Exploring Nuclear Dependence of R = σ_L/σ_T at Jefferson Lab

Novel experiments at Jefferson Lab (JLab) are providing new opportunities to probe the internal structure of nucleons through both deep inelastic scattering (DIS) and semi-inclusive DIS (SIDIS). A central quantity of interest is the ratio of longitudinal-to-transverse virtual photon cross sections, R = σ_L/σ_T, which is needed to extract the structure functions F₁, F₂, and F_L. These structure functions characterize the distribution of quarks in nucleons and nuclei, but limited precision in existing measurements of R hinders our understanding of possible nuclear modifications.



Experiments E12-24-001 (R-SIDIS) and E12-14-002 (Nuclear R) aim to close this gap. R-SIDIS will employ semi-inclusive measurements to explore R for pions, kaons, and explore the hadronization process, while Nuclear R aims to extract R across a wide range of nuclear targets and kinematics. Both experiments will employ Rosenbluth separation techniques to provide the highest-precision systematic studies of R = σ_L/σ_T and its nuclear dependence, ΔR = R_A - R_D.



I will present the physics background of these experiments, highlight progress for R-SIDIS, which has recently completed its first phase of data collection, and outline the anticipated scope and impact of these data with respect to our understanding of nucleon and nuclear structure.