Speaker
Eva-Maria Kabuss
(Johannes Gutenberg-Universitat)
Description
The high energy polarised muon beam available at CERN with
the option of using positive or negative muons with opposite
polarisation gives COMPASS an excellent possibility to study
generalised parton distributions via deeply virtual Compton
scattering and hard exclusive meson production.
In a first step we will use an unpolarised proton target to measure
the $x_{Bj}$-dependence of the $t$-slope of the DVCS cross section
to observe a possible shrinkage of the nucleon
with increasing $x_{Bj}$. Furthermore, the beam charge and spin difference
and sum will be measured over a wide kinematic range to determine the
Compton form factor related to real and imaginary parts of the GPD $H$.
As a second step we consider to use a transversely polarised proton
target to collect data to constrain the GPD $E$.
An exploratory measurement was performed in 2012 with the
COMPASS spectrometer upgraded with a proton recoil detector surrounding
a 2.5 m long liquid hydrogen target and an enlarged acceptance for
photon detection. The status of the analysis and the perspectives
for the planned measurements in 2016/17 will be discussed.
Primary author
Eva-Maria Kabuss
(Johannes Gutenberg-Universitat)
