Observation of a ${\Lambda }_b^0-{\overline{\Lambda }}_b^0$ 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 ${\Lambda }_b^0$ and ${\overline{\Lambda }}_b^0$ baryon production rates in proton-proton collisions at centre-of-mass energies of $\sqrt{s}=7$ and $8\text{TeV}$ collected with the LHCb experiment, corresponding to an integrated luminosity of $3{\text{fb}}^{-1}$. The ${\Lambda }_b^0$ baryons are reconstructed through the inclusive semileptonic decay ${\Lambda }_b^0\to {\Lambda }_c^{+}{\mu }^{-}{\overline{\nu }}_{\mu }X$. The production asymmetry is measured both in intervals of rapidity in the range $2.15<y<4.10$ and transverse momentum in $2<p_T<27\text{GeV}/c$. 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)

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Cited by in corpus (11)

• The LHCb upgrade I
• Observation of charge-parity symmetry breaking in baryon decays
• Enhanced production of ${\Lambda }_b^0$ baryons in high-multiplicity $pp$ collisions at $\sqrt{s}=13$ TeV
• Measurement of the photon polarization in ${\Lambda }_b\to \Lambda \gamma$ decays
• Study of $\itΛ_{\it{b}}^\rm{0}$ and $\itΞ_{\it{b}}^\rm{0}$ decays to $\Lambda h^{+}{h}^{{}^{\prime }-}$ and evidence for $CP$ violation in $\itΛ_{\it{b}}^\rm{0}\to\itΛ K^+K^-$ decays
• Measurement of $CP$ asymmetries in ${\Lambda }_b^0\to p{h}^{-}$ decays
• Observation of the suppressed ${\Lambda }_b^0\to Dp{K}^{-}$ decay with $D\to K^{+}{\pi }^{-}$ and measurement of its $CP$ asymmetry
• Towards the understanding of heavy quarks hadronization: from leptonic to heavy-ion collisions
• The Forward Physics Facility at the High-Luminosity LHC
• First observation of the charmless baryonic decay $B^{+}\to \bar{\Lambda }p\bar{p}p$
• Heavy flavour production and spectroscopy