arXiv subjects

Sumit Basu

Publications and source records attributed to Sumit Basu.

At least 19 recordsLinked to original sources

arXiv2025

Probing Partonic Evolution and Hadronization via Balance Functions and Correlations of Charmed Hadrons

Predictions of charm correlation functions and more specifically balance functions are presented in proton--proton (pp) collisions at sqrt(s_NN) = 13 TeV based on the PYTHIA 8.3 event generator. Correlations are computed for identical and cross-species charmed hadrons in both minimum bias and high-pT biased collisions. We study the strength of correlations as a function of the number of balanced flavors and investigate the impact of variations of PYTHIA parameters controlling the Lund string fragmentation on the shape and strength of the correlation functions. The feasibility of measurements of the charm balance function presented is discussed in the context of the future LHC experiments.

hep-ex↗

arXiv2024

Investigating late-stage particle production in pp collisions with Balance Functions

Balance functions have been regarded in the past as a method of investigating the late-stage hadronization found in the presence of a strongly-coupled medium. They are also used to constrain mechanisms of particle production in large and small collision systems. Measurements of charge balance functions for inclusive and identified particle pairs are reported as a function of charged particle multiplicity in proton--proton collisions simulated with the PYTHIA8 and the EPOS4 models. The charge balance functions of inclusive, pion, kaon, and proton pairs exhibit amplitudes and shapes that depend on particle species and differ significantly in the two models due to the different particle production mechanisms implemented in PYTHIA and EPOS. The shapes and amplitudes also evolve with multiplicity in both models. In addition, the evolution of the longitudinal rms width and that of balance functions integrals with multiplicity (and average transverse momentum) feature significant differences in the two models.

hep-ph↗

arXiv2024

Mixed Species Charge and Baryon Balance Functions Studies with PYTHIA

Mixed species charge and baryon balance functions are computed based on proton--proton (pp) collisions simulated with the PYTHIA8 model. Simulations are performed with selected values of the collision energy $\sqrt{s}$ and the Monash tune and the Ropes and Shoving modes of PYTHIA8 to explore whether such measurements provide useful new information and constraints on mechanisms of particle production in pp collisions. Charge balance functions are studied based on mixed pairs of pions, kaons, and protons, whereas baryon balance functions are computed for mixed low mass strange and non-strange baryons. Both charge and baryon balance functions of mixed particle pairs feature shapes and amplitudes that sensitively depend on the particle considered owing largely to the particle production mechanisms implemented in PYTHIA. The evolution of balance functions integrals with the longitudinal width of the acceptance are presented and one finds that sums of such integrals for a given reference particle obey expected sum rules for both charge and baryon balance functions. Additionally, both types of balance functions are found to evolve in shape and amplitude with increasing collision energy $\sqrt{s}$ and the PYTHIA tunes considered.

hep-ph↗

arXiv2023

Multi-particle Integral and Differential Correlation Functions

This paper formalizes the use of integral and differential cumulants for measurements of multi-particle event-by-event transverse momentum fluctuations, rapidity fluctuations, as well as net charge fluctuations. This enables the introduction of multi-particle balance functions, defined based on differential correlation functions (factorial cumulants), that suppress two and three prong resonance decays effects and enable measurements of underlying long range correlations obeying quantum number conservation constraints. These multi-particle balance functions satisfy simple sum rules determined by quantum number conservation. It is additionally shown that these multi-particle balance functions arise as an intrinsic component of high-order net charge cumulants. This implies that the magnitude of these cumulants, measured in a specific experimental acceptance, is strictly constrained by charge conservation and primarily determined by the rapidity and momentum width of these balance functions. The paper also presents techniques to reduce the computation time of differential correlation functions up to order $n=$10 based on the methods of moments.

hep-ex↗

arXiv2022

Effects of Non-Vanishing Net Charge in Balance Functions

We investigate the impact of non-vanishing net-charge in collision systems on measurements of balance functions and their integrals. We show that the nominal balance function definition yields integrals that deviate from unity because of the non-vanishing net-charge. However, the integral of unified balance functions is shown to appropriately converge to unity when measured in a sufficiently wide experimental acceptance. We furthermore explore the rate of convergence of unified balance functions integrals and study distortions imparted on the shape of balance functions when measurements are carried out in limited transverse momentum ($p_{\rm T}$) and rapidity ($y$) acceptances, such as those featured by experiments at the Large Hadron Collider or the Relativistic Heavy Ion Collider. We show that the shape and integral of unified balance functions may be strongly biased by reductions in the rapidity and transverse momentum acceptances of existing experiments.

hep-ph↗

arXiv2022

Unified Balance Functions

The use of charge balance functions in heavy-ion collision studies was initially proposed as a probe of delayed hadronization and two-stage quark production in these collisions. It later emerged that general balance functions can also serve as a probe of the diffusivity of light quarks as well as the evolution of the systems formed in heavy-ion collisions. In this work, we reexamine the formulation of general balance functions and consider how to best define and measure these correlation functions in terms of differences of conditional densities of unlike-sign and like-sign particle pairs. We define general balance functions in terms of associated particle functions and show these obey a simple sum rule. We additionally proceed to distinguish between balance functions expressed as differences of conditional densities valid irrespective of experimental acceptance boundaries and bound balance functions that explicitly account for the limited acceptance of experiments. General balance functions are additionally extended to accommodate strange, baryon, as well as charm and bottom quantum numbers based on the densities of these quantum numbers.

hep-ph↗

arXiv2021

Probing the Gluon Plasma with Charm Balance Functions

Recent theoretical explanations for how hydrodynamic-like flow can build up quickly in small collision systems (hydrodynamization) has led to a microscopic picture of flow building up in a gluon-dominated phase before chemical equilibrium between quarks and gluons has been attained. The goal of this contribution to Offshell-2021 is to explore consequence of assuming a long-lived gluon-dominated phase, which we shall denote a gluon plasma (GP). As these consequences are naturally enhanced in a large systems, we assume and explore the extreme scenario in which a GP would be created in AA collisions and exist for significant time before the formation of a chemically-equilibrated quark-gluon plasma (QGP). The GP and its formation would be impossible to probe with light-quark hadrons, which are first produced later in this scenario. As charm quarks are produced early in the collision, they can circumvent the limitations of light quarks and we propose charm balance functions as an effective tool to test this idea and constrain the dynamics of the GP.

hep-ph↗

arXiv2021

Azimuthal dependence of two-particle transverse momentum current correlations

Two-particle transverse momentum correlation functions are a powerful technique for understanding the dynamics of relativistic heavy-ion collisions. Among these, the transverse momentum correlator $G_{2}\left(\Delta\eta,\Delta\varphi\right)$ is of particular interest for its potential sensitivity to the shear viscosity per unit of entropy density $\eta/s$ of the quark-gluon plasma formed in heavy-ion collisions. We use the UrQMD, AMPT, and EPOS models for Au--Au at $\sqrt{s_{\rm NN}}$ = 200~GeV and Pb--Pb at $\sqrt{s_{\rm NN}}$ = 2760~GeV to investigate the long range azimuthal dependence of $G_{2}\left(\Delta\eta,\Delta\varphi\right)$, and explore its utility to constrain $\eta/s$ based on charged particle correlations. We find that the three models yield quantitatively distinct transverse momentum Fourier harmonics coefficients $a^{p_{\rm T}}_{\rm n}$. We also observe these coefficients exhibit a significant dependence on $\eta/s$ in the context of the AMPT model. These observations suggest that exhaustive measurements of the dependence of $G_{2}\left(\Delta\varphi \right)$ with collision energy, system size, collision centrality, in particular, offer the potential to distinguish between different theoretical models and their underlying assumptions. Exhaustive analyses of $G_{2}\left(\Delta\varphi \right)$ obtained in large and small systems should also be instrumental in establishing new constraints for precise extraction of $\eta/s$.

nucl-th↗

arXiv2020

Extraction of the specific shear viscosity of quark-gluon plasma from two-particle transverse momentum correlations

The specific shear viscosity, $\eta/s$, of the quark-gluon plasma formed in ultrarelativistic heavy-ion collisions at RHIC and LHC is estimated based on the progressive longitudinal broadening of transverse momentum two-particle correlators, $G_2$, reported as a function of collision centrality by the STAR and ALICE experiments. Estimates are computed as a function of collision centrality using the Gavin ansatz which relates the $G_2$ longitudinal broadening to the specific shear viscosity. Freeze out times required for the use of the ansatz are computed using a linear fit of freeze out times reported as a function of the cubic root of the charged particle pseudorapidity density $({\rm d}N_{\rm ch}/{\rm d}\eta)^{1/3}$. Estimates of $\eta/s$ based on ALICE data exhibit little to no dependence on collision centrality at LHC energy, while estimates obtained from STAR data hint that $\eta/s$ might be a function of collision centrality at top RHIC energy.

nucl-ex↗

arXiv2020

Multiplicity and pseudorapidity density distributions of charged particles produced in pp, pA and AA collisions at RHIC \& LHC energies

Multiplicity and pseudorapidity ($\eta$) density ($dN_{\rm ch}/d\eta$) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of high-energy heavy-ion collisions. However, detector constraints limit the $\eta$-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large $\eta$-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present study, we use three different ans$\ddot{\mathrm a}$tze to obtain quantitative descriptions of the shape of pseudorapidity distributions of charged hadrons produced in pp, p-A, and A-A collisions for beam energies ($\sqrt{s_{\rm NN}}$) ranging from a few GeV to a few TeV corresponding to RHIC and LHC energies. We study the limiting fragmentation behavior in these collisions and report evidence for participant-scaling violations in high-energy collisions at the TeV scale. We additionally examine measured pseudorapidity distributions to constrain models describing initial conditions of particle production. We predict the centrality dependence of charged particle multiplicity distributions at FAIR and NICA energies and give an estimation of charged particle multiplicity at $\eta=0$ for the proposed HE-LHC and FCC energies.

nucl-ex↗

arXiv2020

Differential two-particle number and momentum correlations with the AMPT, UrQMD, and EPOS models in Pb-Pb collisions at $\sqrt{\textit{s}_{_{\rm NN}}}$= 2.76 TeV

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential number correlation functions, $R_{2} \left( \Delta \eta, \Delta \varphi \right)$, and transverse momentum correlation functions, $P_2 \left( \Delta \eta, \Delta \varphi \right)$ of charged particles produced in \PbPb\ collisions at the LHC centre-of-mass energy $\sqrt{s_{\rm NN}} =$ 2.76 TeV with the UrQMD, AMPT and EPOS models. Model predictions for $R_2$ and $P_2$ correlation functions are presented for inclusive charged hadrons ($h^\pm$) in selected transverse momentum ranges and with full azimuthal coverage in the pseudorapidity range $|\eta|< 1.0$. We compare these predictions for the strength, shape, and particularly the width of the correlation functions with recent measurements of these observables by the ALICE collaboration. Our analysis indicate that comparative studies of $R_2$ and $P_2$ correlation functions provide valuable insight towards the understanding of particle production in Pb--Pb collisions. We find, in particular, that these models have quantitatively different predictions for these three observables but none reproduce the measured correlation functions reported by the ALICE collaboration. Accounting for quantum number conservation in models, particularly charge conservation, is mandatory to reproduce the detailed measurements of number and transverse momentum correlation functions.

nucl-ex↗

arXiv2018

Simulation studies of $\rm{R_{2}}(\Delta\eta, \Delta\varphi)$ and $\rm{P_{2}}(\Delta\eta, \Delta\varphi)$ correlation functions in pp collisions with the PYTHIA and HERWIG models

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential-number correlation functions, $\rm{R_{2}}(\Delta\eta, \Delta\varphi)$, and transverse momentum ($p_{\rm T}$) correlation functions, $\rm{P_{2}}(\Delta\eta, \Delta\varphi)$, of charged particles in $\sqrt{\textit{s}}$ = 2.76 TeV pp collisions with the PYTHIA and HERWIG models. Model predictions are presented for inclusive charged hadrons ($h^\pm$), as well as pions ($\pi^\pm$), kaons (K$^\pm$), and (anti-)protons ($\rm \bar{p}$/p) in the ranges $0.2 < \textit{p}_{\rm T} \le 2.0~\rm{GeV}/\textit{c}$, $2.0 < \textit{p}_{\rm T} \le 5.0~\rm{GeV}/\textit{c}$, and $5.0 < \textit{p}_{\rm T} \le 30.0~\rm{GeV}/\textit{c}$, with full azimuthal coverage in the range $|\eta|< 1.0$. We compare the model predictions for the strength and shape of the $\rm{R_{2}}$ and $\rm{P_{2}}$ correlators as these pertain to recent measurements by the ALICE collaboration. The $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions estimated with PYTHIA and HERWIG exhibit qualitatively similar near-side and away-side correlation structures but feature important differences. Our analysis indicates that comparative studies of $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions would provide valuable insight towards the understanding of particle production in pp collisions, and by extension, should also be useful in studies of heavy-ion collisions. Comparison of the $\Delta \eta$ dependence of $\rm{R_{2}}$ and $\rm{P_{2}}$ could contribute, in particular, to a better understanding and modeling of the angular ordering of particles produced by hadronization in jets, as well as a better description of jet fragmentation functions of identified species at low momentum fraction $(z)$.

nucl-ex↗

arXiv2018

Effect of centrality bin width corrections on two-particle number and transverse momentum differential correlation functions

Two-particle number and transverse momentum differential correlation functions are powerful tools for unveiling the detailed dynamics and particle production mechanisms involved in relativistic heavy-ion collisions. Measurements of transverse momentum correlators $P_2$ and $G_2$, in particular, provide added information not readily accessible with better known number correlation functions $R_2$. However, it is found that the $R_2$ and $G_2$ correlators are somewhat sensitive to the details of the experimental procedure used to measure them. They exhibit, in particular, a dependence on the collision centrality bin width, which may have a rather detrimental impact on their physical interpretation. A technique to correct these correlators for collision centrality bin-width averaging is presented. The technique is based on the hypothesis that the shape of single- and pair- probability densities vary slower with collision centrality than the corresponding integrated yields. The technique is tested with Pb-Pb simulations based on the HIJING and ultrarelativistic quantum molecular dynamics models and shown to enable a precision better than 1% for particles in the kinematic range $0.2 \leq p_{\rm T} \leq 2.0$ GeV/$c$.

physics.data-an↗

arXiv2017

Isothermal compressibility of hadronic matter formed in relativistic nuclear collisions

We present the first estimates of isothermal compressibility (\kT) of hadronic matter formed in relativistic nuclear collisions ($\sqrt{s_{\rm NN}} = 7.7$ GeV to 2.76~TeV) using experimentally observed quantities. \kT~is related to the fluctuation in particle multiplicity, temperature, and volume of the system formed in the collisions. Multiplicity fluctuations are obtained from the event-by-event distributions of charged particle multiplicities in narrow centrality bins. The dynamical components of the fluctuations are extracted by removing the contributions to the fluctuations from the number of participating nucleons. From the available experimental data, a constant value of \kT~has been observed as a function of collision energy. The results are compared with calculations from UrQMD, AMPT, and EPOS event generators, and estimations of \kT~are made for Pb-Pb collisions at the CERN Large Hadron Collider. A hadron resonance gas (HRG) model has been used to calculate \kT~as a function of collision energy. Our results show a decrease in \kT~at low collision energies to \sNN~$\sim$~20~GeV, beyond which the \kT~values remain almost constant.

nucl-ex↗

arXiv2016

Beam energy dependence of pseudorapidity distributions of charged particles produced in heavy-ion collisions at RHIC and LHC energies

Heavy-ion collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory and the Large Hadron Collider at CERN probe matter at extreme conditions of temperature and energy density. Most of the global properties of the collisions can be extracted from the measurements of charged particle multiplicity and pseudorapidity ($\eta$) distributions. We have shown that the available experimental data on beam energy and centrality dependence of \Eta-distributions in heavy-ion (Au+Au or Pb+Pb) collisions from \sNN=7.7 GeV to 2.76 TeV are reasonably well described by the AMPT model, which is used for further exploration. The nature of the \Eta-distributions has been described by a double Gaussian function using a set of fit parameters, which exhibit a regular pattern as a function of beam energy. By extrapolating the parameters to a higher energy of \sNN~=~5.02 TeV, we have obtained the charged particle multiplicity densities, \Eta-distributions and energy densities for various centralities. Incidentally, these results match well with some of the recently published data by the ALICE collaboration.

nucl-ex↗

arXiv2016

Fluctuations in Charged Particle Multiplicities in Relativistic Heavy-Ion Collisions

Multiplicity distributions of charged particles and their event-by-event fluctuations have been compiled for relativistic heavy-ion collisions from the available experimental data at Brookhaven National Laboratory and CERN and also by the use of an event generator. Multiplicity fluctuations are sensitive to QCD phase transition and to the presence of critical point in the QCD phase diagram. In addition, multiplicity fluctuations provide baselines for other event-by-event measurements. Multiplicity fluctuation expressed in terms of the scaled variance of the multiplicity distribution is an intensive quantity, but is sensitive to the volume fluctuation of the system. The importance of the choice of narrow centrality bins and the corrections of centrality bin width effect for controlling volume fluctuations have been discussed. It is observed that the mean and width of the multiplicity distributions monotonically increase as a function of increasing centrality at all collision energies, whereas the multiplicity fluctuations show minimal variations with centrality. The beam energy dependence shows that the multiplicity fluctuations have a slow rise at lower collision energies and remain constant at higher energies.

nucl-ex↗

arXiv2016

Specific Heat of Matter Formed in Relativistic Nuclear Collisions

We report the excitation energy dependence of specific heat (\cv) of hadronic matter at freeze-out in Au+Au and Cu+Cu collisions at the Relativistic Heavy Ion Collider energies by analyzing the published data on event-by-event mean transverse momentum (\meanpt) distributions. The \meanpt~distributions in finite \pt~ranges are converted to distributions of effective temperatures, and dynamical fluctuations in temperature are extracted by subtracting widths of the corresponding mixed event distributions. The heat capacity per particle at the kinetic freeze-out surface is presented as a function of collision energy, which shows a sharp rise in \cv~below \sNN~=~62.4~GeV. We employ the Hadron Resonance Gas (HRG) model to estimate \cv~at the chemical and kinetic freeze-out surfaces. The experimental results are compared to the HRG and other theoretical model calculations. HRG results show good agreement with data. Model predictions for \cv~at the Large Hadron Collider energy are presented.

nucl-ex↗

arXiv2015

Characterization of relativistic heavy-ion collisions at the Large Hadron Collider through temperature fluctuations

We propose to characterize heavy-ion collisions at ultra-relativistic energies by using fluctuations of energy density and temperature. Temperature fluctuations on an event-by-event basis have been studied both in terms of global temperature of the event, and locally by constructing fluctuation maps in small phase space bins in each event. Global temperature fluctuations provide an estimation of the specific heat of the system. Local temperature fluctuations of the event may be ascribed to the remnants of initial energy density fluctuations. Together these two observables give an insight into the system created in heavy-ion collisions and its evolution. Event-by-event hydrodynamic calculations indeed provide adequate theoretical basis for understanding the origin of the fluctuations. We demonstrate the feasibility of studying global and local temperature fluctuations at the Large Hadron Collider energy by the use of AMPT event generator.

nucl-ex↗