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This thesis presents a study of the flavour-changing neutral-current radiative B+ to K+pi-pi+gamma decay performed using 3 fb-1 of data collected with the LHCb detector in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The study of radiative decays with three scalar hadrons in the final state gives access to the polarisation of the photon, one of the very few predictions of the Standard Model of particle physics that has not been precisely tested experimentally and that is sensitive to new physics effects in the b to s gamma penguin loop. Nearly 14 000 signal events, containing all possible intermediate resonances with a K+pi-pi+ final state in the [1,2] GeV/c2 mass interval, are reconstructed and selected in the data sample. The distribution of the angle of the photon direction with respect to the plane defined by the final-state hadrons in their rest frame is studied in intervals of K+pi-pi+ mass and the asymmetry between the number of signal events with the photon emitted on each side of the plane is obtained. The first direct observation of the photon polarisation in the b to s gamma transition is reported with a significance of 5.2 sigma. The contributions of the resonances populating the studied K+pi-pi+ mass interval are then disentangled by means of a three-dimensional amplitude analysis of the invariant squared masses of the K+pi-pi+, K+pi- and pi+pi- systems, integrating out the angular dimensions that describe the direction of the photon. The results of this analysis are the most precise ever obtained in this decay channel, allowing for an accurate description of the decay modes of the intermediate resonances and their interference patterns: the K1(1270)+ to K+rho(770)0 channel has been found to be the dominant kaon resonance decay mode, followed by K1(1270)+ to K(892)0pi+; the fraction of the K1(1270)+ decaying to K(1430)0pi+ has been found to be much lower than the world average, analogously to already existing experimental and theoretical studies; a significant interference between the K1(1270)+ and K1(1400)+ kaon resonances decay modes is observed. Based on the results of these studies, the full five-dimensional amplitude analysis of the invariant masses and the angular variables is introduced, aiming at the first determination of a numerical value for the polarisation of the photon.
Jian Wang, Matthias Finger, Qian Wang, Yiming Li, Matthias Wolf, Varun Sharma, Yi Zhang, Konstantin Androsov, Jan Steggemann, Xin Chen, Rakesh Chawla, Matteo Galli, Anna Mascellani, João Miguel das Neves Duarte, Tagir Aushev, Tian Cheng, Yixing Chen, Werner Lustermann, Andromachi Tsirou, Alexis Kalogeropoulos, Andrea Rizzi, Ioannis Papadopoulos, Paolo Ronchese, Hua Zhang, Siyuan Wang, Tao Huang, David Vannerom, Michele Bianco, Sebastiana Gianì, Sun Hee Kim, Kun Shi, Abhisek Datta, Federica Legger, Gabriele Grosso, Ji Hyun Kim, Donghyun Kim, Zheng Wang, Sanjeev Kumar, Wei Li, Yong Yang, Geng Chen, Ajay Kumar, Ashish Sharma, Georgios Anagnostou, Joao Varela, Csaba Hajdu, Muhammad Ahmad, Ioannis Evangelou, Milos Dordevic, Meng Xiao, Sourav Sen, Xiao Wang, Kai Yi, Jing Li, Rajat Gupta, Zhen Liu, Hui Wang, Seungkyu Ha, Long Wang, Pratyush Das, Anton Petrov, Xin Sun, Valérie Scheurer, Giovanni Mocellin, Muhammad Ansar Iqbal, Lukas Layer
Jian Wang, Matthias Finger, Qian Wang, Yiming Li, Matthias Wolf, Varun Sharma, Yi Zhang, Konstantin Androsov, Jan Steggemann, Leonardo Cristella, Xin Chen, Davide Di Croce, Rakesh Chawla, Matteo Galli, Anna Mascellani, João Miguel das Neves Duarte, Tagir Aushev, Lei Zhang, Tian Cheng, Yixing Chen, Werner Lustermann, Andromachi Tsirou, Alexis Kalogeropoulos, Andrea Rizzi, Ioannis Papadopoulos, Paolo Ronchese, Hua Zhang, Siyuan Wang, Tao Huang, David Vannerom, Michele Bianco, Sebastiana Gianì, Sun Hee Kim, Kun Shi, Wei Shi, Abhisek Datta, Jian Zhao, Federica Legger, Gabriele Grosso, Ji Hyun Kim, Donghyun Kim, Zheng Wang, Sanjeev Kumar, Wei Li, Yong Yang, Geng Chen, Ajay Kumar, Ashish Sharma, Georgios Anagnostou, Joao Varela, Csaba Hajdu, Muhammad Ahmad, Ekaterina Kuznetsova, Ioannis Evangelou, Muhammad Shoaib, Milos Dordevic, Meng Xiao, Sourav Sen, Xiao Wang, Kai Yi, Jing Li, Rajat Gupta, Zhen Liu, Muhammad Waqas, Hui Wang, Seungkyu Ha, Long Wang, Pratyush Das, Miao Hu, Anton Petrov, Xin Sun, Xin Gao, Chen Chen, Valérie Scheurer, Giovanni Mocellin, Muhammad Ansar Iqbal, Lukas Layer