Measurement of $f_s / f_u$ variation with proton-proton collision energy and $B$-meson kinematics

Abstract

The ratio of the $\mathrm{B}^0_\mathrm{s}$ and $\mathrm{B}^+$ fragmentation fractions $f_\mathrm{s}$ and $f_u$ is studied with $B^0_\mathrm{s}\to\mathrm{J}/\psi \phi $ and $B^+\to\mathrm{J}/\psi K^+$ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8 and 13$\text{ TeV}$ center-of-mass energies. The analysis is performed in bins of $\mathrm{B}$-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity and rapidity. The fragmentation-fraction ratio $f_\mathrm{s} / f_u$ is observed to depend on the $\mathrm{B}$-meson transverse momentum with a significance of $6.0\,\sigma$. This dependency is driven by the 13$\text{ TeV}$ sample ($8.7\,\sigma$) while the results for the other collision energies are not significant when considered separately. Furthermore the results show a $4.8\,\sigma$ evidence for an increase of $f_\mathrm{s} / f_u$ as a function of collision energy.