Exclusive $\ddot{I}‰$ meson muoproduction on transversely polarised protons

Abstract

Exclusive production of $\ddot{I}‰$ mesons was studied at the COMPASS experiment by scattering $160\mathrm{GeV}/c$ muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality $1(\mathrm{GeV}/c{)}^2<Q^2<10(\mathrm{GeV}/c{)}^2$, Bjorken scaling variable $0.003<x_{Bj}<0.3$ and transverse momentum squared of the $\ddot{I}‰$ meson $0.05(\mathrm{GeV}/c{)}^2<p_T^2<0.5(\mathrm{GeV}/c{)}^2$. 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 $\ddot{I}€\ddot{I}‰$ transition form factor. The results are compared to recent calculations of a GPD-based model.

23 pages, 9 figures