Deep Inelastic Scattering at CLAS12

My research within the CLAS12 collaboration focuses on Semi-Inclusive Deep Inelastic (SIDIS) processes, which provide valuable insights into the 3-D spin structure of nucleons. The CLAS12 detector, with its large acceptance, is ideal for studying transverse-momentum dependent parton distribution functions in the mid- to high-momentum fraction $x$ region and at energy scales below ~12 GeV2.

One of our group’s primary focuses is investigating the cross sections and their azimuthal modulations in SIDIS processes with an unpolarized hydrogen target. This enables us to get access to the Boer-Mulders transverse momentum dependent (TMD) parton distribution in the quark valence region by analyzing the $\cos(2\phi)$ azimuthal modulations of the unpolarized SIDIS cross section. The Boer-Mulders TMD provides insights into quark spin-orbit correlations within an unpolarized nucleon. The high statistical precision of this experiment allows us to study the azimuthal modulations of the cross section in the full five-dimensional phase space $(x, Q^2, z, p_T, \phi)$, providing also access to higher-twist effects through the $\sin(\phi)$ and $\cos(\phi)$ moments of the cross section. Additionally, our group has been involved in studying the reaction mechanisms and hadronization processes in semi-inclusive deep inelastic scattering through pion multiplicities measurements. These data will significantly contribute to our understanding of the transition from the non-perturbative to the perturbative regime. The anticipated total statistics for this experiment are two orders of magnitude greater than the existing HERMES and CLAS data. The E12-06-112 experiment at CLAS12 has received most of its allocated beam time during FY2018-FY2020 as part of Run Group A. Similarly, the E12-09-008 experiment has received its allocated beam time as part of Run Group B.

Looking ahead, the analysis can be naturally extended to investigate pion and kaon multiplicities and azimuthal modulations with hydrogen, deuteron, and nuclear targets. These studies will provide deep insights into the 3-D structure of nucleons and nuclei in momentum space.

Cover image credit: Jefferson Lab,