The cross sections for inelastic photoproduction of J/psi and psi' mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 38.0 pb-1. The events were required to have 0.1 < z < 0.9 and 50 < W < 180 GeV, where z is the fraction of the incident photon energy carried by the J/psi in the proton rest frame and W is the photon-proton centre-of-mass energy. The psi' to J/psi cross-section ratio was measured in the range 0.55 < z < 0.9. The J/psi data, for various ranges of transverse momentum, are compared to theoretical models incorporating colour-singlet and colour-octet matrix elements. Predictions of a next-to-leading-order colour-singlet model give a good description of the data, although there is a large normalisation uncertainty. The J/psi helicity distribution for z > 0.4 is compared to leading-order QCD predictions.
Measurment of the total cross section, with various PT thresholds, in the high Z > 0.9 region.
Ratio of cross section for PSI(2S) to J/PSI production. as a function of PT. Statistical errors only.
Ratio of cross section for PSI(2S) to J/PSI production. as a function of W. Statistical errors only.
The leptoproduction of J/psi mesons is studied in inelastic reactions for four momentum transfers 2<Q^2<100GeV^2. The data were taken with the H1 detector at the electron proton collider HERA and correspond to an integrated luminosity of 77 pb-1. Single differential and double differential cross sections are measured with increased precision compared with previous analyses. New leading order calculations within the non-relativistic QCD factorisation approach including colour octet and colour singlet contributions are compared with the data and are found to give a reasonable description of most distributions. An exception is the shape of the distribution in the J/psi fractional energy, z, which deviates significantly from that of the data. Comparisons with photoproduction are made and the polarisation of the produced J/psi meson is analysed.
J/PSI leptoproduction differential cross section as a function of Q**2.
J/PSI leptoproduction differential cross section as a function of Z.
J/PSI leptoproduction differential cross section as a function of W.
An analysis of inelastic photoproduction of J/Psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80pb-1. Differential and double differential cross sections are measured in a wide kinematic region: 60<W_gammap<260 GeV, 1<p_t^2< 60 GeV^2 and 0.05<z<0.9, where z is the fraction of the energy of the exchanged photon transferred to the J/Psi meson in the rest frame of the target proton. Cross sections at z<0.3 are presented for the first time. Theoretical calculations within the Colour Singlet Model at NLO for direct photon processes are shown to give a good description of the data in the medium z region (0.3<z<0.9) up to the highest p_t^2 values. A calculation using a k_t factorisation approach in LO in the Colour Singlet Model is also able to describe these data. The data in the full z range are also compared to LO calculations within a non-relativistic QCD framework including color octet and colour singlet contributions for direct and resolved photons. It seems possible to reconcile data and theory with modest contributions from colour octet processes. The polarisation of the J/Psi meson is measured as a function of z and p_t,psi and is reasonably described by the theoretical predictions.
The inelastic J/PSI production cross section as a function of W.
The inelastic J/PSI production cross section as a function of Z.
The double differential cross section for J/PSI production as a function of Z and PT**2.
The electroproduction of J/psi and psi(2S) mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers 2 < Q^2 < 80 GeV^2 and photon-proton centre of mass energies 25 < W < 180 GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic J/psi production is measured as a function of Q^2 and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic psi(2S) and J/psi meson production is measured as a function of Q^2. The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of J/psi mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
We present a measurement of the inelastic, non diffractive J/$\psi$ photoproduction cross section in the reaction $e^{+} p \to e^{+} {J}/\psi X$ with the ZEUS detector at HERA. The J/$\psi$ was identified using both the $\mu^{+}\mu^{-}$ and $e^{+}e^{-}$ decay channels and events were selected within the range $0.4<z<0.9$ ($0.5<z<0.9$) for the muon (electron) decay mode, where $z$ is the fraction of the photon energy carried by the J/$\psi$ in the proton rest frame. The cross section, the $p^2_T$ and the $z$ distributions, after having subtracted the contributions from resolved photon and diffractive proton dissociative processes, are given for the photon-proton centre of mass energy range $50<W<180$ GeV; $p^2_T$ is the square of the J/$\psi$ transverse momentum with respect to the incoming proton beam direction. In the kinematic range $0.4 < z < 0.9$ and $p^2_T > 1$ GeV$^2$, NLO calculations of the photon-gluon fusion process based on the colour-singlet model are in good agreement with the data. The predictions of a specific leading order colour-octet model, as formulated to describe the CDF data on J/$\psi$ hadroproduction, are not consistent with the data.
Cross section for the MU+ MU- decay channel.
Cross section for the MU+ MU- decay channel.
Cross section for the MU+ MU- decay channel.
The production of D * and D mesons has been studied in e + e − annihilations at √s = 29GeV. The data, corresponding to an integrated luminosity of 300 pb −1 , were obtained using the HRS detector at PEP. The cross section is measured to be R (D 0 + D + ) = 2.40±0.35 and we determine the electroweak asymmetry to be −9.9 ± 2.7%, which corresponds to an axial vector coupling constant product g e g c = 0.26 ± 0.07.
No description provided.
No description provided.
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Inclusive distributions of ρ0 and ω mesons have been measured in deep inelastic μ-p interactions at 280 GeV/c. A comparison of the ρ0 cross sections with other leptoproduction experiments is presented. The ω results represent the first observation of this inclusive channel in high energy leptoproduction. The ρ0 and ω yields are found to be equal as may be expected from the available density of states in isospin space. This contrasts with spin angular momentum where the vector to pseudoscalar meson ratio is suppressed relative to the available number of spin states.
No description provided.
No description provided.
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In this paper, results are presented from a study of the hadronic final states in e+e− annihilation at 29 GeV. The data were obtained with the High Resolution Spectrometer (HRS) at the SLAC PEP e+e− colliding-beam facility. The results are based on 6342 selected events corresponding to an integrated luminosity of 19.6 pb−1. The distributions of the events in sphericity (S), thrust (T), and aplanarity (A) are given and compared to other e+e− data in the same energy range. We measure 〈S〉=0.130±0.003±0.010 and 〈1-T〉=0.100±0.002. The sphericity distribution is compared to sphericity measurements made for beam jets in hadronic collisions as well as jets studied in neutrino scattering. The data sample is further reduced to 4371 events with the two-jet selections, S≤0.25 and A≤0.1. The single-particle distributions in the longitudinal and transverse directions are given. For low values of the momentum fraction (z=2p/W), the invariant distribution shows a maximum at z∼0.06, consistent with a QCD expectation. The data at high Feynman x (xF) show distribution consistent with being dominated by a (1-xf)2 variation for the leading quark-meson transition. The rapidity distribution shows a shallow central minimum with a height (1/NevdNh/dY‖Y=0=2.3±0.02±0.07. The mean charged multiplicity is measured to be 〈nch〉=13.1±0.05±0.6. The mean transverse momentum relative to the thrust axis 〈pT〉 rises as a function of z to a value of 0.70±0.02 GeV/c for z≳0.3. The distributions are compared to those measured in other reactions.
New values supplied 6.7.87 by M.Derrick.
No description provided.
New values supplied 6.7.87 by M. Derrick.
Inclusive ϱ 0 meson production has been measured in 120 GeV and 280 GeV muon-proton interactions. Distributions of z and p T 2 are presented. Primary ϱ 0 production is found to be equal to that of π 0 production within errors.
No description provided.
No description provided.
Dimuon and trimuon events produced by the interaction of 250 GeV muons in an iron target have been studied and are shown to originate predominantly from charm production. The data are used to measure the contribution of charm to the nucleon structure function F 2 . The cross sections for real photoproduction ( Q 2 =0) of charm in the current fragmentation region are derived as a function of photon energy and are found to be ∼0.6% of the total, hadronic photoproduction cross section in this energy range. The measured cross sections are found to be well represented by the photon-gluon fusion model. The charmed quark fragmentation function is obtained by using this model to fit the measured decay muon energy distribution and is found to be well represented by exp(1.6±1.6) Z . The data are used to study the momentum distribution of the gluons in the nucleon. An upper limit of 1.4% (90% confidence level) is set on the branching ratio D→ μν and a model-dependent upper limit on the branching ratio F→ μν is derived.
The charm contribution to the nucleon structure function from the dimuon data.
No description provided.
No description provided.
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