Nuclear dependence of light neutral meson production in p-A collisions at 400 GeV with NA60

The NA60 experiment has studied low-mass muon pair production in proton-nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the $\rho \mathrm{/}\omega$ and $\varphi$ mesons are measured in the full $p_{\mathrm{T}}$ range accessible, from $p_{\mathrm{T}}=0$ up to 2 GeV/$c$. The nuclear dependence of the production cross sections of the $\eta$, $\omega$ and $\varphi$ mesons has been found to be consistent with the power law $\sigma_$\mathrm{p}\mathrm{A}$ \propto $\mathrm{A}$^\alpha$,withthe$\alpha$ parameter increasing as a function of $p_{\mathrm{T}}$ for all the particles, and an approximate hierarchy ${\alpha }_{\eta }\approx {\alpha }_{\varphi }>{\alpha }_{\omega }$. The cross section ratios ${\sigma }_{\eta }\mathrm{/}{\sigma }_{\omega }$, ${\sigma }_{\rho }\mathrm{/}{\sigma }_{\omega }$ and ${\sigma }_{\varphi }\mathrm{/}{\sigma }_{\omega }$ have been studied as a function of the size A of the production target, and an increase of the $\eta$ and $\varphi$ yields relative to the $\omega$ is observed from p-Be to p-U collisions.