Light neutral mesons production in p-A collisions at $\sqrt{s} = 27.5$ GeV with the NA60 Experiment

TL;DR

The NA60 experiment measured light neutral meson production in proton-nucleus collisions at 27.5 GeV, providing precise data on meson form factors, line shapes, and nuclear dependence, revealing how production varies with target size and transverse momentum.

Contribution

This study provides the most precise measurements of electromagnetic form factors and meson line shapes in p-A collisions, and investigates the nuclear dependence of meson production cross sections.

Findings

Precise electromagnetic form factors for η and ω mesons.

First measurement of the ρ line shape and effective temperature in elementary collisions.

The nuclear dependence parameter α increases with transverse momentum.

Abstract

The NA60 experiment has studied low-mass muon pair production in proton-nucleus (p-A) collisions with a system of Be, Cu, In, W, Pb and U targets using a 400 GeV/$c$ proton beam at the CERN SPS. Thanks to the collected data sample of 180\,000 low mass muon pairs, the most precise measurement currently available was performed for the electromagnetic transition form factors of the $\eta$ and $\omega$ mesons. The $\rho$ line shape was quantitatively investigated, and its effective temperature measured for the first time in elementary collisions. The transverse momentum spectra for the $\omega$ and $\phi$ mesons have been studied in the full $\pt$ range accessible, up to 2 GeV/$c$. The cross section ratios $\sigma_\rho/\sigma_\omega$ and $\sigma_\phi/\sigma_\omega$ have been considered in full $\pt$ as a function of the size of the production target. The nuclear dependence of the production cross sections of the $\eta$, $\omega$ and $\phi$ mesons has finally been studied in terms of the power law $\sigma_\mathrm{pA} \propto \mathrm{A}^\alpha$, where the $\alpha$ parameter has been found to increase as a function of $\pt$.