Dijet angular distributions in photoproduction of charm at HERA (original) (raw)
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The European Physical Journal C, 1999
Inclusive photoproduction of D * ± mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 280 GeV and photon virtuality Q 2 < 1 GeV 2. The data sample used corresponds to an integrated luminosity of 37 pb −1. Total and differential cross sections as functions of the D * transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured results in a kinematic region where the resolved photon contribution is significant.
Dijet angular distributions in direct and resolved photoproduction at HERA
Physics Letters B, 1996
Jet photoproduction, where the two highest transverse energy (E jet T ) jets have E jet T above 6 GeV and a jet-jet invariant mass above 23 GeV, has been studied with the ZEUS detector at the HERA ep collider. Resolved and direct photoproduction samples have been separated. The cross section as a function of the angle between the jet-jet axis and the beam direction in the dijet rest frame has been measured for the two samples. The measured angular distributions differ markedly from each other. They agree with the predictions of QCD calculations, where the different angular distributions reflect the different spins of the quark and gluon exchanged in the hard subprocess.
Inclusive jet cross sections and dijet correlations in D ∗ ± photoproduction at HERA
Nuclear Physics B, 2005
Inclusive jet cross sections in photoproduction for events containing a D * meson have been measured with the ZEUS detector at HERA using an integrated luminosity of 78.6 pb −1 . The events were required to have a virtuality of the incoming photon, Q 2 , of less than 1 GeV 2 , and a photon-proton centre-ofmass energy in the range 130 < W γp < 280 GeV. The measurements are compared with next-to-leadingorder (NLO) QCD calculations. Good agreement is found with the NLO calculations over most of the measured kinematic region. Requiring a second jet in the event allowed a more detailed comparison with QCD calculations. The measured dijet cross sections are also compared to Monte Carlo (MC) models which incorporate leading-order matrix elements followed by parton showers and hadronisation. The NLO QCD predictions are in general agreement with the data although differences have been isolated to regions where contributions from higher orders are expected to be significant. The MC models give a better description than the NLO predictions of the shape of the measured cross sections.
Dijet photoproduction at HERA and the structure of the photon
The European Physical Journal C - Particles and Fields, 2002
The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb −1 . The events were required to have a virtuality of the incoming photon, Q 2 , of less than 1 GeV 2 and a photon-proton centre-of-mass energy in the range 134 < W γp < 277 GeV. Each event contains at least two jets satisfying transverse-energy requirements of E jet1 T > 14 GeV and E jet2 T > 11 GeV and pseudorapidity requirements of −1 < η jet1,2 < 2.4. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested.
European Physical Journal C, 2006
A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum ptjet1(2)>11(8) GeV in the central range of pseudo-rapidity -0.9<ηjet1(2)<1.3. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudo-rapidity of the two jets and the observable xγobs. Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in next-to-leading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.
Inclusive D*± meson cross sections and D*±-jet correlations in photoproduction at HERA
The European Physical Journal C, 2007
Differential photoproduction cross sections are measured for events containing D * ± mesons. The data were taken with the H1 detector at the ep collider HERA and correspond to an integrated luminosity of 51.1 pb −1 . The kinematic region covers small photon virtualities Q 2 < 0.01 GeV 2 and photon-proton centre-of-mass energies of 171 < W γ p < 256 GeV. The details of the heavy quark production process are further investigated in events with one or two jets in addition to the D * ± meson. Differential cross sections for D * +jet production are determined and the correlations between the D * ± meson and the jet(s) are studied. The results are compared with perturbative QCD predictions applying collinear-or k t -factorisation.
Inclusive jet cross sections and dijet correlations in photoproduction at HERA
Nuclear Physics B, 2005
Inclusive jet cross sections in photoproduction for events containing a D * meson have been measured with the ZEUS detector at HERA using an integrated luminosity of 78.6 pb −1. The events were required to have a virtuality of the incoming photon, Q 2 , of less than 1 GeV 2 , and a photon-proton centre-of-mass energy in the range 130 < W γp < 280 GeV. The measurements are compared with nextto-leading-order (NLO) QCD calculations. Good agreement is found with the NLO calculations over most of the measured kinematic region. Requiring a second jet in the event allowed a more detailed comparison with QCD calculations.
Measurement of beauty and charm photoproduction using semi-muonic decays in dijet events at HERA
The European Physical Journal C, 2012
Measurements of cross sections for beauty and charm events with dijets and a muon in the photoproduction regime at HERA are presented. The data were collected with the H1 detector and correspond to an integrated luminosity of 179 pb −1 . Events with dijets of transverse momentum P jet1 T > 7 GeV and P jet2 T > 6 GeV in the pseudorapidity range −1.5 < η jet < 2.5 in the laboratory frame are selected in the kinematic region of photon virtuality Q 2 < 2.5 GeV 2 and inelasticity 0.2 < y < 0.8. One of the two selected jets must be associated to a muon with P µ T > 2.5 GeV in the pseudorapidity range −1.3 < η µ < 1.5. The fractions of beauty and charm events are determined using the impact parameters of the muon tracks with respect to the primary vertex and their transverse momentum relative to the axis of the associated jet. Both variables are reconstructed using the H1 vertex detector. The measurements are in agreement with QCD predictions at leading and next-to-leading order.
Measurement of dijet cross sections in photoproduction at HERA
The European Physical Journal C, 2002
Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises e + p data with an integrated luminosity of 34.9 pb −1. Jets are selected using the inclusive k ⊥ algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x p and photon longitudinal momentum fraction x γ in the ranges 0.05 < x p < 0.6 and 0.1 < x γ < 1. The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.