Inclusive D^* production in photon-photon collisions at next-to-leading order QCD}

The next-to-leading order cross section for the inclusive production of charm quarks in collisions is calculated as a function of the transverse momentum and the rapidity y in approaches using massive or massless charm quarks. For the direct cross section we derive the massless limit from the massive theory with the result that this limit differs from the massless version with factorization by finite corrections. Subtracting or adding these corrections allows us to compare the two approaches on equal footing. We establish massless and massive versions with 3 and 4 initial flavours which are shown to approach the massless approximations very fast with increasing . With these results we calculate the inclusive cross section in collisions using realistic evolved fragmentation functions with appropriate factorization scales and compare with recent data for from three LEP collaborations after single- and double-resolved contributions have been added. Received: 25 September 2001 / Published online: 5 November 2001