Observation of a $\hat{I}{›}_b^0-\overline{\hat{I}}{›}_b^0$ production asymmetry in proton-proton collisions at $\sqrt{s}=7\text{ and }8\text{TeV}$

Abstract

This article presents differential measurements of the asymmetry between $\hat{I}{›}_b^0$ and $\overline{\hat{I}}{›}_b^0$ baryon production rates in proton-proton collisions at centre-of-mass energies of $\sqrt{s}=7$ and $8\text{TeV}$ collected with the LHCb experiment, corresponding to an integrated luminosity of $3{\text{fb}}^{-1}$. The $\hat{I}{›}_b^0$ baryons are reconstructed through the inclusive semileptonic decay $\hat{I}{›}_b^0\to \hat{I}{›}_c^{+}\hat{I}{¼}^{-}\overline{\hat{I}}{½}_{\hat{I}}¼X$. The production asymmetry is measured both in intervals of rapidity in the range $2.15<y<4.10$ and transverse momentum in $2<p_T<27\text{GeV}/c$. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both $\sqrt{s}=7$ and $8\text{TeV}$ data, assuming no $CP$ violation in the decay. There is evidence for a trend as a function of rapidity with a significance of 4 standard deviations. Comparisons to predictions from hadronisation models in PYTHIA and heavy-quark recombination are provided. This result constitutes the first observation of a particle-antiparticle asymmetry in $b$-hadron production at LHC energies.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-016.html (LHCb public pages)