Transverse target spin asymmetries in exclusive $\rho^0$ muoproduction

TL;DR

This study measures transverse target spin asymmetries in exclusive $ ho^0$ meson production at COMPASS, providing evidence for chiral-odd, transverse generalized parton distributions and comparing results with GPD-based models.

Contribution

First measurement of multiple azimuthal asymmetries in exclusive $ ho^0$ muoproduction on transversely polarized protons, supporting the existence of chiral-odd GPDs.

Findings

$ ext{sin} \, heta_S$ asymmetry is small and consistent with zero.

Results agree with GPD-based theoretical calculations.

Data supports the presence of chiral-odd, transverse GPDs.

Abstract

Exclusive production of $\rho^0$ mesons was studied at the COMPASS experiment by scattering 160 GeV/$c$ muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured as a function of $Q^2$, $x_{Bj}$, or $p_{T}^{2}$. The $\sin \phi_S$ asymmetry is found to be $-0.019 \pm 0.008(stat.) \pm 0.003(syst.)$. All other asymmetries are also found to be of small magnitude and consistent with zero within experimental uncertainties. Very recent calculations using a GPD-based model agree well with the present results. The data is interpreted as evidence for the existence of chiral-odd, transverse generalized parton distributions.