Search

Data in which a proton is tagged along the beampipe after the primary interaction represents the cleanest way to measure diffraction. Data from both H1 and ZEUS collaborations on inclusive diffractive deep inelastic scattering, with a tagged proton, have been combined. Inclusive diffractive deep inelastic scattering can be considered as the exchange of a colourless object and is amenable to QCD fits in which the structure of this object, sometimes called a Pomeron, is determined. Given such processes are ex- pected to factorise, such a Pomeron structure can be used to predict the rates of jet production in e.g. diffractive photoproduction. The comparison of jet data with the predictions of next-to-leading order QCD are discussed in the context of factorising breaking. Another way to study diffraction is through the production of vector mesons which is also characterised by a colourless exchange with the proton which in lowest order QCD is realised as a colourless gluon pair. Therefore, consideration of the dependence of the J= cross section on the photon–proton centre-of-mass energy is re- lated to the rise of the square of the gluon density towards low values of Bjorken x . Comparisons of HERA data with such theories and other data are presented

McGill University, Diss., 2004; 278 pp., (2004). doi:10.3204/DESY-THESIS-2004-012, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

McGill University, Diss., 2003; 184 pp., (2003). doi:10.3204/DESY-THESIS-2003-005, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

Universität Hamburg, Diss., 2001; 183 pp. (2001). = Universität Hamburg, Diss., 2001

140 pp. (1997)., In this thesis the measurement of the differential semi-inclusive cross section in Photoproduction with a leading proton is presented. The data were taken 1995 using the H1 detector at the HERA $ep$ storage ring, the corresponding integrated Luminosity is $\mathcal{L}$ = $2.05 pb^{-1}$. Protons were measured in the energy range of $580 GeV < E_{p\prime} < 740 GeV$ having a transverse momentum of $p\bot < 200MeV/c$. The cross section $d\sigma(\gamma p \to X p \prime)$/$dE_{p\prime}$, was calculated at $< W >$ = $$ = $90, 187 and 231 GeV$. The detection of leading protons with the H1 Forward Proton Spectometer (FPS) was possible for the first time in 1995. The FPS consists of two detector stations at 81 and 90 m and the proton magnets located between these stations and the interaction vertex. Using the measured proton track and the known beam optics, the proton energy $E_{p\prime}$ and the scattering angle $\vartheta_p \prime$, at vertex position are reconstructed. The resolution is $\Delta E_p \prime$ = $2 - 6 GeV, \Delta \vartheta_x$ = $5 - 10 \mu rad$ and $\Delta \vartheta_y$ = $5 - 100 \mu rad$ depending on the other quantities at a time. These values meet the design requirements.The selection efficiency and acceptance as well as corrections used for the cross section measurement are calculated. The differential cross section is of the order of $7 nb/GeV$ and does within errors not depend on $E_p \prime$ and $< W >$. A Regge fit shows the data to be compatible with $\pi^\circ$ exchange. To get information about the contribution from hard Photoproduction 2-jet events have been selected using a cone algorithm. The 2-jet cross section is of the order of $140 pb/GeV$. A comparison with predictions of the POMPYT model shows that the jet data can be described by Pion and Pomeron exchange within the Regge picture.

Photoproduction at HERA is studieci in ep colüsions, using the ZEUS detector, for $\gamma$p center-of-mass energies ranging from 130-270 GeV. A sample of events with two high-pt Jets (pt > 6 GeV, $\eta$ < l .6) and a third düster in the approximate direction of the eiectron beam is isolated using a clustering algorithm. These events are mostly due to resolved photoproduction. The third cluster is identified äs the photon remnant. Its properties, such äs the transverse and longitudinal energy flows around the axis of the cluster, are consistent with those commonly attributed to jets, and in particular with those found for the other two jets in these events. The mean value of the photon remnant pj with respect to the beam axis, measured to be 2.1 ± 0.2 GeV, is substatltial

At the HERA storage ring two jet photoproduction is measured for jets with a minimum transverse energy $E_{\tau}$, > 6 GeV and for pseudorapidities in the $ep$-laboratory range $-l < \eta_{jet}$ < 2, for photon-proton center-of-mass energies 132 GeV < $\sqrt{s_{\gamma\rho}}$ < 265 GeV. The outgoing electron is not detected, limiting the maximum virtuaüty of the exchanged photon to $Q^2_{max}$ = 4 $GeV^2$, with a median value of approximately $10^{-3} GeV^2$. Dijet events are extracted from the data taken hy the ZEUS experiment in 1993 using an integrated luminosity of $545pb^{-1}$. The measured differential cross section is compared with the LO-QCD parton cross section as generated with the PYTHIA 5.6 program without use of fragmentation, a LO-QCD hadron jet cross section including Jet fragmentation, and hadron jet cross sections using fragmentation, intrinsic $k_t$ smearing and parton shower evolution for cutoff values of $p_{t,min}$ = 5.0 GeV and $p_{t,min}$ = 2.5 GeV. Resolved and direct processes are included using the MRSD- proton parameterization and the GRV-LO and LACl parton density functions for resolved photoproduction. In the backward direction ($\eta$ < 0) the data are described within the systematic uncertainties hy each of the hadron jet cross sections using the GRV-LO and LACl photon parameterization, while the LO-QCD parton cross section is above the data. The best description of the forward direction ($\eta$ > 0) is obtained using intrinsic $k_t$ smearing, fragmentation, and parton shower evolution with the low cut-off $P_{t, min}$ — 2.5 GeV. In this model, the data agree with the expectation of the LACl parameterization in the forward direction, while GRV-LO is below the data. A measurement of the energy flow shows a satisfactory agreement between the data and the PYTHIA 5.6 Monte Carlo Simulation, except in the forward (proton) direction close to the beam pipe. The energy deposition in the region $5^{\circ}$ < 0 < $15^{\circ}$ is approximately 30% larger as compared to the Monte Carlo Simulation. This energy excess in the forward direction is traced back to the resolved photoproduction process. It can be explained by the simple multiple interacttonfi model implemented in PYTHIA 5.7.