Speaker
Description
We investigate the sensitivity of photon-induced dilepton production in proton-proton collisions to the proton charge radius. The analysis is performed using both momentum-space and impact-parameter formulations within the equivalent photon approximation, which have been shown to provide consistent results for exclusive processes. The proton structure is modeled through the electromagnetic form factor, and its impact is explored by varying the dipole parameter $\lambda^2$ corresponding to different proton-radius values within the range reported by the Particle Data Group. In addition to the dominant electric contribution, the calculations also include the magnetic term in the proton form factor structure.
By comparing theoretical predictions with ATLAS and CMS measurements at $\sqrt{s} =$ 7 and 13 TeV, we quantify the current experimental sensitivity using a $\chi^2$ analysis. We show that the existing fiducial kinematic coverage significantly limits the ability to resolve differences between proton-radius scenarios, despite measurable effects at the few-percent level.
Our results indicate that exclusive dilepton production at the LHC provides a complementary and independent probe of the proton electromagnetic structure. We emphasize that extending the accessible kinematic range, particularly to forward rapidities and higher invariant masses, would substantially enhance sensitivity to the proton charge radius.
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