The photon PDF within the CT18 global analysis

Understand

Building upon the most recent CT18 global fit, we present a new calculation of the photon content of the proton based on an application of the LUX formalism.

• In this work, we explore two principal variations of the LUX ansatz.
• In one approach, which we designate "CT18lux," the photon PDF is calculated directly using the LUX formula for all scales, $\mu$.
• In an alternative realization, "CT18qed," we instead initialize the photon PDF in terms of the LUX formulation at a lower scale, $\mu\! \sim\! \mu_0$, and evolve to higher scales with a combined QED+QCD kernel at $\mathcal{O}(\alpha),~\mathcal{O}(\alpha\alpha_s)$ and $\mathcal{O}(\alpha^2)$.