Study of the penguin-dominated decay B0 s - K 0K 0 at LHCb

Abstract

This thesis is devoted to the search for and subsequent analysis of the decay channel B0s -> K*0 anti-K*0,using the first data acquired by LHCb during 2010 and 2011 from the LHC proton-proton collisions at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 35/pb and 1/pb respectively. As a result of the work presented here, the first observation of the B0s -> K*0 anti-K*0 decay was performed. With the extended data sample collected in 2011, a combined angular and mass analysis was carried out, in order to asses the longitudinal polarisation fractions of the K*0, obtaining f_L = 0.201 +/- 0.057(stat.) +/- 0.040(syst.). The branching fraction for this decay was also measured to be BR(B0s -> K*0 anti-K*0) = (10.6 +/- 1.8(stat.) +/- 1.0(syst.) +/- 0.6 (f_d/f_s)) x 10^{â^6},in agreement with the Standard Model prediction. All of the triple product and CP direct asymmetries measurable in the time-integrated and flavour-untagged analysis of B0s -> K+ pi- K- pi+ were also determined. No signs of CP violation was found, in agreement with the Standard Model expectation.