Speaker
Description
We perform the first simultaneous extraction of parton collinear and transverse degrees of freedom from low-energy $pA$ and $\pi A$ fixed-target Drell-Yan data in order to compare the transverse momentum dependent (TMD) parton distribution functions (PDFs) of the pion and proton. Specifically, we extract both pion PDFs and TMD PDFs simultaneously, and at the same time, we extract proton TMD PDFs in this analysis. We demonstrate that the average transverse separation of the quark field encoded in TMDs of the pion is less than that in the proton by more than $5 \sigma$. The behavior of this average transverse separation of the quark field is that it decreases as its longitudinal momentum fraction, $x$ decreases. In studying the nuclear modification of TMDs, we find clear evidence for a transverse EMC effect. We comment on possible explanations for these intriguing behaviors, which call for a deeper examination of tomography in a variety of strongly interacting quark-gluon systems.
