Part of the COMPASS-II program is dedicated to the investigation of Generalized Parton Distributions (GPDs) via lepton-induced hard exclusive reactions, in particular Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production. Data have been taken in 2016 -17 using a high intensity muon beam of 160 GeV and a 2.5 m-long liquid hydrogen target surrounded by a barrel-shaped time-of-flight system to detect the recoiling particles and optimize the selection of exclusive events.
The DVCS cross-section and its |t|-dependence are extracted from the sum of cross-sections measured with opposite beam charge and polarization. From a pilot measurement, a first estimate of the transverse extension of partons in the proton in the sea quark range (xBj ~0.06), where no world data was available up to now, will be reported. The analysis method and the preliminary results from a part of the long run will be discussed.