Broadening of $\rho (\to e^{+}{e}^{-})$ meson produced coherently in the photonuclear reaction

Abstract

The $e^{+}{e}^{-}$ invariant mass distribution spectra are calculated to estimate the hadron parameters of the $\rho$ meson produced coherently in the photonuclear reaction. The elementary reaction occurring in the nucleus is considered to proceed as $\gamma N\to {\rho }^{0}N;{\rho }^0\to e^{+}{e}^{-}$. We describe the elementary $\rho$ meson photoproduction by the experimentally determined reaction amplitude $f_{\gamma N\to {\rho }^{0}N}$. The $\rho$ meson propagator is presented by the eikonal form, and the $\rho$ meson nucleus optical potential $V_{O\rho }$ appearing in it is estimated using the "$t\varrho$" approximation. The $\rho$ meson nucleon scattering amplitude $f_{\rho N}$ extracted from the measurements is used to generate this potential. The calculated $e^{+}{e}^{-}$ invariant mass distribution spectra are compared with those measured at Jefferson Laboratory. The calculated results for the transparency ratio are also presented.

Comments: 22 pages, 8 figures