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A. De Roeck

Publications and source records attributed to A. De Roeck.

140 records · Page 8Linked to original sources
arXiv1998

Instantons in the Large Q^2, x Region at HERA

A new mechanism for an increased event production in the large $Q^2$, $x$ region at HERA is suggested. This mechanism results from a new type of instanton-induced quark-quark interaction, which is related to non-zero quark modes in the instanton field. We estimate the contribution of this interaction to the valence quark structure function $F_2^v$ using the gas instanton model approximation for the QCD vacuum. It is shown that this interaction can give a large contribution to $F_2^v$, especially at large values of $Q^2$. The strong dependence of this contribution on the quark masses and $Q^2$ is discussed, and it is concluded that a large charm quark contribution to events at high $Q^2$ can result from charm pair creation in the instanton field. We also obtain a sizeable contribution to the valence quark longitudinal structure function $F_L^v$ at high $Q^2$. Experimental observables which can check this instanton mechanism in the high $Q^2$ region at HERA are suggested.

hep-ph↗
arXiv1997

Structure Functions of the Nucleon and their Interpretation

The current status of measurements of the nucleon structure functions and their understanding is reviewed. The fixed target experiments E665, CCFR and NMC and the HERA experiments H1 and ZEUS are discussed in some detail. The extraction of parton momentum distribution functions from global fits is described, with particular attention paid to much improved information on the gluon momentum distribution. The status of alpha_s measurements from deep inelastic data is reviewed. Models and non-perturbative approaches for the parton input distributions are outlined. The impact on the phenomenology of QCD of the data at very low values of the Bjorken x variable is discussed in detail. Recent advances in the understanding of the transition from deep inelastic scattering to photoproduction are summarised. Some brief comments are made on the recent HERA measurements of the ep NC and CC cross-sections at very high Q2.

hep-ph↗
arXiv1997

Physics with Polarized Protons at HERA

The operation of HERA with polarized proton and electron beams will allow to study a wide variety of observables in polarized electron-proton collisions at $\sqrt s=300$ GeV. The physics prospects of this project have been elaborated in detail in a dedicated working group, whose results we summarize in this report. We show that several important and often unique measurements in spin physics could be made at HERA. These include measurements of the polarized structure function $g_1(x,Q^2)$ at low $x$, a direct determination of the polarized gluon distribution $ΔG(x,Q^2)$ for the region $0.002<x<0.2$ from polarized di-jet rates and hadrons with high $p_t$, polarized quark distributions from weak structure functions and semi-inclusive asymmetries, parton distributions in the polarized photon and information on the helicity structure of possible new physics at large $Q^2$. HERA could therefore make a significant contribution to our understanding of spin effects in high energy collisions and to the spin structure of the nucleon.

hep-ph↗
arXiv1997

Delta G(x) from high p_t hadrons in DIS at a polarised HERA

We investigate the possibility to identify photon-gluon fusion (PGF) events in polarised deep inelastic ep scattering, assuming the kinematics of the HERA collider, by a pair of charged high p_t particles. In a Monte Carlo study we find possible selection criteria and show the expected measurable asymmetries. We discuss the sensitivity to $ΔG(x)$ and compare the result to the one obtained using di-jets to tag PGF events.

hep-ph↗
arXiv1997

The polarised gluon density from di-jet events in DIS at a polarised HERA

We present a possible direct measurement of the polarised gluon density $ΔG(x)$ in LO from di-jet production in polarised deep inelastic ep scattering, assuming the kinematics of the HERA collider. We show the sensitivity to the x-dependence of $ΔG(x)$ and to the first moment $\int ΔG(x) dx$ in the range $0.002< x <0.2$, assuming the electron and proton beam of HERA being polarised to 70% and an integrated luminosity of at least 200 pb$^{-1}$. We include in our study hadronisation and higher order effects, as well as realistic detector smearing and acceptance. We find that the statistical and systematic uncertainties are small enough to distinguish between different parametrizations for $ΔG(x)$, which all are in accordance with present data. We stress that at HERA an x-range could be measured, that is not accessible to any other present or proposed experiment.

hep-ph↗
arXiv1997

The gamma* gamma* Total Cross Section and the BFKL Pomeron at the 500 GeV e+e- Collider

We present a numerical estimate of the $γ^* γ^*$ total cross section at the designed 500 GeV $e^+e^-$ Linear Collider, based upon the BFKL Pomeron. We find that the event rate is substantial provided electrons scattered under small angles can be detected, and a measurement of this cross section provides an excellent test of the BFKL Pomeron.

hep-ph↗
arXiv1996

Prospects for Measuring Delta G from Jets at HERA with Polarized Protons and Electrons

The measurement of the polarized gluon distribution function Delta G(x) from photon-gluon fusion processes in electron-proton deep inelastic scattering producing two jets has been investigated. The study is based on the MEPJET and PEPSI simulation programs. The size of the expected spin asymmetry and corresponding statistical uncertainties for a possible measurement with polarized beams of electrons and protons at HERA have been estimated. The results show that the asymmetry can reach a few percent, and is not washed out by hadronization and higher order processes.

hep-ph↗
arXiv1996

Structure Functions

We summarize recent developments in the understanding of nucleon structure. New data on F2, R and F2c, over a wide range of Q2 and x, are described. Conventional leading twist NLO perturbative QCD gives an excellent account of all the new data with Q2 above a GeV, leaving very little room for either higher twists or higher logarithms. We summarize the current status of NLO fits, and the determination of the gluon distribution and the strong coupling constant from structure function data. Finally we consider some of the theoretical issues raised by the new data.

hep-ph↗
arXiv1996

An Observation on F_2 at Low x

A simple parametrisation of H1 and ZEUS data at HERA is given for the ranges in x and Q^2 of 10^{-4} - 5.10^{-2} and 5 - 250 GeV^2, respectively. This empirical expression is based on a strikingly similar dependence of the average charged particle multiplicity on the centre of mass system energy sqrt{s} in e+e- collisions on the one hand, and the x dependence of the proton structure function F_2 as measured at small x on the other hand. To the best of our knowledge, this similarity has not been noted before.

hep-ph↗
arXiv1996

Working Group Report on the Structure of the Proton

We summarize the developments on the structure of the proton that were studied at the Workshop on "HERA Physics" that was held in Durham in September 1995. We survey the latest structure function data; we overview the QCD interpretations of the measurements of the structure functions and of final state processes; we discuss charm production and the spin properties of the proton.

hep-ph↗
arXiv1996

Associated Jet Production at HERA

We compare the BFKL prediction for the associated production of forward jets at HERA with fixed-order matrix element calculations taking into account the kinematical cuts imposed by experimental conditions. Comparison with H1 data of the 1993 run favours the BFKL prediction. As a further signal of BFKL dynamics, we propose to look for the azimuthal dependence of the forward jets.

hep-ph↗