Month: February 2022

In a paper in Physical Review Letters, the CLAS collaboration published some of the first results studying the reaction called Semi-Inclusive Deep Inelastic Scattering (SIDIS), in which a quark is violently ejected from a proton, eventually combining with an anti-quark to form a pi meson, which is detected. This reaction is one of the best ways to learn about the transverse momentum of quarks inside protons.

One of the leaders of the data analysis (and one of the leading authors on the paper) was our group’s own Giovanni Angelini. Giovanni recently defended his PhD thesis, which studied not only at beam spin asymmetries, the subject of this paper, but also pion multiplicities.

One of the strengths of this result is that SIDIS is studied over a multi-dimensional space. The paper presents results mapped in bins of momentum transfer, Q2, longitudinal momentum fraction, xB, pion momentum fraction, z, and pion transverse momentum: essentially the full set of possible dependencies. These results provide valuable constraints on models of how the proton is built from quarks and gluons.

In a recent paper published in the European Physical Journal A, Bill, Igor, and collaborators examine the world’s data on pion photoproduction on deuteron targets in order to learn about photoproduction on neutrons. Studying neutrons directly is not practical, since there is no way to make a stable target on which to perform an experiment. Instead, nuclear physicists must rely on scattering experiments on light nuclei containing neutrons. Among these, deuterium, a nucleus consisting of one proton and one neutron, is the most straightforward to analyze. Nevertheless, neutrons in deuterium are moving, experience binding effects, and any reaction products can re-interact with the nearby proton. This paper describes a theoretical framework for overcoming these challenges and shows what we’ve learned about photon-induced excitations of the neutron.