How bright is the proton? A data driven determination of the photon content of the proton.

It is well known that a fast moving charge particle is accompanied by an ensemble of virtual photons, that in collisions can give rise to photon initiated processes. For electrons the distribution of photons is calculable with arbitrary precision. For hadrons, the accompanying photon system is calculable only for impact parameters larger than the hadron size. There is interest in computing the impact of initial photons subprocesses at the LHC, and it was generally though that
the photon distribution in the proton could only be obtained by experimentally studying certain photon initiated processes. In this talk I will illustrate recent progress on this matter, showing that in fact the photon parton densities can be extracted with negligible errors from existing data on the proton electromagnetic structure functions and form factors.