Analysis of the Rare Decay $B_s \rightarrow f_2' \mu^+ \mu^-$ with $f_2' \rightarrow K^+ K^-$ Final State

This report describes the project that I worked on during my time as a summer student at CERN in summer 2014: A search for the rare decay $B_s \rightarrow f_2' \mu^+ \mu^-$ at the LHCb experiment has been performed using data corresponding to an integrated luminosity $\mathcal{L} = 3.0 \text{ fb}^{-1}$. In the Standard Model (SM), this decay is highly suppressed as it proceeds via an electroweak penguin transition. New Physics (NP) effects can enter the loop and influence observables like the branching ratio $\mathcal{B}$. A theoretical prediction of the branching ratio in the SM is given by $\mathcal{B}_\text{th}(B_s \rightarrow f_2' \mu^+ \mu^-) = \left( 1.8\,^{+1.1}_{-0.7} \right) \cdot 10^{-7}$. We found $N_\text{obs} = 17.2 \pm 2.9$ signal candidates using a two dimensional mass fit which is in the same order of magnitude as the theoretical prediction $N_\text{pred} = 15_{-7}^{+10}$. Though, further systematic effects in the analysis still have to be investigated before converting this into a reliable value for the branching ratio $\mathcal{B}(B_s \rightarrow f_2' \mu^+ \mu^-)$.