Associated vector boson production with b-jets at LHCb and Beam-Gas Vertexing at LHC for beam instrumentation

This thesis presents the cross-section measurements of associated vector bosons production with bottom quarks jets at 7 and 8 TeV of centre-of-mass energies. The first channel for cross-section measurement is the Z+b-jet with $Z/\gamma^* \to \mu^+\mu^-$ in proton-proton collisions at $\sqrt s = \text {7 TeV}$ using data collected by the LHCb experiment in 2011. The second channel is the $W + b\overline b$, requiring two b-jets and one lepton. Apart from cross-section measurement this channel is also used to calculate limits of the Higgs boson produced in association with a vector boson and decaying into a pair of bottom or charm quarks. One of the main source of systematic errors in these analyses is the jet energy resolution and correction. Reduction of this error is achieved by performing a calibration of the neutral jet energy component, named neutral recovery, where empirical functions of the ratio between the charged particle energy of the jet and the particle momentum are determined. This method improves the jet energy resolution. The precision of the results depends directly on the absolute calibration of the integrated luminosity at LHCb. Luminosity calibration at LHCb profits from both van der Meer scan and beam-gas imaging. Based on the latter method, a vertex detector for LHC beam-gas collisions are proposed. Contributions to the development of the pattern recognition and track fitting software, detector modules metrology and cooling system of this experiment are made.