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Volume 346 - 23rd International Spin Physics Symposium (SPIN2018) - Parallel Session: 3D Structure of the Nucleon: GPDs and Form Factors (C. Lorce and S. Niccolai)
Spin-density matrix elements in hard exclusive muoproduction of $\omega$ mesons at COMPASS
B. Marianski* on behalf of the COMPASS Collaboration
*corresponding author
Full text: pdf
Pre-published on: 2019 August 19
Published on: 2019 August 23
Spin density matrix elements (SDMEs) have been determined for
$\omega$ meson production on unpolarized protons, in the COMPASS
kinematic region of 1.0 (GeV/c)$^2$ $< Q^{2} <$ 10.0 (GeV/c)$^2$, 5.0
GeV/$c^2$ $< W <
$ 17.0 GeV/$c^2$ and
0.01 (GeV/c)$^2$ $<p^{2}_{T} < $ 0.5 (GeV/c)$^2$ which corresponds to
$\left< Q^{2} \right>= 2.1$~(GeV/c)$^2$), $\left< W \right>= 7.6$~GeV/$c^2$
$\left<p^{2}_{T} \right> = 0.16$~(GeV/c)$^2$) mean values.
Using extracted SDMEs values the contribution of unnatural parity exchange
amplitudes and
the hypothesis of s-channel helicity conservation (SCHC) were
studied. Certain matrix elements e.g. $ r^{5}_{00}$ corresponding to
transition $\gamma^*_T \to
V_L$ indicate violation of SCHC in exclusive $\omega $ production.
A sizable contribution of unnatural parity exchange amplitudes is
found for the exclusive $\omega$ meson muoproduction, and there is a
indication of its decrease with increasing W.
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