Yoshio Yoshimura | Searcharxiv

arXiv2025

Velocity dependence of the mass modifications of $\rho$ and $\omega$ mesons in 12 GeV $p+A$ reactions

This study measured the invariant mass spectra of $\rho$ and $\omega$ mesons in the $e^+e^-$ decay channel for 12 GeV (12.9 GeV/$c$) $p+\mathrm{C}$ and $p+\mathrm{Cu}$ reactions ($\sqrt{s}_{NN}=5.1$ GeV) at the KEK 12-GeV Proton Synchrotron. The measured spectra were divided into three $\beta\gamma$ regions to examine their velocity dependence. Across all regions, significant excesses were observed on the low-mass side of the $\omega$ meson peak, beyond the contributions of known hadronic sources, in the data of the C and Cu targets. Model calculations were subsequently performed to evaluate the magnitudes of the mass modifications of $\rho$ and $\omega$ mesons.

nucl-ex↗

arXiv2025

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

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.

nucl-ex↗