Tomography of pions and protons via transverse momentum dependent distributions

Abstract

We perform the first simultaneous extraction of parton collinear and transverse degrees of freedom from low-energy fixed-target Drell-Yan data in order to compare the transverse momentum dependent (TMD) parton distribution functions (PDFs) of the pion and proton. We demonstrate that the transverse separation of the quark field encoded in TMDs of the pion is more than $4\sigma$ smaller than that of the proton. Additionally, we find the transverse separation of the quark field decreases as its longitudinal momentum fraction 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.

7 pages, 3 figures; version to appear in Phys. Rev. D

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• Strong Interaction Physics at the Luminosity Frontier with 22 GeV Electrons at Jefferson Lab
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• Measurement of $J/\psi$-pair production in $pp$ collisions at $\sqrt{s}=13$ TeV and study of gluon transverse-momentum dependent PDFs
• New insights from the flavor dependence of quark transverse momentum distributions in the pion
• Transverse distortion and single-spin asymmetries for low-lying octet baryons
• Deep Neural Network extraction of Unpolarized Transverse Momentum Distributions
• Tomography of Pions and Kaons in the QCD Vacuum: Transverse Momentum Dependent Parton Distribution Functions
• Lattice QCD Benchmark of Proton Helicity and Flavor-Dependent Unpolarized Transverse Momentum-Dependent Parton Distribution Functions at Physical Quark Masses