Study of the intrinsic 3D-structure of the proton at CERN
The structure of strongly interacting particles, like nucleons and mesons, is provided by the theory of strong interactions – Quantum Chromo-Dynamics (QCD). In the framework of QCD the internal structure and properties of nucleons and mesons are determined by the interactions between their elementary constituents, quarks and gluons (commonly referred to as ‘partons’).
The objective of the project is an experimental study of the proton intrinsic three-dimensional structure in terms of its elementary constituents, which situates this project in the new domain of QCD studies that surpass the commonly used one-dimensional picture. The phenomenological description of the three-dimensional structure is provided by the formalism of Generalised Parton Distributions (GPDs). They describe correlations between longitudinal momentum of a parton (along the proton momentum) and its transverse degrees of freedom; i.e. parton position in the plane perpendicular to the momentum of the proton. The investigation of such a correlation is frequently referred to as ‘the proton tomography’. In addition, GPDs correlate parton distributions with the proton spin and allow us to investigate the role of total and orbital angular momenta of quarks and gluons in explaining the proton spin ½.
In this project the GPDs studies will be performed by measuring various observables for processes of exclusive deeply virtual muoproduction of photons or mesons. The studies will be carried out in the framework of the COMPASS Collaboration by scattering high energy muons off unpolarised protons. The COMPASS apparatus consists of a high precision forward spectrometer, which is supplemented by the 4-m long recoil proton detector surrounding the liquid hydrogen target. The set-up is located at the unique CERN SPS M2 beam line that delivers naturally polarised μ± beams in the energy range between 50 and 280 GeV. The majority of the available data for the GPD programme was collected in 2016 and 2017.
The results of this project will improve considerably our knowledge in the domain of research on the three-dimensional proton structure by providing the data for GPDs parameterisation in a kinematic range that was not available before. It is expected that the results will be reported at international conferences and published in peer reviewed international journals.
Professor Andrzej Sandacz
NCBJ, High Energy Physics Division (BP3)
69, Hoza str., 00-681 Warsaw, Poland
phone: (+48) 603 515 762