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The Large Hadron Collider (LHC) at CERN near Geneva is an accelerator designed to collide protons at a centre-of-mass energy of √s = 14 TeV. It is operational since November 2009 and has delivered collisions up to an energy of √s = 7 TeV in 2010. The LHCb experiment is one of the four major LHC experiments, together with ATLAS, CMS and ALICE. It is a single-arm forward spectrometer designed to study CP-violation and rare decays in the b-quark sector. The tracking system of the LHCb experiment is composed of the silicon Vertex Locator (VELO), the silicon Tracker Turicensis (TT), the dipole magnet, the silicon Inner Tracker (IT) and the straw-tube Outer Tracker (OT). The IT is covering the innermost acceptance region close to the beam-pipe, where the track multiplicity is highest (20% of the tracks for 1.5% of the acceptance). Two topics have been addressed in this doctoral thesis. The first part is dedicated to the IT commissioning phase. In particular the first version of the data-quality online monitoring is described. Several histograms and cluster maps have been developed, in order to watch the detector operation and ensure fast problem identification. The online monitoring allowed the identification of cosmic ray tracks which where used for a first spatial alignment. In September 2008 and June 2009, LHC injection tests from the SPS to the LHC ring were performed. Bunches of 2–5×109 protons were dumped onto a beam stopper (TED), producing a shower of secondary particles heading towards LHCb. These events were recorded by the LHCb detector and allowed a time-alignment of the IT up to a precision of 1 ns. The second part describes an analysis of a data sample corresponding to an integrated luminosity of 6.8 ± 1.0 μb-1 and recorded in 2009 from proton-proton collisions at a centre-of-mass energy of √s = 0.9 TeV. The double-differential V0 (KS, Λ and Λ) production cross-sections as a function of transverse momentum pT and rapidity y have been measured using only the tracking system of the experiment. A simple selection using an ad hoc geometrical variable based on the impact parameters of the daughters and mother particles has been developed. The results are compared with a few Monte Carlo (MC) generator tunings. They indicate that the KS production cross-section is mostly overestimated for pT < 0.4 GeV/c and underestimated for pT > 1 GeV/c for all considered models. For Λ and Λ, the production cross-section is mostly underestimated by all models for pT > 0.8 GeV/c. In addition, the data seem to indicate that the Λ/Λ ratio is smaller than predicted by the considered models.
Olivier Schneider, Aurelio Bay, Yi Zhang, Yi Wang, Guido Haefeli, Frédéric Blanc, Tatsuya Nakada, François Fleuret, Elena Graverini, Renato Quagliani, Federico Betti, Sebastian Schulte, Veronica Sølund Kirsebom, Jian Wang, Mingkui Wang, Zhirui Xu, Zheng Wang, Lei Zhang, Christoph Frei, Jessica Prisciandaro, Mark Tobin, Minh Tâm Tran, Niko Neufeld, Matthew Needham, Marc-Olivier Bettler, Michel De Cian, Greig Alan Cowan, Maurizio Martinelli, Vladislav Balagura, Liang Sun, Pietro Marino, Luca Pescatore, Mirco Dorigo, Xiaoxue Han, Liupan An, Federico Leo Redi, Chitsanu Khurewathanakul, Plamen Hristov Hopchev, Thibaud Humair, Maxime Schubiger, Hang Yin, Guido Andreassi, Violaine Bellée, Maria Vieites Diaz, Olivier Göran Girard, Axel Kuonen, Preema Rennee Pais, Pavol Stefko, Tara Nanut, Maria Elena Stramaglia, Tommaso Colombo, Vladimir Macko, Guillaume Max Pietrzyk, Evgenii Shmanin, Dipanwita Dutta, Yiming Li, Hans Dijkstra, Gerhard Raven, Peter Clarke, Frédéric Teubert, Victor Coco, Adam Davis, Paolo Durante, Yu Zheng, Anton Petrov, Maxim Borisyak, Chunhui Chen, Zhipeng Tang