pANUCSTR · Study of the distribution of gluons and quarks inside the nucleon through ultra-peripheral collisions

Study of the distribution of gluons and quarks inside the nucleon through ultra-peripheral collisions

It is astonishing but true that we do not fully understand 95% of our mass and that of the visible universe. Visible matter is made of atoms, the atom's nucleus is made of protons and neutrons (collectively referred to as nucleons) and these nucleons consist of a highly-energetic soup of very-fast moving and constantly interacting quarks and gluons. Gluons have no mass and quarks a negligibly small one, yet together they generate most of the mass we can see. Understanding how that occurs is the objective of the present project. The project provides crucial information on the quarks and gluons inside the nucleon: where they are located, how they move and how they orbit each other, and the pressure distribution they generate. This work is of fundamental importance in our investigations into the origin of mass and will influence our understanding of the nuclear elements and nuclear astrophysics. I use data from the LHCb experiment at the Large Hadron Collider at CERN, obtained when protons and nuclei are smashed together at unprecedented energies. In glancing collisions, the projectiles do not break up, but turn some of their energy into mass, through Einstein’s famous E=mc2. By studying the newly created system, the structure of the original protons and nuclei can be inferred. In particular, I have been studying the exclusive process in which the newly created system consists of exactly one J/psi meson and the process in which the newly system consists of a pair of oppositely charged muons. The former process provides information about gluons, while the latter process is also sensitive to quarks. The production of J/psi mesons has already been studied by the LHCb experiment in proton-proton collisions. I provide the first measurement, using LHCb data, in the collision of protons and lead ions. The process with pairs of muons has never previously been studied and my work breaks new ground in the measurement of this process and what we know about the structure of quarks in the nucleon.

Data: CORDIS, © European Union