Fate of $\Sigma_c$, $\Xi_c'$ and $\Omega_c$ baryons at high temperature with chiral restoration

TL;DR

This paper investigates how the masses and decay widths of singly heavy baryons change at high temperatures near chiral restoration, using a diquark model with NJL dynamics, predicting mass degeneracies and decay modifications relevant for heavy-ion experiments.

Contribution

It introduces a novel approach to study medium modifications of heavy baryons at finite temperature through diquark dynamics and chiral symmetry restoration, including effects of the U(1)_A anomaly.

Findings

Mass degeneracies between parity partners of SHBs at high temperature.

Predicted mass degeneracy of $ ext{Σ}_c$ and $ ext{Ω}_c$ above the pseudocritical temperature.

Decay width of $ ext{Σ}_c o ext{Λ}_c ext{π}$ vanishes above $T_{pc}$.

Abstract

Masses of the singly heavy baryons (SHBs), composed of a heavy quark and a light diquark, are studied from the viewpoints of heavy-quark spin symmetry (HQSS) and chiral-symmetry restoration at finite temperature. We consider the light diquarks with spin-parity $J^P=0^\pm$ and $1^\pm$. Medium corrections to the SHBs are provided through the diquarks whereas the heavy quark is simply regarded as a spectator. The chiral dynamics of the diquark are described by the Nambu-Jona-Lasinio (NJL) model having (pseudo)scalar-type and (axial)vector-type four-point interactions and the six-point ones responsible for the $U(1)_A$ axial anomaly. The divergences are handled by means of the three-dimensional proper-time regularization with both ultraviolet and infrared cutoffs included, in order to eliminate unphysical imaginary parts. As a result, the mass degeneracies between the parity partners of all the SHBs are predicted in accordance with the chiral restoration. In particular, the HQS-doublet SHBs exhibit clear mass degeneracies due to the absence of the direct anomaly effects. We also predict a mass degeneracy of $\Sigma_c$ and $\Omega_c$ above the pseudocritical temperature $T_{\rm pc}$ of chiral restoration, which results in a peculiar mass hierarchy for positive-parity HQS-doublet SHBs where $\Xi_c'$ becomes heavier than $\Omega_c$ Besides, it is found that the decay width of $\Sigma_c\to\Lambda_c\pi$ vanishes above $T_{\rm pc}$ reflecting a closing of the threshold. The predicted modifications of masses and decay widths of the SHBs are expected to provide future heavy-ion collision experiments and lattice simulations with useful information on chiral dynamics of the diquarks.