Polarization measurement of $\Lambda^+_c$ and $\overline{\Lambda}{}^-_c$ baryons in $p$Ne collisions at $\sqrt{s_{NN}} = 68.6$ GeV

TL;DR

This paper reports the first measurement of charm baryon polarization in fixed-target proton-neon collisions at 68.6 GeV, revealing charge-dependent polarization differences and their dependence on kinematic variables.

Contribution

It provides the first-ever measurement of separate-charge polarizations for $ ext{Lambda}_c^+$ and $ ext{Lambda}_c^-$ baryons in fixed-target collisions at this energy.

Findings

Measured $ ext{Lambda}_c^+$ polarization as 24% with uncertainties.

Measured $ ext{Lambda}_c^-$ polarization as -8% with uncertainties.

Observed polarization dependence on transverse momentum and Feynman-$x$.

Abstract

The first measurement of the polarization of charm baryons by the LHCb experiment recorded in fixed-target mode is presented. The polarization of $\Lambda_c$ baryons is studied in collisions of protons, at an energy of 2.51 TeV, incident on a gaseous target of neon, at a nucleon-nucleon center-of-mass energy of $68.6$ GeV. The world's first measurement of separate-charge polarizations for $\Lambda^+_c$ and $\overline{\Lambda}{}^-_c$ baryons is performed, determining $$ P_{\Lambda^+_c} = ( 24 \pm 9 \pm 2 \, )\% , $$ $$ P_{\overline{\Lambda}{}^-_c} = (-8 \pm 12 \pm 3 \, ) \% , $$ where the first uncertainty is statistical and the second systematic. The polarization is also measured in intervals of baryon transverse momentum and the Feynman-$x$ variable.