Exclusive $\omega$ meson muoproduction on transversely polarised protons

TL;DR

This paper reports on the measurement of azimuthal asymmetries in exclusive $mbda$ meson production using muon scattering on transversely polarized protons, providing insights into nucleon structure and GPDs.

Contribution

First measurement of multiple azimuthal asymmetries in exclusive $mbda$ meson production on transversely polarized protons at COMPASS, probing GPDs related to nucleon spin structure.

Findings

Asymmetries sensitive to GPD $E$ and $H_T$ were measured.

Results provide constraints on nucleon helicity-flip and transversity GPDs.

Data compared with GPD-based theoretical models.

Abstract

Exclusive production of $\omega$ mesons was studied at the COMPASS experiment by scattering $160~\mathrm{GeV}/\mathit{c}$ muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality $1~(\mathrm{GeV}/\mathit{c})^2 < Q^2 < 10~(\mathrm{GeV}/\mathit{c})^2$, Bjorken scaling variable $0.003 < x_{\mathit{Bj}} < 0.3$ and transverse momentum squared of the $\omega$ meson $0.05~(\mathrm{GeV}/\mathit{c})^2 < p_{T}^{2} < 0.5~(\mathrm{GeV}/\mathit{c})^2$. The measured asymmetries are sensitive to the nucleon helicity-flip Generalised Parton Distributions (GPD) $E$ that are related to the orbital angular momentum of quarks, the chiral-odd GPDs $H_{T}$ that are related to the transversity Parton Distribution Functions, and the sign of the $\pi\omega$ transition form factor. The results are compared to recent calculations of a GPD-based model.