arXiv subjects

E. Levin

Publications and source records attributed to E. Levin.

At least 91 records · Page 5Linked to original sources

arXiv2005

Proton-proton interaction in constituent quarks model at LHC energies

In this paper we consider the soft processes at LHC energies in the framework of the Constituent Quark Model (CQM). We show that this rather naive model is able to describe all available soft data at lower energies and to predict the behavior of the total cross section, elastic and diffractive cross sections at the LHC energy. It turns out that the ''input'' Pomeron, which has been used in this approach, has parameters that are close to so called ''hard'' Pomeron with rather large intercept $Δ\approx 0.12$ and small value of the slope $α'_P \approx 0.08 GeV^{-2}$. We show that the elastic amplitude has a minimum at impact parameter $b =0$ and a maximum at $b \approx 2 GeV^{-1}$. Such a behavior is a result of overlapping the parton clouds that belong to different quarks in the hadron.

hep-ph↗

arXiv2005

High energy amplitude in the dipole approach with Pomeron loops: asymptotic solution

In this paper an analytical solution for the high energy scattering amplitude is suggested. This solution has several unexpected features:(i) the asymptotic amplitude is a function of dipole sizes and, therefore, this amplitude shows the gray disc structure at high energy, instead of black disc behaviour which was expected; (ii) the amplitude approaches the asymptotic limit in the same way as the solution to the Balitsky-Kovchegov equation does ($\propto \exp(- C Y^2) $), but the coefficient $C$ in eight times smaller than for the Balitsky-Kovchegov equation; (iii) the process of merging of two dipoles into one, only influences the high energy asymptotic behaviour by changing the initial condition from $Z(Y; [u_i = 1]) = 1 $ to $Z(Y; [u_i = 1 - γ_{0,i}]) =1$. The value of $γ_0$ is determined by the process of merging of two dipoles into one. With this new initial condition the Balitsky-JIMWLK approach describes the high energy asymptotic behaviour of the scattering amplitude without any modifications recently suggested.

hep-ph↗

arXiv2005

Survival Probability of Large Rapidity Gaps

Our presentation centers on the consequences of s-channel unitarity, manifested by soft re-scatterings of the spectator partons in a high energy diffractive process, focusing on the calculations of gap survival probabilities. Our emphasis is on recent estimates relevant to exclusive diffractive Higgs production at the LHC. To this end, we critically re-examine the comparison of the theoretical estimates of large rapidity gap hard di-jets with the measured data, and remark on the difficulties in the interpretation of HERA hard di-jet photoproduction.

hep-ph↗

arXiv2005

Saturation effects at LHC energies

Within the framework of a modified Balitsky-Kovchegov equation, we calculated and provide estimates of non-linear saturation effects expected in the LHC range of energies.

hep-ph↗

arXiv2005

Solution to the Balitsky-Kovchegov equation in the saturation domain

The solution to the Balitsky-Kovchegov equation is found in the deep saturation domain. The controversy between different approaches regarding the asymptotic behaviour of the scattering amplitude is solved. It is shown that the dipole amplitude behaves as $ 1 - \exp (- z + \ln z)$ with $ z = \ln (r^2 Q^2_s)$ ($ r$ -size of the dipole, $Q_s$ is the saturation scale) in the deep saturation region. This solution is developed from the scaling solution to the homogeneous Balitsky-Kovchegov equation. The dangers associated with making simplifications in the BFKL kernel, to investigate the asymptotic behaviour of the scattering amplitude, is pointed out . In particular, the fact that the Balitsky-Kovchegov equation belongs to the Fisher-Kolmogorov-Petrovsky-Piscounov -type of equation, needs further careful investigation.

hep-ph↗

arXiv2004

A modified Balitsky-Kovchegov equation

We propose a modified version of the Balitsky-Kovchegov (B-K) evolution equation, which includes the main NLO corrections. We use the result that the main NLO corrections to the BFKL kernel are the LO DGLAP corrections. We present a numerical solution of the modified nonlinear equation, and compare with the solution of the unmodified B-K equation. We show that the saturation momentum has a sharp increase in the LHC energy range. Our numerical solution indicates that the influence of the pre-asymptotic corrections, related to the full anomolous dimensions of the DGLAP equation, are rather large. These corrections moderate the energy behaviour of the amplitude, as well as the value of the saturation scale. All our calculations are made with a fixed value of $α_{s}$.

hep-ph↗

arXiv2004

The Iancu-Mueller factorization and high energy asymptotic behaviour

We show that the Iancu-Mueller factorization has a simple interpretation in the Reggeon - like technique based on the BFKL Pomeron. The formula for calculating the high energy asymptotic behaviour for the colour dipole-dipole amplitude is proposed which suggests a procedure to calculate this amplitude through the solution to the Balitsky-Kovchegov non-linear equation. We confirm the Iancu - Mueller result that a specific set of enhanced diagrams is responsible for the high energy behaviour for fixed QCD coupling. However, it is argued that in the case of running QCD coupling, this asymptotic behaviour originates from the Balitsky-Kovchegov non-linear equation. A new solution to the non-linear equation is found which leads to a different asymptotic behaviour of the scattering amplitude even for fixed QCD coupling..

hep-ph↗

arXiv2004

QCD in curved space-time: a conformal bag model

We construct an effective low energy Lagrangian of gluodynamics which (i) satisfies all constraints imposed by the Renormalization Group; (ii) is scale and conformally invariant in the limit of vanishing vacuum energy density; (iii) matches onto the perturbative theory at short distances. This effective theory has a dual description as classical gluodynamics on a curved conformal background. Color fields are dynamically confined, and the strong coupling freezes at distances larger than the glueball size. We also make specific predictions (in particular, on the Nc dependence of glueball properties) which can be tested in lattice simulations of gluodynamics.

hep-ph↗

arXiv2004

QCD Saturation and Deuteron-Nucleus Collisions

We make quantitative predictions for the rapidity and centrality dependencies of hadron multiplicities in dA collisions at RHIC basing on the ideas of parton saturation in the Color Glass Condensate.

hep-ph↗

arXiv2004

Search for Chargino and Neutralino Production at sqrt(s) = 192-209 GeV at LEP

Approximately 438 pb-1 of e+e- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 Gev, are analyzed to search for evidence of chargino pair production, e+e- -> tilde chi^+_1 tilde chi^-_1, or neutralino associated production, e+e- -> tilde chi^0_2 tilde chi^0_1. Limits are set at the 95% confidence level on the product of the cross-section for the process e+e- -> tilde chi^+_1 tilde chi^-_1 and its branching ratios to topologies containing jets and missing energy, of jest with a lepton and missing energy, and on the product of the cross-section for e+e- -> tilde chi^0_2 tilde chi^0_1 and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the tilde chi^+-_1, tilde chi^0_1 and tilde chi^0_2, and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on sigma(e+e- -> tilde chi^+_1 tilde chi^-_1) with the assumption that each chargino decays via a W boson, and on sigma(e+e- -> tilde chi^0_2 tilde chi^0_1) with the tilde chi^0_2 assumed to decay via a Z^0.

hep-ex↗

arXiv2003

A Linear Evolution for Non-Linear Dynamics and Correlations in Realistic Nuclei

A new approach to high energy evolution based on a linear equation for QCD generating functional is developed. This approach opens a possibility for systematic study of correlations inside targets, and, in particular, inside realistic nuclei. Our results are presented as three new equations. The first one is a linear equation for QCD generating functional (and for scattering amplitude) that sums the 'fan' diagrams. For the amplitude this equation is equivalent to the non-linear Balitsky-Kovchegov equation. The second equation is a generalization of the Balitsky-Kovchegov non-linear equation to interactions with realistic nuclei. It includes a new correlation parameter which incorporates, in a model dependent way, correlations inside the nuclei. The third equation is a non - linear equation for QCD generating functional (and for scattering amplitude) that in addition to the 'fan' diagrams sums the Glauber-Mueller multiple rescatterings.

hep-ph↗

arXiv2003

QCD Saturation and Photoproduction on Proton and Nuclei Targets

We calculate inclusive photoproduction cross-sections for both proton and nuclei targets, using a saturation model derived from an approximate solution to the Balitsky-Kovchegov nonlinear evolution equation. This paper extends our hypothesis, that one can successfully use the dipole picture and saturation models to describe soft processes, instead of the soft Pomeron Regge parametrization. Our fit is compatible with our previous fit to DIS data, and utilizes the same phenomenological parameters as in our paper devoted to soft hadronic interactions. Using the Glauber formalism, and no additional parameters, we calculate the cross-sections for photoproduction on various nuclei, and compare our results with the relevant data.

hep-ph↗

arXiv2003

QCD Saturation in the Semi-classical Approach

In this paper the semi-classical approach to the solution of non-linear evolution equation is developed. We found the solution in the entire kinematic region to the non-linear evolution equation that governs the dynamics in the high parton density QCD. The large impact parameter ($b_t$) behavior of the solution is discussed as well as the way how to include the non-perturbative QCD corrections in this region of $b_t$. The geometrical scaling behavior and other properties of the solution in the saturation (Color Glass Condensate) kinematic domain are analyzed. We obtain the asymptotic behavior for the physical observables and found the unitarity bounds for them.

hep-ph↗

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

Gamma^* - Gamma^* Scattering: Saturation and Unitarization in the BFKL approach

In this paper $γ^* - γ^*$ scattering with large, but more or less equal virtualities of two photons is discussed using BFKL dynamics, emphasizing the large impact parameter behavior ($b_t$) of the dipole-dipole amplitude. It is shown that the non-perturbative contribution is essential to fulfill the unitarity constraints in the region of $b_t > 1/2 m_π$, where $m_π$ is pion mass. The saturation and the unitarization of the dipole-dipole amplitude is considered in the framework of the Glauber-Mueller approach. The main result is that we can satisfy the unitarity constraints introducing the non-perturbative corrections only in initial conditions (Born amplitude).

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

Parton saturation and N_part scaling of semi--hard processes in QCD

We argue that the suppression of high p_t hadrons discovered recently in heavy ion collisions at RHIC may be a consequence of saturation in the Color Glass Condensate. We qualitatively and semi-quantitatively describe the data, in particular, the dependence upon the number of nucleon participants. We show that if parton saturation sets in at sufficiently small energy, then in nucleus-nucleus collisions at RHIC and LHC energies the cross sections of semi-hard processes should scale approximately with the number of participants, N_{part}. Our results provide a possible explanation of both the absence of apparent jet quenching at SPS energies and its presence at RHIC. Under the same assumption we predict that in semi--central and central pA (dA) collisions at collider energies the dependence of semi--hard processes on the number of participating nucleons of the nucleus will change to \sim (N_{part}^A)^{1/2}. The forthcoming data on dA collisions will provide a crucial test of this description.

hep-ph↗

arXiv2002

Diffractive dissociation from non-linear evolution in DIS on nuclei

The process of single diffractive dissociation off nuclei is considered on a basis of solutions to the nonlinear evolution equation. The relevant saturation scales $Q_{s A}^D(x,x_0)$ are determined and their dependences on Bjorken $x$, atomic number $A$, and minimal rapidity gap $Y_0\equiv \ln 1/x_0$ are investigated. The solutions are shown to posses the geometrical scaling in a broad kinematic region for $x$ well below $x_0$. A detailed theoretical discussion of saturation scale and scaling is presented. The ratio $σ^{diff}/σ^{tot}$ is computed for several nuclei. We predict that at $x\simeq 10^{-4}$ this ratio is of the order 25% which is much larger to the one of proton. This result indicates a possibility to observe a very strong nuclear shadowing.

hep-ph↗