Measurement of $V^0$ production ratios in $pp$ collisions at $\sqrt{s} = 0.9$ and 7\,TeV

TL;DR

This paper measures the ratios of anti-Lambda to Lambda and anti-Lambda to K0s in proton-proton collisions at two different energies, revealing discrepancies with theoretical predictions and providing insights into baryon transport and strange quark hadronisation.

Contribution

First measurements of $\bar{\Lambda}/\Lambda$ and $\bar{\Lambda}/K^0_s$ ratios at 0.9 and 7 TeV, comparing results with models and previous data.

Findings

$\bar{\Lambda}/\Lambda$ ratio is lower than predicted, especially at high rapidity.

$\bar{\Lambda}/K^0_s$ ratio is larger than expected, indicating differences in hadronisation.

Results are consistent across energies when plotted against rapidity loss.

Abstract

The $\bar{\Lambda} / \Lambda$ and $\bar{\Lambda} / K^0_\mathrm{S}$ production ratios are measured by the LHCb detector from $0.3\,\mathrm{nb}^{-1}$ of $pp$ collisions delivered by the LHC at $\sqrt{s} = 0.9$\,TeV and $1.8\,\mathrm{nb}^{-1}$ at $\sqrt{s} = 7$\,TeV. Both ratios are presented as a function of transverse momentum, $p_\mathrm{T}$, and rapidity, $y$, in the ranges {$0.15 < p_\mathrm{T} < 2.50\,\mathrm{GeV}/c$} and {$2.0<y<4.5$}. Results at the two energies are in good agreement as a function of rapidity loss, $\Delta y = y_\mathrm{beam} - y$, and are consistent with previous measurements. The ratio $\bar{\Lambda} / \Lambda$, measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted in simulation, particularly at high rapidity. The ratio $\bar{\Lambda} / K^0_\mathrm{S}$, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected.