Measurement of the CKM matrix elements |V$_{ub}$|/|V$_{cb}$| from semileptonic $B_s$ decays

Abstract

This thesis presents the determination of the CKM matrix elements |Vub|/|Vcb| from measuring the ratio of branching fractions of the Bs meson decays Bs->Kmunu with respect to Bs->Dsmunu. The analysis is based on proton-proton collisions corresponding to an integrated luminosity of 2fb^(-1) produced at a center of mass energy of sqrt(s)=8Tev provided by the Large Hadron Collider and collected by the LHCb experiment in 2012. The branching fraction ratio is measured to be BF(Bs->Kmunu)/BF(Bs->Dsmunu)=(6.079 +- 0.201 +- 0.476 ) x 10^(-3)where the first uncertainty is statistical and the second one systematic. This experimental measured ratio is combined with theoretical form factor predictions for Bs->Kmunu and Bs->Dsmunu which results in the determination of the CKM matrix elements |Vub|/|Vcb|=0.114 +- 0.005 +- 0.013 where the first uncertainty is the combined experimental uncertainty and the second one is from theoretical predictions.This measurement provides an important constraint to global fits to the unitary triangle of the CKM sector of the SM.The branching fraction ratio together with theoretical predictions and external input can also be used to extract the total branching fraction for the signal decay, which is measured to be BF(Bs->Kmunu)=(1.31 +- 0.14) x 10^{-4} for the first time.