Measurement of inclusive D_s^+- and D^*+- cross sections in photoproduction at HERA

Abstract

The first measurement of inclusive D_s^+- photoproduction cross sections has been performed with the ZEUS detector at the HERA ep collider using an integrated luminosity of 38pb^-1. The measurement has been performed for photon-proton centre of mass energies in the range 130<W<280 GeV and photon virtuality Q²<1 GeV². These measurements are compared with inclusive D^*+- cross sections measured previously in the same kinematic range and the results are confronted with theoretical expectations. A new measurement of D^*+- differential cross sections at lower energies 80<W<120 GeV and Q²<0.015 GeV² is also presented and compared with available perturbative QCD calculations using several fragmentation models.

Complete Paper:

Postscript

Figures:

Figure 1: DeltaM distributions for the low-W events inside the D⁰ mass region. The wrong charge distribution is shown as a dashed histogram.

Figure 2: Mass distribution of the D_s candidates for events inside the phi mass region ( 1.0115< M(K⁺K^-)<1.0275 GeV). The solid curve is an unbinned fit to a Gaussian-shaped resonance plus an exponential background.

Figure 3: Differential D_s and D^* cross sections in p_t^D, where D stands for D^* or D_s. The D_s (dots) and D^* (triangles) data are compared with massive NLO predictions a) for nominal and b) for extreme parameter settings.

Figure 4: Differential D_s and D^* cross sections in eta^D, where D stands for D^* or D_s. The D_s (dots) and D^* (triangles) data are compared with massive NLO predictions a) for nominal and b) for extreme parameter settings.

Figure 5: Differential cross sections a) dsigma/dp_t^Ds and b) dsigma/deta^Ds compared to the BKL model. The octet-to-singlet ratio is 1.3, as tuned for the high-W D^* region.

Figure 6: Low-W differential cross sections compared to massive NLO calculations. a) dsigma/dp_t^D* ; b) dsigma/deta^D* for the full p_t^D* region ; c) dsigma/deta^D* for the low p_t^D* region ; d) dsigma/deta^D* for the high p_t^D* region. The full (dotted) curves correspond to the nominal (extreme) parameter setting with the Peterson fragmentation parameter epsilon=0.036, while the dashed (dashed-dotted) curves correspond to the PYTHIA fragmentation.

Figure 7: Low-W differential cross sections a) dsigma/dp_t^D* and b) dsigma/deta^D* for the high p_t^D* region, compared to massless NLO calculations with several photon structure functions. Peterson fragmentation was used with epsilon=0.116.

Figure 8: Low-W differential cross sections compared to the BKL model. a) dsigma/dp_t^D* ; b) dsigma/deta^D* for the full p_t^D* region ; c) dsigma/deta^D* for the low p_t^D* region ; d) dsigma/deta^D* for the high p_t^D* region. The octet-to-singlet ratio is 1.3, as tuned for the high-W D^* region.

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