Department of Physics Colloquium

Aspects of proton structure
(Sanjin Benić, Department of Physics, PMF)

I discuss the contemporary physics trends in exploring the structure of the proton in terms of its constituent partons: quarks and gluons. I start off with the textbook example of the parton model and the collinear parton distributions that are probed by the deep inelastic scattering experiment. I emphasize the physics case to go beyond this simple one-dimensional picture and into the multidimensional description of the proton which has nowadays developed into two large research streams. The first one covers the transverse momentum dependent distributions inside the proton and I explain for example how it leads to an interesting correlation between the proton spin and the transverse motion of the partons. The second research stream concerns the proton imaging whereby we wish to understand how are the individual quarks and gluons distributed in the space inside the proton. In the final part I consider these generalizations in the limit of high energy where a new state of matter entirely composed of randomly correlated maximally packed state of gluons is hypothesized to emerge and hold universally for any hadron and for any nuclei. These developing ideas are expected to fully blossom in the years to come, marking the era of new high energy electron-ion colliders worldwide.