Fate of ${\Sigma }_c$, ${\Xi }_c^{\prime }$ and ${\Omega }_c$ baryons at high temperature with chiral restoration

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 $T_{\mathrm{pc}}$ of chiral restoration, which results in a peculiar mass hierarchy for positive-parity HQS-doublet SHBs where ${\Xi }_c^{\prime }$ becomes heavier than ${\Omega }_c$ Besides, it is found that the decay width of ${\Sigma }_c\to {\Lambda }_c\pi$ vanishes above $T_{\mathrm{pc}}$ 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.

Comments: 21 pages, and 6 figures