short-lived par-ticles. A spatial resolution below 100 µm is required and simulations showthat 11 µm can be achieved [1]. The MVD is surrounded by the STT or theTPC, which will be used for a main track reconstruction. The position reso-lution in x and y coordinates of about 150 µm and the resolution of 3mm inz direction is expected. The TPC or the STT will be combined with the sub-system consisting of Gas Electron Multiplier (GEM) detectors to performtracking in the FS at angles below 22◦. The GEMs have rate capabilitiesthousand times larger than achievable with drift chambers, therefore theycan handle a higher flux of particles. The generator for background reac-tions (DPM [6]) was used to generate events at the momentum of 3.6GeV/cand the reconstructed paths from the MVD combined with the TPC tracksare presented in Fig. 2(a). This graph shows a very good matching of tracksegments coming from these two detectors. One of the systems used for PIDin PANDA is the DIRC detector, used for identifying particles with momentaabove 1 GeV/c. The velocity information determined from the CherenkovFig. 2. (a) Reconstructed tracks of charged particles from track segments in MVD(dots in the middle) and TPC (outer curves) detectors. (b) Identification of chargedparticles with different momenta and charge using the MVD, TPC and DIRC de-tectors. The Y axis represents the Cherenkov angle Θ. Plots are taken fromS. Spataro, INFN Torino.280 A. Biegunangle Θ = arccos(1/nβ) of a charged particle, propagating in the mediumwith the refractive index n, is combined with the momentum informationfrom the tracking detectors. Fig. 2(b) presents the identification of 104 par-ticles generated with the DPM and reconstructed by the MVD, TPC andDIRC detectors. A very good separation of charged particles, pi+, pi− andprotons, has been shown. The EMC detector, Fig. 3(a), is mainly used forphoton detection, but it also measures the deposited energy of electrons,positrons, muons and hadrons. Muons and hadrons lose only a certain frac-tion of their kinetic energy by ionisation processes, while e− and e+ deposittheir complete energy in the electromagnetic shower. This information canbe used for PID as illustrated in Fig. 3(b). The PANDA physics program reliesheavily on the capability to measure photons with high energy, position and,partly, time resolutions over a wide dynamic range. Thus, a highly granularEMC detector will be employed with fast PWO scintillators having a shortradiation length, X0 = 0.89 cm, a high energy resolution for photons andelectrons, 1.5%/√E(GeV) + 1.3%, and a very good time resolution, < 1 nsfor deposited energy above 80 MeV, obtained from a measurement with a re-alistic prototype equipped with a 1 cm2 Avalanche Photo Diode (APD) andSampling ADC readout [7]. In the final configuration the PWO crystals willbe equipped with two APDs of 1 cm2 size each, thus gaining an improvementfactor up to√2 for the energy and time resolution. Such photon detectorsare needed to cope with high count rates and with the proposed compactdesign of the TS.Fig. 3. (a) A 3D view of the electromagnetic calorimeter in the target spectrometerof PANDA. The barrel EMC (Barrel) and both, forward (FwEndCap) and back-ward (BwEndCap) EMC end-caps are shown. (b) E/p versus track momentum forelectrons and pions in the momentum range between 0.3GeV/c and 5GeV/c.Feasibility Studies for the PANDA Experiment at FAIR 2814. The charmonium hc (11P1) reconstructionThe invariant mass reconstruction requires a precise determination of theenergy deposited by photons and the opening angle between them, which canbe achieved only by a highly granulated calorimeter; the PANDA EMC fulfilsthis requirement. The EMC plays a crucial role in the reconstruction ofthe singlet (11P1) state of charmonium, hc, presented below. The followingdecay mode of the hc:p+ p→ hc → ηc + γ →(pi0 + pi0 + η)+ γ → 7γ (1)has been studied in this work. The chain (1) was generated with the Evt-Gen generator and the invariant mass analysis was done using the Rhopackage [1]. The two-photon invariant-mass spectra, reconstructed fromcombinations of seven photons in the final state are presented in Fig. 4.Peaks which stem from pi0 and η masses are found on top of a combinatorialbackground. A Gaussian function, describing the signal convoluted with asecond-order polynomial, describing the background, was fitted. Cuts witha window of 3σ around the pi0 and η mass peaks were applied in a fur-ther analysis and the background was reduced significantly. With thesecuts, a clean ηc invariant mass spectrum was extracted to finally identifythe hc state, as demonstrated in Fig. 5. The hc reconstruction efficiency,εReco, obtained from the presented analysis was found to be 26%. The ex-pected number of events to be measured during the PANDA experiment wasestimated taking into account the production cross-section, σp, which wascalculated from the Breit–Wigner formula at the resonance energy for theprocess: pp→ hc → ηc+γ [1]. Also, the total branching ratio for the processηc → pi0pi0η, BRηc→pi0pi0ηtot , was used. In the table on the right hand site ofFig. 4. The two-photon invariant mass spectra reconstructed in the EMC detectorfrom combinations of seven photons in the final state from chain (1). A Gaussianfit combined with a second-order polynomial is shown.282 A. BiegunParameters Eventsper dayσp 33 [nb]BRηc→pi0pi0ηtot 6.153× 10−3εReco 26 [%]t 1 [day]LHL 2×1032 [cm−2s−1] 931LHR 1031 [cm−2s−1] 47Fig. 5. Left: ηcγ invariant mass reconstructed after 3σ window cuts on pi0, η andηc masses. Right: Parameters used to calculate the collected number of events perday, expected to reveal the signal of charmonium hc. The calculated numbers ofmeasured events/day are presented in the lower part of the table.Fig. 5 the most important ingredients, which were used in the analysis, aresummarized. The calculation was done for two modes available for PANDA:the high luminosity mode, LHL, with σp/p ∼ 10−4, and the high resolutionmode, LHR, with σp/p ≤ 4 × 10−5 and the estimated numbers of collectedevents/day are presented in that table. The obtained numbers are by factorsof 5 and 10 larger for LHR and LHL, respectively, than for other decay modesof the charmonium hc state, such as hc → ηcγ → ΦΦγ (2), described in [1].This is mainly due to the total branching ratio BRηc→pi0pi0ηtot = 6.153× 10−3,which is one order of magnitude larger than the total branching ratio ofBRηc→ΦΦtot = 6.24 × 10−4. The disadvantage might be an insufficient back-ground suppression of the decay channel (1) compared to the channel (2).A complete background analysis of the competing channels as pp→ pi0pi0pi0and pp→ pi0pi0η is ongoing.5. Summary and conclusionsWith the PANDA detector a broad range of physics studies will be covered.The precise measurement of the momentum and position of a particle willbe possible using highly tuned tracking, PID and EMC sub-detectors. The11P1 state of charmonium is one of several benchmark channels studied forPANDA, where masses and widths will be measured precisely. Recently, thehc was studied in e+e− experiments (CLEO-c [8], BES3 [9]), but so-far onlyan upper limit for the total width, Γ < 1MeV, has been published. Inthe pp annihilation experiment, such as PANDA, the exact value of Γ will bemeasured. In this work we analysed the decay of the hc → ηcγ → pi0pi0η.Preliminary studies show that the observation of this channel is feasible andfurther investigations of its background are under way.Feasibility Studies for the PANDA Experiment at FAIR 283This work is supported by Veni-grant 680-47-120 from the NetherlandsOrganisation for Scientific Research (NWO), the University of Groningenand the Helmholtzzentrum für Schwerionenforschung GmbH (GSI), Darm-stadt.REFERENCES[1] http://www-panda.gsi.de; Technical Progress Report (2005); Physics Per-formance Report (2009) [arXiv:0903.3905v1].[2] [PANDA Collaboration] S. Spataro, J. Phys. 119, 032035 (2008).[3] http://root.cern.ch[4] http://fairroot.gsi.de[5] http://www.fluka.org[6] A. Capella et al., Phys. Rep. 236, 225 (1994).[7] M. Kavatsyuk et al., IEEE Nuclear Science Symposium and Medical ImagingConference, 25–31 Oct. 2009, Orlando, USA.[8] S. Dobbs et al., Phys. Rev. Lett. 101, 182003 (2008) [arXiv:0805.4599v1].[9] http://bes3.ihep.ac.cn

   University of GroningenFeasibility Studies for the PANDA Experiment at FAIRBiegun, A.; PANDA CollaborationPublished in:Acta Physica Polonica BIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2010Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Biegun, A., & PANDA Collaboration (2010). Feasibility Studies for the PANDA Experiment at FAIR. ActaPhysica Polonica B, 41(2), 277-283.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 07-06-2022Vol. 41 (2010) ACTA PHYSICA POLONICA B No 2FEASIBILITY STUDIES FOR THE PANDAEXPERIMENT AT FAIR∗A. Biegunfor the PANDA CollaborationKVI/University of Groningen, 9747 AA Groningen, The Netherlands(Received January 14, 2010)PANDA, the detector to study AntiProton ANnihilations at DArmstadt,will be installed at the future international Facility for Anti-proton and IonResearch (FAIR) in Darmstadt, Germany. The PANDA physics program isoriented towards the studies of the strong interaction and hadron struc-ture performed with the highest quality beam of anti-protons [1]. In thepreparation for PANDA experiments, large-scale simulation studies are beingperformed to validate the performance of all individual detector compo-nents and to advice on detector optimisation. The feasibility of the analysisstrategies together with the calibration methods are being studied. Simu-lations were carried out using the framework called PandaROOT [2], basedon ROOT and the Virtual Monte Carlo concept [3].PACS numbers: 13.25.Ft, 87.64.Aa, 01.50.hv, 29.40.Mc1. IntroductionWith the PANDA physics program various questions related to the prop-erties of the strong interaction will be answered. This experiment operatesin the transition region between the perturbative and the non-perturbativeQCD regimes and, thereby, will gain insight into the mechanism of hadronmass generation and quark confinement.The highest quality beam of anti-protons, in terms of intensity and reso-lution, is the key ingredient for the PANDA project. The momentum range ofanti-protons of 1.5–15 GeV/c gives access to a center-of-mass energy rangefrom 2.2–5.5 GeV/c2 in pp annihilations. The PANDA detector will measureprecisely momenta and scattering angles of both charged and neutral parti-cles of the reaction products to detect the complete spectrum of final statesrelevant for the PANDA physics cases.∗ Presented at the XXXI Mazurian Lakes Conference on Physics, Piaski, Poland,August 30–September 6, 2009.(277)278 A. Biegun2. The PandaROOT frameworkThe offline software for PANDA, PandaROOT, is an extension of theFairROOT [4] framework being designed for the FAIR project. The PandaROOTframework, being developed by the PANDA Collaboration, is being used forboth simulation and data analysis of the PANDA physics studies. It containstools adapted from high energy physics experiments, such as event gener-ators, to produce the reaction of interest and its decay chain, to generatethe background from pp annihilation or to study the pA collision. Also, var-ious tools allowing to test the reconstruction algorithm, and the completedigitization and reconstruction chain, and allowing to perform a detailedanalysis together with the full geometry model are included in this frame-work. PandaROOT is highly versatile and enables a user-friendly interface tovarious transport engines, like GEANT3, GEANT4 and Fluka [5].3. The PANDA setupTo enable a rich physics program with the PANDA detector, all componentshave to be carefully designed and tuned.The PANDA detector, with its compo-nents, is presented in Fig. 1 and consists of two parts, a Target Spectrometer(TS) and a Forward Spectrometer (FS). Precise tracking and Particle IDen-tification (PID) are crucial to measure momenta of particles with a gooddetection efficiency. This is achieved by exploiting a Micro-Vertex-Detector(MVD), Straw Tube Tracker (STT) or, alternatively Time Projection Cham-ber (TPC), six Drift Chambers (DC), a muon and Cherenkov (DIRC De-tection of Internally Reflected Cherenkov) detectors, marked in Fig. 1. Thehigh resolution Electro Magnetic Calorimeter (EMC) in the TS and the FS isFig. 1. The PANDA detection system.Feasibility Studies for the PANDA Experiment at FAIR 279particular important to detect photons in a very broad energy range, startingfrom a few tens of MeV up to several GeV, as expected in the reactions aimedfor PANDA. All sub-detectors together will cover nearly the full solid angle.A very high precision anti-proton beam, ∆p/p ∼ 10−4–10−5, together witha high luminosity, L ∼ 1031–1032 cm−2s−1, allow to measure very narrow,50–100 keV, mass states of charmonium and reactions with cross-sectionsdown to in the order of pb. The main requirements addressed to the track-ing devices are a good momentum resolution at the percent level and theability to handle high count rates. The MVD is the detector closest to theinteraction point. This tracking device for charged particles is essential fora very precise determination of secondary decay vertices of short-lived par-ticles. A spatial resolution below 100 µm is required and simulations showthat 11 µm can be achieved [1]. The MVD is surrounded by the STT or theTPC, which will be used for a main track reconstruction. The position reso-lution in x and y coordinates of about 150 µm and the resolution of 3mm inz direction is expected. The TPC or the STT will be combined with the sub-system consisting of Gas Electron Multiplier (GEM) detectors to performtracking in the FS at angles below 22◦. The GEMs have rate capabilitiesthousand times larger than achievable with drift chambers, therefore theycan handle a higher flux of particles. The generator for background reac-tions (DPM [6]) was used to generate events at the momentum of 3.6GeV/cand the reconstructed paths from the MVD combined with the TPC tracksare presented in Fig. 2(a). This graph shows a very good matching of tracksegments coming from these two detectors. One of the systems used for PIDin PANDA is the DIRC detector, used for identifying particles with momentaabove 1 GeV/c. The velocity information determined from the CherenkovFig. 2. (a) Reconstructed tracks of charged particles from track segments in MVD(dots in the middle) and TPC (outer curves) detectors. (b) Identification of chargedparticles with different momenta and charge using the MVD, TPC and DIRC de-tectors. The Y axis represents the Cherenkov angle Θ. Plots are taken fromS. Spataro, INFN Torino.280 A. Biegunangle Θ = arccos(1/nβ) of a charged particle, propagating in the mediumwith the refractive index n, is combined with the momentum informationfrom the tracking detectors. Fig. 2(b) presents the identification of 104 par-ticles generated with the DPM and reconstructed by the MVD, TPC andDIRC detectors. A very good separation of charged particles, π+, π− andprotons, has been shown. The EMC detector, Fig. 3(a), is mainly used forphoton detection, but it also measures the deposited energy of electrons,positrons, muons and hadrons. Muons and hadrons lose only a certain frac-tion of their kinetic energy by ionisation processes, while e− and e+ deposittheir complete energy in the electromagnetic shower. This information canbe used for PID as illustrated in Fig. 3(b). The PANDA physics program reliesheavily on the capability to measure photons with high energy, position and,partly, time resolutions over a wide dynamic range. Thus, a highly granularEMC detector will be employed with fast PWO scintillators having a shortradiation length, X0 = 0.89 cm, a high energy resolution for photons andelectrons, 1.5%/√E(GeV) + 1.3%, and a very good time resolution, < 1 nsfor deposited energy above 80 MeV, obtained from a measurement with a re-alistic prototype equipped with a 1 cm2 Avalanche Photo Diode (APD) andSampling ADC readout [7]. In the final configuration the PWO crystals willbe equipped with two APDs of 1 cm2 size each, thus gaining an improvementfactor up to√2 for the energy and time resolution. Such photon detectorsare needed to cope with high count rates and with the proposed compactdesign of the TS.Fig. 3. (a) A 3D view of the electromagnetic calorimeter in the target spectrometerof PANDA. The barrel EMC (Barrel) and both, forward (FwEndCap) and back-ward (BwEndCap) EMC end-caps are shown. (b) E/p versus track momentum forelectrons and pions in the momentum range between 0.3GeV/c and 5GeV/c.Feasibility Studies for the PANDA Experiment at FAIR 2814. The charmonium hc (11P1) reconstructionThe invariant mass reconstruction requires a precise determination of theenergy deposited by photons and the opening angle between them, which canbe achieved only by a highly granulated calorimeter; the PANDA EMC fulfilsthis requirement. The EMC plays a crucial role in the reconstruction ofthe singlet (11P1) state of charmonium, hc, presented below. The followingdecay mode of the hc:p+ p→ hc → ηc + γ →(π0 + π0 + η)+ γ → 7γ (1)has been studied in this work. The chain (1) was generated with the Evt-Gen generator and the invariant mass analysis was done using the Rhopackage [1]. The two-photon invariant-mass spectra, reconstructed fromcombinations of seven photons in the final state are presented in Fig. 4.Peaks which stem from π0 and η masses are found on top of a combinatorialbackground. A Gaussian function, describing the signal convoluted with asecond-order polynomial, describing the background, was fitted. Cuts witha window of 3σ around the π0 and η mass peaks were applied in a fur-ther analysis and the background was reduced significantly. With thesecuts, a clean ηc invariant mass spectrum was extracted to finally identifythe hc state, as demonstrated in Fig. 5. The hc reconstruction efficiency,εReco, obtained from the presented analysis was found to be 26%. The ex-pected number of events to be measured during the PANDA experiment wasestimated taking into account the production cross-section, σp, which wascalculated from the Breit–Wigner formula at the resonance energy for theprocess: pp→ hc → ηc+γ [1]. Also, the total branching ratio for the processηc → π0π0η, BRηc→π0π0ηtot , was used. In the table on the right hand site ofFig. 4. The two-photon invariant mass spectra reconstructed in the EMC detectorfrom combinations of seven photons in the final state from chain (1). A Gaussianfit combined with a second-order polynomial is shown.282 A. BiegunParameters Eventsper dayσp 33 [nb]BRηc→π0π0ηtot 6.153× 10−3εReco 26 [%]t 1 [day]LHL 2×1032 [cm−2s−1] 931LHR 1031 [cm−2s−1] 47Fig. 5. Left: ηcγ invariant mass reconstructed after 3σ window cuts on π0, η andηc masses. Right: Parameters used to calculate the collected number of events perday, expected to reveal the signal of charmonium hc. The calculated numbers ofmeasured events/day are presented in the lower part of the table.Fig. 5 the most important ingredients, which were used in the analysis, aresummarized. The calculation was done for two modes available for PANDA:the high luminosity mode, LHL, with σp/p ∼ 10−4, and the high resolutionmode, LHR, with σp/p ≤ 4 × 10−5 and the estimated numbers of collectedevents/day are presented in that table. The obtained numbers are by factorsof 5 and 10 larger for LHR and LHL, respectively, than for other decay modesof the charmonium hc state, such as hc → ηcγ → ΦΦγ (2), described in [1].This is mainly due to the total branching ratio BRηc→π0π0ηtot = 6.153× 10−3,which is one order of magnitude larger than the total branching ratio ofBRηc→ΦΦtot = 6.24 × 10−4. The disadvantage might be an insufficient back-ground suppression of the decay channel (1) compared to the channel (2).A complete background analysis of the competing channels as pp→ π0π0π0and pp→ π0π0η is ongoing.5. Summary and conclusionsWith the PANDA detector a broad range of physics studies will be covered.The precise measurement of the momentum and position of a particle willbe possible using highly tuned tracking, PID and EMC sub-detectors. The11P1 state of charmonium is one of several benchmark channels studied forPANDA, where masses and widths will be measured precisely. Recently, thehc was studied in e+e− experiments (CLEO-c [8], BES3 [9]), but so-far onlyan upper limit for the total width, Γ < 1MeV, has been published. Inthe pp annihilation experiment, such as PANDA, the exact value of Γ will bemeasured. In this work we analysed the decay of the hc → ηcγ → π0π0η.Preliminary studies show that the observation of this channel is feasible andfurther investigations of its background are under way.Feasibility Studies for the PANDA Experiment at FAIR 283This work is supported by Veni-grant 680-47-120 from the NetherlandsOrganisation for Scientific Research (NWO), the University of Groningenand the Helmholtzzentrum für Schwerionenforschung GmbH (GSI), Darm-stadt.REFERENCES[1] http://www-panda.gsi.de; Technical Progress Report (2005); Physics Per-formance Report (2009) [arXiv:0903.3905v1].[2] [PANDA Collaboration] S. Spataro, J. Phys. 119, 032035 (2008).[3] http://root.cern.ch[4] http://fairroot.gsi.de[5] http://www.fluka.org[6] A. Capella et al., Phys. Rep. 236, 225 (1994).[7] M. Kavatsyuk et al., IEEE Nuclear Science Symposium and Medical ImagingConference, 25–31 Oct. 2009, Orlando, USA.[8] S. Dobbs et al., Phys. Rev. Lett. 101, 182003 (2008) [arXiv:0805.4599v1].[9] http://bes3.ihep.ac.cn

PANDA, the detector to study AntiProton ANnihilations at DArmstadt, will be installed at the future international Facility for Anti-proton and Ion Research (FAIR) in Darmstadt, Germany. The PANDA physics program is oriented towards the studies of the strong interaction and hadron structure performed with the highest quality beam of anti-protons [1]. In the, preparation for PANDA experiments, large-scale simulation studies are being performed to validate the performance of all individual detector components and to advice on detector optimisation. The feasibility of the analysis strategies together with the calibration methods are being studied. Simulations were carried out using the framework called PandaROOT [2], based on ROOT and the Virtual Monte Carlo concept [3]

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