Photon-Jet cross sections in Deep-Inelastic Scattering

We present the complete next-to-leading order calculation of isolated prompt photon production in association with a jet in deep-inelastic scattering. The calculation involves, direct, resolved and fragmentation contributions. It is shown that defining the transverse momenta in the proton virtual-photon frame (CM*), as usually done, or in the laboratory frame (LAB), as done in some experiments, is not equivalent and leads to important differences concerning the perturbative approach. In fact, using the latter frame may preclude, under certain conditions, the calculation of the next-to-leading order correction to the important resolved component. A comparaison with the latest ZEUS data is performed and good agreement is found in the perturbatively stable regions.