Measurement of the $\eta$ and $\omega$ Dalitz decays transition form factors in p-A collisions at 400 GeV/$c$ with the NA60 apparatus

TL;DR

This study measures the electromagnetic transition form factors of the $ ext{eta}$ and $ ext{omega}$ mesons in proton-nucleus collisions at 400 GeV/$c$, confirming previous results with higher precision and highlighting discrepancies with the Vector Meson Dominance model.

Contribution

It provides new, more precise measurements of the $ ext{eta}$ and $ ext{omega}$ Dalitz decay form factors in p-A collisions, extending previous experimental data.

Findings

Form factors agree with previous measurements, with improved uncertainties.

Results confirm discrepancy with Vector Meson Dominance model for $ ext{omega}$.

High-statistics data allows detailed analysis of meson decay contributions.

Abstract

The NA60 experiment has studied low-mass muon pairs production in proton-nucleus collisions at 400 GeV/$c$ at the CERN SPS. The mass spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons $\eta$, $\rho$, $\omega$, $\eta'$ and $\phi$. The large collected statistics allows to isolate the contributions due to the Dalitz decays of the $\eta$ and $\omega$ mesons, from which the electromagnetic transition form factors of the two mesons have been extracted. The found values agree with the previous available measurements, improving their uncertainty thanks to the higher statistics. The results thus confirm the discrepancy with the prediction of the Vector Meson Dominance model in the case of the electromagnetic form factor of the $\omega$ meson.