Abstrakt
The focus of the COMPASS experiment at CERN is exploration of the proton structure. One of the orientations of the experimental programme is the measurement of exclusive processes.
The exclusive processes, such as Deep Virtual Compton Scattering (DVCS) or Hard Exclusive Meson Production, are important inputs for constraining the General Parton Distributions (GPDs). Exclusive pi0 production is the main source of background for DVCS process, while it provides important information on chiral-odd GPDs.
The dedicated GPD program started with a one month pilot run in 2012, followed by two full years of data taking in 2016-2017, using 160 GeV/c positive and negative muon beams, a liquid hydrogen target and new detectors such as a recoil proton detector and a large-angle electromagnetic calorimeter. Our results of the exclusive pi0 production from the 2012 pilot run, recently submitted to publication, are presented.
Using average of both mu+ and mu- data, the gamma*p cross section is extracted as a function of the squared four-momentum transfer t, and of the azimuthal angle phi between the scattering plane and the pi0 production plane. The average kinematics of the measurement are = 2.0 (GeV/c)^2, = 12.8 GeV, = 0.093, and = 0.256 (GeV/c)^2.
A comparison of our results with the phenomenological Goloskokov-Kroll model are shown. Prospect are given on upcoming results of the 2016/17 measurement.