Observation of a Λb0 − Λ¯b0 production asymmetry in proton-proton collisions at √s = 7 and 8 TeV

This article presents differential measurements of the asymmetry between Λb0 and Λ¯b0 baryon production rates in proton-proton collisions at centre-of-mass energies of s = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity of 3 fb⁻¹. The Λb0 baryons are reconstructed through the inclusive semileptonic decay Λb0 → Λc+μ⁻ν¯ _μX. 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 GeV/c. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both s = 7 and 8 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. [Figure not available: see fulltext.]