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

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>This article presents differential measurements of the asymmetry between <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\varLambda}_b^0 $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>b</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> and <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\overline{\varLambda}}_b^0 $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mover> <mml:mi>Λ</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>b</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> baryon production rates in proton-proton collisions at centre-of-mass energies of <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity of 3 fb<jats:sup><jats:italic>−</jats:italic>1</jats:sup>. The <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\varLambda}_b^0 $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>b</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> baryons are reconstructed through the inclusive semileptonic decay <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\varLambda}_b^0 $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>b</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> → <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {\varLambda}_c^{+} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>c</mml:mi> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula><jats:italic>μ</jats:italic><jats:sup><jats:italic>−</jats:italic></jats:sup><jats:inline-formula><jats:alternatives><jats:tex-math>$$ \overline{\nu} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math></jats:alternatives></jats:inline-formula><jats:sub><jats:italic>μ</jats:italic></jats:sub><jats:italic>X</jats:italic>. The production asymmetry is measured both in intervals of rapidity in the range 2<jats:italic>.</jats:italic>15 <jats:italic>< y <</jats:italic> 4<jats:italic>.</jats:italic>10 and transverse momentum in 2 <jats:italic>< p</jats:italic><jats:sub>T</jats:sub><jats:italic><</jats:italic> 27 GeV/<jats:italic>c</jats:italic>. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 7 and 8 TeV data, assuming no <jats:italic>CP</jats:italic> 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 P<jats:sc>ythia</jats:sc> and heavy-quark recombination are provided. This result constitutes the first observation of a particle-antiparticle asymmetry in <jats:italic>b</jats:italic>-hadron production at LHC energies.</jats:p>