arXiv subjects
Publications and source records attributed to E. Gotsman.
We show that when screening corrections are included $ \frac{\partial F_{2}(x,Q^{2})}{\partial \ln Q^{2}}$ is consistent with the behaviour that one expects in pQCD. Screening corrections explain the enigma of the Caldwell plot.
This paper shows that the approach based on Gribov's ideas for the photon-proton interaction, is able to describe the experimental data over a wide range of photon virtualities $Q^2 = 0 - 100 GeV^2$ and energies $\sqrt{s} = W = 3 - 300 GeV$. A simple model is suggested which provides a quantitative way of describing the matching between short and long distances (between "soft" and "hard" processes) in photon-proton interaction at high energy. The main results of our analysis are: (i) the values of the separation parameters differentiating the "soft" and "hard" interactions are determined; (ii) the additive quark model can be used to calculate the "soft" contribution to the photon - proton interaction; (iii) a good description of the ratio $σ_L/σ_T$ is obtained ; and (iv) a considerable contribution of the "soft" process at large $Q^2$, and of "hard" processes at small $Q^2$ was found.
The values and energy dependence for the survival probability $< \mid S\mid^2 >$ of large rapidity gaps (LRG) are calculated in a three channel model. This model includes single and double diffractive production, as well as elastic rescattering. It is shown that $< \mid S \mid^2 >$ decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron. This is in spite of the weak dependence on energy of the ratio $ (σ_{el}+ σ_{SD})/σ_{tot}$.
We present a two channel eikonal calculation in which the rescattering through a diffractive channel is included in addition to the elastic channel. Considering the spread of the experimental data, we find that we can obtain a very good description of $\s_{tot}$, $\s_{el}$ and $B_{el}$ in the ISR - Tevatron energy range. In this range of energy the diffractive channel, that was included in our calculation, leads to a ratio of $\s_{SD}/\s_{el}$ which varies between 1 and 0.5 for $20 GeV \leq \sqrt{s} \leq 14 TeV$ in agreement with the experimental data. The calculated survival probability of dijet production with a large rapidity gap is consistent with the data.
A systematic study of $\frac{\partial F_2(x,Q^2)}{\partial \ln Q^2}$ and $\frac{\partial \ln F_2(x,Q^2)}{\partial \ln (1/x)}$ is carried out in pQCD taking screening corrections into account. The result of calculations, which are different from the non screened DGLAP prediction, are compared and shown to agree with the available experimental data as well as a pseudo data base generated from the ALLM'97 parameterization. This pseudo data base allows us to study in detail our predictions over a wider kinematic region than is available experimentally, and allows us to make suggestions for future experiments. Our results are compared with the GRV'94 parameterization (which is used as an input for our calculations) as well as the recently proposed MRST structure functions.
The energy dependence for the survival probability of large rapidity gaps (LRG) $< \mid S \mid^2 >$, is calculated in an Eikonal model assuming a Gaussian opacity. The parameters determining $< \mid S \mid^2 >$ are evaluated directly from experimental data, without further recourse to models. We find that $< \mid S \mid^2 >$ decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron.
Recent HERA low $Q^2$ data show that the logarithmic slope of the protonstructure function ($\frac{\partial F_2}{\partial \ln Q^2}$) is significantly different from perturbative QCD expectations for smallvalues of $Q^2$ at exeedingly small values of $x$. We show that shadowing (screening) corrections provide a natural explanation for this experimental observation.
We show how and why the small distance ("hard") interaction, calculable in perturbative QCD, provides a mass cutoff in Gribov's formula for photon-proton collisions. This enables us to find a new and more restrictive bound for this process, $σ(γ^{*}p)\leq C(ln 1/x)^{5/2}$.A simple model the published experimental data over a wide range of photon virtualities ($Q^2$) and energies ($W$), is developed. This model provides a quantitative way of evaluating the relative rate of the small and large distance contributions, in the different kinematic regions. The main results of the analysis are (i) that even at $Q^2 =0$ and high energies the short distance contribution is not small, and it provides a possible explanation for the experimental rise of the photoproduction cross section; and (ii) at large values of $Q^2$, the long distance processes still contribute to the total cross section.
A new mechanism for hard inclusive production, which leads to a violation of the factorization theorem, is suggested. The mechanism is illustrated by a detailed discussion of Higgs meson production in high energy deutron-deutron scattering. Numerical estimates for the effect are given for high energy hadron (nucleus) scattering.
The measured forward slope in elastic and inelastic leptoproduction of vector mesons differ by a substantial amount. In an attempt to describe this phenomenon we construct a two radii model for the target proton, and estimate the effective parameters of the hard Pomeron obtained from a pQCD dipole model with eikonal shadowing corrections (SC). We show that the SC reduce the intercept of the hard Pomeron and generate an effective shrinkage of the forward peak and a diffractive dip at $|t| \approx 1 GeV^2$, which appears to affect the value of the experimentally measured slope.
In this letter we show that the behaviour of $F_{2}$, at very small $x_B$, agrees with the behaviour expected from the BFKL evolution equation, when screening corrections are included. We obtain a description which is consistent with the data, however, we require the screening corrections to be relatively large (about a quarter of the total DIS cross section). The relation between the screening corrections and the diffractive DIS cross section is discussed.
The formulae for shadowing corrections in deep inelastic leptoproduction of vector mesons are presented. These formulae are also applicable for photoproduction of vector mesons constituted of heavy quarks. Our results are conveniently presented by the definition of a damping factor giving the reduction of the calculated cross sections due to shadowing. Our calculated cross sections are compared with those obtained with no shadowing and with the available experimental data including the recent data from HERA. We have also investigated the importance of shadowing on the relationship between $\frac{\pa F_2(Q^2,x)}{ \pa ln Q^2}$ and the cross section for virtual photoproduction of vector mesons. A discussion of shadowing corrections to the proton's gluon density is presented and numerical estimates are given.
The effects of shadowing in double Pomeron exchange processes are investigated within an eikonal approach with a Gaussian input. Damping factors due to screening are calculated for this process and compared with the factors obtained for total, elastic and single diffraction cross sections. Our main conclusion is that counting rate calculations, of various double Pomeron exchange processes (without screening corrections) such as heavy quark and Higgs production are reduced by a factor of 5 in the LHC energy range, when screening corrections are applied.
The role of screening corrections, calculated using the eikonal model, is discussed in the context of soft photoproduction. We present a comprehensive calculation considering the total,elastic and diffractive cross sections jointly. We examine the differences between our results and those obtained from the supercritical Pomeron-Reggeon model with no unitarity corrections.
We show that eikonal corrections imposed on diffraction dissociation processes calculated in the triple Regge limit, produce a radical change in the energy dependence of the predicted cross section. The induced correction is shown to be in general agreement with the new experimental data measured at the Tevatron.
The survival probability of large rapidity gaps in pp collisions is calculated for several different eikonal models of the Gaussian form. Results obtained for models based on partonic interactions are quite similar. The Regge-pole model predicts a higher value of $ < \vert S \vert^{2} > $ .
A comparative investigation of various Pomeron models is carried out through the study of their predicted values of $ σ_{tot}$, B, and $\frac{σ_{el}}{σ_{tot}}$ in high energy pp and p$\bar{p}$ scattering. Our results strongly support a picture of the Pomeron in which we have both moderate blackening and expansion of the p($\bar{p}$) - p amplitude in impact parameter space as a function of energy in the ISR-SSC domain. In particular, we obtain an excellent reproduction of the data with a hybrid eikonal model which combines the hard Lipatov-like QCD Pomeron with the old fashioned soft Pomeron and Regge terms. Our analysis shows that the additive quark model, at least in the naive form, is not compatible with the data.