Sensibilidade ao Parâmetro $\phi_s$ com o Canal de Decaimento $B_s \rightarrow \phi \phi$ e Efeitos Sistemáticos no Experimento LHCb

LHCb is one of the experiments being made to study the proton-proton collisions that will take place at the LHC. Its main goal is to make precise measurements of CP violation in the b quark system. In this thesis are presented two different studies based on LHCb. As the start of data taking is expected to the end of 2007, the studies were performed based on simulations. The first study was done to measure systematic effects due to the trigger selection in the flavour tagging. It was shown that this selection alters the phase space in a different way for distinct decay channels. This fact creates a systematic error in the measurement of the flavour of neutral mesons. A method is proposed to correct for this effect. It is based on sorting the events in different categories, taking into account the correlation between the particles. The method works for the majority of the events and has the advantage of depending only in data that will be measured. Another study was performed to estimate the sensitivity in the measurement of $\rm \phi_s$, which is a parameter that measures CP violation in the $\rm B_s$ system, using the decay channel $\rm B_s \rightarrow \phi \phi$. A selection for this channel was developed and a fast Monte Carlo simulation performed to obtain the sensitivity.