are reviewed. Final states containing charm are mainly identified by reconstruction.pdf

are reviewed. Final states containing charm are mainly identified by reconstruction.pdf

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are reviewed. Final states containing charm are mainly identified by reconstruction

Heavy Flavour Production at HERAChristoph GrabOn behalf of the H1 and ZEUS CollaborationsInstitute for Particle Physics, ETH-Zurich, CH-8093 Zurich, SwitzerlandMeasurements of charm production in lepton-proton collisions at a centre-of-massenergy of ps = 300 GeV performed at HERA by the experiments H1 and ZEUSare reviewed. Final states containing charm are mainly identi ed by reconstructionof D and J= mesons. The results cover the region in 4-momentum transfersquared Q2, from photoproduction (Q2  0) to deep-inelastic scattering at highQ2. The experimental results are compared with theoretical predictions, basedprimarily on QCD and in some cases on phenomenological models inspired byRegge-theory.1 IntroductionThe study of heavy quark production in lepton-proton scattering provides animportant testing ground for the standard model. At the electron-proton col-lider HERA with an e p centre-of-mass energy ps = 300 GeV, heavy quarksare produced predominantly by the photon gluon fusion process g ! cc;where a real or virtual photon emitted by the electron a and a gluon from theproton generate a cc pair. In this case colour is transferred from the protonso that the proton breaks up (inelastic scattering). In general, also elasticscattering may occur where no colour is transferred and the proton can remainintact (di ractive interactions).The dominant contribution to charm production is due to exchange ofan almost real photon (photoproduction), where the negative squared four-momentum transfer carried by the photon is Q2  0. The charm quarkshadronize and are then either detected as \open charm, i.e. in nal states withcharmed hadrons, or alternatively as \hidden charm states, such as J= .The kinematics of charm production is described by three independentvariables, the centre-of-mass energy ps, the photon four-momentum squaredq2 = Q2 and either one of the scaling variables y = (q P=lP ), the inelasticityof the ep-interaction, or Bjorken-x x = Q2=(2P  l). Here P

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