First observation of the decay $B_s^0 \to K^-\mu^+\nu_\mu$ and a measurement of $|V_{ub}|/|V_{cb}|$

TL;DR

This paper reports the first observation of the decay $B_s^0 o K^- u__$ and measures the ratio of CKM matrix elements $|V_{ub}|/|V_{cb}|$ using data from the LHCb detector, providing new insights into flavor physics.

Contribution

It presents the first observation of a suppressed semileptonic decay of $B_s^0$ and introduces a method to determine $|V_{ub}|/|V_{cb}|$ using form factor calculations.

Findings

Branching fraction of $B_s^0 o K^- u__$ measured as $(1.06\u00b1 0.05 1 0.08) imes 10^{-4}$.

Ratio of CKM elements $|V_{ub}|/|V_{cb}|$ determined at different momentum transfers.

Normalization channel $B_s^0 o D_s^-_$ used to reduce systematic uncertainties.

Abstract

The first observation of the suppressed semileptonic $B_s^0 \to K^-\mu^+\nu_\mu$ decay is reported. Using a data sample recorded in {\it pp} collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of 2 $\mathrm{fb}^{-1}$, the branching fraction \mbox{$\mathcal{B}(B_s^0 \to K^-\mu^+\nu_\mu)$} is measured to be $(1.06\pm0.05~(\mathrm{stat})\pm0.08~(\mathrm{syst}))\times 10^{-4}$, where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay $B_s^0 \to D_s^-\mu^+\nu_\mu$, where $D_s^-$ is reconstructed in the final state $K^+K^-\pi^-$, is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the $B_s^0 \to K^-$ and $B_s^0 \to D_s^-$ transitions are employed to determine the ratio of the CKM matrix elements ${|V_{ub}|}/{|V_{cb}|}$ at low and high $B_s^0 \to K^-$ momentum transfer.