| Abstract: | This article presents differential measurements of the asymmetry between
$Lambda_b^0$ and $overline{Lambda}_b^0$ baryon production rates in
proton-proton collisions at centre-of-mass energies of $sqrt{s}=7$ and
$8, extrm{TeV}$ collected with the LHCb experiment, corresponding to an
integrated luminosity of $3, extrm{fb}^{-1}$. The $Lambda_b^0$ baryons are
reconstructed through the inclusive semileptonic decay
$Lambda_b^0
ightarrowLambda_c^+mu^-overline{
u}_{mu}X$. The production
asymmetry is measured both in intervals of rapidity in the range $2.15<y<4.10$
and transverse momentum in $2<p_T<27, extrm{GeV}/c$. The results are found to
be incompatible with symmetric production with a significance of 5.8 standard
deviations for both $sqrt{s}=7$ and $8, extrm{TeV}$ data, assuming no $C!P$
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. |
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