Speaker
Mr
Philipp Jörg
(University of Freiburg)
Description
A major part of the COMPASS-II program will be dedicated to the investigation of generalized parton distributions (GPDs)
and transverse momentum dependent parton distributions (TMDs), which aim for the most complete
description of the partonic structure of the nucleon.
GPDs are experimentally accessible via lepton-induced exclusive reactions, in particular
the Deeply Virtual Compton Scattering (DVCS)
and Deeply Virtual Meson Production (DVMP). At COMPASS, those processes are investigated using an high intensity
muon beam of 160 GeV and a 2.5 m-long liquid hydrogen target. In order to optimize the selection of exclusive reactions at those
energies, the target is surrounded by a new barrel-shaped time-of-flight system to detect the recoiling particles.
COMPASS-II covers the up to now unexplored $x_{Bj}$ domain ranging from 0.01 to 0.15.
The option to change simultaneously the charge and polarization of the muon beam allows to perform DVCS measurements on a proton target and to
access the Compton form factor related to the dominant GPD $H$, and thus to provide new experimental constraints
on the theoretical GPD models in the intermediate $x_{Bj}$ regime.
From the sum of cross-sections measured with positive and negative beam polarity, the pure DVCS cross-section can be extracted.
Pilot measurements for the COMPASS II program allow for an extraction of the $t$-dependence of the pure DVCS cross-section in a single $x_{Bj}$ bin.
This provides first information on the nucleon transverse size in an up to now uncharted $x_{Bj}$ regime.
Primary author
Mr
Philipp Jörg
(University of Freiburg)
