Search for medium modification of the $\rho$ meson

TL;DR

This study investigates potential in-medium modifications of the $ ho$ meson by analyzing its spectral function in various nuclei, finding no mass shift but evidence of resonance broadening in heavier nuclei.

Contribution

It provides the first detailed spectral function measurements of the $ ho$ meson in different nuclei using $e^+e^-$ decay channels, highlighting in-medium broadening effects.

Findings

No significant $ ho$ mass shift observed.

Resonance broadening in titanium and iron.

Consistent with collisional broadening expectations.

Abstract

The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. The vector mesons, $\rho$, $\omega$, and $\phi$, are observed via their decay to $e^+e^-$, in order to reduce the effects of final state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the $\rho$ meson. The $\rho$ spectral function is extracted from the data on various nuclei, carbon, iron, and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no significant mass shift for the $\rho$ meson; however, there is some widening of the resonance in titanium and iron, which is consistent with expected collisional broadening.