arXiv subjects

V. V. Vechernin

Publications and source records attributed to V. V. Vechernin.

At least 19 recordsLinked to original sources

arXiv2020

The strongly intensive observable in pp collisions at LHC energies in the string fusion model

The properties of the strongly intensive variable characterizing correlations between the number of particles in two separated rapidity interval in pp interactions at LHC energies are studied in the framework of the string fusion model. We perform the MC simulations of string distributions in the impact parameter plane to take into account the experimental conditions of pp collisions. We account the string fusion processes, leading to the formation of string clusters, embedding a finite lattice (a grid) in the impact parameter plane. As a result, we found the dependence of this variable both on the distance between the centers of the observation windows and their width for the minbias pp collisions at several initial energies. Analyzing these dependencies we can extract the important information on the properties of string clusters. We show that in pp collisions at LHC energies the string fusion effects have a significant impact on the behavior of this strongly intensive variable. The role of these effects is increasing with the initial energy and centrality of collisions. In particular, we found that the increase of this variable with initial energy takes place due to the growth of the portion of the fused string clusters in string configurations arising in pp interactions.

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arXiv2015

Restrictions on pp scattering amplitude imposed by first diffraction minimum data obtained by TOTEM at LHC

We present the systematic analysis of the behavior of elastic pp scattering cross section in the region of the diffraction peak and the first diffraction minimum in the framework of quasi-eikonal Gribov-Regge approach, taking into account the unitarity condition. We use the formalism taking into consideration the dependence of pomeron signature factor on $t$. We show that although in this approach one can describe the general features of pp scattering, the behavior of pp elastic differential cross section in the vicinity of the first diffraction minimum measured by the TOTEM experiment at LHC can not be reproduced under any parameter values at standard assumptions of the model. Physically, in the quasi-eikonal Regge approach the proton proved to be "gray" and rather large, whereas the TOTEM data indicate that it is smaller and closer to "black" at LHC energies.

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arXiv2014

Ridge from Strings

In the colour string picture with fusion and percolation it is shown that long range azimuthal-rapidity correlations (ridge) can arise from the superposition of many events with exchange of clusters of different number of strings and not from a single event. Relation of the ridge with the flow harmonics coefficients is derived. By direct Monte-Carlo simulations, in the technique previously used to calculate these coefficients, ridge correlations are calculated for AA, pA and pp collisions. The azimuthal anisotropy follows from the assumed quenching of the emitted particles in the strong colour fields inside string clusters. It is confirmed that in pp collisions the ridge structure only appears in rare events with abnormally high multiplicity. Comarison with the experimental data shows a good agreement. Also a good agreement is found for pPb collisions. For AA collisions a reasonable agreement is found for both near-side and away-side angular correlations although it worsens at intermediate angles.

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arXiv2014

On description of the correlation between multiplicities in windows separated in azimuth and rapidity

The forward-backward (FB) multiplicity correlations in two windows separated in rapidity and azimuth are analyzed in the framework of the model with independent identical emitters (strings). Along with the short-range contribution, originating from the correlation between particles produced by a single string, the long-range contribution, originating from the fluctuation in the number of strings, is taken into account. The connection of the FB multiplicity correlation coefficient with the two-particle correlation function and the di-hadron correlation analysis is traced. It's also shown that the direct azimuthal flow leads to the forward ridge structure in the resulting two-particle correlation function.

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arXiv2012

Anisotropic flows from colour strings: Monte-Carlo simulations

By direct Monte-Carlo simulations it is shown that the anisotropic flows can be successfully described in the colour string picture with fusion and percolation provided anisotropy of particle emission from the fused string is taken into account. Quenching of produced particles in the strong colour field of the string is the basic mechanism for this anisotropy. The concrete realization of this mechanism is borrowed from the QED. Due to dependence of this mechanism on the external field strength the found flows grow with energy, with values for $v_2$ at LHC energies greater by ~15% than at RHIC energies.

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arXiv2012

Fluctuations of the number of participants and binary collisions in AA interactions at fixed centrality in the Glauber approach

In the framework of the classical Glauber approach, the analytical expressions for the variance of the number of wounded nucleons and binary collisions in AA interactions at a given centrality are presented. Along with the optical approximation term, they contain additional contact terms arising only in the case of nucleus-nucleus collisions. The magnitude of the additional contributions, e.g., for PbPb collisions at SPS energies, is larger than the contribution of the optical approximation at some values of the impact parameter. The sum of the additional contributions is in good agreement with the results of independent Monte Carlo simulations of this process. Due to these additional terms, the variance of the total number of participants for peripheral PbPb collisions and the variance of the number of collisions at all values of the impact parameter exceed several multiples of the Poisson variances. The correlator between the numbers of participants in colliding nuclei at fixed centrality is also analytically calculated.

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arXiv2010

Long-Range Rapidity Correlations in the Model with Independent Emitters

The correlation between multiplicities in two separated rapidity windows, the so-called long-range correlation (LRC), is studied in the framework of the model with independent identical emitters. It's shown that the LRC coefficient, defined for the scaled (relative) variables, nevertheless depends on the absolute width of the forward rapidity window and does not depend on the width of the backward one. The dependence of the LRC coefficient on the forward rapidity acceptance is explicitly found with only one theoretical parameter. The preliminary comparison with ALICE 7TeV pp collisions data shows that the multiplicity LRC in the data can be described in the framework of the suggested approach.

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arXiv2008

Space-time picture of the string fragmentation and the fusion of colour strings

It is shown that naive two stage scenario of the soft multiparticle production in hadronic and nuclear collisions at high energy, when at first stage the colour strings are formed and at the second stage these strings, or some other (higher colour) strings formed due to fusion of primary strings, are decaying, emitting observed particles, encounters some difficulties at the attempt to analyse the space-time picture of the process. Simple analysis shows the dominant is the process when the formation and the decay of a string occur in parallel - a string breaks into two parts already at rather small length (about 1-2 fm in its c.m. system), then the process repeats in the pieces and so on. Nevertheless it is proved to be possible to agree the string fusion idea with the space-time picture of a string decay. In the framework of the Artru-Mennessier model of a string fragmentation the simple interpretation of the homogeneity of the rapidity distribution for hadrons produced from the decay of a single string at high energy is presented and the analytical estimate for the density of this rapidity distribution is obtained.

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arXiv2007

On Participants Number Fluctuations for Given Centrality AA-Interactions in the Classical Glauber Approach

In the framework of the classical Glauber approach the exact analytical expression for the variance of the number of participants (wounded nucleons) for given centrality AA interactions is presented. It's shown, that in the case of nucleus-nucleus collisions along with the optical approximation term the additional "contact" term appears. The numerical calculations for PbPb collisions at SPS energies show that at intermediate values of the impact parameter the "optical" and "contact" terms contributions to the variance of the participants number are of the same order and their sum is in a good agreement with the results of independent MC simulations of this process. The correlation between the numbers of participants in colliding nuclei is taken into account. In particular it's demonstrated that in PbPb collisions at SPS energies the variance of the total number of participants approximately three times exceeds the Poisson one in the impact parameter region 10-12 Fm. The fluctuations of the number of collisions are also discussed.

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arXiv2005

Multiplicity and Pt Correlations in AA-interactions at High Energies

The theoretical description of the correlations between observables in two separated rapidity intervals in relativistic nuclear collisions is presented. It is shown, that the event-by-event pt-pt correlation defined as the correlation between event mean values of transverse momenta of all particles emitted in two different rapidity intervals does not decrease to zero with the increase of the number of strings in contrast with two particle pt-pt correlation - the correlation between the transverse momenta of single particles produced in these two rapidity windows. In the idealized case with the homogeneous string distribution in the transverse plane in the framework of the cellular analog of string fusion model (SFM) the asymptotic of pt-pt correlation coefficient is analytically calculated and compared with the results of the Monte-Carlo (MC) calculations fulfilled both in the framework of the original SFM and in the framework of its cellular analog, which enables to control the MC algorithms. In the case with the realistic nucleon distribution density of colliding nuclei the results of the MC calculations of the pt-pt correlation function for minimum bias nuclear collisions at SPS, RHIC and LHC energies are presented and analysed.

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arXiv2005

Multiplicity and Pt Correlations in Relativistic Nuclear Collisions

The theoretical description of the correlations between observables in two separated rapidity intervals for AA-interactions at high energies is presented. In the case with the realistic nucleon distribution density of colliding nuclei the MC calculations of the long-range correlation functions at different values of impact parameter are done. For n-n and pt-n correlations it is shown that the impact parameter fluctuations at a level of a few fermi, unavoidable in any experiment, significantly change the magnitude of correlation coefficients. The rise of pt-n and especially pt-pt correlation coefficients is found when one passes from SPS to RHIC and LHC energies.

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arXiv2003

Leptoproduction of nucleons in the cumulative region

Leptoproduction of nucleons into the backward hemisphere on nuclear targets is studied at relativistic subasymptotic energies and momenta. The relativistic internucleon potential is extracted from appropriate photoproduction data. Different production mechanisms are found to work together and interfere. Whenever rescattering is kinematically possible, it gives the bulk of the contribution, except at very high Q^2. Comparison with the existing data at E=2.4 GeV shows a reasonable agreement.

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arXiv2003

Correlations between multiplicities and average transverse momentum in the percolating colour strings approach

Long range correlations multiplicity-multiplicity, $p_T^2$-multiplicity and $p^2 - p^2_T$ are studied in the percolating colour string picture under different assumptions of the dynamics of string interaction. It is found that the strength of these correlations is rather insensitive to these assumptions nor to the geometry of formed fused string clusters. Both multiplicity-multiplicity and $p_T^2$-multiplicity correlations are found to scale and depend only on the string density. The $p_T^2$-multiplicity correlations, which are absent in the independent string picture, are found to be of the order of 10% for central heavy ion collisions and can serve as a clear signature of string fusion. In contrast the $p^2_T - p^2_T$ correlations turned out to be inversely proportional to the number of strings and so very small for relaistic collisions.

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arXiv2003

Cellular Approach to Long-Range $p_t$ and Multiplicity Correlations in the String Fusion Model

The long-range $p_t$ and multiplicity($n$) correlations in high-energy nuclear collisions are studied in the framework of a simple cellular analog of the string fusion model. Two cases with local and global string fusion is considered. The $p_t$--$n$ and $n$--$n$ correlation functions and correlation coefficients are calculated analytically in some asymptotic cases using suggested Gauss approximation. It's shown that at large string density the $p_t$--$n$ and $n$--$n$ correlation coefficients are connected and the scaling takes place. The behavior of the correlations at small string density is also studied. The asymptotic results are compared with results of the numerical calculations in the framework of proposed cellular approach.

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arXiv2003

Simple Cellular Model of Long-Range Multiplicity and $p_t$ Correlations in High-Energy Nuclear Collisions

A simple cellular model for the description of the long-range multiplicity and $p_t$ correlations in high-energy nuclear collisions originating from the string fusion model is proposed. Three versions of the model: without fusion, with local and with global string fusion are formulated. A Gauss approximation which enables explicit analytical calculations of the correlation functions in some asymptotic cases in the framework of the model is developed. The assumptions of the model and the validity of a Gauss approximation are checked up in the simplest (no fusion) case when the explicit solution of the model can be found. The role of a size of cells is analysed. The modification of the results in the case of non-Poissonian distributions is also discussed.

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arXiv2000

On the forward-backward correlations in a two-stage scenario

It is demonstrated that in a two-stage scenario with elementary Poissonian emitters of particles (colour strings) arbitrarily distributed in their number and average multiplicities, the forward- backward correlations are completely determined by the final distribution of the forward particles. The observed linear form of the correlations then necessarily requires this distribution to have a negative binomial form. For emitters with a negative binomial distribution of the produced particles distributed so as to give the final distribution also of a negative binomial form, the forward-backward correlations have an essentially non-linear form, which disagrees with the experimental data.

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arXiv1997

Deuteron Disintegration in Quark-Parton Model

The deuteron disintegration process with the emission of fast proton in the vicinity of the kinematical boundary of the reaction, when Feynman variable $x\to 2$, is studied. The consideration is fulfilled in the framework of the quark-parton model of cumulative phenomena based on perturbative QCD calculations of the corresponding quark diagrams near the thresholds, at which some quarks ("donors") in the nuclear flucton transfer all their longitudinal momenta to the distinguished active quarks and become soft. The presence of the multi-quark $6q$-configuration in a deuteron is essentially exploited in the consideration. The different versions of hadronization mechanisms of the produced cumulative quarks into cumulative particles are analyzed. It is shown that in the case of the production of cumulative protons from deuteron the hadronization through the coalescence of three cumulative quarks is favorable and leads to the $(2-x)^5$ cross section threshold behavior whereas the usual hadronization through one cumulative quark fragmentation into proton the same as the calculations predicts for the deuteron structure function $F^d_2(x)$ at $x\to 2$ in DIS processes. The results of the calculations are compared with the available experimental data.

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arXiv1996

Cumulative Phenomena through the Quark-Parton Diagram Summation at Thresholds

A microscopic treatment of cumulative phenomena based on perturbative QCD calculations of the corresponding quark diagrams near the threshold is presented. To sum all diagrams like these the special technique based on the recurrence relations was developed. The x-behaviour of the nuclear structure function $F_{2}(x)$ in the cumulative region x>1 was found to be roughly exponential, governed by an effective coupling constant, which depends on the QCD coupling constant and quark mass. Two mechanisms for cumulative particle production, direct and spectator ones, were analysed. It was shown that due to final state interactions the leading terms of the direct mechanism contribution are cancelled and the spectator mechanism is the dominant one. It leads to a smaller slope of the particle production rates compared to the slope of the nuclear structure function in the cumulative region, in agreement with the recent experimental data. The slope difference is due to additional multiple interactions between nuclear and projectile partons which enter the spectator mechanism for the cumulative production. The different versions of hadronization mechanisms of the produced cumulative quarks into hadrons are also discussed.

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