arXiv subjects

Ramni Gupta

Publications and source records attributed to Ramni Gupta.

13 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$\eta$), transverse-momentum ($p_{\mathrm{T}}$) spectra for pions ($\pi^{\pm}$), 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, $\sqrt{\langle \langle \Delta p_{\mathrm{T},i}\Delta p_{\mathrm{T},j} \rangle \rangle}\mathrm{/} \langle \langle p_{\mathrm{T}} \rangle \rangle$. 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 ($\eta$, $\varphi$) 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 ($\eta$, $\varphi$) 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↗

arXiv2025

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 ($\varphi_{\text{q}}$). Relating $q^{\rm{th}}$ order Normalised Factorial Moment (NFM) with $F_{2}$, the scaling exponent ($\nu$) 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 ($\Delta p_\text{T}$). Results presented may be interpreted as model predictions and baseline expectations.

hep-ph↗

arXiv2023

Normalized factorial moments of spatial distributions of particles in high multiplicity events: A Toy model study

In ultra-relativistic heavy-ion collisions a strongly interacting complex system of quarks and gluons is formed. The nature of the system so created and the mechanism of multi-particle production in these collisions may be revealed by studying the normalized factorial moments ($F_{\rm{q}}$) as function of various parameters. The resilience of $F_{\rm{q}}$ moments studied using Toy model events shows that these are sensitive to the presence of dynamical fluctuations in the system and are robust against the uniform efficiencies in the data measurements. Results of this study serve as a suitable reference baseline for the experimental and simulation studies.

hep-ph↗

arXiv2023

Local multiplicity fluctuations in Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV with ALICE at the LHC

Local multiplicity fluctuations are an useful tool to understand the dynamics of the particle production and the phase-space changes from quarks to hadrons in ultrarelativistic heavy-ion collisions. The study of scaling behavior of multiplicity fluctuations in geometrical configurations in multiparticle production can be performed using the factorial moments and recognized in terms of a phenomenon referred to as intermittency. In this contribution, the analysis of the factorial moment is presented for the multiplicity distributions of charged particles produced in Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV, recorded with the ALICE detector at the LHC. The normalized factorial moments (NFM), $F_{q}$ of the spatial configurations of charged particles in two-dimensional angular ($η,φ$) phase space are calculated. For a system with dynamic fluctuations due to the characteristic critical behavior near the phase transition, $F_{q}$ exhibits power-law growth with increasing bin number or decreasing bin size which indicates self-similar fluctuations. Relating the $q^{\rm{th}}$ order NFM ($F_{q}$) to the second-order NFM ($F_{2}$), the value of the scaling exponent ($ν$) is extracted, which indicates the order of the phase transition within the framework of Ginzburg-Landau theory. The dependence of scaling exponent on the $p_{\rm{T}}$ bin width will be presented. The measurements are also compared with the corresponding results from the AMPT model and a Toy Monte Carlo (MC) simulation.

nucl-ex↗

arXiv2022

Intermittency analysis of charged hadrons generated in Pb-Pb collisions at $\sqrt{s_{NN}}$= 2.76 TeV and 5.02 TeV using PYTHIA8/Angantyr

Local density fluctuations are expected to scale as a universal power-law when the system approaches critical point. Such power-law fluctuations are studied within the framework of intermittency through the measurement of normalized factorial moments in ($η$, $ϕ$) phase space. Observations and results from the intermittency analysis performed for charged particles in Pb-Pb collisions using PYTHIA8/Angantyr at 2.76 TeV and 5.02 TeV are reported. We observe no scaling behaviour in the particle generation for any of the centrality studied in narrow p$_T$ bins. The scaling exponent $ν$ shows no dependence on the centrality ranges.

nucl-ex↗

arXiv2022

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

The multiplicity fluctuations are sensitive to QCD phase transition and to the presence of critical point in QCD phase diagram. At critical point a system undergoing phase transition is characterized by large fluctuations in the observables which is an important tool to understand the dynamics of particle production in heavy-ion interactions and phase changes. Multiplicity fluctuations of produced particles is an important observable to characterize the evolving system. Using scaling exponent obtained from the normalized factorial moments of the number of charged hadrons in the two dimensional ($η,ϕ$) phase space, one can learn about the dynamics of system created in these collisions. Events generated using Xe-Xe collisions at $\sqrt{s_{\rm{NN}}} = 5.44 $ TeV with string-melting (SM) version of the AMPT model are analyzed and the scaling exponent $(ν)$ for various $p_T$ intervals is determined. It is observed that the calculated value of $ν$ is larger than the universal value 1.304, as is obtained from Ginzburg-Landau theory for second order phase transition. Here we will also present the results of the dependence of the scaling exponent on the transverse momentum bin width.

hep-ph↗

arXiv2022

Intermittency Analysis of Toy Monte Carlo Events

Event-by-event intermittency analysis of Toy Monte Carlo events is performed in the scenario of high multiplicity events as is the case at recent colliders RHIC and LHC for AA collisions. A power law behaviour of Normalized Factorial Moments (NFM), $F_{q}$ as function of number of bins ($M$) known as intermittency, is a signature of self-similar fluctuations. Dependence of NFM on the detector efficiencies and on the presence of fluctuations have been studied. Results presented here provide a baseline to the experimental results and clarity on the application of efficiency corrections to the experimental data.

hep-ph↗

arXiv2020

Intermittency study of charged particles generated in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}\text{= 2.76 TeV}$ using EPOS3

Charged particle multiplicity fluctuations in Pb-Pb collisions are studied for the central events generated using EPOS3 (hydro and hydro+cascade) at $\sqrt{s_{\mathrm{NN}}}\text{ = 2.76 TeV}$. Intermittency analysis is performed in the mid-rapidity region in two-dimensional ($η$, $ϕ$) phase space within the narrow transverse momentum ($p_\rm{T}$) bins in the low $p_\rm{T}$~region ($p_\rm{T}~\leq~1.0~GeV/\textit{c}$). Power-law scaling of the normalized factorial moments with the number of bins is not observed to be significant in any of the $p_\rm{T}$-bin. Scaling exponent $ν$, deduced for a few $p_\rm{T}$ bins is greater than that of the value 1.304, predicted for the second order phase-transition by the Ginzburg-Landau theory. The link in the notions of fractality is also studied. Fractal dimensions, $D_{q}$ are observed to decrease with the order of the moment $q$ suggesting the multifractal nature of the particle generation in EPOS3.

hep-ex↗

arXiv2018

Scaling Properties of Multiplicity Fluctuations in the AMPT Model

From the events generated from the MC code of a multi-phase transport (AMPT) model with string melting, the properties of multiplicity fluctuations of charged particles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=\rm{~2.76 \,TeV}$ are studied. Normalized factorial moments, $F_{q}$, of spatial distributions of the particles have been determined in the framework of intermittency. Those moments are found in some kinematic regions to exhibit scaling behavior at small bin sizes, but not in most regions. However, in relating $F_{q}$ to $F_{2}$ scaling behavior is found in nearly all regions. The corresponding scaling exponents, $ν$, determined in the low transverse momentum ($p_{\rm{T}}$) region $\le$ 1.0 GeV/c are observed to be independent of the $p_{\rm{T}}$ bin position and width. The value of $ν$ is found to be larger than 1.304, which is the value that characterizes the Ginzburg-Landau type second order phase transition. Thus there is no known signature for phase transition in the AMPT model. This study demonstrates that, for the system under investigation, the method of analysis is effective in extracting features that are relevant to the question of whether the dynamical processes leading phase transition are there or not.

hep-ph↗

arXiv2015

Evidence on the absence of critical transition in AMPT for Pb-Pb collisions at $sqrt{s_{\rm{NN}}}$ = 2.76 TeV

Event-by-event fluctuations in the spatial patterns in charged particles generated in Pb--Pb collisions at the center-of-mass energy $\sqrt{S_{\rm{NN}}}$ = 2.76 TeV are studied within A MultiPhase Transport (AMPT) model. The spatial patterns of the particles generated in the ($η, ϕ$) space for $|η| \le 0.8$ are studied using the methodology of intermittency and erraticity analysis. We find negative intermittency for charged particles generated in a range of $p_{\rm{T}}$ windows. This result contrasts sharply from what is expected for a quark-gluon plasma undergoing hadronization by a second-order phase transition. Appropriate scaling behavior is examined, resulting in definitive scaling exponent $ν_{-}$. Event-by-event fluctuations in the spatial patterns quantified by an index, named erraticity index are determined for different $p_{\rm{T}}$ bins $\leq 1$ GeV/c, for AMPT model. This is the first time that the intermittency and erraticity indices are determined for any model at such high energies. The results presented here can be used for comparison with the fluctuation properties of the experimental data and hence can help the development of a wider scope of understanding of validity of the particle production process by AMPT at these energies on the one hand, and of the true nature of the real data on the other.

nucl-ex↗

arXiv2015

A Monte Carlo Study of Multiplicity Fluctuations in Pb-Pb Collisions at LHC Energies

With large volumes of data available from LHC, it has become possible to study the multiplicity distributions for the various possible behaviours of the multiparticle production in collisions of relativistic heavy ion collisions, where a system of dense and hot partons has been created. In this context it is important and interesting as well to check how well the Monte Carlo generators can describe the properties or the behaviour of multiparticle production processes. One such possible behaviour is the self-similarity in the particle production, which can be studied with the intermittency studies and further with chaoticity/erraticity, in the heavy ion collisions. We analyse the behaviour of erraticity index in central Pb-Pb collisions at centre of mass energy of 2.76 TeV per nucleon using the AMPT monte carlo event generator, following the recent proposal by R.C. Hwa and C.B. Yang, concerning the local multiplicity fluctuation study as a signature of critical hadronization in heavy-ion collisions. We report the values of erraticity index for the two versions of the model with default settings and their dependence on the size of the phase space region. Results presented here may serve as a reference sample for the experimental data from heavy ion collisions at these energies.

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