Orateur
Description
The spectral functions of chiral partners should become degenerate when the QCD chiral symmetry is restored. The axial-vector spectra are experimentally more challenging to construct than those of vector mesons that directly couple to virtual photons and then to dileptons. Chiral mixing of the vector with axial-vector mesons is thus a key phenomenon to probe in-medium modifications of vector spectrum due to the onset of chiral symmetry restoration carried by the axial-vector counterpart. The mixing effect is expected to be stronger at higher density due to a mechanism driven by chiral anomalies [1], in striking contrast to the vanishing mixing at chiral crossover driven by thermal pions [2]. This feature encourages us to perform the experimental search in the high-density regime, where the recent experimental trend has begun to shift toward.
We propose that experiments at medium energies with paying attention to the new mixing mechanism, may provide a direct evidence of the chiral symmetry restoration. In this presentation, we focus on the density-induced mixing and the spectral functions of $\phi$ and its chiral partner $f_1(1420)$. We present the invariant mass distribution of dileptons using a transport approach developed in [3, 4] under the conditions of the J-PARC E16 experiment as a prime example. A potential to discover the mass degeneracy of chiral partners at finite density as a signature of the partial chiral symmetry restoration is advocated.
References
[1] C. Sasaki, Anomaly-induced chiral mixing in cold and dense matter, Phys. Rev. D 106, 054034 (2022).
[2] A. Sakai, M. Harada, C. Nonaka, C. Sasaki, K. Shigaki, and S. Yano, Probing the QCD phase transition with chiral mixing in dilepton production, 2308.03305, arXiv, nucl-th(2023).
[3] W. Cassing, and E. L. Bratkovskaya, Parton transport and hadronization from the dynamical quasiparticle point of view, Phys. Rev. C 78, 034919 (2008).
[4] P. Gubler, E. L. Bratkovskaya, and T. Song, $\phi$ meson properties in nuclear matter from dilepton spectra in a transport approach, EPJ Web Conf. 274, 07015 (2022).
