The ratio of the $B_s^0$ and $B^{+}$ fragmentation fractions $f_s$ and $f_u$ is studied with $B_s^0\to J/\psi \varphi$ and $B^{+}\to J/\psi K^{+}$ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of $B$-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio $f_s/f_u$ is observed to depend on the $B$-meson transverse momentum with a significance of $6.0\sigma$. This dependency is driven by the 13 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 $f_s/f_u$ as a function of collision energy.

• Received 22 October 2019
• Revised 13 December 2019
• Accepted 2 March 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.122002

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