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Determination of the Polarization Amplitudes and CP Asymmetries in B 0 → Φ K*(892)0 at Lhcb

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Determination of the Polarization Amplitudes and CP Asymmetries in B 0 → Φ K*(892)0 at Lhcb Determination of the polarization amplitudes and CP asymmetries 0 0 in B → φ K*(892) at LHCb THÈSE NO 6725 (2015) PRÉSENTÉE LE 23 OCTOBRE 2015 À LA FACULTÉ DES SCIENCES DE BASE LABORATOIRE DE PHYSIQUE DES HAUTES ÉNERGIES 1 PROGRAMME DOCTORAL EN PHYSIQUE ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE POUR L'OBTENTION DU GRADE DE DOCTEUR ÈS SCIENCES PAR Anh Duc NGUYEN acceptée sur proposition du jury: Prof. V. Savona, président du jury Dr M. T. Tran, Prof. A. Bay, directeurs de thèse Dr G. Cowan, rapporteur Prof. M.-C. Nguyen, rapporteur Prof. M. Q. TRAN, rapporteur Suisse 2015 ii iii Abstract The LHCb experiment is one of the large experiments installed around the LHC collider. Its aim is the study of CP violation and rare b-hadrons decays. This thesis addresses these two objectives. CP violation was found in 1964 in the decays of neutral kaons by J. H. Christenson, J. W. Cronin, V. L. Fitch, and R. Turlay. It was reconfirmed in 2001 in B meson systems by BaBar and Belle experiments. CP violation can be explained in the Standard Model (SM) using the Cabibbo-Kobayashi-Maskawa (CKM) matrix with three quark generations. 0 0 The B φK∗(892) is a rare flavour changing neutral decay which processes via the ! gluonic penguin diagram (b s transition). In SM, the predicted CP asymmetry is so ! small for this decay channel that any deviation from the SM value would signal \New Physics". 0 0 This decay is a pseudo-scalar (B ) decaying to vector mesons (φ and K∗(892) ) with spin-1. Conservation of angular momentum leads to three possible helicity states of the vector mesons which reflects into three amplitudes: these will be unravelled by an + 0 + angular analysis of the final-state particles, φ K K− and K∗(892) K π−. ! ! 0 0 An angular analysis of the decay B φK∗(892) is reported based on data of pp collision ! at a centre-of-mass energy of ps = 8 TeV and corresponding to an integrated luminosity 1 of 2.0 fb− , with the LHCb detector. The analysis includes both the contribution of + + K π− and K K−S{waves and a significant contribution from them is found. The measurements of P{wave amplitudes and phases is consistent with the one of BaBar and Belle experiments, but are much more precise. Our results also confirm the previous 1 LHCb one bay on a statistics corresponding to an integrated luminosity of 1.0 fb− . The longitudinal polarization fraction f for the P{wave is measured to be 0:499 L ± 0:011(stat) 0:010(syst). The differences between the polarization amplitudes and phases ± 0 0 0 0 of the B φK∗(892) and B φK∗(892) decays have been derived as well as the ! ! triple-product asymmetries. The results show no evidence for direct CP violation. Keywords: LHCb experiment, CKM matrix, CP violation, flavour physics, charmless B decays. iv v R´esum´e L'exp´erienceLHCb est l'une des grandes exp´eriencesinstall´eessur l'anneau du colli- sionneur LHC. Le but de LHCb est d'´etudierla violation de la sym´etrie CP et les d´esint´egrations rares de hadrons comportant un quark b. La violation de CP a ´et´ed´ecouverte en 1964 dans les d´esint´egrationsdes kaons neutres par J.H. Christenson, J.W. Cronin, V.L. Fitch et R. Turlay. Elle a ´et´econfirm´eeen 2001 dans le syst`emedes m´esonsB aupr`esdes exp´eriencesBaBar et Belle. Dans le cadre du mod`ele standard (MS), la violation de CP peut ^etreexpliqu´eepar la th´eoriede Cabibbo, Kobayashi et Maskawa (CKM) faisant intervenir trois g´en´erationsde quarks. 0 0 La d´esint´egration B φK∗(892) est une d´esint´egrationrare, neutre, changeant la ! saveur des quarks et proc`edevia un diagramme pingouin pour la transition b s. Dans ! le MS, l'assym´etrie CP pour cette d´esint´egrationest pr´editecomme ´etant faible et toute d´eviationde cette pr´ediction signalerait la pr´esenced'une \Nouvelle Physique". Dans cette d´esint´egration,un m´esonpseudo-scalaire (le B0) se d´esint`egreen deux m´esons 0 vectoriels (les m´esons φ et K∗(892) ). La conservation du moment angulaire conduit `atrois ´etatsd'h´elicit´epossibles qui se retrouvent dans trois amplitudes de transition, + lesquelles peuvent ^etreobtenues par une analyse angulaire de l'´etatfinal φ K K− et ! 0 + K∗(892) K π−. ! Dans ce m´emoire,nous pr´esentons une analyse angulaire de la d´esint´egration B0 ! 0 φK∗(892) bas´eesur les donn´eesenregistr´ees`al'exp´erience LHCb dans les collisions pp `a une ´energiedans le centre de masses de ps = 8 TeV pour une luminosit´eint´egr´eede 1 + + 2.0 fb− . Dans l'analyse, les contributions des ondes S des syst`emes K π− et K K− sont prises en compte et nous avons trouv´eque leur contribution est significative. Les amplitudes et les phases des ondes P trouv´eessont consistantes avec celles obtenues des exp´eriencesBaBar et Belle. Par ailleurs, nos r´esultatsconfirment aussi les r´esultats pr´ec´edents de LHCb bas´essur une statistique moins importante et correspondante `aune 1 luminosit´ede 1.0 fb− . La proportion de l'amplitude de polarisation longitudinale fL dans l'onde P est de 0.499 0.011 (stat) 0.010 (syst), confirmant le d´esaccordobserv´epar les exp´eriences ± ± pr´ec´edentes avec l'attente na¨ıve d'une dominance de l'amplitude de polarisation longitu- vi dinale. L'assym´etrie CP brute et les assym´etriesdans les produits mixtes ont aussi ´et´e d´eduitesde l'analyse angulaire; les r´esultatsne montre pas d'´evidencede la violation directe de CP . Mots clefs: exp´erienceLHCb, matrice CKM, violation de CP , physique de la saveur, d´esint´egration hadronique du m´eson B sans apparition de charme. vii Tóm t­t luªn ¡n LHCb là mët trong nhúng th½ nghi»m lớn ho¤t động tr¶n m¡y gia tèc LHC. Mục đích cõa th½ nghi»m là nghi¶n cùu vi ph¤m đối xùng CP và c¡c k¶nh ph¥n r¢ hi¸m cõa hadron b. Trong b£n luªn ¡n này s³ tr¼nh bày hai v§n đề n¶u tr¶n. Vi ph¤m đối xùng CP được ph¡t hi»n n«m 1964 trong k¶nh ph¥n r¢ kaon trung háa bởi J. H. Christenson, J. W. Cronin, V. L. Fitch, and R. Turlay. Hi»n tượng tr¶n được kh¯ng định trong h» meson B bởi c¡c th½ nghi»m BaBar và Belle vào n«m 2001. Vi ph¤m đối xùng CP có thº được gi£i th½ch trong khuôn khê Mô h¼nh Chu©n b¬ng c¡ch sû dụng ma trªn CKM với ba th¸ h» quark. 0 0 K¶nh B φK∗(892) là qu¡ tr¼nh ph¥n r¢ trung háa hi¸m, trong đó “flavour” được ! thay đổi (chuyºn đổi b s) thông qua gi£n đồ Feynman gluon. ! Theo Mô h¼nh Chu©n, gi¡ trị cõa vi ph¤m đối xùng CP được ti¶n đoán cho k¶nh này nhỏ đến mùc mà b§t cù độ l»ch nào ra khỏi gi¡ trị cõa Mô h¼nh Chu©n cũng được coi là thông tin v· Vªt lý mới (New Physics). Trong k¶nh được nghi¶n cùu, meson gi£ vô hướng (B0) ph¥n r¢ thành hai vector meson 0 (φ và K∗(892) ) có spin-1. Do b£o toàn mômen xung lưñng d¨n đến ch¿ tồn t¤i ba tr¤ng th¡i helicity cõa c¡c vector meson. Bi¶n độ cõa ba tr¤ng th¡i helicity tr¶n s³ được x¡c + định thông qua ph¥n t½ch ph¥n bè góc cõa c¡c h¤t con trong hai ph¥n r¢, φ K K− ! 0 + và K∗(892) K π−. ! 0 0 K¸t qu£ nghi¶n cùu ph¥n bè góc cõa k¶nh B φK∗(892) thu được dựa tr¶n vi»c ph¥n ! t½ch sè li»u va ch¤m pp với n«ng lượng trong h» khèi t¥m ps = 8 TeV được ghi nhªn bởi 1 detector LHCb; sè li»u tr¶n tương ùng với Luminosity têng cëng là 2.0 fb− . Qu¡ tr¼nh + ph¥n t½ch có t½nh đến và cho th§y sự đóng góp rã r»t tø sóng S cõa tê hñp K π− và + K K−. C¡c bi¶n độ và pha ph¥n cực thu được tø sóng P trong luªn ¡n này phù hñp với k¸t qu£ cõa hai th½ nghi»m BaBar và Belle nhưng với độ ch½nh c¡c cao hơn nhi·u. Tỷ sè ph¥n cực dọc fL cho sóng P nhªn gi¡ trị 0:499 0:011(stat) 0:010(syst). Sự sai kh¡c ± ± 0 0 0 0 giúa bi¶n độ và pha ph¥n cực trong hai ph¥n r¢ B φK∗(892) và B φK∗(892) ! ! được x¡c định cũng như b§t đối xùng cõa t½ch bë ba (triple-product asymmetries). C¡c k¸t qu£ cho th§y không có b¬ng chùng rã r»t cõa vi ph¤m đối xùng CP trực ti¸p. Tø khóa: Th½ nghi»m LHCb, ma trªn CKM, vi ph¤m đối xùng CP , Vªt lý “flavour”, ph¥n r¢ B meson.
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