CROSS-SECTIONS FOR CHARM PRODUCTION IN EP COLLISIONS - MASSIVE VERSUSMASSLESS SCHEME

The next-to-leading order inclusive cross section for large-pr photopr oduction of charm quarks at HERA is calculated in two different approa ches. Ln the first approach the charm quarks are treated as massive ob jects which are strictly external to the proton and the photon while i n the second approach the charm mass is neglected and the c quark is a ssumed to be one of the active flavours in the proton and photon struc ture functions. We present single-inclusive distributions in transvers e momentum and rapidity including direct and resolved photons. The cro ss section in the massless approach is found to be significantly large r than in the massive scheme. The deviation originates from several co ntributions which are disentangled. We argue that large-p(perpendicula r to) photoproduction of charm quarks at HERA will be sensitive to the charm content of the photon structure function.