Sensitivity of the photon-induced processes to the proton radius

We study the exclusive production of dileptons in proton–proton collisions as a probe of the proton radius. Using a dipole form factor model, we compare the conventional choice of ${\mathrm{\Lambda }}^2=0.71$~GeV${}^2$ with PDG test scenarios corresponding to $r_p=0.8751$~fm and $r_p=0.84087$~fm. The sensitivity is greatest at large dilepton invariant masses and forward/backward rapidity. Fitting to the current ATLAS and CMS data within the adopted model gives ${\mathrm{\Lambda }}^2=0.465\pm 0.056{\mathrm{G}\mathrm{e}\mathrm{V}}^2$, corresponding to an effective radius $r_p=1.002\pm 0.038\mathrm{f}\mathrm{m}$, which indicates non-trivial sensitivity on the proton radius scale, but is not yet a definitive solution to the proton radius puzzle.