arXiv subjects

J. Milosevic

Publications and source records attributed to J. Milosevic.

10 recordsLinked to original sources

arXiv2023

Decomposition of multi-particle azimuthal correlations in Q-cumulant analysis

The method of Q-cumulants is a powerful tool to study the fine details of azimuthal anisotropies in high energy nuclear collisions. This paper presents a new method, based on mathematical induction, to evaluate the analytical form of the high-order Q-cumulants. The ability of this method is demonstrated via a toy model that uses the elliptic power distribution to simulate anisotropic emission of particles, quantified in terms of Fourier flow harmonics v_{n}. The method can help in studying the large amount of event statistics that can be collected in the future, and to allow measurements of very high central moments of the v_{2} distribution. This can in turn facilitate progress in understanding the initial geometry, input to hydrodynamic calculations of medium expansion in high energy nuclear collisions, as well as constraints on it.

hep-ph↗

arXiv2021

Statistical uncertainties of the $v_{n}\{2k\}$ harmonics from Q-cumulants

Analytic formulas to calculate statistical uncertainties of $v_{n}\{2k\}$ harmonics extracted from the Q-cumulants are presented. The Q-cumulants are multivariate polynomial functions of the weighted means of $2m$-particle azimuthal correlations, $\llangle 2m \rrangle$. Variances and covariances of the $\llangle 2m \rrangle$ are included in the analytic formulas of the uncertainties that can be calculated simultaneously with the calculations of the $v_{n}\{2k\}$ harmonics. The calculations are performed using a simple toy model which roughly simulates elliptic flow azimuthal anisotropy with magnitudes around 0.05. The results are compared with the results obtained by the many data sub-sets, and by the bootstrapping method. The first one is a common way of estimation of the statistical uncertainties of the $v_{n}\{2k\}$ harmonics in a real experiment. In order to increase precision in the measurement of the $v_{n}\{2k\}$ harmonics, a large number of 15000 sub-sets and the same number of the re-sampling in the bootstrap method is used. A very good agreement in the comparison with the proposed way of the analytic calculation of the $v_{n}\{2k\}$ statistical uncertainties is found. Additionally, a recurrence equation for Q-cumulants calculation is also presented.

nucl-th↗

arXiv2020

Correlations between azimuthal anisotropy Fourier harmonics in PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV in the HYDJET++ and AMPT models

Correlations between azimuthal anisotropy Fourier harmonics $v_{n}$ ($n = 2, 3, 4$) are studied using the events from PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV generated by the HYDJET++ and AMPT models, and compared to the corresponding experimental results obtained by the ATLAS Collaboration. The Fourier harmonics $v_{n}$ are measured over a wide centrality range using the two-particle azimuthal correlation method. The slopes of the $v_{2}$--$v_{3}$ correlation from both models are in a good agreement with the ATLAS data. The HYDJET++ model predicts a stronger slope for the $v_{2}$--$v_{4}$ and $v_{3}$--$v_{4}$ correlations than the ones experimentally measured, while the results from the AMPT model are in a rather good agreement with the experimental results. In contrast to the HYDJET++ predictions, the AMPT model predicts a boomerang-like shape in the structure of the correlations as found in the experimental data.

nucl-th↗

arXiv2019

Skewness of the elliptic flow distribution in $\sqrt{s_{_{\mathrm{NN}}}}$ = 5.02~TeV PbPb collisions from HYDJET++ model

The elliptic flow ($v_{2}$) event-by-event fluctuations in PbPb collisions at 5.02~TeV are analyzed within the HYDJET++ model. Using the multi-particle, so called Q-cumulant method, $v_{2}\{2\}$, $v_{2}\{4\}$, $v_{2}\{6\}$ and $v_{2}\{8\}$ are calculated and used to study their ratios and to construct skewness ($γ^{exp}_{1}$) as a measure of the asymmetry of the elliptic flow distribution. Additionally, in order to check if there is a hydrodynamics nature in the elliptic collectivity generated by the HYDJET++ model, the ratio of $v_{2}\{6\} - v_{2}\{8\}$ and $v_{2}\{4\} - v_{2}\{6\}$ distribution is calculated. The analysis is performed as a function of the collision centrality. In order to check the HYDJET++ model responses, the results of this analysis are compared to the corresponding experimental measurements by CMS. A good qualitative and rather good quantitative agreement is found.

hep-ph↗

arXiv2017

Sub-leading flow modes in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV from HYDJET++ model

Recent LHC results on the appearance of sub-leading flow modes in PbPb collisions at 2.76~TeV, related to initial-state fluctuations, are analyzed and interpreted within the HYDJET++ model. Using the newly introduced Principal Component Analysis (PCA) method applied to two-particle azimuthal correlations extracted from the model calculations, the leading and the sub-leading flow modes are studied as a function of the transverse momentum ($p_{T}$) over a wide centrality range. The leading modes of the elliptic ($v^{(1)}_{2}$) and triangular ($v^{(1)}_{3}$) flow calculated within the HYDJET++ model reproduce rather well the $v_{2}\{2\}$ and $v_{3}\{2\}$ coefficients experimentally measured using the two-particle correlations. Within the $p_{T} \le $~3~GeV/c range where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest $p_{T}$ of around 3~GeV/c. The sub-leading elliptic flow mode ($v^{(2)}_{2}$), which corresponds to $n = 2$ harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode ($v^{(2)}_{3}$), which corresponds to $n = 3$ harmonic, is even smaller and does not depend on centrality. For $n = $~2, the relative magnitude of the effect measured with respect to the leading flow mode shows a shallow minimum for semi-central collisions and increases for very central and for peripheral collisions. For $n = $~3 case, there is no centrality dependence. The sub-leading flow mode results obtained from the HYDJET++ model are in a rather good agreement with the experimental measurements of the CMS Collaboration.

nucl-ex↗

arXiv2008

Two Particle Azimuthal Correlations in 4.2A GeV C+Ta Collisions

Two particle azimuthal correlations are studied in 4.2A GeV C+Ta collisions observed with the 2-m propane bubble chamber exposed at JINR Dubna Synchrophasotron. The correlations are analyzed both for protons and negative pions, and their dependence on the collision centrality, rapidity and rapidity difference is investigated. It is found that protons show a weak back-to-back correlations, while a side-by-side correlations are observed for negative pions. Restricting both protons to the target or projectile fragmentation region, the side-by-side correlations are observed for protons also. Using the two particle correlation function, the flow analysis is performed and intensity of directed flow is determined without event-by event estimation of the reaction plane.

nucl-ex↗

arXiv2008

Azimuthal dependence of pion source radii in Pb+Au collisions at 158 A GeV

We present results of a two-pion correlation analysis performed with the Au+Pb collision data collected by the upgraded CERES experiment in the fall of 2000. The analysis was done in bins of the reaction centrality and the pion azimuthal emission angle with respect to the reaction plane. The pion source, deduced from the data, is slightly elongated in the direction perpendicular to the reaction plane, similarly as was observed at the AGS and at RHIC.

nucl-ex↗

arXiv2005

Strange and charged particle elliptic flow in Pb+Au collisions at 158 AGeV/c

We present $Λ$ and $π$ elliptic flow measurements from Pb+Au collisions at the highest SPS energy. The data, collected by the CERES experiment which covers $η=2.05,2.70$ with full azimuthal coverage and wide $p_{T}$ sensitivity up to 3.5 GeV/c, can be used to test hydrodynamical models and show sensitivity to the EoS. The value of $v_{2}$ as a function of centrality and $p_{T}$ is presented. Values of $v_{2}$ observed by STAR at RHIC are larger by about 1/3. Our measurements are compared to results from other SPS experiments and to hydrodynamical calculations. Huge statistics allows for a precise measurement of the differential pion elliptic flow.

nucl-ex↗

arXiv2002

Anisotropic flow in 4.2A GeV/c C+Ta collisions

Anisotropic flow of protons and negative pions in 4.2A GeV/c C+Ta collisions is studied using the Fourier analysis of azimuthal distributions. The protons exhibit pronounced directed flow. Directed flow of pions is positive in the entire rapidity interval and indicates that the pions are preferentially emitted in the reaction plane from the target to the projectile. The elliptic flow of protons and negative pions is close to zero. Comparison with the quark-gluon-string model (QGSM) and relativistic transport model (ART 1.0) show that they both yield a flow signature similar to the experimental data.

nucl-ex↗

arXiv2001

Event anisotropy in 4.2A GeV/c C+C collisions

The directed and elliptic flow of protons and negative pions in 4.2A GeV/c C+C collisions is studied using the Fourier analysis of azimuthal distributions. It is found that the protons exhibit pronounced directed flow, while the flow of pions is either non existent or too weak to be detected experimentally. Also, it is found that in the entire rapidity interval the elliptic flow is very small if not zero. These results are confirmed by the Quark-Gluon-String Model (QGSM) and the relativistic transport model (ART 1.0), except that these models predict very weak antiflow of pions. The more detailed comparison with the QGSM suggests that the decay of resonances and rescattering of secondaries dominantly determine the proton and negative pion flow at this energy.

nucl-th↗