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 pT range accessible, from pT= 0 up to 2GeV/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 σpA∝ A α, with the α parameter increasing as a function of pT for all the particles, and an approximate hierarchy αη≈ αϕ> αω. The cross section ratios ση/ σω, σρ/ σω and σϕ/ σω 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.