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E. Gotsman

Publications and source records attributed to E. Gotsman.

At least 73 records · Page 4Linked to original sources
arXiv2003

J/ψPhoto- and DIS Production via Nonlinear Evolution

We apply our solution of the nonlinear evolution equation to the case of $J/ψ$ photo and DIS production on nucleons and nuclei targets. The uncertainty in the $J/ψ$ wave function normalization due to Fermi motion is treated as a free parameter. We obtain good reproduction of the HERA experimental data on a proton target. Calculations of $J/ψ$ mesons coherent production on nuclei targets are presented and discussed. Our analysis supports the conclusions reached in our previous studies, stressing the importance of nonlinear evolution in the kinematical domain of high-density QCD.

hep-ph↗
arXiv2003

The Dipole Picture and Saturation in Soft Processes

We attempt to describe soft hadron interactions in the framework of saturation models, one based upon the Balitsky-Kovchegov non-linear equation and another one due to Golec-Biernat and Wüsthoff. For $pp$, $Kp$, and $πp$ scattering the relevant hadronic wave functions are formulated, and total, elastic cross-sections, and the forward elastic slope are calculated and compared to experimental data. The saturation mechanism leads to reasonable reproduction of the data for the quantities analyzed, except for the forward elastic slope, where the predicted increase with energy is too moderate.

hep-ph↗
arXiv2002

Towards a new global QCD analysis: low x DIS data from non-linear evolution

A new approach to global QCD analysis is developed. The main ingredients are two QCD-based evolution equations. The first one is the Balitsky-Kovchegov nonlinear equation, which sums higher twists while preserving unitarity. The second equation is linear and it is responsible for the correct short distance behavior of the theory, namely it includes the DGLAP kernel. Our approach allows extrapolation of the parton distributions to very high energies available at the LHC as well as very low photon virtualities, $Q^2\ll 1 {\rm GeV^2}$. All existing low $x$ data on the $F_2$ structure function is reproduced using one fitting parameter. The resulting $χ^2/df=1$. Analyzing the parameter $λ\equiv \partial\ln F_2/\partial(\ln 1/x)$ at very low $x$ and $Q^2$ well below $1 {\rm GeV^2}$ we find $λ\simeq 0.08 - 0.1$. A result which agrees with the "soft pomeron" intercept without involving soft physics.

hep-ph↗
arXiv2002

Momentum Transfer Dependence of the Differential Cross Section for $J/ψ$ Production

We discuss the $t$ dependence of $J/ψ$ production in the region of $0< -t < M^2_ψ$. The forward slope of the elastic differential cross section is calculated assuming a dipole-type dependence for the gluon ladder-proton form factor. The $t$ dependence of $dσ/dt$ is obtained using DGLAP evolution both for the elastic channel at low $-t$ and for the inelastic channel at large values of $-t$, up to $-t\simeq M^2_ψ$. Results are presented and compared with the relevant experimental data.

hep-ph↗
arXiv2001

Higher Twist Corrections and Maxima for DIS on a Proton in the High Density QCD Region

We show that the ratio of different structure functions have a maximum which depends on energy. We argue, using Golec-Biernat and Wusthoff model, that these maxima are the certain functions of the saturation scale. The analysis of leading and higher twist contributions for different observables is given with the aim of determining the kinematic region where high parton density effects could be seen experimentally.

hep-ph↗
arXiv2001

Non-linear evolution and parton distributions at LHC and THERA energies

We suggest a new procedure for extrapolating the parton distributions from HERA energies to higher energies at THERA and LHC. The procedure suggested consists of two steps: first, we solve the non-linear evolution equation which includes the higher twists contributions, however this equation is deficient due to the low ($log(1/x)$) accuracy of our calculations. Second, we introduce a correcting function for which we write a DGLAP type linear evolution equation. We show that this correcting function is small in the whole kinematic region and decreases at low $x$. The nonlinear evolution equation is solved numerically and first estimates for the saturation scale, as well as for the value of the gluon density at THERA and LHC energies are made. We show that non-linear effects lead to damping of the gluon density by a factor of $2 ÷3$ at $x \approx 10^{-7}$.

hep-ph↗
arXiv2001

High density QCD at THERA

These notes are a summary of our predictions for the new THERA project, related to deep inelastic scattering in the region of ultra low $x$ ($x \to 10^{-7}$). We collect here predictions that satisfy two criteria (i) they do not depend on specific features of the model that we have to use to estimate a possible effect; and (ii) they do not contradict the HERA data.

hep-ph↗
arXiv2001

Screening Corrections in Photo and DIS Production of $J/Ψ$

Photo and DIS production of $J/Ψ$ are investigated and compared with calculations based on pQCD in the LLA approximation without and with screening corrections. The calculation includes corrections induced by the real part of the production amplitude, the skewed (off diagonal) gluon structure function and the relativistic Fermi motion within the charmonium system. Our pQCD results are also compared with the predictions obtained from a Regge type two Pomeron model. Our results suggest some preference for our screened model, but the available data does not enable us to exclude any of the three models we have examined. The properties of these models, when extrapolated to both low and very high energies may provide a more effective discrimination between the different parameterizations.

hep-ph↗
arXiv2000

Scaling Violations in the $Q^2$ Logarithmic Derivative of $F_2$

We examine the latest HERA experimental measurements of the $Q^2$ logarithmic derivative of the proton structure function. We analyze the characteristics of DGLAP with and without screening, as well as a Regge type model, and compare their predictions to all available data on $\slope$ including those for fixed W. Our results show that the present data can be described in pQCD taking into account shadowing corrections. However, such a description cannot be considered a conclusive signal of gluon saturation since the experimental data on $\slope$ do not allow one to discriminate between the various approaches, in spite of their very different construction.

hep-ph↗
arXiv2000

Has HERA reached a new QCD regime?

These notes are a summary of our efforts to answer the question in the title. Our answer is in the affirmative as: (i) HERA data indicate a large value of the gluon structure function; (ii) no contradictions with the asymptotic predictions of high density QCD have been observed; and (iii) the numerical estimates of our model give a natural description of the size of deviation from the routine DGLAP explanation. We discuss the alternative approaches and possible new experiments.

hep-ph↗
arXiv2000

Energy Dependence of σ^{DD}/σ_{tot} in DIS and Shadowing Corrections

We gereralize the Kochegov-McLerran formula for the ratio $σ^{DD}/σ_{tot}$ in perturbative QCD, using Mueller-Glauber approach for shadowing corrections and AGK cutting rules. We investigate several phenomenological approaches with the goal of obtaining results consisent with experimental data. We fail to reproduce the observed weak energy dependence of the ratio, and conclude that the soft nonperturbative contribution present at short distances must also be included.

hep-ph↗
arXiv2000

Higher twists and maxima for DIS on nuclei in high density QCD region

We show that the ratio of different structure functions have a maximum which depends on $x_B$ and $A$. We argue that these maxima are proportional to the saturation scale. The analysis of leading and higher twist contributions for different observables is given with the aim of determining the kinematic region where high parton density effects could be seen experimentally.

hep-ph↗
arXiv2000

Screening corrections in DIS at low Q^2 and x

In this investigation we present a detailed study of $\partial F_2/\partial \ln Q^2$ which is supported by a coupled analysis of $J/Ψ$ photo and DIS production. Both channels are directly proportional to $xG(x,Q^2)$, and as such serve as excellent discriminators between different approaches and models. We then show that taking GRV98NLO as input and correcting it for SC, we can reproduce the recent HERA data well. The calculation depends on one parameter $R^2=8.5GeV^{-2}$ which is directly determined from the $J/Ψ$ photoproduction forward differential slope. With this input we obtain an excellent fit to the $J/Ψ$ photo and DIS production data. Our calculations made in the LLA of pQCD take into account the corrections implied by the real part of the production amplitude, off diagonal (skewed) gluon distributions and the Fermi motion of the charm quarks within the bound Charmonium system.

hep-ph↗
arXiv2000

Shadowing Corrections and Diffractive Production in DIS on Nuclei

We calculate, in the Glauber-Mueller approach, the ratio of the diffractive dissociation cross section to the total cross section on nuclei. We observe that shadowing corrections (SC) are significant, in the calculated $\ddt$ ratio but they do not lead to a smooth energy dependence of the ratio for a proton target as was observed at HERA.

hep-ph↗
arXiv2000

A Pomeron Approach to Hadron-Nucleus and Nucleus-Nucleus "Soft" Interactions at High Energy

We formulate a generalization of the Glauber formalism for hadron-nucleus and nucleus-nucleus collisions based on the Pomeron approach to high energy interactions. Our treatment is based on two physical assumptions (i.e. two small parameters) : (i) that only sufficiently small distances contribute to the Pomeron structure; and (ii) the triple Pomeron vertex $G_{3P}/g_{P-N} \ll 1$ (where $g_{P-N}$ is the Pomeron-nucleon vertex) is small. A systematic method is developed for calculating the total, elastic and diffractive dissociation cross sections as well as the survival probability of large rapidity gap processes and inclusive observables, both for hadron - nucleus and nucleus-nucleus collisions. Our approach suggests saturation of the density of the produced hadrons in nucleus-nucleus collisions, the value of the saturation density turns out to be large and depends on the number of nucleons in the lightest nucleus.

hep-ph↗
arXiv2000

The Components of the $γ^*γ^*$ Cross Section

We extend our previous treatment of $γ^*p$ cross section based on Gribov's hypothesis to the case of photon-photon scattering. With the aid of two parameters, determined from experimental data, we separate the interactions into two categories corresponding to short ("soft") and long ("hard") distance processes. The photon-photon cross section, thus, receives contributions from three sectors, soft-soft, hard-hard and hard-soft. The additive quark model is used to describe the soft-soft sector, pQCD the hard-hard sector, while the hard-soft sector is determined by relating it to the $γ^{*}$p system. We calculate and display the behaviour of the total photon-photon cross section and it's various components and polarizations for different values of energy and virtuality of the two photons, and discuss the significance of our results.

hep-ph↗
arXiv1999

The Logarithmic Derivative of the F_{2} Structure Function and Saturation

We show that when screening corrections are included $\frac{\partial F_{2}(x,Q^{2})}{\partial ln(Q^{2}/Q_{0}^{2})}$ is consistent with the behaviour that one expects in pQCD. Screening corrections explain the enigma of the Caldwell plot. Saturation has not been reached at present HERA energies.

hep-ph↗