Drell-Yan at the Electron-Ion Collider

Abstract

The photon is arguably the most universally important particle across all fields of physics. Despite its status as a fundamental particle, at high energies the photon can be seen as a hadronic source of partons. The partonic content of the photon is very poorly constrained compared to that of the proton, with photon PDF uncertainties typically one or two orders of magnitude larger than their proton counterparts, despite the fact that its source, the $γ\to q\bar{q}$ splitting, is perturbatively calculable. The high luminosity, excellent particle identification, and far-backward electron tagging capabilities of the Electron-Ion Collider make it an ideal environment for studying photon parton distribution functions. Similar to the $p+p$ or $π+p$ systems, photoproduction at the EIC can be thought of as two parton distributions colliding. One of the most powerful processes in such collisions is production of lepton pairs, i.e. $h+p\rightarrow l^+l^-+X$, known as the Drell--Yan process. This process has the ability to access for the first time the transverse-momentum-dependent parton distributions of the photon. The transversely polarized proton beam of the EIC additionally provides a possible means of accessing the transversity distribution of the proton without relying on fragmentation functions.

Figures (14)

• Figure 1: Example diagram of the leading-order Drell--Yan process in photoproduction.
• Figure 2: Acceptance of the ePIC low-$Q^2$ tagger as a function of inelasticity $y=E_\gamma/E_e$. The polar angle of the scattered electron is assumed to be negligible.
• Figure 3: Left: Pseudorapidity distributions of leptons produced in the Drell--Yan process for the 10x275 GeV configuration, as predicted by Sherpa with the SAS2M and SAS1M PDF sets. The nominal ePIC acceptance of $|\eta|\leq3.5$ is the region between the black dashed lines. Center: Distribution of lepton pseudorapidity as a function of the true $x_{\gamma}$. Right: Lab frame $p_T$ distributions of Drell--Yan leptons.
• Figure 4: Response matrix of $x_{\gamma}^{\mathrm{LO}}=\frac{M_{\ell\ell}}{\sqrt{s_{\gamma p}}} e^{-y_{\ell\ell}}$, assuming the experimental acceptances and resolutions discussed in Appendix \ref{['sec:appendix']}. Note the logarithmic color scale.
• Figure 5: Example diagrams for QED processes contributing to inclusive dilepton production. Left: Bethe--Heitler process. Right: QED Drell--Yan Process where an antilepton from the photon annihilates with a lepton from the proton PDF.