Le Département d'Électronique des Détecteurs et d'Informatique pour la Physique

Protons and neutrons are known to be the main constituents of the visible matter in the universe, however they still remain nowadays not fully understood in modern physics. These constituents of matter are actually made out of quarks and gluons (collectively referred to as partons), and are governed by the laws of quantum chromodynamics (QCD). Nevertheless at energies close to the proton mass, the perturbative methods cannot be used, and the partons dynamics is described by structure functions. The Generalised Partons Distributions (GPDs) encode the correlation between longitudinal momentum and transverse position of partons inside the nucleon. GPDs can be studied through Deeply Virtual Compton Scattering (DVCS) in which the proton interacts with a virtual photon to produce a single real photon leaving the proton intact in the final state.

The COMPASS experiment at CERN has measured DVCS cross section using positive and negative polarised muon beams of 160 GeV impinging on a liquid hydrogen target. All the involved particles of this process are detected: the magnetic and tracking system before the target allows to measure the incident muon, while the produced muon and photon are detected in the forward COMPASS spectrometer and the three electromagnetic calorimeters. The recoiled proton is detected in a time of flight detector placed around the target. In addition to these independent measurements, a deterministic multivariate analysis tool (kinematically constrained fit) is applied to improve the values of the measured observables.

This thesis is based on the 2016 and 2017 data taking and shows the most recent results on the DVCS analysis in the COMPASS experiment, up to the study of the differential DVCS cross section with respect to the four-momentum transfer to the recoiled proton. An interpretation in terms of transverse extension of partons inside the proton is acquired at x_Bj = 0.06.
 

The presentation will be in English.  

Location: conference room 135 building 703, CEA Saclay (Orme des Merisiers) or in the virtual room available at this link: 

https://cern.zoom.us/j/9856735938?pwd=UjZST0ZBRXRqeWFDQ0czQ1J3aWRQdz09