Observation of a $\Lambda_b^0-\overline{\Lambda}_b^0$ production asymmetry in proton-proton collisions at $\sqrt{s} = 7 \textrm{ and } 8\,\textrm{TeV}$

International audienceThis article presents differential measurements of the asymmetry between $ {\varLambda}_b^0 $ and $ {\overline{\varLambda}}_b^0 $ baryon production rates in proton-proton collisions at centre-of-mass energies of $ \sqrt{s} $ = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity of 3 fb$^{−1}$. The $ {\varLambda}_b^0 $ baryons are reconstructed through the inclusive semileptonic decay $ {\varLambda}_b^0 $ → $ {\varLambda}_c^{+} $μ$^{−} \overline{\nu} _{μ}$X. The production asymmetry is measured both in intervals of rapidity in the range 2.15 < y < 4.10 and transverse momentum in 2 < p$_{T}$< 27 GeV/c. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both $ \sqrt{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.[graphic not available: see fulltext