Speaker
Description
In relativistic heavy ion collisions, a dense hot matter called quark-gluon plasma (QGP) is formed [1]. Information about the properties of formed medium can be obtained from data on the energy loss of quarks and gluons (partons) with high transverse momenta $p_{T}≫Λ_{QCD}$ produced in hard parton-parton interactions [2]. The energy loss of partons in QGP leads to the jet quenching effect in nucleus-nucleus collisions [2], which is studied experimentally based on data on hadron yields.
One of the most important experimental quantities related to the parton energy loss in the QGP is the fractional parton energy loss $S_{loss}$, which is defined as the ratio of the average parton energy loss $∆E$ to their average initial energy $E_{in}$ [2,3]. The suppression of hadron yields at high $p_T$ caused by the energy loss of parent partons is characterized by the nuclear modification factor $R_{AB}$ [2,3]. Therefore, using the relationship between $S_{loss}$ and $R_{AB}$ [3], the dependence of $S_{loss}$ on the hadron transverse momentum $p_T$ and the collision centrality (the number of participating nucleons $N_{part}$) can be obtained. The azimuthal anisotropy of hadrons produced in heavy ion collisions relative to the reaction plane (the plane formed by the beam axis and the impact parameter vector) in the intermediate rapidity region ($|η|<0.35$) is quantitatively characterized by the elliptic flow $v_2$ [4]. Based on the previously obtained values of $v_2$ of hadrons at $p_T > 5 GeV/c$, it is possible to calculate the dependences of the $S_{loss}$ value on the azimuthal angle $Δφ$ [3] of hadrons (in particular $π^0$) emission which allows to study the anisotropy in the distribution of the QGP characteristics. For all values of $N_{part}$ and $Δφ$, the effective parton path-length $L_{eff}$ was calculated using the Glauber model [5], considering the distribution of the color charge density in the QGP, the time dependence during the longitudinal expansion of QCD matter, and the distribution of parton creation points.
In this work, the values of the fractional parton energy losses depending on the azimuthal angle of π0 emission $S_{loss}(Δφ)$ and the effective parton path-length $S_{loss}(L_{eff})$ were obtained for different values of $N_{part}$ and $p_T$ in Cu+Au and U+U collisions at $\sqrt{s_{NN}}=200$ GeV and $193$ GeV, respectively.
The results of the work can be expanded for use in the MPD and SPD experiments at the NICA collider.
We acknowledge support from the Ministry of Science and Higher Education of the Russian Federation, state assignment for fundamental research (code FSEG-2025-0009).
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