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 $ρ/ω$ and $ϕ$ 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 $η$, $ω$ and $ϕ$ mesons has been found to be consistent with the power law $σ_\mathrm{pA} \propto \mathrm{A}^α$, with the $α$ parameter increasing as a function of $p_\mathrm{T}$ for all the particles, and an approximate hierarchy $α_η\approx α_ϕ> α_ω$. The cross section ratios $σ_η/σ_ω$, $σ_ρ/σ_ω$ and $σ_ϕ/σ_ω$ have been studied as a function of the size A of the production target, and an increase of the $η$ and $ϕ$ yields relative to the $ω$ is observed from p-Be to p-U collisions.