Measurement of the forward-backward asymmetry of $\Lambda$ and $\bar{\Lambda}$ production in $p \bar{p}$ collisions

TL;DR

This paper measures the forward-backward production asymmetry of Lambda and anti-Lambda particles in proton-antiproton collisions at the Tevatron, revealing asymmetries dependent on rapidity and confirming the universality of the production ratio across experiments.

Contribution

It provides the first detailed measurement of Lambda asymmetries as a function of rapidity in p-pbar collisions at Tevatron energies, confirming the universality of the production ratio with respect to rapidity loss.

Findings

Lambda particles are produced more in the proton direction.

The Lambda/anti-Lambda ratio is a universal function of rapidity loss.

Forward-backward asymmetry varies with rapidity.

Abstract

We study $\Lambda$ and $\bar{\Lambda}$ production asymmetries in $p \bar{p} \rightarrow \Lambda (\bar{\Lambda}) X$, $p \bar{p} \rightarrow J/\psi \Lambda (\bar{\Lambda}) X$, and $p \bar{p} \rightarrow \mu^\pm \Lambda (\bar{\Lambda}) X$ events recorded by the D0 detector at the Fermilab Tevatron collider at $\sqrt{s} = 1.96$ TeV. We find an excess of $\Lambda$'s ($\bar{\Lambda}$'s) produced in the proton (antiproton) direction. This forward-backward asymmetry is measured as a function of rapidity. We confirm that the $\bar{\Lambda}/\Lambda$ production ratio, measured by several experiments with various targets and a wide range of energies, is a universal function of "rapidity loss", i.e., the rapidity difference of the beam proton and the lambda.