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.