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Monte Carlo Simulations of D-Mesons with Extended Targets in the PANDA Detector

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Monte Carlo Simulations of D-Mesons with Extended Targets in the PANDA Detector UPTEC F 16016 Examensarbete 30 hp April 2016 Monte Carlo simulations of D-mesons with extended targets in the PANDA detector Mattias Gustafsson Abstract Monte Carlo simulations of D-mesons with extended targets in the PANDA detector Mattias Gustafsson Teknisk- naturvetenskaplig fakultet UTH-enheten Within the PANDA experiment, proton anti-proton collisions will be studied in order to gain knowledge about the strong interaction. One interesting aspect is the Besöksadress: production and decay of charmed hadrons. The charm quark is three orders of Ångströmlaboratoriet Lägerhyddsvägen 1 magnitude heavier than the light up- and down-quarks which constitue the matter we Hus 4, Plan 0 consist of. The detection of charmed particles is a challenge since they are rare and often hidden in a large background. Postadress: Box 536 751 21 Uppsala There will be three different targets used at the experiment; the cluster-jet, the untracked pellet and the tracked pellet. All three targets meet the experimental Telefon: requirements of high luminosity. However they have different properties, concerning 018 – 471 30 03 the effect on beam quality and the determination of the interaction point. Telefax: 018 – 471 30 00 In this thesis, simulations and reconstruction of the charmed D-mesons using the three different targets have been made. The data quality, such as momentum Hemsida: resolution and vertex resolution has been studied, as well as how the different targets http://www.teknat.uu.se/student effect the reconstruction efficiency of D-meson have been analysed. The results are consistent with the results from a similar study in 2006, but provide additional information since it takes the detector response into account. Furthermore, a new target distribution have been implemented in the software package. This is the first results obtained from a cylindrical target distribution. The results are very important for PANDA since they show the limitations of different target types regarding the possibilities to reduce background. Simulations with the new target distribution have been made for all three targets and the results are presented. Handledare: Karin Schönning Ämnesgranskare: Tord Johansson Examinator: Tomas Nyberg ISSN: 1401-5757, UPTEC F 16016 Populärvetenskaplig sammanfattning Den starka kraften är den kraft som binder ihop kvarkar till partiklar, s.k. hadroner. Hadroner delas in i två grupper; Baryoner, som består av tre kvarkar, och mesoner, som består av två kvarkar. Hadronfysik studerar således hur den starka kraften växelverkar mellan olika kvarkar. Teorin bakom den starka kraften kallas QCD (Quantum ChromoDynamics) och den beskriver hur kvarkar och gluoner växelverkar. Teorin beskriver växelverkan mellan kvarkar och gluoner väl vid höga energier, då kopplingskonstanten är låg och man kan använda sig utav störningsteorier för att beskriva kvark- gluon växelverkan. Vid lägre energier så blir kopplingskonstanten större, man kan inte längre använda sig utav störningsteorier för att beskriva vad som händer. Detta är ett mindre känt område inom fysiken, man hoppas att forskningsprojektet PANDA kommer lösa några av de frågeställningar man har om den staka kraften och samtidigt öka förståelsen om den. I Darmstadt, Tyskland ligger forskningscentrumet för Heavy Ion Research (GSI). Man håller nu på att utöka GSI med Facility for Antiproton and Ion Research (FAIR), där PANDA detektorn kommer att vara ett av de viktigaste projekten för att utföra hadronfysikexperiment. Projektet är en kollaboration mellan ca 20 länder och mer än 500 forskare världen över. PANDA, antiProton Annhilation at Darmstadt, kommer att studera kollisioner mellan protoner och antiprotoner. Strålmålsmaterialet som kommer att användas i de flesta experimenten kommer att vara väte, d.v.s. protoner, men även tyngre gaser kan komma att användas. De strålmål som kommer att användas i PANDA-experimenten är: kluster jet och pelletar. Kluster jet skapas då man använder nedkyld vätgas som leds genom vakuum via ett munstycke, när gasen passerar munstycket så kyls den ner adiabatiskt och kommer att skapa atomer/molekyler som formar en jet av klusters. Pelletar skapas då man använder flytande väte som passerar ett vibrerande munstycke som skapar droppar av det flytande vätet. Dropparna fryser till fast form genom att passera vakuum och pelletar har bildats. I detta arbete har simuleringar med antiproton – proton kollisioner utförts, fokus har legat på reaktionen . sönderfaller inom 10^-23s, vilket kan ses som direkt, till D mesoner. D mesoner har en livslängd på ca 1040 *10^-15s, vilket motsvarar att de färdas ca 0.3 mm innan de sönderfaller. Alltså kan man skilja på när sönderfaller och när D mesonerna sönderfaller. Eftersom överlappet mellan antiprotonstrålen och strålmålet utgör en volym, en så kallad interaktions volym där kollisionen äger rum, så är det intressant att studera om D mesonerna sönderfaller innanför volymen eller utanför. Då detta har stor inverkan på hur väl man kan rekonstruera sönderfallskedjan. 2006 så gjordes en likande studie av Örjan Nordhage, där han visade genom simuleringar hur stor andel av de simulerade D mesonerna som skulle sönderfalla utanför en given interaktions volym. Detta gjordes med beräkningar för rörelsemängd för de olika partiklarna och med beräkningar av sönderfallslängd. I detta arbete så har samma simulationer genomförts, men här har även detektorns upplösning tagits med. Det har även gjorts jämförelser, med sluttillståndspartiklarna, hur datakvalitén påverkas av valt strålmål. Det har även gjorts en första studie med en cylindrisk interaktions volym, då man tidigare använde sig utav en gaussisk distribution av antiprotonstrålen. Här har en cirkulär distribution av antiproton strålen använts för att se hur detta påverkar hur många D mesoner som kommer att sönderfalla utanför den givna interaktionsvolymen. Resultaten från 2006 överensstämmer väl med de resultat som gjorts i denna studie, när man även tar med detektorns upplösning i simuleringarna. Det är ingen signifikant skillnad i datakvalitén mellan de olika strålmålen. Varken mellan upplösningen i rörelsemängd eller i rekonstruktions effektivitet. Resultaten från simuleringar med en cylindrisk interaktions volym visar att man kan välja en volym där 20 % av D mesonerna sönderfaller utanför volymen. Medans för en klusterjet så ligger värdet endast på 8 %. Acknowledgements First I would like to pay most gratitudes to Tord Johansson and Karin Sch¨onning, for letting me do this project at the Hadron division at Uppsala University. Many thanks to my supervisor Karin, for always have time to answer questions when I ran into trouble spots. With all the help with the report, regarding structure and for through reading. Also for letting me go to the FAIR facility in Darmstadt, I have learned so much during the work of this thesis. I would also like to thank Hans Carl´enfor your discussions regarding targets and for showing me the pellet at TSL. Finally, I want to express my most profound gratitude to Louise for always supporting me. I will always be grateful for having you in my life. i Contents Acknowledgementsi Contents ii List of Figuresv List of Tables vii Abbreviations ix 1 Aim of this thesis1 2 Introduction3 2.1 Subatomic physics and the Standard Model.............3 2.1.1 Quarks and Leptons......................4 2.1.2 Fundamental forces.......................5 2.2 Spin, Parity and Charge conjugation.................6 2.3 Hadrons.................................8 2.4 Charmonium.............................. 10 2.5 D-meson/ Open Charm......................... 11 2.6 Aim of this thesis............................ 11 2.7 Curiosity driven research........................ 11 3 The PANDA Experiment 13 3.1 Introduction............................... 13 3.2 The PANDA Physics Program..................... 14 3.2.1 Charmonium spectroscopy................... 14 3.2.2 Electromagnetic structure of baryons............. 15 3.2.3 Baryon spectroscopy and hyperon physics.......... 16 3.2.4 Electroweak physics....................... 16 3.2.5 Hypernuclear studies...................... 16 3.3 The Target Spectrometer........................ 17 3.3.1 MVD............................... 17 3.3.2 STT............................... 18 3.3.3 GEM............................... 18 ii Contents iii 3.3.4 Particle identification detectors................ 19 3.3.5 The Electromagnetic Calorimeter............... 20 3.4 Muon detector.............................. 21 3.5 Forward Spectrometer......................... 21 3.5.1 Forward Trackers........................ 21 3.5.2 Forward Particle ID....................... 21 3.5.3 Forward Electromagnetic Calorimeter............. 22 3.5.4 Forward muon detector..................... 22 3.6 Targets.................................. 22 3.6.1 The Pellet Target........................ 24 3.6.1.1 The Pellet TRacking system............. 24 3.6.2 The Cluster-jet target..................... 25 4 Motivation for this work 27 4.1 Motivation................................ 27 4.2 Previous study............................. 28 4.2.1 Particle decay length...................... 29 4.3 This work................................ 31 5 Software tools 32 5.1 PandaRoot............................... 32 5.1.1 Simulation............................ 33 5.1.2 Digitization........................... 33 5.1.3 Reconstruction......................... 33 5.1.4 Particle Identification...................... 34 6 Analysis 35 6.1 Physics Reaction............................ 35 6.2 Input to simulations: Extended targets
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