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

TL;DR

This study investigates how the production of light neutral mesons in proton-nucleus collisions varies with nuclear size and transverse momentum, revealing nuclear effects and hierarchy in meson production cross sections.

Contribution

It provides the first detailed measurement of nuclear dependence of light neutral meson production across multiple targets and transverse momenta at 400 GeV.

Findings

The nuclear dependence follows a power law with increasing alpha for higher pT.

Alpha values show a hierarchy: alpha_eta ≈ alpha_phi > alpha_omega.

Yields of eta and phi mesons increase relative to omega from p-Be to p-U collisions.

Abstract

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 $\rho/\omega$ and $\phi$ 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 $\phi$ mesons has been found to be consistent with the power law $\sigma_\mathrm{pA} \propto \mathrm{A}^\alpha$, with the $\alpha$ parameter increasing as a function of $p_\mathrm{T}$ for all the particles, and an approximate hierarchy $\alpha_\eta \approx \alpha_\phi > \alpha_\omega$. The cross section ratios $\sigma_\eta/\sigma_\omega$, $\sigma_\rho/\sigma_\omega$ and $\sigma_\phi/\sigma_\omega$ have been studied as a function of the size A of the production target, and an increase of the $\eta$ and $\phi$ yields relative to the $\omega$ is observed from p-Be to p-U collisions.