Experimental study of hard photon radiation processes at HERA

We present an experimental study of theep→eγ+p andep→eγ+X processes using data recorded by the H1 detector in 1993 at the electron-proton collider HERA. These processes are employed to measure the luminosity with an accuracy of 4.5 %. A subsample of theep→eγ+X events in which the hard photon is detected at angles θγ′ ≤ 0.45 mrad with respect to the incident electron direction is used to verify experimentally the size of radiative corrections to theep→eX inclusive cross section and to investigate the structure of the proton in theQ2 domain down to 2 GeV2, lower than previously attained at HERA.