arXiv subjects

Haifa I. Alrebdi

Publications and source records attributed to Haifa I. Alrebdi.

12 recordsLinked to original sources

arXiv2026

Photon-calibrated event-activity bias and subcollision geometry in d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with PYTHIA 8 Angantyr

Event-activity selections in small nuclear collision systems couple collision geometry to the soft response accompanying a hard scattering. We examine this coupling in d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with PYTHIA 8.316 Angantyr, using direct photons, terminal pre-decay neutral pions, and anti-kT jets. A hard-bias factor compares the probability for a hard event to enter an activity class with an $N^{ND}_{coll}$ -weighted minimum-bias reference. The model predicts a depleted most-active class and an enhanced peripheral class for both photons and pions. Photon-tagged events also sample a smaller mean impact parameter and more nondiffractive subcollisions than pion-tagged or inclusive HardQCD events. Comparing fully correlated Angantyr events with an Ncoll-reweighted minimum-bias reference and a factorized diagnostic separates the explicit geometric contribution from residual hard-soft correlations. STAR-like and PHENIX-like particle-level activity proxies preserve the class ordering but give different class probabilities. The calculation is generator-level and does not identify a unique microscopic origin for the residual correlations.

hep-ph↗

arXiv2026

A B-factory continuum retune of PYTHIA 8 hadronization parameters using BELLE and BABAR identified-hadron data

We refine the hadronization sector of a pp PYTHIA~8 tune in $e^+e^-\to q\bar q$ production using selected BELLE and BABAR measurements near the $Υ(4S)$ region. The study is performed with PYTHIA~8.316 and Rivet~4.1.1 and is restricted to parameters used in this $e^+e^-$ setup. Starting from the five-parameter hadronization subset of the pp tune, we carry out a staged extension guided by the remaining differences in the BELLE and BABAR data. The final comparison uses a fixed common set of 20,803 bins and samples of 1,000,000 generated events per analysis and tune point. On this basis, the selected refined tune gives a bin-weighted score of 73.42, compared with 76.49 for the Skands $e^+e^-$ reference and 79.22 for Monash~2013 $e^+e^-$. It remains the best-scoring tune for the BELLE charged-hadron, baryon, and single- and dihadron measurements, while Skands still performs better for the BABAR charged-hadron sample and the BELLE meson sample. The bin-weighted ordering is driven primarily by the BELLE 2020 sample. The refined tune gives a small but stable improvement for the selected BELLE and BABAR measurements, although clear differences between the individual datasets remain.

hep-ph↗

arXiv2026

Comparing EPOS-4, EPOS-LHC, and SMASH for identified-hadron observables in the NICA energy range

We present a systematic simulation study of identified hadron production in minimum bias Au+Au collisions at sqrt(sNN) = 6, 7, and 8 GeV. The event samples were generated with three modern frameworks based on different microscopic pictures: EPOS-LHC, EPOS-4, and the purely hadronic transport model SMASH. We compare observables that probe baryon stopping, transverse dynamics, hadron formation, and strangeness production: rapidity densities dN/dy, transverse momentum spectra dN/dpT, two dimensional pT-y distributions, v2/nq versus pT/nq, and the yield ratios pi-/pi+, K-/K+, pbar/p, K+/pi+, K-/pi-, p/pi+, and Lambda/pi+. For charged and neutral pions, the three models give broadly similar yields and spectral shapes in both dN/dy and dN/dpT. At these energies, resonance decays and isospin constraints reduce the sensitivity to early stage dynamics. In contrast, strange mesons and baryons remain strongly model dependent. EPOS-4 gives the largest midrapidity K+ and Lambda yields and the hardest kaon and strange baryon pT spectra. EPOS-LHC is generally intermediate, while SMASH gives lower strange hadron production. The two dimensional pT-y maps show that the EPOS models populate higher pT over a broader rapidity range. For NCQ scaled elliptic flow, the best approximate scaling is seen in EPOS-LHC, while SMASH and EPOS-4 show only partial scaling. This suggests that EPOS-LHC carries a more coherent partonic anisotropy to the hadronic stage in this energy range. Overall, the model separation grows from 6 to 8 GeV. The clearest discriminators in the NICA domain are intermediate pT baryon to meson ratios, Lambda/pi+, the rapidity dependence of pT, the pT dependence of K-/K+, and NCQ scaled v2.

hep-ph↗

arXiv2026

Sequential retuning of PYTHIA~8.316 to a global soft-QCD basis in pp collisions at $\sqrts=0.9-13$ TeV

We present a sequential nine-parameter retune of PYTHIA 8.316, built on the Monash 2013 baseline, for soft-QCD observables in proton--proton collisions at $\sqrt{s}=0.9$--$13$ TeV. The tune is constructed with direct generator evaluation and developed in stages: an initial five-parameter localization in the hadronization-sensitive sector, successive extensions driven by multi-energy minimum-bias tensions, and a final expansion to a broader soft-QCD fit basis. The fitted set includes minimum-bias charged-particle data, identified-hadron spectra and ratios, underlying-event observables, and event-shape distributions. A separate held-out validation basis is kept outside the fit. The final tune retunes nine non-perturbative parameters controlling fragmentation, strangeness suppression, diquark production, color reconnection, MPI regularization and its energy dependence, the impact-parameter overlap profile, and transverse-momentum generation in string breaking. On the common fit basis, the grouped score density improves from $99.18$ for Monash 2013 to $85.67$. The strongest gains occur in the 13 TeV minimum-bias and underlying-event sectors, with further improvement in the ALICE identified-hadron blocks and a smaller gain in the CMS 13 TeV identified-hadron sector. Monash remains better in the CMS 7 TeV underlying-event block and the ATLAS 7 TeV event-shape block, while the low-energy charged-particle sector remains the main unresolved tension for both tunes. The held-out validation basis supports the same picture. Monash remains slightly better in the low-energy CMS validation blocks, but the present tune performs better in the ATLAS early underlying-event block and in both held-out 13 TeV charged-particle sectors. We interpret it as a controlled soft-QCD retune that improves a broad set of observables while keeping its limitations explicit.

hep-ph↗

arXiv2026

Collectivity Signatures in High-Multiplicity pp Collisions from Hybrid Hydro+Tsallis Modeling of Pion Spectra

The transverse momentum (pT) distributions up to pT = 20 GeV/c for pions produced in the ten different multiplicity classes (MCs) of symmetric pp collisions at sqrt(s) = 7 TeV have been investigated. Two distinct models, the Tsallis-Pareto type function (model) and the combined BGBW model and Tsallis-Pareto type model have been employed to fit the pT distributions via the minimum chi-square method. The combined Hydro+Tsallis model is more reliably describing the pT spectra than the Tsallis-Pareto model. The Tsallis temperature (T), non-extensivity parameter (q), normalization constant (N0), Kinetic freeze-out temperature (T0), transverse flow velocity (betaT), and (mean pT) have been extracted through the fitting procedure via the employed models. The Tsallis-Pareto model gives T, q, N0 and mean pT while Hydro+Tsallis model gives T0, betaT, T, q, N0 and mean pT. Incorporating the values of the extracted T and q the thermodynamic quantities and response functions, including energy density (epsilon), particle density (n), entropy density (s), pressure (P), specific heat at constant volume (CV), squared speed of sound (cs2), mean free path (lambda), Knudsen number (Kn), isothermal compressibility (kappaT), and expansion coefficient (alpha) have been calculated at the freeze-out stage. It has been observed that T, betaT, mean pT, N0, epsilon, n, s, P, CV, cs2, and alpha increase with increasing(decreasing) the charged particles multiplicity density dNch/deta(MCs). While T0, q, lambda, Kn, and kappaT decrease with increasing(decreasing) dNch/deta(MCs). These systematic variations in the trends of parameters might suggest the gradual transition towards collectivity and thermal equilibration in the high multiplicity pp events, possibly signalling enhanced collective dynamics and partial thermalization in small collision systems.

hep-ph↗

arXiv2026

Exploring Thermalization and Multi-Freeze-Out Effects in Pb-Pb collisions Based on Tsallis pT Distributions

This study investigates transverse-momentum (pT) distributions of pi-, pi+, K-, K+, p, pbar, K0s, and Lambda in several centrality classes of Pb-Pb collisions at sqrt(sNN) = 2.76 TeV. The measured spectra are analyzed with the Tsallis non-extensive distribution, from which the effective temperature T, non-extensive parameter q, and the mean transverse momentum mean_pT are extracted for each particle species and centrality interval. To disentangle thermal and collective effects, the mean kinetic freeze-out temperature T0 is obtained from the intercept of the T-versus-mass relation, while the average transverse flow velocity betaT is extracted from the slope of mean_pT versus the mean moving mass for pions, kaons, and protons. The results show that T increases and q decreases with increasing centrality, indicating a hotter and more equilibrated system in central collisions. A clear mass dependence of T supports a multi-freeze-out scenario, with heavier particles decoupling earlier. Both T0 and betaT rise from peripheral to mid-central collisions before saturating toward central events, which may suggest the onset of collective behavior or changes in freeze-out dynamics. These observations provide new insights into the thermal and dynamical properties of the medium created in heavy-ion collisions at the LHC.

hep-ph↗

arXiv2025

Thermodynamic Analysis of Transverse Momentum Spectra in Pb-Pb Collisions at 2.76 TeV: Centrality Dependence of Temperature, Freezeout Parameters and Non-Extensitivity

We study properties of Pb-Pb collisions at 2.76 TeV in mid-rapidity, $|y|<0.5$, based on data by the ALICE Collaboration. In particular, we examine the transverse momentum ($p_T$) spectra of positively charged (identified) hadrons, $π^+$, $K^+$ and $p$, generated in various centrality intervals. We perform individual fits using the thermodynamically consistent Tsallis distribution to extract the following quantities: the non-extensitivity parameter, $q$, the effective temperature, $T_{\rm eff}$, the kinetic freezeout volume, $V$, the mean transverse flow velocity, $β_T$, the mean kinetic freezeout temperature, $\langle T_0\rangle$, the thermal temperature, $T_{\rm th}$, and the parameter $ζ$, which characterizes the fluctuating number of generated particles. From peripheral to central collision, and from lower to higher charged particle multiplicity per pseudorapidity unit, $\langle dN_{\rm ch}/dη\rangle$, all these quantities are observed to increase, with the exception of $q$, which has the opposite behavior. The parameters $T_{\rm eff}$, $q$, and $V$ depend on the hadron mass in a way that supports the scenarios of volume differential freezeout and multiple kinetic freezeout. Furthermore, we extracted $\langle T_{\rm eff}\rangle$ and $\langle q\rangle$ for different collisions and energies at LHC and RHIC, and compare their dependencies on $\langle dN_{\rm ch}/dη\rangle$ and $\langle N_{\rm part} \rangle$.

hep-ph↗

arXiv2024

Investigating the Bulk Properties of Charged Particles in Different $η$ Bins Using a Modified Tsallis Model

This paper presents a comprehensive analysis of the double-differential $p_T$ distributions of charged particles in twelve distinct pseudorapidity regions of equal width in $pp$ collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV. Utilizing the modified Tsallis function with mean transverse flow velocity, our study demonstrates a very good agreement between experimental data and the model employed. The fit quality is consistently high across all $p_T$ ranges, as assessed by Data/Fit panels accompanying each plot. Extracted parameters, including kinetic freeze-out temperature ($T_0$), transverse flow velocity ($β_T$), non-extensivity parameter ($q$) and mean transverse momentum $\langle p_T \rangle$ dependencies are shown on pseudorapidity ($η$) and collision energy ($\sqrt{s}$). $T_0$, $β_T$ and $\langle p_T \rangle$ exhibit a decreasing trend with increasing $η$ due to lower in energy transfer along high $η$ regions, while they show a heightened sensitivity to $\sqrt{s}$. $q$ increases with $η$, indicating a closer thermal equilibrium in mid-$η$ particles. The paper also explores correlations among these parameters, emphasizing relationships between $T_0$, $β_T$, $q$ and $\langle p_T \rangle$. Our study provides valuable insights into the thermal and dynamic characteristics of high-energy proton-proton collisions, contributing to the broader understanding of the bulk properties of nuclear matter produced in these interactions.

hep-ph↗

arXiv2024

Comparative Analysis of Jet and Underlying Event Properties Across Various Models as a Function of Charged Particle Multiplicity at 7 TeV

In this study, a comprehensive analysis of jets and underlying events as a function of charged particle multiplicity in proton-proton (pp) collisions at a center-of-mass energy of $\sqrt{s} = 7$ TeV is presented. Various Monte Carlo (MC) event generators, including Pythia8.308, EPOS1.99, EPOSLHC, EPOS4$_{Hydro}$, and EPOS4$_{noHydro}$, are employed to predict particle production. The predictions from these models are compared with experimental data from the CMS collaboration. The charged particles are categorized into those associated with underlying events and those linked to jets. The analysis is restricted to charged particles with $|η| < 2.4$ and $p_{T} > 0.25$ GeV/c. Upon comparing the MC predictions with CMS data, it is observed that EPOS$4_{Hydro}$, EPOSLHC, and Pythia8 consistently reproduce the experimental results for all charged particles, underlying events, intrajet, and leading charged particles. For charged jet rates with $p_{T}^{ch.jet} > 5$ GeV/c, EPOS4$_{Hydro}$ and Pythia8 perform exceptionally well. In the case of charged jet rates with $p_{T}^{ch.jet} > 30$ GeV/c, EPOSLHC reproduces satisfactorily good results, while EPOS4$_{Hydro}$ exhibits good agreement with the data at higher charged particle multiplicities as compared to the other models. This can be attributed to the conversion of energy into flow when "Hydro=on," leading to an increase in multiplicity. EPOSLHC model described the data well due to the new collective flow effects, correlated flow treatment, and parametrization as compared to the EPOS1.99. However, the examination of the jet $p_{T}$ spectrum and normalized charged $p_{T}$ density reveals that EPOS4$_{Hydro}$, EPOS4$_{noHydro}$, and EPOSLHC exhibit good agreement with the experimental results, while Pythia8 and EPOS1.99 do not perform as well due to the lack of correlated flow treatment.

hep-ph↗

arXiv2024

Thermodynamic Signatures and Phase Transitions in High-Energy Au-Au Collisions

In this study, we systematically investigate the dynamics of various hadrons namely $ π^+ $, $ π^- $, $ K^+ $, $ K^- $, $ p $, $ \bar{p} $, $ Λ$, $ \barΛ $, $ Ξ^- $ and $ \barΞ^+ $ produced in central Au-Au collisions. We analyze data of AGS and RHIC, which span a broad range of collision energies, ranging from $ \sqrt{s_{NN}}$ = 1.9 to 200 GeV. To analyze the transverse momentum ($ p_T $) and transverse mass ($ m_T $) distributions, we employ a two-component standard distribution function, achieving a very good representation of the experimental data across these energy regimes. We extract key thermodynamic parameters, including the effective temperature $ T $, the mean transverse momentum $ \langle p_T \rangle $, and the initial temperature $ T_i $, and analyze their dependence on the values of collision energy and particle mass. Our findings reveal a distinct transition behaviour around $ \sqrt{s_{NN}} = 19.6 $ GeV. Below $ \sqrt{s_{NN}} = 19.6 $ GeV, the values of $ T $, $ \langle p_T \rangle $, and $ T_i $ increase monotonically for all hadrons due to higher energy transfer into the system. Above this energy threshold, these extracted parameters plateau, suggesting that the additional energy is utilized as latent heat for phase transition rather than increasing the system's temperature. These observations delineate two distinct regions: a hadron-dominated region at lower energies and a parton-dominated region at higher energies, each potentially indicative of different phases of matter, with the latter possibly signalling the onset of a Quark-Gluon Plasma (QGP). The study thus provides critical insights into the complex interplay of thermodynamics, phase transitions, and particle interactions in high-energy Au-Au collisions.

hep-ph↗

arXiv2024

Multiplicity dependence of the freezeout parameters in high energy hadron-hadron collisions

We examined the transverse momentum spectra of various identified particles, across different multiplicity classes in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 7 TeV. Utilizing the Tsallis and Hagedorn models, parameters relevant to the bulk properties of nuclear matter were extracted. Both models exhibit good agreement with experimental data. In our analyses, we observed a consistent decrease in the effective temperature for the Tsallis model and the kinetic or thermal freeze-out temperature for the Hagedorn model, as we transition from higher multiplicity (class-I) to lower multiplicity (class-X). Additionally, the transverse flow velocity experiences a decline from class-I to class-X. The normalization constant which represents the multiplicity of produced particles is observed to decrease as we move towards higher multiplicity classes. While the effective and kinetic freeze-out temperatures, as well as the transverse flow velocity, show a mild dependency on multiplicity for lighter particles, this relationship becomes more pronounced for heavier particles. Various particle species are observed to undergo decoupling from the fireball at distinct temperatures: lighter particles exhibit lower temperatures, while heavier ones show higher temperatures, thereby supporting the concept of multiple freeze-out scenarios. Moreover, we identified a positive correlation between the kinetic freeze-out temperature and transverse flow velocity, a scenario where particles experience stronger collective motion at higher freeze-out temperature. The reason for this positive correlation is that as the multiplicity increases, more energy is transferred into the system. This heightened energy causes greater excitation and pressure within the system, leading to a quick expansion.

hep-ph↗

arXiv2023

Some Specific Wormhole Solutions in Extended $f(R,G,T)$ Gravity

This research work provides an exhaustive investigation of the viability of different coupled wormhole (WH) geometries with the relativistic matter configurations in the $f(R,G,T)$ extended gravity framework. We consider a specific model in the context of $f(R,G,T)$-gravity for this purpose. Also, we assume a static spherically symmetric space-time geometry and a unique distribution of matter with a set of shape functions ($β(r)$) for analyzing different energy conditions (ECs). In addition to this, we examined WH-models in the equilibrium scenario by employing anisotropic fluid. The corresponding results are obtained using numerical methods and then presented using different plots. In this case, $f(R,G,T)$ gravity generates additional curvature quantities, which can be thought of as gravitational objects that maintain irregular WH-situations. Based on our findings, we conclude that in the absence of exotic matter, WH can exist in some specific regions of the parametric space using modified gravity model as, $f(R,G,T) = R +αR^2+βG^n+γG\ln(G)+λT$.

gr-qc↗