Analysis of spectral modification of $\phi$ mesons at finite density using a transport approach in the 12 GeV pA reactions

TL;DR

This study investigates how the spectral properties of phi mesons are modified in nuclear matter at finite density using a transport model, confirming previous findings and emphasizing the importance of momentum dependence for accurate descriptions.

Contribution

The paper introduces a transport approach that accounts for the time evolution of nuclear density, improving the understanding of in-medium phi meson spectral modifications at finite density.

Findings

Significant low-mass excess observed in phi meson decay spectra.

Momentum dependence improves agreement with experimental data.

Modification parameters are consistent with previous analyses.

Abstract

The hadron spectrum at finite density is an important observable for exploring the origin of hadron masses. In the KEK-PS E325 experiment, the di-electron decays of phi mesons inside and outside nuclei were measured using 12 GeV pA reactions. In the previous analysis, a significant excess was observed on the low-mass side of the phi meson peak in the data for slow-moving phi mesons ($\beta\gamma=p_{\phi}/m_{\phi}<1.25$) with the Cu target, and in-medium vector meson spectral modification was verified. We newly employed the PHSD transport approach to take into account the time evolution of spatial density distribution of the target nuclei. Consistent with the previous analysis, a significant excess was observed in the present analysis as well. It was found that incorporating momentum dependence into the spectral modification leads to better agreement with the experimental results. For the slow-moving $\phi$ mesons with the Cu target, the newly obtained modification parameters are consistent with those from the previous analysis within the uncertainties.