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.
A thrust analysis of Large-Rapidity-Gap events in deep-inelastic ep collisions is presented, using data taken with the H1 detector at HERA in 1994. The average thrust of the final states X, which emerge from the dissociation of virtual photons in the range 10 < Q2 < 100 GeV2, grows with hadronic mass M_X and implies a dominant 2-jet topology. Thrust is found to decrease with growing Pt, the thrust jet momentum transverse to the photon-proton collision axis. Distributions of Pt2 are consistent with being independent of MX. They show a strong alignment of the thrust axis with the photon-proton collision axis, and have a large high-Pt tail. The correlation of thrust with MX is similar to that in e+e- annihilation at sqrt(see)=MX, but with lower values of thrust in the ep data. The data cannot be described by interpreting the dissociated system X as a qqbar state but inclusion of a substantial fraction of qqbarg parton configurations leads naturally to the observed properties. The soft colour exchange interaction model does not describe the data.
PT distribution of the photon-originated jet relative to the to the GAMMA* P collision axis in the jet center-of-mass frame, divided by the total GAMMA* P cross section for the respective M_x bin. Jet momentum defined as vector sum of momenta in the positive(negative) thrust hemisphere (thrust jet momentum).
PT distribution of the photon-originated jet relative to the to the GAMMA* P collision axis in the jet center-of-mass frame, divided by the total GAMMA* P cross section for the respective M_x bin. Jet momentum defined as vector sum of momenta in the positive(negative) thrust hemisphere (thrust jet momentum).
PT distribution of the photon-originated jet relative to the to the GAMMA* P collision axis in the jet center-of-mass frame, divided by the total GAMMA* P cross section for the respective M_x bin. Jet momentum defined as vector sum of momenta in the positive(negative) thrust hemisphere (thrust jet momentum).
Inclusive $K^0$ and $\Lambda$ photoproduction has been investigated at HERA with the H1 detector at an average photon-proton center of mass energy of 200 GeV in the transverse momentum range 0.5 <p_t <5 GeV. The production rates as a function of $p_t$ and center of mass rapidity are compared to those obtained in deep inelastic scattering at $\av{Q^2}=23 GeV^2$. A similar comparison is made of the rapidity spectra of charged particles. The rate of strangeness photoproduction is compared with $p\bar p$ measurements. The observations are also compared with next-to-leading order QCD calculations and the predictions of a Monte Carlo model.
Additional systematic uncertainty given above.
Additional systematic uncertainty given above.
Additional systematic uncertainty given above.
We present a study of J ψ meson production in collisions of 26.7 GeV electrons with 820 GeV protons, performed with the H1-detector at the HERA collider at DESY. The J ψ mesons are detected via their leptonic decays both to electrons and muons. Requiring exactly two particles in the detector, a cross section of σ(ep → J ψ X) = (8.8±2.0±2.2) nb is determined for 30 GeV ≤ W γp ≤ 180 GeV and Q 2 ≲ 4 GeV 2 . Using the flux of quasi-real photons with Q 2 ≲ 4 GeV 2 , a total production cross section of σ ( γp → J / ψX ) = (56±13±14) nb is derived at an average W γp =90 GeV. The distribution of the squared momentum transfer t from the proton to the J ψ can be fitted using an exponential exp(− b ∥ t ∥) below a ∥ t ∥ of 0.75 GeV 2 yielding a slope parameter of b = (4.7±1.9) GeV −2 .
No description provided.
No description provided.
QED background subtracted.
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