Light Vector Mesons in the Nuclear Medium

TL;DR

This study investigates potential in-medium modifications of light vector mesons in various nuclear targets by analyzing their decay spectra, finding no significant mass shift but observing expected broadening effects.

Contribution

It provides the first comprehensive measurement of $ ho$, $ ho$, and $ ho$ meson properties in different nuclear media using leptonic decay channels to minimize final-state interactions.

Findings

No significant $ ho$ meson mass shift observed.

Measured widths are consistent with nuclear many-body effects.

Used model-independent background subtraction techniques.

Abstract

The light vector mesons ($\rho$, $\omega$, and $\phi$) were produced in deuterium, carbon, titanium, and iron targets in a search for possible in-medium modifications to the properties of the $\rho$ meson at normal nuclear densities and zero temperature. The vector mesons were detected with the CEBAF Large Acceptance Spectrometer (CLAS) via their decays to $e^{+}e^{-}$. The rare leptonic decay was chosen to reduce final-state interactions. A combinatorial background was subtracted from the invariant mass spectra using a well-established event-mixing technique. The $\rho$ meson mass spectrum was extracted after the $\omega$ and $\phi$ signals were removed in a nearly model-independent way. Comparisons were made between the $\rho$ mass spectra from the heavy targets ($A > 2$) with the mass spectrum extracted from the deuterium target. With respect to the $\rho$-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion.