Forward-backward multiplicity correlations in pp collisions at high energy in Monte Carlo model with string fusion

The correlations between multiplicities in two separated rapidity windows, is studied in the framework of the Monte Carlo model based on the picture of string formation in elementary collisions of colour dipoles. The hardness of the elementary collisions is defined by a transverse size of the interacting dipoles. The dependencies of the forward-backward correlation strength on the width and position of the pseudorapidity windows, as well as on transverse momentum range of observed particles were studied. It is demonstrated that taking into account of the string fusion effects improves the agreement with the available experimental data.Comment: 4 pages, 3 figures, proc. PANIC 201

Long-range rapidity correlations in high energy AA collisions in Monte Carlo model with string fusion

The magnitude of long-range correlations between observables in two separated rapidity windows, proposed as a signature of the string fusion and percolation phenomenon, is studied in the framework of non-Glauber Monte Carlo string-parton model, based on the picture of elementary collisions of color dipoles. The predictions, obtained with and without string fusion, demonstrate effects of color string fusion on the observables in Pb-Pb collisions at the LHC: decrease of n-n correlation coefficient with centrality and negative pt-n correlations, if the sufficiently effective centrality estimator is applied. In general case it is shown that the values of n-n and pt-n correlation coefficients strongly depend on the method of collision centrality fixation. In contrast, the predictions obtained for pt-pt correlation have almost no effect of centrality determination method and the corresponding experimental data would produce the strong limitation on the transverse radius of a string.Comment: 5 pages, 4 figures, to be published in EPJ Web of Conferences (INPC2013 proceedings

Determination of the quark-gluon string parameters from the data on pp, pA and AA collisions at wide energy range using Bayesian Gaussian Process Optimization

Bayesian Gaussian Process Optimization can be considered as a method of the determination of the model parameters, based on the experimental data. In the range of soft QCD physics, the processes of hadron and nuclear interactions require using phenomenological models containing many parameters. In order to minimize the computation time, the model predictions can be parameterized using Gaussian Process regression, and then provide the input to the Bayesian Optimization. In this paper, the Bayesian Gaussian Process Optimization has been applied to the Monte Carlo model with string fusion. The parameters of the model are determined using experimental data on multiplicity and cross section of pp, pA and AA collisions at wide energy range. The results provide important constraints on the transverse radius of the quark-gluon string ($r_{str}$) and the mean multiplicity per rapidity from one string ($\mu_0$).Comment: 9 pages, 5 figures, proc. XIIIth Quark Confinement and the Hadron Spectru

Strongly intensive fluctuations and correlations in ultrarelativistic nuclear collisions in the model with string fusion

The several types of strongly intensive correlation variables are studied in nuclear collisions at LHC energy. These quantities are expected not to depend on centrality class width. They have been calculated in the dipole-based parton-string Monte Carlo model with string fusion. The centrality dependence of the mean transverse momentum correlation coefficient and strongly intensive quantity $\Sigma$ between multiplicity and $P_T$ have been obtained. Dynamical charge fluctuation $\nu_{dyn}$ has been also calculated and compared with experimental data. It is shown that string fusion improves agreement with the experiment.Comment: 6 pages, 4 figures. Proceedings of Baldin ISHEPP XXI

Model of pp and AA collisions for the description of long-range correlations

Soft processes in pp and AA interactions are considered in the framework of phenomenological model with color strings formation and fusion. Elementary parton collisions are realized in the model as the interaction of two colour dipoles from projectile and target nucleons. Modeling of the exclusive distributions of parton momentum fractions and transverse coordinates is performed. The interaction of colour strings in transverse plane is carried out in the framework of local string fusion model with the introduction of the lattice in the impact parameter plane and taking into account the finite rapidity length of strings. The parameters were fixed with experimental data on pp total inelastic cross section and charged multiplicity. The model was used for the calculation of long-range correlations between the multiplicities (n) and the mean transverse momenta (pt) of charged particles. The dependence of n-n, pt-n, pt-pt correlations on the width and position of the backward and forward rapidity windows was studied. Note that the model enables to describe the AA interactions without referring to the Glauber picture based on the concept of elementary nucleon-nucleon collisions. In this connection the charged multiplicity, the mean numbers of participant nucleons and binary collisions and their variances in the case of PbPb collisions were calculated and compared with the predictions of alternative models and the experimental data. The influence of different ways of centrality determination on the multiplicity fluctuations and long-range correlations was also discussed.Comment: 20 pages, 14 figures, proc. Baldin ISHEPP XX

Classifiers for centrality determination in proton-nucleus and nucleus-nucleus collisions

Centrality, as a geometrical property of the collision, is crucial for the physical interpretation of nucleus-nucleus and proton-nucleus experimental data. However, it cannot be directly accessed in event-by-event data analysis. Common methods for centrality estimation in A-A and p-A collisions usually rely on a single detector (either on the signal in zero-degree calorimeters or on the multiplicity in some semi-central rapidity range). In the present work, we made an attempt to develop an approach for centrality determination that is based on machine-learning techniques and utilizes information from several detector subsystems simultaneously. Different event classifiers are suggested and evaluated for their selectivity power in terms of the number of nucleons-participants and the impact parameter of the collision. Finer centrality resolution may allow to reduce impact from so-called volume fluctuations on physical observables being studied in heavy-ion experiments like ALICE at the LHC and fixed target experiment NA61/SHINE on SPS.Comment: To be published in proceedings of the "XIIth Quark Confinement and the Hadron Spectrum" conference (Thessaloniki, 2016

Long-range correlations in proton-nucleus collisions in MC model with string fusion

The study of long-range correlations between observables in two rapidity windows was proposed as a signature of the string fusion and percolation phenomenon. In the present work we calculate the correlation functions and coefficients for p-Pb collisions in the framework of the Monte Carlo string-parton model, based on the picture of elementary collisions of color dipoles. It describes pA and AA scattering without referring to the Glauber picture of independent nucleons collisions and includes effects of string fusion. Different types of correlations are considered: n-n, pt-n, pt-pt, where n is the event multiplicity of charged particles in a given rapidity window and pt is their mean transverse momentum. The results, obtained in the present work for p-Pb collisions, are compared with available experimental results for pt-n correlations in one window and further predictions are made.Comment: 6 pages, 4 figures, to appear in proc. Esp-Rus201