Research on 3D structure of protons

Tutor: Professor Andrzej Sandacz

Internal structure and properties of hadrons are described by Quantum Chromo-Dynamics (QCD), the theory of strong interactions between quarks and gluons, constituents of nucleons and  mesons. Generalised Parton Distributions which help to describe 3D structure of nucleons take into account correlations between lateral component of quark/gluon momentum (along the nucleon momentum vector) and quark/gluon space distribution in the plane perpendicular to the vector (the so-called nucleon tomography), as well as correlation with nucleon spin. In particular GPDs provide insight into the role of the orbital angular momentum of quarks in explaining proton spin.

Information on GDP may be retrieved from data on cross-sections and various asymmetries observed in exclusive processes of single photon/meson production  in deep inelastic scattering of leptons on nucleons. Although theoretical studies of GPDs are well advanced, amount of available experimental data is still limited. An experiment started a few years ago in the Jefferson Laboratory (USA), the HERMES, H1, and ZEUS experiments are run at DESY (Germany), but COMPASS-II experiment run in CERN is presently the only experiment providing data at higher energies.

The proposed topic is a part of physical programme of that that latter experiment. The subject of the thesis will be exclusive production of high-energy photons and mesons in deeply inelastic scattering of polarized 160 GeV muons on unpolarized protons. An additional 4-metres-long recoil proton detector with a liquid hydrogen target and an additional electromagnetic calorimeter capable to extend range of accepted angles for the produced photons had to be installed at the COMPASS-II experiment to be able to accomplish the GPD project. Analysis of data acquired during the first run in 2012 is in progress. Next run is scheduled for 2016 and 2017. 

If accomplished, the project should produce some world-class results in pure research on 3D structure of nucleons. The results should help to verify basic predictions of the QCD theory and should significantly increase precision of parameters of nucleon structure phenomenological models.


More info:
Professor Andrzej Sandacz
NCBJ High Energy Physics Division (BP3)
69, Hoża str.
00-681 Warsaw