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Deeply Virtual Compton Scattering off Helium-4

Abstract : The Generalized Parton Distributions (GPDs) are rich structure functions that contain information on quark/anti-quark correlations, and on correlation between longitudinal momentum and the transverse spatial position of partons. These GPDs are accessible via hard exclusive reactions such as Deeply Virtual Compton Scattering (DVCS), i.e. the leptoproduction of a real photon where the photon is emitted by the target hadron. Nuclear DVCS opens a new avenue to explore the nature of medium modifications at the partonic level. In this work, we present the first exclusive measurement of the DVCS process off helium-4 with a longitudinally polarized electron beam of 6 GeV using the CLAS detector in the experimental Hall-B at Jefferson Lab, USA. The helium-4 is of particular interest since the number of GPDs is reduced to one, because of its spin zero. The aim of this study is to understand the nuclear medium modifications of parton distributions. In our experiment, the CLAS detector was upgraded with a Radial Time Projection Chamber (RTPC) to detect the low-energy recoil nuclei, and an Inner Calorimeter (IC) to detect the forward going photons. The details of the structure, calibration and working principle of the RTPC will be presented. Then, the measurement of the beam-spin asymmetries in the DVCS channel will be presented.
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Submitted on : Wednesday, October 21, 2015 - 4:32:41 PM
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  • HAL Id : tel-01218756, version 1

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Mohammad Hattawy. Deeply Virtual Compton Scattering off Helium-4. Nuclear Experiment [nucl-ex]. Université Paris Sud - Paris XI, 2015. English. ⟨NNT : 2015PA112161⟩. ⟨tel-01218756⟩

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