arXiv subjects

Niseem Magdy

Publications and source records attributed to Niseem Magdy.

At least 19 recordsLinked to original sources

arXiv2026

Rapidity-even Dipolar Flow in Relativistic Heavy-Ion Collisions

Rapidity-even directed flow, ($v_{1}^{even}$), provides a sensitive probe of fluctuation-driven dipolar asymmetry in the initial state of relativistic heavy-ion collisions. Its extraction is complicated by large first-harmonic non-flow correlations, particularly those induced by global momentum conservation (GMC). In this work, we study ($v_{1}^{even}$) and its multi-particle correlations in Au+Au collisions at ($\sqrt{s_{NN}}=200$) GeV using the AMPT and HIJING models. An ($\eta$)-dependent weighting procedure is employed to suppress the leading GMC contribution. HIJING is used as a non-collective baseline, while AMPT is used to investigate sensitivity to final-state partonic transport. The GMC-corrected HIJING results are strongly reduced for most ($v_1$)-related observables, indicating that the leading HIJING-like recoil contribution is effectively mitigated. The AMPT calculations reproduce the characteristic sign-changing ($p_T$) dependence of ($v_{1}^{even}$) and show sensitivity to the partonic scattering strength. Mixed-harmonic and normalized correlations involving ($v_1$), ($v_2$), and ($v_3$) suggest that the dipolar mode is correlated with both the elliptic geometry and fluctuation-driven triangular structure. These results demonstrate that GMC-suppressed rapidity-even dipolar-flow correlations provide a promising framework for constraining initial-state fluctuations and final-state transport in heavy-ion collisions.

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arXiv2026

Measure charge transport in high-energy nuclear collisions with an energy scan of isobaric collisions

We present a method to measure electric-charge transport in high-energy nuclear collisions using a beam-energy scan of isobaric systems. Comparing collisions of nuclei with identical mass number but different atomic number allows the charge difference ($\Delta Q$) to be extracted with a double-ratio technique that suppresses most experimental systematic uncertainties. By varying the beam energy, the rapidity gap ($\Delta y$) over which electric charge is transported can be systematically scanned. Simulations of Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\rm NN}}$=19.6-200GeV with UrQMD and PYTHIA Angantyr show that midrapidity $\Delta Q$ decreases exponentially with increasing $\Delta y$, with the slope parameter exhibiting strong model dependence. Comparisons with the baryon number transport reveal distinct patterns. In both UrQMD and PYTHIA Angantyr (with and without final-state baryon junctions), where baryon number is carried solely by valence quarks, the rapidity slope for baryon transport is larger than that for electric-charge transport. In contrast, scenarios that include baryon junctions in the initial state are expected to produce the opposite trend. This demonstrates that an isobar beam-energy scan provides a sensitive probe of electric-charge transport and offers new constraints on the microscopic mechanisms governing conserved-charge redistribution in QCD matter.

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arXiv2026

Producing and Studying Rare Isotopes in $e+A$ Collisions at the Electron-Ion Collider

The Electron--Ion Collider (EIC) offers a unique environment to study kinematically controlled lepton--nucleus ($e{+}A$) reactions, where a primary hard scattering is followed by an intranuclear cascade and the subsequent statistical de-excitation of the nuclear remnant. Utilizing the \soft{BeAGLE} model, we demonstrate that event-by-event fluctuations in nucleon removal and energy deposition populate a diverse ensemble of excited remnants. Furthermore, we show that varying the target mass systematically shifts the distribution of these remnants across the $(N, Z)$ plane. Although this excited prefragment remnant is not directly observable, its properties are shown to be strongly correlated with final-state fragments; specifically, the largest nuclear residue and the intensity of evaporation yield serve as effective experimental proxies for event-level remnant characterization. We also evaluate photon observables essential for nuclear spectroscopy. While various photon sources overlap significantly in pseudorapidity, we find that in the nucleus-rest frame, the low-energy spectrum is dominated by de-excitation $\gamma$ rays and exhibits distinct discrete structures. These findings motivate an EIC research program that correlates rare-isotope production and de-excitation radiation with well-defined initial conditions, providing a collider-based approach to nuclear spectroscopy that is complementary to existing fixed-target facilities.

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arXiv2025

Tracing the Evolution of Nuclear Excitation at the Electron-Ion Collider

We investigate the evolution of nuclear excitation in electron-nucleus (e+A) collisions at the upcoming Electron-Ion Collider (EIC) using the BeAGLE event generator. Leveraging the EIC's unique collider kinematics, we demonstrate the remarkable capability to separate distinct nuclear reaction stages, hard scattering, intranuclear cascade, and nuclear de-excitation, in the laboratory frame. Our systematic analysis reveals that event-by-event fluctuations in the mean transverse momentum (k) are highly sensitive to the intranuclear cascade formation time and nuclear geometry, while minimally affected by variations in electron beam energy. These findings establish k as a robust observable for constraining nuclear excitation mechanisms, providing critical benchmarks for future EIC experiments and guiding theoretical advancements in nuclear transport modeling.

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arXiv2025

Model Comparisons of Transverse Energy and Charged-Particle Multiplicity in A+A Collisions at Midrapidity from $\sqrt{s_{NN}}$ $=$ 7.7 to 200~GeV

We present a comprehensive comparison of PHENIX measurements of transverse energy production ($dE_T/dη$) and charged-particle multiplicity ($dN/dη$) at midrapidity to simulations from PYTHIA-8, AMPT, HIJING, and SMASH. These comparisons span both small systems (d+Au, $^3$He+Au) and large systems (Cu+Cu, Cu+Au, Au+Au, and U+U) at $\sqrt{s_{NN}}$ $\sim$ 200~GeV and Au+Au over a range of beam energies $\sqrt{s_{NN}} = 7.7$--200~GeV. Using the Rivet framework, we assess the performance of these models. While general trends are captured, significant deviations persist, particularly in low-energy and peripheral collisions, underscoring the need for improved modeling of baryon stopping and energy deposition mechanisms.

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arXiv2025

Understanding baryon stopping at the BNL Relativistic Heavy Ion Collider top energies

The nucleon exhibits a rich internal structure governed by Quantum Chromodynamics (QCD), where its electric charge arises from valence quarks, while its spin and mass emerge from complex interactions among valence quarks, sea (anti-)quarks, and gluons. At the advent of QCD, an alternative hypothesis emerged suggesting, at high energies, the transport of a nucleon's baryon number could be traced by a non-perturbative configuration of gluon fields connecting its three valence quarks, forming a $Y$-shaped topology known as the gluon junction. Recent measurements by the STAR experiment are compatible with this scenario. In light of these measurements, this study aims to explore the mechanisms of baryon transport in high-energy nuclear collisions using the PYTHIA-8 framework, which incorporates a state-of-the-art hadronization model with advanced Color Flow (CF) and Color Reconnection (CR) mechanisms that mimic signatures of a baryon junction. Within this model setup, we investigate (i) the rapidity slope of the net-baryon distributions in photon-included processes ($\gamma$+p) and (ii) baryon over charge transport in the isobaric (Ru+Ru and Zr+Zr) collisions. Our study highlights the importance of the CF and CR mechanisms in PYTHIA-8, which play a crucial role in baryon transport. The results show that the CF and CR schemes significantly affect the isobaric baryon-to-charge ratio, leading to different predictions for baryon stopping and underscoring the need to account for CF and CR effects in comparisons with experimental measurements.

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arXiv2025

Reconstructing jet anisotropies with cumulants

In relativistic heavy-ion collisions, where quark-gluon plasma forms, hadron production is anisotropic at both low and high transverse momentum, driven by flow dynamics and spatial anisotropies. To better understand these mechanisms, we use multi-particle correlations to reconstruct jet anisotropies. We simulate data using \textsc{TennGen}\xspace as a hydro-like background and combine it with \textsc{Pythia-8}\xspace generated jets, clustering them with the anti-$k_{\mathrm{t}}$\xspace algorithm. Jet anisotropies are unfolded using a Bayesian technique, ensuring the robustness of the reconstructed signals. Our results demonstrate that multi-particle cumulant methods can accurately capture the differential jet azimuthal anisotropies, providing crucial insights into high-$p_{T}\xspace$ behavior and the dynamics within heavy-ion collisions.

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arXiv2024

Search for baryon junctions in e+A collisions at the Electron Ion Collider

Constituent quarks in a nucleon are the essential elements in the standard ``quark model" associated with the electric charge, spin, mass, and baryon number of a nucleon. Quantum Chromodynamics (QCD) describes nucleon as a composite object containing current quarks (valence quarks and sea (anti-)quarks) and gluons. These subatomic elements and their interactions are known to contribute in complex ways to the overall nucleon spin and mass. In the early development of QCD theory in the 1970s, an alternative hypothesis postulated that the baryon number might manifest itself through a non-perturbative configuration of gluon fields forming a Y-shaped topology known as the gluon junction. In this work, we propose to test such hypothesis by measuring (i) the Regge intercept of the net-baryon distributions for $e$+($p$)Au collisions, (ii) baryon and charge transport in the isobaric ratio between $e$+Ru and $e$+Zr collisions, and (iii) target flavor dependence of proton and antiproton yields at large rapidity, transported from the hydrogen and deuterium targets in $e+p$(d) collisions. Our study indicates that these measurements at the EIC can help determine what carries the baryon number.

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arXiv2024

Centrality definition in e+A collisions at the Electron-Ion Collider

In this work, we investigate the feasibility of defining centrality in electron-ion collisions at the Electron-Ion Collider (EIC) by examining the correlation between the impact parameter and several observables, including total energy, total transverse momentum, and total number of particles. Using the BeAGLE Monte Carlo generator, we simulate e+Au and e+Ru collisions at different energies and analyze the correlation between the impact parameter and these observables across different kinematic regions. Our findings indicate that the correlation is weak in the central rapidity region but becomes stronger in the forward and far-forward rapidity regions. However, the correlation is not sufficiently robust to allow for precise centrality determination. We conclude that defining centrality in electron-ion collisions is more challenging than in ion-ion collisions, necessitating further studies to develop a robust centrality definition for the EIC.

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arXiv2024

A study of nuclear structure of light nuclei at the Electron-Ion Collider

Understanding the substructure of atomic nuclei, particularly the clustering of nucleons inside them, is essential for comprehending nuclear dynamics. Various cluster configurations can emerge depending on excitation energy, the number and types of core clusters, and the presence of excess neutrons. Despite the prevalence of tightly bound cluster formations in low-lying states, understanding the correlation between clusters and their formation mechanisms remains incomplete. This exploring study investigates nuclear clustering at the Electron-Ion Collider (EIC) using simulations based on the modified BeAGLE model. By simulating collisions involving $e$+$^{9}$Be, $e$+$^{12}$C, and $e$+$^{16}$O nuclei, we find that the average energy of particles $\langle E \rangle$ and the system size ratios of particles at forward rapidity exhibit sensitivity to alpha clustering and its various configurations. These findings offer valuable insights into the dynamics of nuclear clustering and its implications for future studies at the EIC.

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arXiv2024

Exploring Rapidity-Even Dipolar Flow in Isobaric Collisions at RHIC

Employing the AMPT transport model, we investigate the response of the rapidity-even dipolar flow ($\mathrm{v^{even}_{1}}$) and its associated Global Momentum Conservation (GMC) parameter $\mathrm{K}$ to structural disparities within $^{96}$Ru and $^{96}$Zr nuclei. We analyze $\rm Ru+Ru$ and $\rm Zr+Zr$ collisions at a center-of-mass energy of $\sqrt{\textit{s}_{NN}}$ = 200 GeV. Our analysis demonstrates that the eccentricity $\varepsilon_1$, $\mathrm{v^{even}_{1}}$ and $\mathrm{K}$ exhibit subtle yet discernible sensitivity to the input nuclear structure distinctions between $^{96}$Ru and $^{96}$Zr isobars. This observation suggests that measuring $v^{\rm even}_{1}$ and the GMC parameter in these isobaric collisions could serve as a means to fine-tune the comprehension of their nuclear structure disparities and offer insights to enhance the initial condition assumptions of theoretical models.

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arXiv2024

Measuring differential particle correlations in relativistic nuclear collisions

This study explores the transverse momentum ($p_T$) dependencies of Symmetric and Asymmetric Correlations (SC and ASC) with one and two particles of interest in Au+Au collisions at 200 GeV. Leveraging the AMPT model, the investigation delves into the sensitivity of these correlations to the final state effects, providing valuable insights into their potential for constraining the final state effects' $p_T$ dependencies. The HIJING model is employed as a benchmark for non-flow correlations, shedding light on their impact on interpreting SC and ASC data. Moreover, the study points out that differential SC and ASC with one and two particles of interest (POIs) typically incorporate contributions from event-plane angle fluctuations. Consequently, this work highlights the significance of SC and ASC with one and two POIs as valuable tools for investigating the $p_T$ nature of the final state effects and advocates for comprehensive experimental measurements across various beam energies and system sizes to enhance our understanding and provide additional constraints for theoretical models.

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arXiv2024

Impact of nuclear deformation on collective flow observables in relativistic U+U collisions

A Multi-Phase Transport (AMPT) model is used to investigate the efficacy of several flow observables to constrain the initial-state deformation of the Uranium nuclei in U$+$U collisions at nucleon-nucleon center-of-mass energy $\sqrt{\textit{s}_{NN}}$ = 193 GeV. The multiparticle azimuthal cumulant method is used to investigate the sensitivity of (I) a set of quantities that are sensitive to both initial- and final-state effects as well as (II) a set of dimensionless quantities that are more sensitive to initial-state effects to the Uranium nuclei quadrupole shape deformation. We find that the combined use of the flow harmonics, flow fluctuations and correlations, linear and non-linear flow correlations to the quadrangular flow harmonic, and the correlations between elliptic flow and the mean-transverse momentum could serve to constrain the nuclear deformation of the Uranium nuclei. Therefore, a comprehensive set of measurements of such observables can provide a quantifying tool for the quadrupole shape deformation via data-model comparisons.

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arXiv2024

Characterizing the initial and final state effects in isobaric collisions at energies available at the BNL Relativistic Heavy Ion Collider

The Multi-Phase Transport model (AMPT) is employed to predict Symmetric Correlations (SC), Asymmetric Correlations (ASC), Normalized Symmetric Correlations (NSC), and Normalized Asymmetric Correlations (NASC) in $^{96}Ru+^{96}Ru$ and $^{96}Zr+^{96}Zr$ collisions at 200~GeV. Our study offers insights into the behavior of SC, ASC, NSC, and NASC, considering various nuclear structure scenarios to account for differences between the two isobars. Additionally, we emphasize the importance of detailed experimental measurements as they will serve as a critical constraint for refining the predictions of theoretical models.

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arXiv2023

Beam Energy Dependence of the Linear and Mode-Coupled Flow Harmonics Using the A Multi-Phase Transport Model

In the framework of the A Multi-Phase Transport (AMPT) model, the multi-particle azimuthal cumulant method is used to calculate the linear and mode-coupled contributions to the quadrangular flow harmonic ($v_{4}$), mode-coupled response coefficient as a function of centrality in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200, 39, 27 and 19.6 GeV. This study indicated that the linear and mode-coupled contributions to the $v_{4}$ are sensitive to the beam energy change. Nevertheless, the correlations between different order flow symmetry planes and the mode-coupled response coefficients show a weak beam energy dependence. In addition, the presented results suggest that the experimental measurements that span a broad range of beam energies can be an additional constraint for the theoretical models' calculations.

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arXiv2023

Characterizing the initial and final state effects of relativistic nuclear collisions

The Multi-Phase Transport model (AMPT) is used to study the final state effects on the Symmetric Correlations (SC), Asymmetric Correlations (ASC), Normalized Symmetric Correlations (NSC), and Normalized Asymmetric Correlations (NASC) in Au+Au collisions at 200~GeV. The correlators' sensitivity to non-flow effects associated with long- and short-range non-flow correlations are also discussed using the HIJING model. The results indicate that SC, ASC, NSC, and NASC can give accompanying constraints for initial and final state effects. In addition, conducting further detailed experimental measurements spanning a broad range of collision systems and beam energies will serve as an additional constraint for the theoretical models' calculations.

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arXiv2022

Measuring differential flow angle fluctuations in relativistic nuclear collisions

Recently studies of the differential nature of the flow angle fluctuations, known as event plane angular decorrelation, indicated that measurements that assume a common symmetry plane may need to consider the flow angle fluctuations effect. Using the HIJING and AMPT models, it is shown that the flow angle fluctuations measurements, obtained with the two- and three-subevents correlation method, could have significant non-flow effects associated with long- and short-range non-flow correlations. The current study demonstrates the four-subevents cumulant methods' ability to reduce the non-flow effects. It is further argued that the measurements using the four-subevents correlation method can be used to provide accurate quantification of the differential flow angle fluctuations.

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arXiv2022

Rebuttal to: "Comment on Scaling properties of background- and chiral-magnetically-driven charge separation in heavy ion collisions at $\sqrt{s}_{\rm NN}=200$ GeV"

Recently, F. Wang commented on our work "Scaling properties of background- and chiral-magnetically-driven charge separation in heavy ion collisions at $\sqrt{s}_{\rm NN} = 200$ GeV" and made several claims to support his conclusion that our results are fallacious. His conclusion and claims are not only incorrect; they show a fundamental disconnect with the rudiments of the $R_{Ψ_2}(ΔS)$ correlator. This rebuttal addresses the root misconception responsible for Wang's false claims.

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