Abstract

The LHCb Experiment -> LHCb	The LHCb experiment will take place at the future LHC accelerator at CERN and will start in 2006. It is a forward single-arm spectrometer dedicated to precision measurements of CP violation and rare decays in the b quark sector. Recent experimental results have shown that CP violation is large in this sector. In the Standard Model, CP violation arises via the complex phase of the 3x3 CKM quark mixing matrix. The LHCb experiment will test the unitarity of this matrix by measuring in several theoretically unrelated ways all angles and all sides of the unitarity triangle. This will allow to over-constrain the model and - hopefully - to exhibit inconsistencies which will be a signal of physics beyond the Standard Model.
Rare b → lls,d Decays -> Rare B Decays	This thesis presents the sensitivity of the LHCb experiment to the recently observed flavour changing neutral current decays b → lld,s. Comparing the inclusive branching ratios of the B → μμXs and B → μμXd decays allows to extract the CKM matrix elements ratio Vtd/Vts. This constrains the length of the Rt side - opposite to gamma - of the unitarity triangle. We present an event generator for these decays and assess the sensitivity of the LHCb experiment to these branching ratios using the full Geant-based simulation of the detector. We find that the relative statistical uncertainty on the Vtd/Vts ratio will be 11.5 (+2.8,-3.2)% after one year of data taking (2 fb-1) assuming Vtd/Vts)2=1/30. Over the whole allowed range of this ratio, the limit of 5% statistical uncertainty can be reached in less than 10 years of data taking. This makes this way of extracting this ratio the most precise available at LHC. Because rare semileptonic decays occur via loop and penguin diagrams they are very sensitive to physics beyond the Standard Model. Several observables using inclusive or exclusive channels are discussed and the physics sensitivity of the LHCb experiment presented. The most promising is the measurement of the dilepton mass for which the forward-backward charge asymmetry vanishes in the B → μμK* decay. This allows to extract the ratio of two Wilson coefficients for which precise SM and supersymmetry predictions exist.
The VeLo	The LHCb experiment is presently finishing its R&D. We have participated to the development of the vertex locator (VeLo) and to the writing of the VeLo Technical Design Report submitted in May 2001. We have contributed via the development of a simulation of interacting particles in silicon and the study of the off detector electronics (ODE). The crucial part of the ODE is the L1 Pre-Processor Interface, which provides the hit information to the second level topological trigger. We present an algorithm which allows to correct for correlated noise. We show that the trigger efficiency is not affected by noise for S/N>10.

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