arXiv subjects

A. M. Khan

Publications and source records attributed to A. M. Khan.

11 recordsLinked to original sources

arXiv2026

Measurement of isolated prompt photon production in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV with the sPHENIX detector

The differential cross section of isolated prompt photon production is measured as a function of photon transverse energy ($E_{\mathrm{T}}^γ$) in proton--proton ($p$+$p$) collisions at $\sqrt{s} = 200$ GeV. The data were recorded in $2024$ with the sPHENIX detector at the Relativistic Heavy Ion Collider. Photons are reconstructed in $|η^γ| < 0.7$ and $12 < E_{\mathrm{T}}^γ < 32$ GeV using the electromagnetic calorimeter, and an isolation requirement is imposed using both the electromagnetic and hadronic calorimeters. The measured cross section is compared with the PYTHIA Monte Carlo event generator and perturbative quantum chromodynamics (pQCD) calculations at next-to-leading and next-to-next-to-leading order. The pQCD calculations are consistent with the result within the quoted uncertainties. This measurement provides a test of pQCD calculations for a process with sensitivity to the gluon parton distribution function of the proton and establishes the $p$+$p$ baseline for forthcoming sPHENIX measurements of isolated prompt photons in heavy-ion collisions.

nucl-ex↗

arXiv2026

Impact of nuclear deformation on particle production in $Ne+Ne$ collisions at \texorpdfstring{\five}{sqrt(sNN)=5.36 TeV} from AMPT-SM

We present a systematic study of particle production in $Ne+Ne$ collisions at $\sqrt{s_{\mathrm{NN}}} = 5.36$ TeV using the A Multi-Phase Transport (AMPT) model with string melting (SM) configuration. The analysis compares spherical and deformed configurations of ${}^{20}\mathrm{Ne}$ to investigate the influence of initial-state nuclear deformation on bulk observables. Charged-particle pseudorapidity ($\langle dN_{\mathrm{ch}}/dη\rangle$) densities, identified particle yields ($dN/dy$), transverse momentum ($p_T$) spectra, mean transverse momentum ($\langle p_{\mathrm{T}} \rangle$), and $p_{\mathrm{T}}$-differential particle ratios ($K/π$ and $p/π$) are studied as functions of multiplicity and centrality. The results show that all observables exhibit the expected dependence on event activity, including smooth multiplicity scaling, mass ordering in $\langle p_{\mathrm{T}} \rangle$, and characteristic features associated with radial flow and quark coalescence. Differences between the two configurations on bulk observables remain small across all observables, typically at the level of a 2\%--6\% percent, with slightly enhanced sensitivity observed in peripheral collisions. These findings suggest that, within the AMPT-SM framework, the collective dynamics and hadrochemical composition are primarily governed by the overall system density and interaction dynamics, while the influence of initial-state deformation is subleading. This study provides a baseline for understanding deformation effects in light-ion collision systems and highlights the limited sensitivity of bulk observables to initial nuclear geometry in transport-based approaches.

hep-ph↗

arXiv2025

Strangeness production in $O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}=7$ TeV using various model approaches

We present the predictions of various observables for strange ($\mathrm{K}^{0}_{\mathrm S}$, $Λ$($\overlineΛ$)) and multi-strange hadrons ($Ξ^-$($\overlineΞ^+$), $ϕ$, and $Ω^-$($\overlineΩ^+$)) using the recently updated 3+1D hydrodynamics-based EPOS4 framework and AMPT model. In this study, we report the transverse momentum (${p_{\rm T}}$) spectra, particle yields (${\mathrm{d}N/\mathrm{d}y}$), and ${p_{\rm T}}$ integrated yield ratios relative to pions for $O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}=7$~TeV. The results reveal that there are indications of stronger radial flow in EPOS4 compared to AMPT. We observe a final state multiplicity overlap with small ($p+p$ and $p+Pb$) and large ($Pb+Pb$) collision systems.

nucl-th↗

arXiv2025

Multiplicity dependence of (multi)strange hadrons in oxygen-oxygen collisions at $\sqrt{s_{\mathrm{NN}}}~=~7$ TeV using EPOS4 and AMPT

It is anticipated that the Large Hadron Collider (LHC) will collect data from oxygen-oxygen ($O+O$) collisions at a center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}$ = 7 TeV to explore the effects observed in high multiplicity proton-proton ($p+p$) and proton-lead ($p+pb$) collisions that closely related to lead-lead ($Pb+Pb$) collisions. These effects include azimuthal asymmetries in particle production, as well as variations in the abundances and momentum distributions across different hadron species, which are indicative of collective particle production mechanisms induced by the interactions in the presence of a QGP. The upcoming data on $O+O$ collisions at the LHC are expected to constrain the model parameters and refine our understanding of theoretical models. In this work, the predicted transverse momentum ($p_T$) spectra, rapidity density distributions ($dN/dy$), particle yield ratios, and $p_T$-differential ratios of (multi)strange hadrons produced in $O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7 TeV using AMPT and EPOS4 models are presented. AMPT focuses on preformed hadronic interactions, while EPOS4 incorporates a QGP phase. Stronger radial flow in EPOS4 as compared to AMPT is also observed. AMPT incorporates some flow effects, but the implementation of full hydrodynamic flow in EPOS4 appears to be significantly more effective in reproducing the existing experimental data. Both models predict the final state multiplicity overlap with $p+p$, $p+pb$, and $Pb+Pb$ collisions.

hep-ph↗

arXiv2025

Anisotropic flow predictions for identified and strange hadrons in $O+O$ collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7 TeV using model approaches

In this study, we report the predictions for the flow observables for different centrality classes in $O+O$ collisions. Our predictions utilize two different approaches, hydrodynamic and transport models, to analyze the behavior of the flow coefficients for identified ($π^\pm$, $K^\pm$ and $p (\overline{p})$) and strange ($\mathrm{K}^{0}_{\mathrm S}$, $Λ$ ($\overlineΛ$), $Ω^{-}$ ($\overlineΩ^{+}$), $Ξ^{-}$ ($\overlineΞ^{+}$), $ϕ$) hadrons. We explore particle-by-particle flow and compare the response of the system to initial conditions across various models, which provide insights into the underlying partonic and hadronic dynamics. The study presents comparisons of flow harmonics with the existing experimental measurements and demonstrates how $O+O$ collisions can serve as a benchmark to understand the transition from small to large systems, contributing to our knowledge of the Quark-Gluon Plasma (QGP) and collective phenomena in heavy-ion collisions.

nucl-th↗

arXiv2025

Predictions for Identified Hadron ($π^\pm$, $K^\pm$ and $p(\overline{p})$) Production and Collective Dynamics in Oxygen-Oxygen Collisions at $\sqrt{s_{NN}}$= 7 TeV with EPOS4, AMPT-SM, and Angantyr in Pythia 8

We study the dynamics of identified hadrons ($π^\pm$, $K^\pm$ and $p(\overline{p})$) production in $O+O$ collisions at $\sqrt{s_{\mathrm{NN}}} = 7$TeV using recently updated version of EPOS4, string melting version of A Multi-Phase Transport Model (AMPT-SM) and Angantyr model, incorporated within Pythia 8. We examine the interplay between different mechanisms implemented in these models. Predictions for charged particle multiplicity ($dN_{ch}/dη$), transverse momentum ($p_T$) spectra of identified hadrons, particle yield ($dN/dy$) and mean transverse mass ($\langle m_T \rangle$) are presented. To probe the collective behavior of the produced particles, the $p_T$-differential kaons-to-pion and proton-to-pion ratios are studied. While AMPT incorporates some flow effects, EPOS4's implementation of full hydrodynamic flow proves significantly more effective. In contrast, the flow effects in Pythia 8 are substantially weaker compared to the other models. The upcoming $O+O$ data from the LHC will help constrain the parameters of these models.

hep-ph↗

arXiv2024

Dynamics of identified particles production in oxygen-oxygen collisions at \sqrt{s_{\mathrm{NN}} = 7 TeV using EPOS4

The Large Hadron Collider (LHC) aims to inject oxygen (${}^{16}O$) ions in the next run into its experiments. This include the anticipated one-day physics run focusing on $OO$ collisions at center-of-mass energy \sqrt{s_{\mathrm{NN}} = 7 Tev. In this study, we have used recently developed version of the EPOS (EPOS4) to study the production of identified particles ($π^\pm$, $K^\pm$ and $p(\overline{p})$) in $OO$ collisions at 7 Tev. Predictions of transverse momentum ($p_T$) spectra, $\langle p_T \rangle$, integrated yield (dN/dy) for different centrality classes are studied. To provide insight into the collective nature of the produced particles, we look into the $p_T$-differential particle ratios ($K/π$ and $p/π$) and $p_T$-integrated particle ratios to ($π^++π^-$) as a function of charge particle multiplicity. The shape of the charge particle multiplicity ($dN/dη$) and $\langle p_T \rangle$ is well described by the EPOS4. The EPOS4 predictions for the ratios of $K/π$ and $p/π$ exhibit a systematic overestimation compared to the observed trends as a function of charged-particle multiplicity. Interestingly, the $OO$ results of $p_T$-integrated particle ratios shows a clear final state multiplicity overlap with $pp$, $p-Pb$ and $Pb-Pb$ collisions. EPOS4 mimics signs of collectivity and is one of the suitable candidates to study ultra-relativistic heavy-ion collisions. Furthermore, the foreseen data from $OO$ collisions at the LHC, when available, will help to better understand the heavy-ion-like behavior in small systems as well as help to put possible constraints on the model parameters.

hep-ph↗

arXiv2024

Effect of hadronic cascade time on freeze-out properties of Identified Hadrons in Au+Au Collisions at $\sqrt{s_{NN}}$ = 7.7-39 GeV from AMPT Model

We report the transverse momentum $p_T$ spectra of identified hadrons ($π^\pm$, $K^\pm$ and $p(\bar p)$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 39 GeV from A Multi Phase Transport Model with string melting effect (AMPT-SM). During this study, a new set of parameters are explored to study the effect of hadronic cascade by varying hadronic cascade time $t_{max}$ = 30 $f$m/$c$ and 0.4 $f$m/$c$. No significant effect of this change is observed in the $p_T$ spectra of light hadrons and the AMPT-SM model reasonably reproduces the experimental data. To investigate the kinetic freeze-out properties the blast wave fit is performed to the $p_T$ spectra and it is found that the blast wave model describes the AMPT-SM simulations well. We additionally observe that the kinetic freeze-out temperature ($T_{kin}$) increases from central to peripheral collisions, which is consistent with the argument of short-lived fireball in peripheral collisions. Whereas the transverse flow velocity, $<β_T>$ shows a decreasing trend from central to peripheral collisions indicating a more rapid expansion in the central collisions. Both, $T_{kin}$ and $<β_T>$ show a weak dependence on the collision energy at most energies. We also observe a strong anti-correlation between $T_{kin}$ and $<β_T>$. The extracted freeze-out parameters from the AMPT-SM simulations agree with the experimental data as opposed to earlier studies that reported some discrepancies. Whereas, no significant effect is found on the freeze-out parameters by varying the $t_{max}$. We also report the $p_T$ spectra of light hadrons and their freeze-out parameters by AMPT-SM simulations at $\sqrt{s_{NN}}$ = 14.5 GeV, where no experimental data is available for comparison. Overall, the set of parameters used in this study well describes the experimental data at BES energies.

hep-ph↗

arXiv2023

Study of Baryon number transport using model simulations in $pp$ collisions at LHC Energies

We report on the excitation function of anti-baryon to baryon ratios ($\overline{p}/p$, {\alam /\lam} and {\axi / \xim}) in $pp$ collisions at {\sqrts} = 0.9, 2.76, 7 TeV from DPMJET-III, Pythia~8, EPOS~1.99, and EPOS-LHC model simulations. To study the predictions of these models at {\sqrts} = 13.6 TeV. The anti-baryon to baryon ratios are extremely important for the study of baryon number transport mechanisms. These ratios help determine the carriers of the baryon number and in the extraction of baryon structure information. Even though all models show a good agreement between model simulations and data, the ratios extracted from DPMJET-III model closely describes data at all energies. It is observed that these ratios converge to unity for various model predictions. This convergence also indicates that the anti-baryon to baryon ratios follow the mass hierarchy, such that the hyperon specie containing more strange quarks ({\alam /\lam} and {\axi / \xim}) approaches unity faster than specie containing fewer strange quarks ($\overline{p}/p$). It is also observed that the $\overline{B}/B$ ratio approaches unity more rapidly with the increase in {\sqrts} energy. At lower energies we observe an excess production of baryons over anti-baryons. However, this effect vanishes at higher energies due to the baryon-anti-baryon pair production and the baryon-anti-baryon yield becomes equal. Using model simulations, we additionally compute the asymmetry, ($A\equiv\frac{N_{p}-N_{\bar{p}}}N_{p}+N_{\bar{p}}}$) for protons. The asymmetry shows a decreasing trend with increase in energy from 0.9 to 7 TeV for all energies. This asymmetry trend is confirmed by model predictions at {\sqrts} = 13.6 TeV which will help to put possible constraints on model calculations at {\sqrts} = 13.6 TeV once the Run-III data for LHC becomes available.

hep-ph↗

arXiv2022

Freeze-out Properties of Different Strange Hadrons from {\auau} Collisions at {\sqrtsNN}~= 54.4 GeV

We analyzed the transverse momentum {\ppt} spectra of different particle species containing strange quark {\ks}, {\lam (\alam)} and {\xim ({\axi})} in different centrality intervals at mid-rapidity ($y$) from {\auau} collisions at {\sqrtsNN}= 54.4 GeV. The {\ppt} spectra of these strange hadrons are investigated by Tsallis-like distribution. The Tsallis-like distribution satisfactorily fits the experimental data. The effective temperature, entropy based parameter $q$ and mean {\ppt} extracted from the Tsallis-like distribution function while the kinetic freeze-out temperature ($T_0$) and transverse flow velocity ($β_T$) are extracted by an alternative method. The effective temperature, entropy based parameter $q$ and mean {\ppt} are found to be strongly dependent on centrality. The effective temperature of multi-strange particle ({\xim ({\axi})}) is larger as compared to singly-strange particles {\lam (\alam)} and {\ks}. Furthermore, the extracted parameters from alternative approach decreases from central collisions to peripheral collisions, except the parameter $q$ which shows an opposite behaviour. A mass dependent kinetic freeze-out scenario is observed as the effective flow is larger for massive particles than the lighter one. Furthermore, the $T$, $β_T$ and mean {\ppt} ($\langle p_T \rangle$) shows decreasing trend as we go from central collisions to peripheral collisions. The entropy parameter $q$ increases from central to peripheral collisions.

hep-ph↗

arXiv2022

A Comprehensive Study of Energy Dependence of Particle Ratios in $pp$ Collisions from SPS to LHC Energies

A comprehensive study has been performed to estimate the kaon to pion ($K^\pm$/$π^\pm$) yield ratio and total kaon to total pion ($K$/$π$) yield ratio as a function of centre of mass energy in $pp$ collisions at different energies i.e., \sqrts~= 6.3, 17.3, 62.4, 200, 900 GeV, 2.76 TeV, 7 TeV, 13 TeV and 14 TeV using EPOS1.99, EPOS-LHC, HIJING, QGSJETII-03 and Sibyll2.3d model simulations. NA61/SHINE experiment reported that $K^+/π^+$ yield ratio exhibits rapid changes at the SPS energy range. A horn like structure appears in $K/π$ yield ratio as a function of collision energy. Significant presence of horn in $K^+$/$π^+$ and $K^-$/$π^-$ yield ratio is suggested by experimental data at lower energies, which is confirmed by HIJING and EPOS-LHC models. A smooth increase in $K/π$ yield ratio is also seen at higher energies. The model simulations predict similar increase in yield ratio with increasing energies. On the basis of previous available measurements, we also study model predictions of these yield ratios at \sqrts~= 13 and 14 TeV where no data is available. Almost all models suggest a saturation in the yield ratio within statistical fluctuations at these energies except EPOS1.99 and QGSJETII-03 which slightly over predict the yield ratio. These systematic comparisons are helpful to apply possible constraints on various hadronic event generators to significantly improve the predictions of Standard Model physics as well as for the understanding of underlying physics mechanisms in high energy collisions.

hep-ph↗