arXiv subjects

Md. Nasim

Publications and source records attributed to Md. Nasim.

At least 19 recordsLinked to original sources

arXiv2026

Anisotropic hadronic rescattering and its impact on $K^{*0}$ yield, and polarization observable

In this work, we investigate the anisotropic suppression of reconstructed $K^{*0}$ resonances arising from hadronic rescattering using the A Multi-Phase Transport (AMPT) model for Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. We demonstrate that the rescattering probability of the decay daughters depends strongly on the decay angle $\theta^{*}$ due to Lorentz boost effects, which lead to smaller laboratory-frame momenta for daughters emitted opposite to the parent particle motion. This anisotropic suppression influences several experimentally measured observables. We show that the reconstructed $K^{*0}$ yield exhibits a strong $\theta^{*}$ dependence. Furthermore, the anisotropic loss of resonances modifies the angular distributions used to extract the spin alignment parameter $\rho_{00}$ in the production-plane and helicity frames. Even in the absence of intrinsic polarization in the model, the reconstructed $K^{*0}$ sample shows deviations of $\rho_{00}$ from the unpolarized value of $1/3$, with opposite trends in the two reference frames. These results demonstrate that hadronic rescattering can generate apparent polarization signals and must be carefully considered in experimental measurements of vector-meson spin alignment using production plane and helicity frame.

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arXiv2026

The study of $K^{*0}$ meson production using a multi-phase transport model at RHIC BES energies

We present the yield, average transverse momentum, and collective flow measurement of $K^{*0}$ resonances in Au+Au collisions at $\sqrt{s_{NN}} = 19.6$, 14.5, and 7.7~GeV using the AMPT model. It is found that, due to hadronic rescattering, the decay daughters of $K^{*0}$ interact with other particles in the medium, causing the yield of reconstructable $K^{*0}$ to be significantly suppressed, especially at low transverse momentum. The model results are compared with recent experimental data from Phase-II of the Beam Energy Scan (BES-II) program at the Relativistic Heavy-Ion Collider. The string-melting version of the AMPT model successfully reproduces the measured $K^{*0}/K$ ratios at all three analysed collision energies. Interestingly, AMPT calculations that exclude the hadronic phase nevertheless provide a reasonable description of the data, thereby challenging the conventional interpretation that hadronic rescattering is the primary mechanism responsible for suppressing the $K^{*0}/K$ ratio in central heavy-ion collisions. In addition, we find that the $K^{*0}/K$ ratio appears to be largely insensitive to the lifetime of the hadronic phase, whereas the average transverse momentum, $\langle p_{T} \rangle$, of the $K^{*0}$ shows a strong dependence, increasing significantly as the lifetime of the hadronic phase becomes longer. We further show that the directed flow ($v_1$) of $K^{*0}$ mesons is strongly influenced by hadronic rescattering, whereas the elliptic flow ($v_2$) exhibits only weak sensitivity to hadronic effects. These results establish $K^{*0}$ directed flow as a sensitive probe of the late-stage hadronic medium in heavy-ion collisions. These model calculations therefore provide valuable insight into the underlying physics governing the observed experimental results at RHIC.

hep-ph↗

arXiv2025

Flow harmonic correlations via multi-particle symmetric and asymmetric cumulants in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

We study multi-particle azimuthal correlations in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. We use initial conditions obtained from a Monte-Carlo Glauber model and evolve them within a viscous relativistic hydrodynamics framework that eventually gives way to a transport model in the late hadronic stage of the evolution. We compute the multi-particle symmetric and asymmetric cumulants and present the results for their sensitivity to the shear and bulk viscosities during the hydrodynamic evolution. We also check their sensitivity to resonance decay and hadronic interactions. We demonstrate that while some of these observables are more sensitive to transport properties than traditional flow observables, others are less sensitive, making them suitable for studying different stages of the evolution.

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arXiv2025

Longitudinal flow decorrelation in heavy-ion collision at RHIC energies using a multi-phase transport model

We present a study on the longitudinal flow decorrelation in heavy-ion collisions at the RHIC Beam Energy Scan (BES) energies ($\sqrt{s_{NN}}$ = 11.5 to 200 GeV in Au+Au collisions) using the AMPT model. We measure the second and third order factorization ratios ($r_{2}$ and $r_{3}$) across BES energies, finding $r_{2}$ weakly dependent on collision energy while $r_{3}$ shows a more prominent collision energy dependent. The effect of parton-parton scattering cross section on $r_{2}$ and $r_{3}$ is studied which suggests that longitudinal decorrelation could be a potential observable to constrain transport properties of the medium. We also analyze the contributions of flow-plane and flow magnitude decorrelation, with flow-plane decorrelation being dominant. we measure a recently proposed observable, the four particle cumulant ($T_{2}$), which remains resilient to non-flow effects and exhibits sensitivity to different decorrelation patterns. Through the measurement of $T_{2}$, we consistently observe a hint of S-shaped or torqued decorrelation across all energy ranges in peripheral collisions (40-80\%). But in central and mid-central collisions, presence of any specific pattern of decorrelation is missing in AMPT model.

hep-ph↗

arXiv2024

The study of hadronic rescattering on $K^{*0}$ resonance yield in baryon-rich QCD matter

The effect of hadronic rescattering on $K^{*0}$ resonance yield can be studied by measuring $K^{*0}/K$ ratio as a function of centrality or multiplicity. This study investigates how the size of the system and the chemical composition (meson-meson versus meson-baryon interaction) of the matter formed in heavy-ion collisions impact the process of hadronic rescattering. It is shown that existing calculation of $K^{*0}/K$ ratio, which considers the interaction of $K^{*0}$ and $K$ mesons with only light mesons in the hadronic medium (neglecting interactions with baryons), fails to explain the measured $K^{*0}/K$ ratio at RHIC BES energies. To understand the multiplicity dependence of the $K^{*0}/K$ ratio at RHIC BES and SPS energies ($\sqrt{s_{NN}}$ $<$ 20 GeV), the Ultra Relativistic Quantum Molecular Dynamics (UrQMD) model is employed. UrQMD calculations suggest that for a given multiplicity, $K^{*0}/K$ is more suppressed in Au+Au collision at $\sqrt{s_{NN}}$ =7.7 GeV, compared to that in $\sqrt{s_{NN}}$ =200 GeV. This is possibly because of formation different type of QCD medium at 200 GeV and 7.7 GeV, and change in interaction cross-section between hadrons with change in particle type and energy.

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arXiv2023

Effect of hadronic interaction on the flow of $K^{*0}$

We explore the implications of the late stage hadronic rescattering phase on the flow of $K^{*0}$. The model calculations are done using a (3+1)-dimensional hybrid framework, incorporating both hydrodynamic evolution and hadronic transport that is calibrated to agree with bulk observables including the elusive rapidity differential $v_1$ of light-flavor hadrons. We find that the late stage hadronic rescattering phase causes significant qualitative modification of the $K^{*0}$ $v_1$ resulting in $\frac{dv_1}{dy}(K^{*0})-\frac{dv_1}{dy}(K^{+})$ and $\frac{dv_1}{dy}(ϕ)-\frac{dv_1}{dy}(K^{+})$ to have opposite signs with the effect being more pronounced in central collisions as compared to peripheral ones due to the larger multiplicity as well as longer duration of the hadronic phase. Further, this effect is enhanced in low-energy collisions owing to a stronger breaking of boost invariance. On the contrary, the influence of the hadronic phase on the $K^{*0}$ elliptic flow $v_2$ is found to be less significant and quantitative.

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arXiv2023

$K^{*0}$ meson production using a transport and a statistical hadronization model at energies covered by the RHIC beam energy scan

In this paper, we discuss the centrality and energy dependence of $K^{*0}$ resonance production using ultrarelativistic quantum molecular dynamics (UrQMD) and thermal models. The $K^{*0}/K$ ratios obtained from the UrQMD and thermal models are compared with measurements done by the STAR experiment in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV. The $K^{*0}/K$ ratio from the thermal model is consistent with data in most-peripheral collisions, however it overpredicts the ratio in central Au+Au collisions. This could be due to the fact that the thermal model does not have a hadronic rescattering phase, which is expected to be dominant in more central collisions. Furthermore, we have studied the $K^{*0}/K$ ratio from UrQMD by varying the hadron propagation time ($τ$) within the range 5 to 50 fm/c. It was found that the $K^{*0}/K$ ratio decreases with increasing $τ$. Comparison between data and UrQMD suggest, one needs to consider a $τ$ $\approx$ 10-50 fm/c to explain data at $\sqrt{s_{NN}}$ = 7.7-39 GeV in Au+Au collisions. We also predict the rapidity distribution of $K^{*0}$ from UrQMD which could be measured in the STAR beam energy scan phase II (BES-II) program.

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arXiv2022

Insight from the elliptic flow of identified hadrons measured in relativistic heavy-ion collisions

In this paper, we have discussed the transverse momentum dependence of elliptic flow measured in relativistic heavy-ion collisions. The transverse momentum dependence of the number of constituent quarks ($n_{q}$) scaled $v_{2}$ is obtained for all the measured identified hadrons. The $n_{q}$ scaled $ϕ$ $v_{2}$ is found to be similar to $n_{q}$ scaled $Ω$ $v_{2}$. This indicates that both $ϕ$ and $Ω$ are produced through quark recombination at RHIC energies. We also find $n_{q}$ scaled proton $v_{2}$ ($v_{2}$ of light quarks) is higher than $n_{q}$ scaled $ϕ$ and $Ω$ $v_{2}$ ($v_{2}$ of strange quarks) at $p_{T}/n_{q}$ $<$ 1.0 GeV/c. This can be explained by considering quark $v_{2}$ is proportional to its transverse kinetic energy considering mass of deconfined light and strange quarks equal to $\sim $4 MeV and $\sim$ 140 MeV, respectively.

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arXiv2020

Constraining input parameters of AMPT model with $ϕ$ meson production

A Multi-Phase Transport Model (AMPT) has been extensively used to understand the physics behind the experimental observation. Like other models, the outcome of the AMPT model depends on the initial parameters. Therefore, one needs to choose suitable initial parameters before using the model. Lund string fragmentation function has been used to create quark-antiquarks pairs in the AMPT model. The Lund string fragmentation parameters determine the yields and transverse momentum ($p_{T}$) spectra of particles produced in nucleus-nucleus collisions. The values of Lund string fragmentation parameters were determined by fitting the charged particle yield and $p_{T}$ spectra measured in the experiment. In this paper, we have shown the yield of strange quarks carrying hadrons, e.g. $ϕ$ mesons, are more sensitive to Lund string fragmentation parameters compared to non-strange pions. Using $ϕ$ meson spectra measured at RHIC, we have obtained new sets of Lund parameters for Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}$ = 11.5, 39, and 200 GeV. We have found that using the same set of parameters, we can explain $ϕ$-meson yield at $\sqrt{s_{\mathrm {NN}}}$ = 39 and 200 GeV, however, we need a different set of parameters for $\sqrt{s_{\mathrm {NN}}}$ = 11.5 GeV. This suggests that at low energy, $\sqrt{s_{\mathrm {NN}}}$ = 11.5 GeV, the underlying mechanism for particle production is different compared to top RHIC energies. We have also predicted invariant yield of $π$ and $ϕ$ mesons as a function of $p_{T}$ in U+U collisions at $\sqrt{s_{\mathrm {NN}}}$ = 196 GeV to be measured by STAR experiment.

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arXiv2017

Insight from elliptic flow of open charm mesons using quark coalescence model at RHIC and LHC energies

A study of elliptic flow of open charm mesons, $D^0$ and $D_S ^\pm$ using quark coalescence as a mechanism of hadronization of heavy quarks implemented in conjunction with A Multi Phase Transport (AMPT) model has been presented. We have studied the transverse momentum dependence of the elliptic flow parameter at mid-rapidity ($|y|$ $<$ 1.0) for Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV (LHC) for different values of partonic interaction cross-section and QCD coupling constant. We have compared our calculations with the experimentally measured data at the LHC energy. We have also studied the effect of shear viscosity on elliptic flow of open charm mesons within the transport model approach. Our study indicates that the elliptic flow of open charmed mesons is more sensitive to viscous properties of QGP medium as compared to light charged hadrons.

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arXiv2017

Systematic study of symmetric cumulants at $\sqrt{s_{NN}}$ = 200 GeV in Au+Au collision using transport approach

Measurement of 4-particle symmetric cumulants has been considered to be a good tool to study the correlations between amplitudes of different orders of anisotropic flow harmonics in the heavy-ion collision. These new observables not yet been measured at RHIC. Using A Multi-Phase Transport model, a set of predictions for the centrality dependence of the normalized 4-particle symmetric cumulants in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV has been given. In addition, the effects of shear viscosity and hadronic rescattering on the magnitude of symmetric cumulants are discussed using AMPT model at $\sqrt{s_{NN}}$ = 200 GeV. It is shown that $sc(2,3)$ is found to be more sensitive to hadronic rescattering, whereas $sc(2,4)$ is more sensitive to the shear viscosity. Rapidity dependence of symmetric cumulants is also shown. A relation between symmetric cumulant and event plane correlation is investigated using AMPT model.

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arXiv2016

An experimental review on heavy flavor $v_{2}$ in heavy-ion collision

For over a decade now, the primary purpose of relativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) has been to study the properties of QCD matter under extreme conditions -high temperature and high density. The heavy-ion experiments at both RHIC and LHC have recorded a wealth of data in p+p, p+Pb, d+Au, Cu+Cu, Cu+Au, Au+Au, Pb+Pb and U+U collisions at energies ranging from $\sqrt{s_{NN}}$ = 7.7 GeV to 7 TeV. Heavy quarks are considered good probe to study the QCD matter created in relativistic collisions due to their very large mass and other unique properties. A precise measurement of various properties of heavy flavor hadrons provides an insight into the fundamental properties of the hot and dense medium created in these nuclei-nuclei collisions, such as transport coefficient and thermalization and hadronization mechanisms. The main focus of this paper is to present a review on the measurements of azimuthal anisotropy of heavy flavor hadrons and to outline the scientific opportunities in this sector due to future detector upgrade. We will mainly discuss the elliptic flow of open charmed meson ($D$-meson), $J/ψ$ and leptons from heavy flavor decay at RHIC and LHC energy.

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arXiv2016

Scaling of elliptic flow in heavy-ion collisions with the number of constituent quarks in a transport model

We studied the number of constituent quark scaling (NCQ) behaviour of elliptic flow ($v_{2}$) under the framework of A Multi-Phase Transport model (AMPT) at both top-RHIC and LHC energies. The NCQ-scaling in $v_{2}$ holds at top-RHIC energy with AMPT string melting version, while it breaks in Pb+Pb collisions at LHC energy using the same framework. The breaking of NCQ-scaling at LHC energy has been studied by varying the magnitude of parton-parton scattering cross-section and lifetime of hadronic cascade as implemented in AMPT. We find that the breaking of NCQ scaling in Pb+Pb collisions at $\sqrt{s_{NN}}$ =2.76 TeV is independent of the magnitude of parton-parton cross-section and the later stage hadronic interactions. Further we observed that scaling holds in a small collision system like Si+Si at $\sqrt{s_{NN}}$ = 2.76 TeV. We discussed that the breaking of NCQ scaling is possibly due to high phase-space density of constituents quarks in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.

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arXiv2015

Measurements of $D_{S}^{\pm}$-meson production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR

We present the first measurement of the nuclear modification factor $R_{AA}$ and elliptic flow $v_{2}$ of $D_{s}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector. These results have been compared with those of other open charm mesons and strange mesons to determine how the (possibly) strangeness equilibrated partonic matter affects the $D_{s}$ meson production. We find that the nuclear modification factor of $D_{S}$ are systematically higher than unity and $D^{0}$ $R_{\rm{AA}}$. The ratio $D_{s}/D^{0}$ is shown as a function of transverse momentum for the 10-40$\%$ most central Au+Au collisions and compared with that in $p+p$ collisions obtained from PYTHIA. It is also compared with that in Pb-Pb collisions at 2.76 TeV by the ALICE experiment. Our measurement indicates a hint of enhancement of $D_{S}$ production in Au+Au collisions with respect to $p+p$ collisions as compared to non-strange $D$ mesons.

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arXiv2015

Probing the QCD phase diagram with measurements of strange hadron elliptic flow in STAR

We present the measurements of strange hadron elliptic flow at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV using the STAR detector in the years 2010 and 2011. The transverse momentum and collision centrality dependence of elliptic flow is presented. At the intermediate transverse momentum $Ω$ baryon and $ϕ$-meson show baryon-meson separation effect similar to proton and pion for minimum-bias Au+Au collision at $\sqrt{s_{NN}}$ =200 GeV. This indicates formation of collective flow at the early partonic phase. The separation between baryons and mesons at intermediate transverse momentum decreases with decrease in beam energy and almost disappears at $\sqrt{s_{NN}}$ $\leq$ 11.5 GeV, indicating hadronic interaction being dominant at the lower beam energy. We observe difference in elliptic flow between particle and anti-particle and this increases with decrease in beam energy. Differences are larger for baryons than mesons. Relative difference between particle and anti-particle elliptic flow is larger in central collisions than in peripheral ones.

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arXiv2014

Using the $ϕ$-meson elliptic flow to map the strength of partonic interaction

A compilation of recently measured STAR data for elliptic flow ($v_{2}$) of $ϕ$ mesons in RHIC Beam Energy Scan program and comparison with a multiphase transport model (AMPT) has been presented. The experimental data at $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV agrees well with string melting version of the AMPT model. The model includes partonic interactions and quark coalescence as a mechanism of hadronization. This indicates that there is a substantial contribution to collectivity from partonic interactions at $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV. The measured $ϕ$-meson $v_{2}$ at $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV are found to be smaller than those obtained from AMPT model without partonic interactions. This indicates negligible contribution of partonic collectivity to the observed $ϕ$-meson $v_{2}$ at $\sqrt{s_{NN}}$ $\leq$ 11.5 GeV.

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arXiv2014

Systematic study of the elliptic flow parameter using a heavy-ion collision model

Elliptic flow parameter, $v_{2}$ is consider as a sensitive probe for early dynamics of the heavy-ion collision. In this work we have discussed the effect of detector efficiency, procedure of centrality determination, effect of resonance decay, procedure to obtain event plane resolution on the measured $v_{2}$ by standard event plane method within the framework of a transport model. The measured value of $v_{2}$ depends on the detector efficiency in particle number counting. The effect of centrality determination is found to be negligible. The method of event-by-event correction of event plane resolution for wide centrality bin yields in results closer to the true value of $v_{2}$. The effect of resonance decay is seen to decrease the $v_{2}$ of $π$, $K$ and $p$. We also propose a procedure to correct for an event bias effect on $v_{2}$ while comparing the minimum bias centrality $v_{2}$ values for different multi-strange hadrons. Finally we have presented a model based confirmation of the recently proposed relation between $v_{2}$ obtained using event plane method and scalar product method to the true value of $v_{2}$.

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arXiv2013

Probing the QCD phase diagram with the measurements of $ϕ$-meson production and elliptic flow in the heavy-ion collision at STAR

We present the measurements of the $ϕ$-meson production and elliptic flow ($v_{2}$) at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV. The data are collected using the STAR detector in the years 2010 and 2011. The energy dependence of nuclear modification factor ($R_{\rm{CP}}$) of $ϕ$ meson is presented. The $ϕ$-meson $R_{\rm{CP}}$ has a value $\geq$ 1.0 for $\sqrt{s_{NN}}$ $\leq$ 39 GeV. The $Ω/ϕ$ ratios are also presented and show a different trend at the intermediate transverse momentum ($p_{T}$) for $\sqrt{s_{NN}}$ = 11.5 GeV compared to higher beam energies. The number-of-constituent quark (NCQ) scaling of $v_{2}$ has been studied at various beam energies. The NCQ scaling holds for particles and anti-particles separately including the $ϕ$ meson for $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV, which can be considered as an evidence of partonic collectivity. We observe at $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV, the $ϕ$-meson $v_{2}$ falls off the trend from the other hadrons at highest measured $p_{T}$ values by 1.8$σ$ and 2.3$σ$, respectively.

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