Nonperturbative Effects in Gluon Radiation and Photoproduction of Quark Pairs

We introduce a nonperturbative interaction for light-cone fluctuations containing quarks and gluons. The $\bar qq$ interaction squeezes the transverse size of these fluctuations in the photon and one does not need to simulate this effect via effective quark masses. The strength of this interaction is fixed by data. Data on diffractive dissociation of hadrons and photons show that the nonperturbative interaction of gluons is much stronger. We fix the parameters for the nonperturbative quark-gluon interaction by data for diffractive dissociation to large masses (triple-Pomeron regime). This allows us to predict nuclear shadowing for gluons which turns out to be not as strong as perturbative QCD predicts. We expect a delayed onset of gluon shadowing at $x \leq 10^{-2}$ shadowing of quarks. Gluon shadowing turns out to be nearly scale invariant up to virtualities $Q^2\sim 4 GeV^2$ due to presence of a semihard scale characterizing the strong nonperturbative interaction of gluons. We use the same concept to improve our description of gluon bremsstrahlung which is related to the distribution function for a quark-gluon fluctuation and the interaction cross section of a $\bar qqG$ fluctuation with a nucleon. We expect the nonperturbative interaction to suppress dramatically the gluon radiation at small transverse momenta compared to perturbative calculations.Comment: 58 pages of Latex including 11 figures. Shadowing for soft gluons and Fig. 6 are added as well as a few reference

A full-acceptance detector at the LHC (FELIX)

peer reviewedThe FELIX collaboration had proposed the construction of a full-acceptance detector for the LHC. The primary mission of FELIX was the study of QCD: to provide comprehensive and definitive observations of a very broad range of strong-interaction processes. This document contains an extensive discussion of this physics menu. In a further paper the FELIX detector will be reviewed

Photoproduction with a leading proton at HERA

The total cross section for the photoproduction process with a leading proton in the final state has been measured at γp centre-of-mass energies W of 91, 181 and 231GeV. The measured cross sections apply to the kinematic range with the transverse momentum of the scattered proton restricted to pT≤0.2GeV and 0.68≤z≤0.88, where z=Ep′/Ep is the scattered proton energy normalised to the beam energy. The cross section dσγp→Xp′(W,z)/dz is observed to be independent of W and z within the measurement errors and amounts to (8.05±0.06(stat)±0.89(syst)) μb on average. The data are well described by a Triple Regge model in which the process is mediated by a mixture of exchanges with an effective Regge trajectory of intercept αi(0)=0.33±0.04(stat)±0.04(syst). The total cross section for the interaction of the photon with this mixture (γαi→X) can be described by an effective trajectory of intercept αk(0)=0.99±0.01(stat)±0.05(syst). Predictions based on previous triple Regge analyses of pp→pX data assuming vertex factorisation are broadly consistent with the γp data. The measured cross sections are compared with deep inelastic scattering leading proton data in the same region of z and pT for photon virtuality Q2 > 2.5GeV2. The ratio of the cross section for leading proton production to the total cross section is found to rise with Q2. © 2001 Elsevier Science B.V.0H1 Collaboration.info:eu-repo/semantics/publishe

Diffractive Photoproduction of Dijets in {\it ep} Collisions at HERA

Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb(-1). The measurements were made in the kinematic range Q(2) 7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5 < eta(jet) < 1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton

Diffractive Photoproduction of~ {\it \boldmath D∗±(2010)D^{*\pm}(2010)} at HERA

Diffractive photoproduction of D*+/-(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb^{-1}. The D* mesons were reconstructed in the kinematic range: transverse momentum p_T(D*) > 1.9 GeV and pseudorapidity |eta(D*)| < 1.6, using the decay D*+ -> D0 pi+_s followed by D0 -> K- pi+ (+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon-proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q^2 < 1 GeV^2, in two ranges of the Pomeron fractional momentum x_pom < 0.035 and x_pom < 0.01. The relative contribution of diffractive events to the inclusive D*+/-(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.Comment: LaTeX2e, 29 pages, 9 Postscript figures, 4 tables, minor revisions, accepted for publication in the European Physical Journal