Photoproduction of $\omega$ mesons off nuclei and impact of polarization on the meson-nucleon interaction

We use photoproduction of $\omega$ mesons off complex nuclei to study interactions of transversely and longitudinally polarized vector mesons with nucleons. Whereas the total cross section for interactions of the transversely polarized vector mesons with nucleons ${\sigma }_T=\sigma \left(V_{T}N\right)$ can be obtained from coherent photoproduction, measurements of vector meson photoproduction in the incoherent region provide a unique opportunity to extract the yet unmeasured total cross section for longitudinally polarized mesons ${\sigma }_L=\sigma \left(V_{L}N\right)$. The predictions for the latter strongly depend on the theoretical approaches. This work is stimulated by the construction of the new experiment GlueX at Jefferson Lab, designed to study the photoproduction of mesons in the beam energy range between 5 and 12 GeV.

Figure 1

Dependence of the nuclear transparency $A_{\mathrm{eff}}$ on the mass number for (a) ${\sigma }_L=13\mathrm{mb}$ and (b) ${\sigma }_L=26\mathrm{mb}$. $A_{\mathrm{eff}}$ is shown for different photon energies: $A_{\mathrm{eff}}\left(\infty \right)$ and $A_{\mathrm{eff}}\left(0\right)$ correspond to infinite energy and energy-independent transparency, respectively.

Figure 2

$A$ dependence of the spin density matrix element ${\rho }_{00}^A$ for (a) ${\sigma }_L=13\mathrm{mb}$ and (b) ${\sigma }_L=26\mathrm{mb}$. ${\rho }_{00}^A$ is shown for different photon energies: $\rho \left(\infty \right)$ and $\rho \left(0\right)$ correspond to infinite energy and energy-independent ${\rho }_{00}^A$, respectively.

Figure 3

(a) The nuclear transparency $A_{\mathrm{eff}}$ and (b) the spin density matrix element ${\rho }_{00}^A$ as a function of ${\sigma }_L$ for lead nucleus. The transverse $\omega$-nucleon cross section ${\sigma }_T$ and the spin density matrix element ${\rho }_{00}$ are taken to be 26 mb and 0.2, respectively.