Light vector mesons in the nuclear medium

Abstract

The light vector mesons ($\ensuremath{\rho}$,$\ensuremath{\omega}$, and $\ensuremath{\phi}$) were produced in deuterium, carbon, titanium, and iron targets in a search for possible in-medium modifications to the properties of the $\ensuremath{\rho}$ meson at normal nuclear densities and zero temperature. The vector mesons were detected with the CEBAF Large Acceptance Spectrometer (CLAS) via their decays to ${e}^{+}{e}^{\ensuremath{-}}$. 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 $\ensuremath{\rho}$-meson mass spectrum was extracted after the $\ensuremath{\omega}$ and $\ensuremath{\phi}$ signals were removed in a nearly model-independent way. Comparisons were made between the $\ensuremath{\rho}$ mass spectra from the heavy targets ($A>2$) with the mass spectrum extracted from the deuterium target. With respect to the $\ensuremath{\rho}$-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.