arXiv subjects

Amal Sarkar

Publications and source records attributed to Amal Sarkar.

12 recordsLinked to original sources

arXiv2026

System-size dependence of strangeness production from p+p to Pb+Pb: quantitative tests of the $K^+/\pi^+$ horn

The pronounced maximum ("horn") in the $K^+/\pi^+$ excitation function observed in central Pb+Pb collisions is well established feature of collision-energy dependence, but its dependence on system size remains poorly understood. We confront hadronic (SMASH) and partonic (PHSD) transport, Glauber core-corona, canonical-ensemble suppression, and the two-phase statistical model of the early stage (SMES) with $K^+/\pi^+$ data spanning the complete NA61/SHINE system-size ladder (p+p, Be+Be, Ar+Sc, Xe+La) together with NA49 Pb+Pb and STAR Au+Au, quantifying every comparison by $\chi^2$. No single framework describes the full range: core-corona is preferred for intermediate systems, SMES with canonical strangeness conservation for heavy systems, and none reproduces the small-system data. Neither transport model generates the horn, with or without partonic degrees of freedom. The data exhibit a step-like enhancement of $K^+/\pi^+$ between Be+Be and Ar+Sc, quantified within the core-corona framework by a step from $\fcore \approx 0.22$ (Be+Be) to $\fcore \approx 0.58$ (Ar+Sc). The strangeness saturation factor $\gs$ rises in two distinct steps, separating geometric core formation from thermodynamic equilibration. The $(K^+/\pi^+)/(K^-/\pi^-)$ double ratio, which at fixed $\sqrts$ cancels the system-independent $\mu_B$ contribution, shows a step between light and heavy systems at a global significance of $3.7\sigma$, providing evidence for genuine strangeness enhancement beyond the pair-production baseline. Preliminary Xe+La data favor core-corona ($\chindf = 5.8$) over SMASH ($\chindf = 23.3$); finalized spectra will sharpen the CC/SMES discrimination at the $27\%$ level.

hep-ph↗

arXiv2026

Performance Enhancement of Gas Electron Multipliers Using an Optimized Single-Conical Hole Geometry for Different Charged Particles

Gas Electron Multipliers (GEMs) are essential detector components in modern high-energy physics experiments, where precise and stable detection of charged particles over a broad energy range is required. We present a comprehensive Garfield$^{++}$ and ANSYS-based study of conventional bi-conical and optimized single-conical GEM detectors to investigate the performance of the GEM detector for muons ($\mu$), pions ($\pi$), kaons ($K$), and protons ($P$), which constitute the dominant charged particles measured directly in collider-based experiments. The aim is to examine the impact of particle-dependent ionization characteristics on charge amplification and ion backflow, and to evaluate the potential of an optimized GEM configuration for different leptons and hadrons. The conventional bi-conical GEM design does not always operate at optimal efficiency, as ion backflow can lead to space-charge accumulation and electric field distortions, ultimately limiting performance in high-rate environments. Thus, geometrical optimization is essential to address these limitations and enhance detector performance. A single-conical hole geometry is introduced and systematically compared with the conventional bi-conical design. For both of these configurations, the results exhibit clear and systematic variations in the detector performance with the particle type and the incident energy. The optimized geometry improves the balance between effective gain and ion backflow, demonstrating its potential for future high-rate MPGD applications.

hep-ex↗

arXiv2026

Evidence for differential kinetic freeze-out of the $\phi(1020)$ meson in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV

In heavy-ion collisions, hadronic species with small interaction cross sections may decouple from the evolving fireball earlier than the bulk, yet quantitative evidence for this differential freeze-out has remained elusive. We report that the $\phi(1020)$ meson does \emph{not} kinetically freeze out with the bulk hadrons in 0--5\% central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV: a Boltzmann-Gibbs blast-wave contour analysis of ALICE $\phi(1020)$ $p_{\rm T}$ transverse-momentum spectra shows that the bulk $\pi/K/p$ freeze-out point is excluded at $4.1\sigma$ ($\Delta\chi^2 = 21.7$). Despite its proton-like mass, the $\phi$ exhibits freeze-out parameters incompatible with those of the bulk hadrons, implying that the observed spectral hardening cannot be attributed solely to mass-dependent collective expansion. Instead, it is naturally explained by the OZI-suppressed $\phi$-hadron interaction cross section which causes $\phi$ to decouple earlier and probe a distinct freeze-out surface. The exclusion is robust under all systematic variations tested and is qualitatively reproduced by SMASH hadronic transport simulations. These findings establish the $\phi$ meson as a clean probe of species-dependent hadronization, and provide quantitative evidence for a kinetic freeze-out hierarchy in ultra-relativistic heavy-ion collisions.

hep-ph↗

arXiv2026

Enhanced sensitivity to the $H \to Zγ\to \ell^+\ell^-γ$ decay at the LHC using machine learning and novel kinematic observables

At LHC energies, the Drell--Yan ($Z/γ^{*}$) processes have a substantially large cross section. Their di-lepton ($\ell^+\ell^-$) final state contributes significantly to many resonant signal regions, making them one of the dominant backgrounds in numerous physics analyses. The study focuses on improving the discrimination and suppression of the $Z/γ^{*} \rightarrow \ell^{+}\ell^{-}$ background from the $H \rightarrow Zγ\rightarrow \ell^{+}\ell^{-}γ$ signal at $\sqrt{s}=13~\text{TeV}$ by leveraging Monte Carlo simulated data. The analysis introduces physics-motivated correlated observables derived from the two-dimensional $(P_{\mathrm{Higgs}}, θ_{Zγ})$ plane. These observables encode differences in angular and momentum information to enhance signal--background separation while maintaining high signal efficiency. We present a multivariate analysis (MVA) employing a Boosted Decision Tree (XGBoost) classifier. By incorporating additional physics-motivated correlated observables, the classifier achieves measurable improvements in performance. A significant increase in the area under the ROC curve (AUC) is observed in both the electron and muon channels, demonstrating the effectiveness of the expanded feature set. Further, optimised background rejection using $(P_{\mathrm{Higgs}}, θ_{Zγ})$ plane increases the signal-to-background ratio to 2.1\% and 3.4\% for the electron and muon channel respectively near the Higgs mass. This work demonstrates that combining kinematic correlations with interpretable multivariate techniques leads to improved sensitivity and robust background rejection. The approach is flexible and can be readily applied to a wide range of analyses, including rare Higgs decays, resonant searches, and studies beyond the Standard Model.

hep-ph↗

arXiv2026

Design Optimization of Triple Gas Electron Multiplier for Superior Gain and Reduced Ion Backflow

Micro-Pattern Gas Detectors (MPGDs) are extensively employed in modern high-energy and nuclear Physics experiments because of their excellent spatial resolution, high rate capability, and operational stability. Among these, the Gas Electron Multiplier (GEM) has emerged as one of the most widely adopted MPGD technologies. Despite their widespread adoption, GEM detectors based on the conventional bi-conical hole geometry do not always achieve optimal performance, particularly in maximizing effective gain while suppressing ion backflow. One of the primary factors limiting a GEM's performance is ion backflow. The accumulation and gradual discharge of these ions might alter the local electric field, resulting in a temporary dead time and complicating responses to subsequent events. These limitations pose challenges for applications requiring high precision and stable long-term operation. In this work, we address these issues by investigating modified GEM geometries designed to enhance gain performance and reduce ion backflow, thereby improving overall detector performance. The current study investigates geometric optimization strategies for a triple-GEM detector to enhance performance, mitigate ion backflow, and augment gain. The detector structures were designed using the ANSYS Mechanical APDL, and the associated electrostatic field configurations were computed using the ANSYS Maxwell. A thorough investigation of gain and ion backflow calculations was carried out when the generated field maps were interfaced with Garfield$^{++}$. The potential enhancements in detector efficiency and stability that the proposed modifications to the GEM foil geometry offers a valuable insights for the design of next-generation gaseous detectors.

physics.ins-det↗

arXiv2025

A Coupled Source Description of Pseudorapidity Distributions from RHIC to LHC: Emergent $1/μ_B$ Scaling and Limiting Fragmentation

One of the most remarkable observations in heavy-ion collisions is the systematic regularity exhibited by pseudorapidity distributions of charged particles across collision energies. While single-source models fail at higher energies and independent multi-source approaches do not reproduce the central dip observed at LHC energies, a unified description across the full RHIC-LHC energy range remains elusive. These distributions from Au+Au collisions at RHIC ($\sqrt{s_{NN}}$ = 19.6--200 GeV) and Pb+Pb collisions at LHC ($\sqrt{s_{NN}}$ = 2.76--5.36 TeV) are analyzed using a novel parametrization based on coupled Gaussian sources where the interaction strength is quantified by parameter $λ$. This coupled two-source model captures the interaction between forward and backward sources through the medium formed in the collision. Remarkably, $λ$ exhibits empirical scaling behavior resembling $1/μ_B$, suggesting sensitivity to baryon stopping and the strongly-interacting medium. All fitting parameters follow systematic energy trends, with the peak-to-peak distance and chemical freeze-out temperature exhibiting identical exponential saturation patterns, indicating that geometric expansion and thermal evolution share a common underlying dynamics governed by QCD phase structure. Furthermore, the approach naturally preserves limiting fragmentation behavior across all energies, in contrast to independent source models that suggest its violation at LHC energies. Although the theoretical basis requires further investigation, these empirical correlations successfully unify charged particle production across nearly two orders of magnitude in collision energy, revealing fundamental connections to underlying collision dynamics.

hep-ph↗

arXiv2025

Net-Charge Fluctuations in Finite Volume PNJL Model: A Probe for the QCD Critical Point

The QCD Critical Point is a pivotal feature of the phase diagram of strongly interacting matter. Signatures of the critical point are expected to manifest through the non-monotonic behavior of higher-order moments of conserved quantities, such as net-baryon ($ΔB$), net-charge ($ΔQ$), and net-strangeness ($ΔS$), as a function of collision energy. These moments are connected to the thermodynamic susceptibilities, as well as to the correlation length developed in the system, which diverges at the critical point. The non-monotonic behavior of higher-order moments and their volume-independent products near the critical region supports the presence of a critical point in a finite system existing for a finite time, due to their sensitivity to critical fluctuations. These fluctuations are believed to provide key evidence in the search for the QCD Critical Point. We present the higher order moments, such as mean (M), variance $(σ^2)$, skewness (S), and kurtosis $(κ)$ and their volume-independent moment products $(M/σ^{2}, sσ, κσ^{2})$ of net-charge multiplicity distributions in the three-flavor finite volume, finite density Polyakov loop enhanced Nambu-Jona-Lasinio (PNJL) model. The work has been performed at energies similar to RHIC BES energies from 7.7 GeV to 200 GeV, including 2.4 and 3 GeV in the present model. Our findings are compared with the STAR net-charge data at various collision energies to explore signals of the QCD critical point. Additionally, we contrast our results with predictions from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, the Hadron Resonance Gas (HRG) model, and available lattice QCD data. The present results offer a useful tool for extracting the freeze-out parameters in the heavy-ion collision by comparing them with the STAR net-charge result and other net-charge theoretical models.

hep-ph↗

arXiv2025

Net-Strangeness Fluctuations and Their Experimental Implications in the SU(3) PNJL Model Using the Subensemble Acceptance Method for the search of QCD Critical Point

The critical end point (CEP) is a key feature of the Quantum Chromodynamics (QCD) phase diagram, where critical phenomena cause higher-order moments of conserved charges net-baryon ($ΔB$), net-charge ($ΔQ$), and net-strangeness ($ΔS$) to exhibit non-monotonic behavior. These moments and their volume-independent products are sensitive to the correlation length, making them crucial observables in the search for the CEP. In this study, we investigate net-strangeness fluctuations using the finite-volume Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model, incorporating six-quark and eight-quark interactions at energy scales relevant to the RHIC beam energy scan. Our results are compared to STAR net-kaon data and the Hadron Resonance Gas (HRG) model to assess the CEP's existence. Since direct measurement of conserved charges is experimentally challenging, net-proton, net-pion, and net-kaon are used as proxies for $ΔB$, $ΔQ$, and $ΔS$. We employ the Subensemble Acceptance Method (SAM) to analyze the acceptance dependence of $κσ^{2}$ for net-strangeness fluctuations. Our findings establish a direct mapping between the subvolume (particle fraction) and the total volume (conserved quantities), providing insights into the role of experimental acceptance in fluctuation measurements.

hep-ph↗

arXiv2025

Dynamics of Hot QCD Matter 2024 -- New facilities and instrumentation

This part of the conference proceeding provides a detailed overview of cutting-edge advancements in detector technologies, focusing on their optimization, characterization, and applications in particle physics experiments. Building on the insights and developments presented at the Hot QCD Matter 2022 conference, this section of the Hot QCD Matter 2024 proceedings highlights significant advancements in detector technologies. The development of Low Gain Avalanche Diodes (LGADs) into Ultra-Fast Silicon Detectors is explored, demonstrating their potential for superior timing resolution in future high-energy experiments. Simulation studies of Micropattern Gaseous Detectors (MPGDs), including MICROMEGAS and Gas Electron Multiplier (GEM) detectors, provide insights into their performance under high-radiation environments using tools like ANSYS and GARFIELD$^{++}$. A novel GEM foil geometry is proposed for improved gain and durability. Characterization of semiconductor detectors, such as Monolithic MALTA pixel detectors and CMS prototype silicon sensors, is also presented, highlighting their radiation tolerance, imaging capabilities, and structural integrity. These studies underscore the critical role of silicon sensors in ensuring detector reliability and performance. Additionally, the J-PARC muon g-2/EDM experiment is reviewed, showcasing its precision measurements to test Standard Model predictions and explore potential physics beyond. By addressing the interplay between detector development, simulation, and characterization, this proceeding showcases a collective effort toward advancing detector technologies and their pivotal role in pushing the boundaries of modern particle physics.

hep-ex↗

arXiv2024

Dynamics of Hot QCD Matter 2024 -- Hard Probes

The hot and dense QCD matter, known as the Quark-Gluon Plasma (QGP), is explored through heavy-ion collision experiments at the LHC and RHIC. Jets and heavy flavors, produced from the initial hard scattering, are used as hard probes to study the properties of the QGP. Recent experimental observations on jet quenching and heavy-flavor suppression have strengthened our understanding, allowing for fine-tuning of theoretical models in hard probes. The second conference, HOT QCD Matter 2024, was organized to bring the community together for discussions on key topics in the field. This article comprises 15 sections, each addressing various aspects of hard probes in relativistic heavy-ion collisions, offering a snapshot of current experimental observations and theoretical advancements. The article begins with a discussion on memory effects in the quantum evolution of quarkonia in the quark-gluon plasma, followed by an experimental review, new insights on jet quenching at RHIC and LHC, and concludes with a machine learning approach to heavy flavor production at the Large Hadron Collider.

nucl-ex↗

arXiv2024

Dynamics of Hot QCD Matter 2024 -- Bulk Properties

The second Hot QCD Matter 2024 conference at IIT Mandi focused on various ongoing topics in high-energy heavy-ion collisions, encompassing theoretical and experimental perspectives. This proceedings volume includes 19 contributions that collectively explore diverse aspects of the bulk properties of hot QCD matter. The topics encompass the dynamics of electromagnetic fields, transport properties, hadronic matter, spin hydrodynamics, and the role of conserved charges in high-energy environments. These studies significantly enhance our understanding of the complex dynamics of hot QCD matter, the quark-gluon plasma (QGP) formed in high-energy nuclear collisions. Advances in theoretical frameworks, including hydrodynamics, spin dynamics, and fluctuation studies, aim to improve theoretical calculations and refine our knowledge of the thermodynamic properties of strongly interacting matter. Experimental efforts, such as those conducted by the ALICE and STAR collaborations, play a vital role in validating these theoretical predictions and deepening our insight into the QCD phase diagram, collectivity in small systems, and the early-stage behavior of strongly interacting matter. Combining theoretical models with experimental observations offers a comprehensive understanding of the extreme conditions encountered in relativistic heavy-ion and proton-proton collisions.

nucl-th↗

arXiv2018

Higher moments on strangeness fluctuation using PNJL model

The strangeness fluctuation of QGP matter has been investigated in three flavor finite volume Polyakov loop extended Nambu-Jona--Lasinio model. The ratio of fourth order moment to second order moment (kurtosis) and the third order moment to second order moment (skewness) of strangeness fuctuations have been studied and compared with the experimental data. The cross correlations related to baryon number, strangeness and electric charge conservation have also been discussed. Skewness and kurtosis of strangeness fluctuation in PNJL model have similar features along the collision energy of heavy ion experiments.

hep-ph↗