arXiv subjects

Igor Altsybeev

Publications and source records attributed to Igor Altsybeev.

15 recordsLinked to original sources

arXiv2020

Reconstruction of moments of particle distributions with Identity Method at MPD

Precise determination of the moments of multiplicity distributions of identified particles could be challenging due to the misidentification in detectors. The so-called Identity Method allows one to solve this problem. In this contribution, performance of the Identity Method was tested on the A-A events simulated in the conditions of the MPD experiment at NICA. With this method, moments within a single kinematic window as well as coefficients of forward-backward pseudorapidity correlations are extracted.

hep-ex↗

arXiv2020

Higher-order cumulants of net-charge distributions from local charge conservation

In studies of heavy-ion collisions, fluctuations of conserved quantities are considered as an important signal of the transition between the hadronic and partonic phases of nuclear matter. In this paper, it is investigated how the local charge conservation affects higher-order cumulants of net-charge distributions at LHC energies. Simple expressions for the cumulants are derived under the assumption that particle-antiparticle pairs are produced in local processes from sources that are nearly uncorrelated in rapidity. For calculations with these expressions, one needs to know only the second cumulant of net-charge distribution and low-order cumulants of particle number distribution, which are directly measurable experimentally. It is argued that if one wishes to relate susceptibilities with cumulants of net-proton distributions, the developed model provides a better baseline than the conventional Skellam limit or models based on monte-carlo simulations.

nucl-th↗

arXiv2020

Cumulants of net-charge distribution from particle-antiparticle sources

It is shown how high-order cumulants of net-charge distribution in hadronic collisions at LHC energies can be expressed via lower-order terms under the assumption that particle-antiparticle pairs are produced in independent local processes. It is argued and tested with HIJING model that this assumption is typically valid for net-proton fluctuations in the case when no critical behaviour is present in the system. Values estimated in such a way can be considered as baselines for direct measurements of high-order net-charge fluctuations in real data.

nucl-th↗

arXiv2020

On feasibility of azimuthal flow studies with Principal Component Analysis

It is shown that the Principal Component Analysis applied to azimuthal single-particle distributions allows to perform flow analysis in ways that are analogous to the traditional approaches based on multi-particle correlations. In particular, symmetric cumulants are considered. It is demonstrated also that statistical fluctuations due to a finite number of particles per event practically do not play a role for higher order PCA-based cumulants.

nucl-th↗

arXiv2019

Application of Principal Component Analysis to establish proper basis for flow studies in heavy-ion collisions

It is shown that Principal Component Analysis (PCA) applied to event-by-event single-particle distributions in A-A collisions allows establishing the most optimal basis for anisotropic flow studies from data itself, in contrast to manual selection of the basis functions. PCA coefficients for azimuthal particle distributions are identical to Fourier coefficients from a conventional analysis techniques. PCA applied in longitudinal dimension reveals optimal basis that is similar to Legendre polynomial series. Analysis in both dimensions simultaneously allows studying the coupling of the longitudinal structure of events with the azimuthal anisotropy of particle emission.

nucl-th↗

arXiv2019

On resonance contribution to balance functions

It is known that resonance decays influence the shape of the charge-balance functions measured in hadronic collisions. That is reflected in their rapidity and azimuthal widths and the integral, and therefore has consequences for different model interpretations. In this paper, we show that the contribution from neutral resonance decays can be removed from the balance function in an analytical way, and test the performance of the removal procedure with PYTHIA events. Prospects for applications of the procedure to real data analysis of balance functions are also discussed.

nucl-th↗

arXiv2019

Recent developments in particle yield fluctuation measurements

In relativistic heavy-ion collisions, properties of the initial state and effects arising during evolution of the medium, such as a transition between the hadronic and partonic phases, should reflect themselves in event-by-event fluctuations of the number of produced particles. In this paper, recent measurements of several event-by-event observables, namely, dynamical fluctuations of relative particle yields and forward-backward correlations of different types, are discussed. Also, new observables for forward-backward correlation studies are proposed: correlations between ratios of identified particle yields in two separated acceptance intervals and the correlation between the ratio in one interval and average transverse momentum in another.

hep-ph↗

arXiv2017

Angular correlations with charmed hadrons in the Monte-Carlo model with string repulsion

Recent experimental results revealed large elliptic flow of the charmed hadrons at LHC energies, unexpectedly similar to that of the charged pions. The mentioned measurements are often interpreted using transport models, which incorporate dissociation and recombination mechanisms for charm quarks. In this report, a modified version of the Monte Carlo model with string repulsion is used to calculate azimuthal correlations with charmed hadrons. The string repulsion mechanism may provide significant angular correlations and can be considered as an alternative to thermalization picture.

nucl-th↗

arXiv2017

Forward-backward correlations between mean transverse momenta in Pb-Pb collisions with ALICE

Forward-backward (FB) correlations are considered to be a powerful tool for the exploration of the early dynamics of hadronic interactions. The FB correlation functions can be constructed from different observables calculated event-by-event in two separated pseudorapidity regions. We report measurements of event-by-event average transverse momentum correlations for charged particles in two separated pseudorapidity regions in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ and 5.02 TeV recorded with ALICE at the LHC. The event-by-event mean transverse momenta correlations are robust against volume fluctuations and thus the centrality determination methods, which provides higher sensitivity to the properties of the initial state and evolution of the medium created in A-A collisions. The strength of the FB correlation is calculated for different centralities of the Pb-Pb collisions. Results are compared with Monte Carlo event generators, such as HIJING and AMPT.

nucl-ex↗

arXiv2017

Azimuthal flow in hadron collisions from quark-gluon string repulsion

Color flux tubes (quark-gluon strings), formed at early stages of hadron-hadron collisions, may overlap in case of sufficiently high densities and interact, producing long-range azimuthal correlations. In the hypothesis of repulsive interaction, each string may acquire, before the hadronization, the additional transverse boost, which is an efficient sum of all accounted string-string interactions. This modifies transverse momenta to the particles formed in string decay, leading to modification of event-wise observables, like azimuthal asymmetry of two-particle correlations, over a wide range of rapidity. In this article we discuss results of Monte Carlo model with string repulsion, where efficient string-string interaction radius is introduced. We show that the effect of string repulsion can be the main dynamic origin of the elliptic flow and of the higher harmonics, which are reflected in the complicated structures observed in two-particle long-range correlation topology in nucleus-nucleus collisions at RHIC and at LHC.

hep-ph↗

arXiv2016

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.

physics.data-an↗

arXiv2016

Long-range correlations in ALICE at the LHC

Long-range correlations between particles separated by a pseudorapidity gap are a powerful tool to explore the initial stages and evolution of the medium created in hadron-hadron collisions. An overview of the long-range correlations measured by the ALICE detector in pp, p-Pb and Pb-Pb will be presented. This includes analyses of forward-backward, two- and multi-particle correlations with the use of the central barrel and forward detectors.

nucl-ex↗

arXiv2015

Forward-backward correlations with strange particles in PYTHIA

We present studies of strange particle yields and correlations in $pp$ collisions in the PYTHIA8 event generator by studying forward-backward correlations. Several key processes that give rise to these correlative effects are identified and manipulated to probe the fundamental properties of strange particle emitting sources. The sensitivity of strange particle production and correlations to PYTHIA's multiparton interaction, color reconnection, and explicit strangeness suppression are shown.

hep-ph↗

arXiv2015

Mean transverse momenta correlations in hadron-hadron collisions in MC toy model with repulsing strings

In the present work, Monte-Carlo toy model with repulsing quark-gluon strings in hadron-hadron collisions is described. String repulsion creates transverse boosts for the string decay products, giving modifications of observables. As an example, long-range correlations between mean transverse momenta of particles in two observation windows are studied in MC toy simulation of the heavy-ion collisions.

hep-ph↗

arXiv2015

Constraints on string percolation model from anomalous centrality evolution data in Au-Au collisions at $\mathbf{\sqrt{s_{NN}}=}$ 62 and 200 GeV

Anomalous centrality evolution of two-particle angular correlations observed in Au-Au collisions at $\sqrt{s_{NN}} = 62$ and 200 GeV and the onset of ridge structures are considered in the model of interacting quark-gluon strings. We assume that at the given energy of nucleus-nucleus collisions the critical energy density may be reached at the specific centrality. In a string percolation model this might be treated equivalently to a formation of a large cluster of strings characterized by the critical string density, with a size comparable to the whole area of interaction of two nuclei. This hypothesis allows to define some constraints on the string percolation model using data on transitional centralities in Au-Au collisions at these two energies. Results are extrapolated to the LHC energy where high string densities (exceeding the critical value) are confirmed for all classes of centralities in Pb-Pb collisions. Interaction between strings inside large clusters formed in nucleus-nucleus collisions is considered in a simplified Monte Carlo model. This model is applied to the qualitative analysis of the onset of collectivity and the ridge formation in Pb-Pb collisions. It is shown that the approach of the repulsive string-string interaction is capable to explain the appearance of elliptic and triangular flow observed in nucleus-nucleus collisions at RHIC and LHC energies.

hep-ph↗