Semi-Exclusive Production of Photons at HERA
  We study the feasibility of measuring semi-exclusive photon production \gamma + p \to \gamma + Y at HERA. The cross section of photons produced at large transverse momenta, recoiling off an inclusive system Y of limited mass, can without photon isolation cuts be simply expressed in terms of hard pQCD subprocesses and standard target parton distributions. With the help of event generators we identify the kinematic region where quark and gluon fragmentation processes can be neglected. The cross section in this semi-exclusive region is large enough to be measured with an upgraded HERA luminosity of L = 100/pb. The subprocesses of lowest order in \alpha_s are suppressed at low recoil masses M_Y, compared to higher order gluon exchange, i.e. BFKL contributions. The distinct M_Y-dependence makes it possible to determine experimentally the kinematic range where the higher order processes dominate. 
Paul Hoyer (NORDITA), Martin Maul (Lund U), Andreas Metz (Saclay)