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Exclusive Production in Pp and Pbpb Collisions at the Lhcb Experiment / Luiz Gustavo Silva De Oliveira

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Exclusive Production in Pp and Pbpb Collisions at the Lhcb Experiment / Luiz Gustavo Silva De Oliveira UNIVERSIDADE FEDERAL DO RIO DE JANEIRO INSTITUTO DE F´ISICA Exclusive production in pp and PbPb collisions at the LHCb experiment Luiz Gustavo Silva de Oliveira Ph.D. Thesis presented to the Graduate Program in Physics of the Institute of Physics of the Federal University of Rio de Janeiro - UFRJ, as part of the requirements to the obtainment of the title of Doctor in Sciences (Physics). Advisor: Murilo Santana Rangel Co-advisor: Erica Ribeiro Polycarpo Macedo CERN-THESIS-2019-058 26/04/2019 Rio de Janeiro June/2019 CIP - Catalogação na Publicação Oliveira, Luiz Gustavo Silva de O48e Exclusive production in pp and PbPb collisions at the LHCb experiment / Luiz Gustavo Silva de Oliveira. -- Rio de Janeiro, 2019. 124 f. Orientador: Murilo Santana Rangel. Coorientadora: Erica Ribeiro Polycarpo Macedo. Tese (doutorado) - Universidade Federal do Rio de Janeiro, Instituto de Física, Programa de Pós Graduação em Física, 2019. 1. LHCb. 2. Produção exclusiva. 3. Seção de choque. 4. Eletrodinâmica Quântica. 5. Cromodinâmica Quântica. I. Rangel, Murilo Santana, orient. II. Macedo, Erica Ribeiro Polycarpo, coorient. III. Título. Elaborado pelo Sistema de Geração Automática da UFRJ com os dados fornecidos pelo(a) autor(a), sob a responsabilidade de Miguel Romeu Amorim Neto - CRB-7/6283. iv Resumo Produ¸c~aoexclusiva em colis~oes pp e PbPb no experimento LHCb Luiz Gustavo Silva de Oliveira Orientador: Murilo Santana Rangel Coorientadora: Erica Ribeiro Polycarpo Macedo Resumo da Tese de Doutorado apresentada ao Programa de P´os-Gradua¸c~ao em F´ısicado Instituto de F´ısicada Universidade Federal do Rio de Janeiro - UFRJ, como parte dos requisitos necess´arios`aobten¸c~aodo t´ıtulode Doutor em Ci^encias(F´ısica). O experimento LHCb ´eum dos quatro principais detectores instalados ao redor dos pontos de colis~aodos feixes acelerados pelo LHC. Inicialmente o LHCb foi idealizado para o estudo de m´esons B e D a fim de esclarecer a viola¸c~aoda simetria CP . Entretanto, este detector se mostrou tamb´embastante eficaz no estudo de processos de produ¸c~ao exclusiva (CEP). Nesta tese apresentamos duas medidas de se¸c~aode choque de processos de produ¸c~aoexclusiva a partir dos dados coletados no LHCb durante os anos de 2011, 2012 e 2015. A se¸c~aode choque de produ¸c~aoeletromagn´eticade dim´uons em colis~oes pp p ´erealizada para duas energias no referencial do centro de massa: s = 7 TeV com dados p de 2011 e s = 8 TeV com dados de 2012. O estudo da produ¸c~aofotonuclear coerente de p J= em colis~oesPbPb com uma energia sNN = 5 TeV no centro de massa ´erealizado com dados coletados durante Novembro e Dezembro de 2015. Palavras-chave: Se¸c~aode choque, Produ¸c~aoexclusiva, Cromodin^amicaQu^antica, Eletrodin^amicaQu^antica, LHCb, Pomeron. v Abstract Exclusive production in pp and PbPb collisions at the LHCb experiment Luiz Gustavo Silva de Oliveira Advisor: Murilo Santana Rangel Co-advisor: Erica Ribeiro Polycarpo Macedo Abstract da Tese de Doutorado apresentada ao Programa de P´os-Gradua¸c~ao em F´ısicado Instituto de F´ısicada Universidade Federal do Rio de Janeiro - UFRJ, como parte dos requisitos necess´arios`aobten¸c~aodo t´ıtulode Doutor em Ci^encias(F´ısica). The LHCb experiment is one of the four main detectors installed around the points where beams collide after accelerated by LHC. Initially the LHCb was designed to study B and D mesons in order to elucidate the CP violation mechanism. However, this detector turned out fairly effective to study central exclusive production (CEP). Two cross-section measurements performed using the data collected during the years of 2011, 2012 and 2015 are described in this thesis. The cross-section of dimuon electromagnetic production is p performed with pp collisions at two center-of-mass energies: s = 7 TeV with 2011 data p and s = 8 TeV with 2012 data. The study of coherent photonuclear production of p J= at a nucleon-nucleon center-of-mass energy sNN = 5 TeV is performed with PbPb collisions collected during November and December of 2015. Keywords: Cross-section, Exclusive production, Quantum Chromodynamics, Quan- tum Electrodynamics, LHCb, Pomeron. vi Acknowledgements I would like to thank God for giving me the opportunity to study and learn the nature He created. It is a pleasure and an honor. I thank my wife for all unconditional support and love. Sometimes I think I don't deserve it so much but I am really grateful for having it in my life. I thank my parents for giving me all the help needed during the hard times and beyond. You are my heroes! I am very grateful to my advisors. Murilo and Erica showed me many times how a true researcher behaves. Your support and guidance were fundamental. I could not reach this day without both of you, literally. I thank the staff and professors of Physics Institute of UFRJ. It was a 11-years journey since the undergraduation admission and through all these years I always found help and support for bureaucracy and the doubts about courses subjects. Last but not least I thank CAPES for all the financial support. vii Contents Contents vii List of figures viii List of tables ix 1 Introduction1 2 Theoretical aspects and previous measurements4 2.1 Strong force...................................5 2.2 Central exclusive production in pp collisions................. 10 2.3 Photonuclear production in PbPb collisions.................. 14 3 LHC machine and LHCb detector 21 3.1 Large Hadron Collider............................. 21 3.2 LHCb detector................................. 23 3.2.1 Vertex detector system......................... 25 3.2.2 Magnet................................. 27 3.2.3 Tracking system............................. 30 3.2.4 Particle identification.......................... 37 3.2.5 Calorimeters............................... 38 3.2.6 Muon system.............................. 40 3.2.7 Trigger.................................. 43 viii 3.2.8 Data storage............................... 46 3.2.9 HeRSCheL............................... 48 4 Cross-section measurement of the exclusive production of muon pairs in pp collisions 53 4.1 Method..................................... 53 4.2 Samples..................................... 54 4.2.1 Simulation samples........................... 55 4.3 Selection..................................... 56 4.4 Selection efficiency............................... 59 4.5 Integrated luminosity.............................. 62 4.6 Determination of the yield of CEP...................... 62 4.7 Cross-section measurement........................... 63 4.8 Conclusions................................... 65 5 Cross-section measurement of J= coherent production in PbPb colli- sions 66 5.1 Analysis Strategy................................ 66 5.2 Samples..................................... 68 5.3 Selection..................................... 68 5.3.1 Trigger selection............................ 69 5.3.2 Offline Selection............................. 69 5.4 Selection efficiency............................... 71 5.5 Signal extraction................................ 74 5.6 Results...................................... 76 5.6.1 Systematic uncertainties........................ 77 5.6.2 Comparison to theory predictions................... 79 5.7 Updated measurement............................. 80 ix 5.7.1 HeRSCheL requirement........................ 80 5.7.2 HeRSCheL selection efficiency..................... 81 5.7.3 Updated cross-section measurement.................. 90 6 Conclusion 98 x List of Figures 2.1 A chart with all six quarks and their respective mass, electrical charges and spins [19]. ........................................6 2.2 The annihilation of e+e− through a virtual photon into qq¯ pair. .........8 2.3 Examples of exclusive processes in proton-proton scatterings......... 10 2.4 Integrated photon flux as given by the equivalent photon approximation, for the elastic, the single- and the double-dissociative proton case. The elastic contri- 2 2 bution is simulated using a maximal momentum transfer Qmax = 2 GeV , while 2 2 the dissociative cases use Qmax = 300 GeV . Figure extracted from reference [29]. 12 2.5 Comparison of the ratios of measured (red points) and predicted (solid green lines) cross-sections to the uncorrected EPA calculations (black dashed line). Results for the muon and electron channels are also compared with a similar CMS measurement [33]. The inner red error bar represents the statistical error, and the blue bar represents the total error on each measurement. The yellow band represents the theoretical uncertainty of 1:8% (1:7%) on the predicted (uncorrected EPA) cross-sections, assumed to be uniform in the phase space of the measurements [34]. .............................. 13 xi 2.6 The exclusive γγ ! µ+µ− differential fiducial cross-section measurements as a function of dimuon invariant mass. (b) Comparison of the ratios of mea- sured and predicted cross-sections to the bare EPA calculations as a function of the average dimuon invariant mass scaled to the pp center-of-mass energy used. Data (markers) are compared to various predictions (lines). Full circle markers represent the four mass points presented in [35], while open circle, up-triangle and down-triangle depict the previous results obtained with mµ+µ− > 11:5 GeV, mµ+µ− > 20 GeV and mµ+µ− > 45 GeV requirements on the dimuon invariant mass. The inner error bars represent the statistical uncertainties, and the outer bars represent the total uncertainty in each measurement. The yellow bands represent the theoretical uncertainty in the predictions. The bottom panel in (a) shows
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