Measurement of b-quark fragmentation fraction ratios at the CMS experiment: a key ingredient for the $B^{0}_{s}\rightarrow \mu^{+}\mu^{-}$ rare decay analysis

The current theoretical basis for Particle Physics, the Standard Model, although extremely successful in its predictions, faces a series of limitations. Many extensions have been proposed, but no clear deviations from the Standard Model have been found. Rare decays are very sensitive to hypothetical New Physics interactions. The precise measurement of the branching fraction (BF) of the $B^{0}_{s}\rightarrow \mu^{+}\mu^{-}$ decay imposes strong constraints on Beyond the Standard Model theories and may give hints on how to explore New Physics processes. This work represents the measurement of one of the main ingredients for the mentioned branching fraction measurement: the $f_{s}/f_{d}$ fragmentation fraction ratio. Data produced at the Large Hadron Collider and detected by the Compact Muon Solenoid at a 13 TeV centre of mass collision energy is used. The measurement of yields, efficiencies and systematic uncertainties is performed. The $f_{s}/f_{d}$ ratio is measured to be 0.186 $\pm$ 0.002 (stat.) $\pm$ 0.021 (syst.) $\pm$ 0.016 (BF). Two other ratios are measured to confirm the robustness of the results: $f_{s}/f_{u}$ = 0.216 $\pm$ 0.003 (stat.) $\pm$ 0.029 (syst.) $\pm$ 0.017 (BF) and $f_{d}/f_{u}$ = 1.164 $\pm$ 0.008 (stat.) $\pm$ 0.120 (syst.) $\pm$ 0.057 (BF). We also conclude that no kinematic dependence is found for the ratios in the acceptance region of the measurement, defined in terms of rapidity, $|y|$ < 2.25, and transverse momentum, 10 < $p_{T}$ < 90 GeV, of the B mesons.