Exclusive vector-meson production in muon-proton scattering

Abstract

From a muon-proton scattering experiment with a streamer chamber at the Stanford Linear Accelerator we present results in the ranges $0.3<{Q}^{2}<4.7$ Ge${\mathrm{V}}^{2}$ and $1.7<W<4.7$ GeV for the reactions ${\ensuremath{\mu}}^{+}p\ensuremath{\rightarrow}\ensuremath{\mu}\mathrm{pV}$ where $V$ is a vector meson (${\ensuremath{\rho}}^{0}$, $\ensuremath{\omega}$, or $\ensuremath{\varphi}$). It is shown that in $\ensuremath{\rho}$ production the skewing parameter and the longitudinal-transverse ratio change significantly as ${Q}^{2}$ increases above 1 Ge${\mathrm{V}}^{2}$. The cross section for ${\ensuremath{\rho}}^{0}$ production as a function of ${Q}^{2}$ falls below the vector-meson-dominance prediction. The ratio of the cross section for exclusive vector-meson production to the total cross section falls by a factor of 10 between photoproduction and a ${Q}^{2}$ of 2 Ge${\mathrm{V}}^{2}$, yet the ratio of $\ensuremath{\omega}$ to $\ensuremath{\rho}$ production remains constant at the photoproduction value out to ${Q}^{2}>2$ Ge${\mathrm{V}}^{2}$.