Beam energy dependence of net-hyperon yield and its implication on baryon transport mechanism

TL;DR

This study investigates baryon transport mechanisms in nuclear collisions by analyzing net-hyperon yields across different energies, finding results consistent with the baryon junction model and challenging valence quark-based explanations.

Contribution

It provides the first detailed analysis of net-hyperon yields supporting the baryon junction picture over valence quark models.

Findings

Net-hyperon yields follow an exponential dependence on rapidity gap.

Slope parameters are consistent across different hyperons and energies.

Valence quark models struggle to reproduce the observed data.

Abstract

In the constituent quark model, each quark inside a baryon carries 1/3 unit of the baryon number. An alternative picture exists where the center of a Y-shaped topology of gluon fields, called the baryon junction, carries a unit baryon number. Studying baryon transport over a large rapidity gap ($\delta y$) in nuclear collisions provides a possible tool to distinguish these two pictures. A recent analysis of global data on net-proton yield at mid-rapidity in Au+Au collisions showed an exponential dependence on $\delta y$ and the exponential slope does not vary with event centrality, favoring the baryon junction picture. Since junctions are flavor blind, hyperons -- baryons containing valence strange quarks -- are expected to exhibit a similar behavior as the proton. This study aims to test this prediction by analyzing hyperon yields in Au+Au collisions at various energies. We observe that net-hyperon yields, after correcting for the strangeness production suppression, adhere to the expected exponential form. The extracted slope parameters for net-$\Lambda$, net-$\Xi$ and net-$\Omega$ are consistent with each other and with those of net-proton within uncertainties, and exhibit no centrality dependence, further substantiating the baryon junction picture. Various implementations of the \texttt{PYTHIA} event generator, primarily based on valence quarks for baryon transport, are unable to simultaneously describe the slope parameters for all baryons.