Abstract
One of the goals of the COMPASS experimental program 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 π0 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 π0 production from the 2012 pilot run, recently submitted to publication, are presented. Using average of both μ+ and μ− data, the γ*p cross section is extracted as a function of the squared four-momentum transfer t, and of the azimuthal angle ϕ between the scattering plane and the π0 production plane. The average kinematics of the measurement are ⟨Q2⟩ = 2.0 (GeV/c)2, ⟨ν⟩ = 12.8 GeV, ⟨xB⟩ = 0.093, and ⟨−t⟩ = 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.
Highlights
The General Parton Distributions (GPDs) provide a comprehensive tool for describing the 3D partonic structure of the nucleon [1, 2, 3, 4, 5]
GPDs correlate the information from Parton Distribution Functions (PDFs) and form factors, encoding the longitudinal momentum fraction and the transverse spatial position of a parton
Deep Virtual Compton Scattering (DVCS) is sensitive to GPDs Hq, Eq, Hq, and Eq At leading-twist, the vector and pseudo-scalar meson productions by longitudinally polarised virtual
Summary
The General Parton Distributions (GPDs) provide a comprehensive tool for describing the 3D partonic structure of the nucleon [1, 2, 3, 4, 5]. GPDs correlate the information from Parton Distribution Functions (PDFs) and form factors, encoding the longitudinal momentum fraction and the transverse spatial position of a parton. They provide an access to the total angular momentum carried by a parton in the nucleon via the Ji’s relation [2]:. DVCS is sensitive to GPDs Hq, Eq, Hq, and Eq At leading-twist, the vector and pseudo-scalar meson productions by longitudinally polarised virtual. Different partonic contents of the produced mesons give different sensitivities to the GPDs. The exclusive π0 production is sensitive to the chiral-odd GPD ETq. the current results from exclusive π0 production at COMPASS, presented in this paper and submitted to publication, support this finding [11]
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