Constituent quark scaling violation due to baryon number transport

TL;DR

This paper investigates how baryon number transport affects the constituent quark scaling in heavy ion collisions, revealing potential violations of scaling due to increased baryon stopping at lower energies.

Contribution

It introduces a specific pattern for NCQ scaling breakdown considering baryon transport effects and flow differences between particles and antiparticles.

Findings

NCQ scaling may break down at lower energies due to baryon transport.

Flow differences between particles and antiparticles contribute to scaling violations.

Baryon stopping impacts the interpretation of QGP signatures.

Abstract

In ultra-relativistic heavy ion collisions at $\roots\approx200$ GeV, the azimuthal emission anisotropy of hadrons with low and intermediate transverse momentum ($p_T\lesssim 4$ GeV/c) displays an intriguing scaling. In particular, the baryon (meson) emission patterns are consistent with a scenario in which a bulk medium of flowing quarks coalesces into three-quark (two-quark) "bags." While a full understanding of this number of constituent quark (NCQ) scaling remains elusive, it is suggestive of a thermalized bulk system characterized by colored dynamical degrees of freedom-- a quark-gluon plasma (QGP). In this scenario, one expects the scaling to break down as the central energy density is reduced below the QGP formation threshold; for this reason, NCQ-scaling violation searches are of interest in the energy scan program at the Relativistic Heavy Ion Collider (RHIC). However, as $\roots$ is reduced, it is not only the initial energy density that changes; there is also an increase in the net baryon number at midrapidity, as stopping transports entrance-channel partons to midrapidity. This phenomenon can result in violations of simple NCQ scaling. Still in the context of the quark coalescence model, we describe a specific pattern for the break-down of the scaling that includes different flow strengths for particles and their anti-partners. Related complications in the search for recently suggested exotic phenomena are also discussed.