NLO QCD predictions for dijet photoproduction in lepton-nucleus scattering at the EIC, LHeC, HE-LHeC, and FCC

We calculate cross sections for inclusive dijet photoproduction in electron-nucleus scattering in the kinematics of the future EIC, a possible LHeC, HE-LHeC, and the FCC using next-to-leading order (NLO) perturbative QCD and nCTEQ15 and EPPS16 nuclear parton density functions (nPDFs). We make predictions for distributions in the dijet average transverse momentum ${\bar p}_T$, the average rapidity $\bar{\eta}$, the observed nuclear momentum fraction $x_A^{\rm obs}$, and the observed photon momentum fraction $x_{\gamma}^{\rm obs}$. Comparing the kinematic reaches of the four colliders, we find that an increase of the collision energy from the EIC to the LHeC and beyond extends the coverage in all four considered variables. Notably, the LHeC and HE-LHeC will allow one to probe the dijet cross section down to $x_A^{\rm obs} \sim 10^{-4}$ (down to $x_A^{\rm obs} \sim 10^{-5}$ at the FCC). The ratio of the dijet cross sections on a nucleus and the proton, $\sigma_A/(A\sigma_p)$, depends on $x_A^{\rm obs}$ in a similar way as the ratio of gluon densities, $g_A(x_A,\mu^2)/[A g_p(x_A,\mu^2)]$, for which current nPDFs predict a strong suppression due to nuclear shadowing in the region $x_A^{\rm obs} < 0.01$. Dijet photoproduction at future lepton-nucleus colliders can therefore be used to test this prediction and considerably reduce the current uncertainties of nPDFs.