Charm Photoproduction using Electron Taggers with the Zeus Detector at HERA

Abstract

Charm production has been studied at a centre-of-mass energy of vs = 318 GeV in the ZEUS experiment at the electron-proton collider HERA. The data from the years 1998 - 2000 are used for this analysis which correspond to an integrated luminosity of <it>L</it> ~ 81 pb^-1 The experimental signature of the process is: <br /> ep -> e c cbar X -> e D* Y.<br /> Photoproduction is identified by reconstructing the D*(2010) meson via the decay chain D*⁺ -> K^- p⁺ p⁺ (+ c.c.) and by selecting the scattered electron in one of the dedicated electron taggers located 44m and 35m away from the interaction point.<br /> The total visible cross section and differential cross sections as a function of p_T(D*), ?(D*) and W were measured in the restricted phase space: -1.0 < η(D*) < 1.5, p_T(D*) > 1.5 GeV, 80 GeV < W < 120 GeV and Q² < 0.015 GeV² in case of the 44m tagger sample, and -1.5 < ηD(*) < 1.0, p_T(D*) > 2.0 GeV, 200 GeV < W < 260 GeV and Q² < 0.02 GeV² in case of the 35m tagger sample. Next-to-leading-order QCD predictions were calculated in the same kinematic region as the data. The comparison of the theoretical predictions with the data shows good agreement within the theoretical uncertainties. <br /> Total charm cross sections were calculated by extrapolating the visible cross sections in the limited (p_T(D*), η(D*)) phase space to the full kinematic region. The measurements with the 35m tagger overlap with previous untagged data while the 44m tagger data are used to study a new intermediate region 80 GeV < W_44m < 120 GeV between fixed target and and the other HERA measurements. The comparison of the NLO QCD predictions with the data shows good agreement.