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Aharon Levy

Publications and source records attributed to Aharon Levy.

34 records · Page 2Linked to original sources
arXiv2007

Exclusive rho0 electroproduction

Exclusive rho0 electroproduction at HERA has been studied with the ZEUS detector, using 120 pb{-1} integrated luminosity, in the kinematic range of photon virtuality of 2 < Q2 < 160 GeV2, and gamma* p center-of-mass energy of 32 < W < 180 GeV. The results include the Q2 and W dependence of the gamma* p --> rho0 p cross section and the distribution of the squared-four-momentum transfer to the proton, t. Also included is the ratio of longitudinal to transverse gamma* p cross section as a function of Q2, W and t. Finally, the effective Pomeron trajectory was extracted. The results are compared to various theoretical predictions, none of which are able to reproduce all the features of the data.

hep-ex↗
arXiv2005

The Pomeron structure and diffractive parton distributions

Measurements of the diffractive structure function, $F_2^D$, of the proton at HERA are used to extract the partonic structure of the Pomeron. Regge Factorization is tested and is found to describe well the existing data within the selected kinematic range. The analysis is based on the next to leading order QCD evolution equations. The results obtained from various data sets are compared. An analysis of the uncertainties in determining the parton distributions is provided. The probability of diffraction is calculated using the obtained results.

hep-ph↗
arXiv2005

NLO photon parton parametrization

An NLO photon parton parametrization is presented based on the existing $F_2^γ$ measurements from $e^+e^-$ data and the low-$x$ proton structure function from $ep$ interactions. Also included in the extraction of the NLO parton distribution functions are the dijets data coming from $γp \to j_1 + j_2 +X$. The new parametrization is compared to other available NLO parametrizations.

hep-ph↗
arXiv2004

The ALLM parameterization of sigma_{tot}(gamma* p) - an update

The ALLM parameterization of sigma_{tot}(gamma* p) has been updated by using all published F_2 data to determine its parameters. The fit yields a chi^2/ndf of 0.97 for the 1356 data points. The updated ALLM parameterization, ALLM97, gives a good description of all the available data in the whole x and Q^2 range studied so far (3\times10^{-6} < x < 0.85, 0 \le Q^2 < 5000 GeV^2).

hep-ph↗
arXiv2003

Measurements of diffractive processes at HERA

In this talk, the recent data on diffractive electron-proton interactions at HERA are reviewed. The question of diffraction as a soft or hard process is addressed and discussed in the context of inclusive diffraction, vector meson production and the DVCS process.

hep-ex↗
arXiv2002

Energy dependence of exclusive vector-meson production in ep interactions at HERA

The energy dependence of exclusive vector meson (V) production is studied using the ZEUS data. The SU(4) universality of V cross sections in the $Q^2+M_V^2$ scale is tested. The energy dependence of the ratio of the cross sections for V production to the total $γ^*p$ cross section is compared with expectations based on pQCD and Regge approaches.

hep-ex↗
arXiv2000

The legacy of HERA - the first decade

The ep HERA collider started operation in summer of 1992. This talk summarizes some of the highlights of physics results obtained since then and discusses their impact on our understanding of Quantum Chromodynamics (QCD).

hep-ph↗
arXiv1998

The structure of the Troika: Proton, Photon and Pomeron, as seen at HERA

HERA, the electron-proton collider, enables to probe the proton with a high resolving power due to the deep inelastic scattering reactions at high $Q^2$ values. In the low $Q^2$ region, one can study the properties of the photon. The large fraction of diffractive events found both in the low and high $Q^2$ region allows the study of the Pomeron. A review of what we have learned from HERA so far about the structure of these three objects is presented.

hep-ph↗
arXiv1997

Evidence for no shrinkage in elastic photoproduction of J/Psi

The differential cross section dsigma/dt of elastic photoproduction of J/Psi at different gamma p center of mass energies W are used to determine the properties of the exchanged trajectory in the reaction gamma p --> J/Psi p. In the region |t| < 1 GeV^2, the resulting trajectory is alpha(t) = (1.153 \pm 0.027) + (-0.001 \pm 0.072)t. The vanishing value of the slope of the trajectory is an experimental evidence for no shrinkage and thus for the perturbative nature of the exchange.

hep-ph↗
arXiv1997

The proton and the photon, who is probing who?

It is shown that by assuming Gribov factorization to hold at low $x$ one obtains a simple relation between the structure function of the proton and that of the photon. By interpreting an observed structure in deep inelastic scattering (DIS) of leptons on protons as belonging to the proton, one can relate it to the structure of the exchanged photon, and visa versa. Predictions are given for the structure function of real and virtual photons at low $x$ by using data on the proton structure function together with the Gribov factorization relations.

hep-ph↗
arXiv1996

The transition from the photoproduction to the DIS region

This is a review of the existing ideas in modelling the transition from the photoproduction ($Q^2 = 0$) to the deep inelastic scattering region. The available data of the proton structure function are analyzed from the point of view of the total $γ^* p$ cross section behavior with $W$ and the results are compared to different parameterizations. The question whether DIS processes are hard or soft is discussed.

hep-ex↗
arXiv1995

Soft interactions at high energy

Soft interactions are not easily disentangled from hard ones. In an operational definition of soft and hard processes one finds that at presently analyzed scales there is an interplay of soft and hard processes. As the scale increases, so does the amount of hard processes. So far, nothing is as soft nor as hard as we would like.

hep-ex↗