00 4 v 1 3 N ov 1 99 8 Charm ‘ in ’ the Photon
نویسنده
چکیده
Some recent ZEUS results on the photoproduction of open charm and possible implications for photon structure are discussed. 1 Open Charm Photoproduction at HERA Photoproduction of ‘open’ charm (as opposed to cc̄ bound states) can take place via several processes at HERA. The most obvious is photon-gluon fusion. The photon interacts directly with a gluon from the proton via t-channel charm quark, producing a high transverse energy charm balanced by an anticharm (Fig. 1a). At high enough transverse energies, the c and c̄ will each lead to the formation of jets of hadrons. One hadron in each jet will in general be charmed. Photon-gluon fusion is often assumed to be the dominant, or indeed only, process. Nevertheless, other possible production mechanisms exist. The photon can fluctuate into a qq̄ state which may be long lived on the timescale of strong interactions. The qq̄ state can thus form a complex partonic structure. Partons from the photon can then undergo hard scattering with partons from the proton so called ‘Resolved Photon’ interactions. This allows the possibility of charm production via gluon-gluon fusion (Fig. 1b), where one gluon comes from the proton, the other from the photon.
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