Measurement of the branching fraction of the rare decay $B^+\to K^{*+}μ^+μ^−$ exploiting the $K^{∗+}\to K^+π^0$ decay at the LHCb experiment

In this thesis, a measurement of the branching fraction of the rare B meson decay $B^+\to K^{*+} μ^+μ^−$ relative to the resonant decay $B^+\to J/ψK^{∗+}$ is presented, whereby the $K ^{∗+}$ decay mode $K^{∗+}\to K^+π^0$ is chosen exclusively. The used data was collected by the LHCb experiment during the years 2011 and 2012 with centre-of-mass energies of s = 7 TeV and s = 8 TeV, respectively. In total, 81 ± 16 $B^+\to K^{∗+} (\to K^+π^0 )μ^+μ^−$ decays with a statistical significance of 6σ are reconstructed. The relative branching fraction is found to be $\frac{B(B^+\to K^{∗+}μ^+μ^− )}{B(B^+\to J/ψ(\to μ^+μ^− )K^{∗+} )}= (1.03 ± 0.20 stat. ± 0.04 syst. ) × 10^{−2}$ where the uncertainties are statistical and systematic, respectively. The total branching fraction of $B^+\to K^{*+} μ^+μ^−$ is calculated to be $B(B^+\to K^{∗+}μ^+μ^− ) = (0.88 ± 0.17 stat. ± 0.06 syst. ) × 10^{−6}$ .