arXiv subjects

Fakhar Ul Haider

Publications and source records attributed to Fakhar Ul Haider.

4 recordsLinked to original sources

arXiv2026

Scaling of soft QGP signatures in relativistic lead, xenon and oxygen collisions in EPOS4

The collective expansion and hydrodynamic evolution in heavy-ion collisions is well-established. However, whether femtometer-scale droplets of QGP are produced in small systems at high energies remains a fundamental open question. Analysis of Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV, Xe$-$Xe at $\sqrt{s_{\mathrm{NN}}}$ = 5.44 TeV and O$-$O collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeV using EPOS4 is reported to make predictions and postdictions. The results are compared with ALICE data for Pb$-$Pb and Xe$-$Xe collisions. Charged particle multiplicity (d$N_{\mathrm{ch}}$/d$η$), transverse-momentum ($p_{\mathrm{T}}$) spectra for pions ($π^{\pm}$), kaons ($K^{\pm}$), and protons ($\text{p}(\overline{\text{p}})$) are studied. The inclusion of hadronic afterburner, UrQMD (Ultra-relativistic Quantum Molecular Dynamics) is found to be necessary to correctly describe baryon yields. $p_{\mathrm{T}}$-fluctuations are also studied via normalized $p_{\mathrm{T}}$ correlator, $\sqrt{\langle \langle Δp_{\mathrm{T},i}Δp_{\mathrm{T},j} \rangle \rangle}\mathrm{/} \langle \langle p_{\mathrm{T}} \rangle \rangle$. Lastly, anisotropic flow harmonics ($v_{\mathrm{2}} \{2\}$, $v_{\mathrm{3}} \{2\}$) are computed as a function of $p_{\mathrm{T}}$ and centrality. Since EPOS4 has not been extensively studied for flow observables, this study thereby provides a non-trivial assessment of its collective dynamics. The results are compared with experiment wherever data is available. Taken together, this study provides a unified description of soft observables from Pb$-$Pb through Xe$-$Xe down to O$-$O and offer quantitative guidance on how such collisions may inform of the properties of the QGP.

hep-ph↗

arXiv2026

Topological analysis of scale-invariant spatial fluctuations in ultrarelativistic heavy-ion collisions

The QGP-to-hadronic matter phase transition and QCD critical point in heavy-ion collisions can be identified by studying spatial fluctuations among final-state particles using intermittency analysis. First CMC-based intermittency analysis in the two-dimensional angular ($η$, $φ$) phase space, using EPOS as the background model is presented. Critical fluctuation signals are extremely weak, constituting only a few percent of the total event sample and are severely diluted by the overwhelming non-critical background, rendering traditional intermittency analyses insufficient for reliable signal extraction. To extract the weak critical signal, we employ a two-stage topological machine learning framework combining Topological Data Analysis (TDA) with deep learning. In the first stage, particle events are represented as two-dimensional point clouds and a Delaunay-based sub-level set filtration is constructed to extract Betti curves as multiscale topological invariants, corrected for multiplicity bias via azimuthal randomisation and classified by two complementary architectures, a TopoPointNet (TPN) and Boosted Decision Trees (BDT). Since event-level classification alone is insufficient to restore the critical scaling, a second stage applies a particle-level density filter, explicitly stripping away the diffuse thermal background and isolating the densely packed critical clusters. The two stage pipeline successfully restores the power-law scaling of the normalized factorial moments, enabling accurate recovery of the intermittency index in ($η$, $φ$) space and establishing topological machine learning as a robust data driven tool for probing the QCD critical point and the phase structure of strongly interacting matter in heavy-ion collisions at LHC energies.

hep-ph↗

arXiv2026

Intermittency and fractal behaviour of charged particles in EPOS4 and PYTHIA8 generated events at LHC energies

Large number density fluctuations of the charged particles produced in heavy-ion collisions are a promising signature for exploring the QCD phase transition and critical point in the nuclear matter phase diagram. Intermittency methodology is used to probe the fractal and scale invariant nature of these fluctuations. Intermittency is the phenomenon of power-law growth of the normalized factorial moments ($F_{\rm{q}}$) of the number density distributions over decreasing bin size. The charged particles generated in the midrapidity region using PYTHIA8 and EPOS4 (UrQMD ON/OFF) for Pb--Pb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV are studied. Scaling behaviour of $F_{\rm{q}}$ are studied as a function of phase space partitioning and second order moments to quantify the particle production nature within the default constraints of the two models. The scaling exponent related to the phase transition and parameters connected to fractal nature obtained for both these models show the absence of fluctuations of critical nature and multifractal behaviour.

hep-ex↗

arXiv2026

Scaling behaviour of charged particles generated in Xe$-$Xe collisions at $\sqrt{s_{\rm{NN}}}$ = 5.44 TeV using the AMPT model

The spatial configurations of particles produced in the kinematic phase space during a heavy-ion collision reflect the characteristics of the system created in the collision. The scaling behaviour of the multiplicity fluctuations is studied for the charged particles generated in Xe--Xe collisions at $\sqrt{s_{\rm{NN}}}$~=~5.44~TeV using the String Melting (SM) mode of the AMPT (A Multi-Phase Transport) model. The scaling behaviour of the normalized factorial moments ($F_\text{q}$) gives significant information about the dynamics of the system under study. A linear power-law growth of the $F_\text{q}$ with the increasing phase space resolution, termed as intermittency, is investigated. The anomalous fractal dimension $D_\text{q}$ is determined, which is linked to the self-similarity and fractal nature of the particle emission spectra, whose dependence on the order of the moment ($q$) is characterised by the intermittency index ($φ_{\text{q}}$). Relating $q^{\rm{th}}$ order Normalised Factorial Moment (NFM) with $F_{2}$, the scaling exponent ($ν$) is determined that quantifies the dynamics of the system created by these collisions and is analyzed for its dependence on the transverse momentum bin width ($Δp_\text{T}$). Results presented may be interpreted as model predictions and baseline expectations.

hep-ph↗