12–16 Apr 2021
Stony Brook, NY
US/Eastern timezone

Spin Density Matrix Elements in Exclusive ρ0 Meson Muoproduction at COMPASS

14 Apr 2021, 10:54
18m
Virtual (Stony Brook, NY)

Virtual

Stony Brook, NY

Online
Contributed Talk Spin Physics Spin Physics

Speaker

Dr Witold Augustyniak (National Centre for Nuclear Research Warsaw,poland)

Description

We will present results on Spin Density Matrix Elements (SDMEs) measured in hard exclusive ρ0 meson muoproduction on the proton at COMPASS using 160 GeV/c polarised μ+ and μ beams scattering off a liquid hydrogen target. The measurement covers the range 5 GeV/c2 < W < 17 GeV/c2, 1.0 (GeV/c)2 < Q2 < 10.0 (GeV/c)2 and 0.01 (GeV/c)2 < pT2 < 0.5 (GeV/c)2. Here, Q2 denotes the virtuality of exchanged photon, W the mass of final hadronic system and pT the transverse momentum of the ρ0 meson with respect to the virtual-photon direction. The kinematic dependences of SDMEs and of related observables will be presented. The measured non-zero SDMEs for transitions of transversely polarised virtual photons to longitudinally polarised vector mesons (γTVL) indicate a significant violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a small contribution of unnatural-parity-exchange transitions at small values of W. The results provide important input for modelling Generalised Parton Distribution (GPDs). In particular, they may allow to evaluate in a model-dependent way the role of parton-helicity flip GPDs ("transversity GPDs") in exclusive ρ0 production.

Primary authors

Dr Witold Augustyniak (National Centre for Nuclear Research Warsaw,poland) Bakur Parsamyan (University of Turin, INFN and JINR)

Presentation materials