Infinite and Finite Nuclear Matter (INFINUM-2023)

Effects of partial restoration of chiral symmetry on particle production in heavy-ion collisions

2 Mar 2023, 16:10

30m

Blokhintsev Auditorium, 4th floor

Speaker

Alexei Larionov (Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia)

Description

QCD predicts that with increasing baryon density the chiral symmetry gets
gradually restored due to the disappearance of the scalar $\overline{q}q$ condensate. This should result in the appearance of the parity doublets in the spectrum of hadrons, like $(\pi ,\sigma )$, $(\rho ,a_1)$, $(N,N^{\ast }(1535))$ etc. In order to connect this prediction with observables one needs to properly modify relativistic mean fields used in many hadronic transport models which usually resort on Walecka-type descriptions. This talk is based on the paper [1] which represents one of the first such attempts. We apply the linear $\sigma$-model with $SU(2{)}_R\times SU(2{)}_L$ symmetry in the mirror assignment, that is called the parity-doublet model (PDM) C.E. DeTar, T. Kunihiro, 1989; D. Jido et al., 2001. We implement the PDM model in the Giessen Boltzmann-Uehling Uhlenbeck (GiBUU) transport model as an option in the calculation of relativistic mean fields. Within this chiral approach we study heavy-ion collisions at the beam energy of 1-2A GeV focusing on the production of $\eta$ mesons. A strong dropping of the Dirac mass of the $N^{\ast }(1535)$ in the high-density stage of a collision leads to a considerable enhancement in the production of this resonance as compared to the non-linear Walecka model. As the system expands, the Dirac masses of these abundant soft $N^{\ast }(1535)$ resonances gradually increase and ultimately cross the $N\eta$ decay threshold. As a result, an enhanced low-energy $\eta$ production is observed in the calculations with chiral mean fields. Comparing with TAPS data on $\eta$ production we find that the chiral model improves the agreement for the $m_t$-spectra of $\eta$'s at small $m_t$ in heavy colliding systems. A similar enhancement is also observed in the soft $\rho$ production resulting in slightly larger dilepton yields.

[1] A.B. Larionov, L. von Smekal, Phys. Rev. C 105, 034914 (2022)

Presentation materials

larionov_INFINUM2023.pdf