arXiv subjects

Sadhana Dash

Publications and source records attributed to Sadhana Dash.

At least 19 recordsLinked to original sources

arXiv2026

Electromagnetic response of a relativistic drifting plasma

We investigate the charge transport properties of a relativistic drifting plasma using the kinetic theory within the relaxation time approximation. The collective drift induced by electromagnetic fields is described in terms of a suitably modified distribution function. The analysis is done for both constant and time dependent field configurations. For constant electromagnetic fields, we obtain the Hall drift current that arises from the transverse motion of charged particles in electric and magnetic fields. Extending the framework to time dependent electric fields, we show that their temporal variations give rise to polarization drift, which significantly alters the structure of the induced current and introduces additional components along both the conventional drift and polarization directions. We present a quantitative estimate of the Hall drift and polarization induced contributions in the quark gluon plasma and study the temperature dependence of the associated charge transport coefficients in the QCD.

hep-ph↗

arXiv2026

Relative transverse activity as a probe of collectivity-like long-range correlations in pp collisions at $\sqrt{s}=13$ TeV

Understanding the origin of collectivity-like signatures in small collision systems is a central open question in high-energy nuclear physics, and two-particle correlation functions offer unique sensitivity to the underlying-event (UE) dynamics that may drive such behavior in proton--proton (pp) collisions. In this work, the two-particle number ($R_{2}$) and transverse-momentum ($P_{2}$) correlation functions are studied in pp collisions at $\sqrt{s}=13$ TeV using PYTHIA 8, for final state charged hadrons within $|\eta|<0.8$ and $0.2<p_{\rm T}<2.0$ GeV/$c$, with events classified by the relative transverse activity $R_{\mathrm{T}}$ to probe how UE activity shapes correlation structures in the soft-QCD-dominated regime. A collectivity-like long-range near-side component is observed in the charge-independent correlator $R_{2}^{\mathrm{CI}}$ exclusively for the highest $R_{\mathrm{T}}$ class ($2.5 < R_{\mathrm{T}} \leq 5.0$), while no corresponding structure appears in the charge-dependent correlators. This indicates that enhanced UE activity, driven by multiple partonic interactions and color reconnection, can generate collectivity-like long-range correlations without hydrodynamic evolution. These findings establish $R_{\mathrm{T}}$ as a differential event classifier to provide a non-hydrodynamic baseline for interpreting such signatures in small-system measurements at the LHC.

hep-ph↗

arXiv2025

Electric, thermal and thermoelectric response of a hot pion gas in a time dependent background magnetic field

The prime focus of the work is to determine the electric, thermal and thermoelectric transport coefficients of a hot pion gas in the presence of time-dependent background magnetic fields. The thermoelectric effect is analyzed by examining the magneto-Seebeck and Nernst coefficients in the hot pionic medium under such conditions. Furthermore, the phenomenologically relevant elliptic flow coefficient, linked to the Knudsen number, is examined. The analysis reveals the significant impact of both the strength and time dependence of the magnetic field on the transport coefficients of the pionic medium. The results are analyzed in contrast to those obtained under a constant magnetic field.

hep-ph↗

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↗

arXiv2025

Deciphering the dynamics of nuclear collisions with elongated structure of $^{20}$Ne

We investigate the role of intrinsic nuclear geometry of $^{20}$Ne nucleus in particle production in small collision systems. Discrete geometrical representations of $^{20}$Ne, including bi-pyramidal $\alpha$-cluster structure in two different configurations along with NLEFT configurations, are implemented within the Monte Carlo Pythia8/Angantyr framework. The resulting particle production observables in $^{20}$Ne-$^{20}$Ne collisions at $\sqrt{s_{NN}}$ = 5.36 TeV are systematically compared with those obtained using conventional Woods-Saxon description as well as with the available hydrodynamic model calculations. We investigate the sensitivity of charged particle multiplicity, transverse momentum distributions and mean transverse momentum $\langle p_T \rangle$ to nuclear geometry, $\alpha$-clustering, and orientation effects of $^{20}$Ne nucleus. While explicit clustering and orientation dependence lead to a noticeable modifications in final state charged particle multiplicity, their impact on transverse momentum spectra and $\langle p_T \rangle$ remain modest in central collisions. The results highlight the role of intrinsic nuclear geometry and specific orientation of the colliding nuclei, providing insight into the dynamics of small systems in non-hydrodynamic particle production framework.

nucl-th↗

arXiv2025

Nonperturbative heavy quark diffusion coefficients in a weakly magnetized thermal QCD medium

In this work, the perturbative and non-perturbative contributions to the heavy quark (HQ) momentum ($\kappa$) as well as spatial ($D_s$) diffusion coefficients are computed in a weak background magnetic field. The formalism adopted here involves calculation of the in-medium potential of the HQ in a weak magnetic field, which then serves as a proxy for the resummed gluon propagator in the calculation of HQ self-energy ($\Sigma$). The self-energy determines the scattering rate of HQs with light thermal partons, which is subsequently used to evaluate $\kappa$ and $D_s$. It is observed that non-perturbative effects play a dominant role at low temperature. The spatial diffusion coefficient $2\pi T D_s$, exhibits good agreement with recent LQCD results. These findings can be applied to calculate the heavy quark directed flow at RHIC and LHC energies. An extension of this formalism to the case of finite HQ momentum has also been attempted.

hep-ph↗

arXiv2025

Effect of $\alpha$-clusters on particle production in O$-$O and p$-$O collisions at LHC energies

In the present work, O$-$O collisions at $\sqrt{s_{NN}}$ = 7 TeV and p$-$O collisions at $\sqrt{s_{NN}}$ = 9.9 TeV are studied using PYTHIA8/Angantyr model for heavy-ion collisions. The theoretically predicted $\alpha$-cluster structure of oxygen nucleus is implemented in the model to investigate the effect of initial configuration of oxygen nucleus on final state observables. The results obtained from $\alpha$-cluster structure are compared with those obtained from Woods-Saxon nuclear charge density distribution. The Angantyr model simulation showed that the radial distribution of oxygen nucleus in $\alpha$-cluster configuration is more compact in comparison to the Woods-Saxon distribution. The results on charged and identified particle pseudorapidity distribution is obtained in the two initial state configuration of the oxygen nucleus. The results demonstrated that the effect of initial geometrical configuration is more distinct in the non-central collisions in comparison to the central collisions for both O$-$O and p$-$O collisions.

hep-ph↗

arXiv2025

Event-by-event fluctuations of mean transverse momentum in proton-proton collisions at $\sqrt{s}$ = 13 TeV with PYTHIA8 and HERWIG7 models

Estimations of event-by-event mean transverse momentum ($\langle p_{\rm T} \rangle$) fluctuations are reported in terms of the integral correlator, $\langle \Delta p_{\rm T} \Delta p_{\rm T}\rangle$, and the skewness of event-wise $\langle p_{\rm T} \rangle$ distribution in proton$-$proton (pp) collisions at $\sqrt{s}=13$ TeV with the Monte Carlo event generators PYTHIA8 and HERWIG7. The final-state charged particles with transverse momentum ($p_{\rm T}$) and pseudorapidity ($\eta$) ranges $0.15 \leq p_{\rm T}\leq 2.0$ GeV/$c$ and $|\eta| \leq 0.8$ were considered for the investigation. The correlator, $\langle \Delta p_{\rm T} \Delta p_{\rm T}\rangle$, is observed to follow distinct decreasing trends with average charged particle multiplicity ($\langle N_{\rm ch} \rangle$) for the models. Furthermore, both models yield positive finite skewness in low-multiplicity events. Fluctuations are additionally studied using the transverse spherocity estimator ($S_{\rm 0}$) to understand the relative contributions of hard scattering (jets) and other soft processes to the observed fluctuations. Comparing model predictions for $\langle p_{\rm T} \rangle$ fluctuations provides valuable insight into the sensitivity of these fluctuations to hadronization and parton shower models. This is essential for a reliable interpretation of the fluctuation dynamics in pp collisions. Moreover, such comparisons would help to establish a crucial baseline for identifying and studying non-trivial fluctuations in heavy-ion collisions.

hep-ph↗

arXiv2025

Viscous effects of a hot QGP medium in time dependent magnetic field and their phenomenological significance

In this work, we have studied, for the first time, the impact of a realistic picture of a time dependent electric and magnetic field on the shear and bulk viscosities of the medium. Both the electric and magnetic fields are considered to be exponentially decaying with time, and the study is valid in the regime where the magnetic field strength is weak ($eB\ll T^2$). The evaluation has been done in the kinetic theory framework wherein we have solved the relativistic Boltzmann transport equation within the relaxation time approximation collision kernel. We have shown that the constant weak field results as well as the $B=0$ results in the literature can be obtained as special cases of our general results. We have observed that the shear and bulk viscosities increase with time or equivalently, decrease with the strength of the magnetic field. To connect these observations with experiments, we have calculated the thermalization time, shear viscosity to entropy ratio ($\eta /s$), and bulk viscosity to entropy ratio ($\zeta /s$).

hep-ph↗

arXiv2024

Simultaneous Estimation of Elliptic Flow Coefficient and Impact Parameter in Heavy-Ion Collisions using CNN

A deep learning based method with Convolutional Neural Network (CNN) algorithm is developed for simultaneous determination of the Elliptic Flow coefficient ($v_{2}$) and the Impact Parameter in Heavy-Ion Collisions at relativistic energies. The proposed CNN is trained on Pb$-$Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with minimum biased events simulated with the AMPT event generator. A total of twelve models were built on different input and output combinations and their performances were evaluated. The predictions of the CNN models were compared to the estimations of the simulated and experimental data. The deep learning model seems to preserve the centrality and $p_{T}$ dependence of $v_{2}$ at the LHC energy together with predicting successfully the impact parameter with low margins of error. This is the first time a CNN is built to predict both $v_{2}$ and the impact parameter simultaneously in heavy-ion system.

hep-ph↗

arXiv2024

Investigating the Seebeck effect of the QGP medium using a novel relaxation time approximation model

The highly energetic particle medium formed in the ultrarelativistic heavy ion collision displays a notable difference in the temperatures between its central and peripheral regions. This temperature gradient can generate an electric field within the medium, a phenomenon referred to as the Seebeck effect. We have estimated the Seebeck coefficient for a dense quark-gluon plasma medium by using the relativistic Boltzmann transport equation in the recently developed novel relaxation time approximation (RTA) model within the kinetic theory framework. This study explores the Seebeck coefficient of individual quark flavors as well as the entire partonic medium. Our observation indicates that, for given current quark masses, the magnitude of the Seebeck coefficient for each quark flavor as well as for the partonic medium decreases as the temperature rises and increases as the chemical potential increases. Furthermore, we have investigated the Seebeck effect by considering the partonic interactions within the quasiparticle model. In addition, we have presented a comparison between our findings and the results of the standard RTA model. We have observed that the Seebeck coefficient of the QGP medium gets conspicuously decreased in the novel RTA model as compared to that in the standard RTA model. A decreased Seebeck coefficient in the novel RTA model describes a smaller magnitude of induced electric field in the medium than that estimated by the standard RTA model. However, the rate of decline gets gradually smaller as the medium gets hotter for both the current quark mass scenario and the quasiparticle mass scenario. It is also found that, in the noninteracting case, the Seebeck coefficient possesses a slightly negative value in the high temperature region, unlike the quasiparticle description, where the Seebeck coefficient remains positive for the entire temperature range.

hep-ph↗

arXiv2024

Probing the onset of hydrodynamization in peripheral p-Pb collisions at $\sqrt{s_{NN}} =$ 5.02 TeV

An attempt has been made to estimate the minimum size of the de-confined matter of Quark-Gluon Plasma (QGP) in small systems like p-Pb system that could be satisfactorily modeled with low-order hydrodynamics. The variation of second order transport coefficient of second order relativistic viscous hydrodynamics, the shear relaxation time has been utilized to study the sensitivity of experimental observables like elliptic flow coefficient. A representative system of p-Pb collisions at $\sqrt{s_{NN}} =$ 5.02 TeV, simulated with the state-of-art framework of JETSCAPE event generator was used to study the variation of elliptic flow coefficient for peripheral collisions. The soft sector dynamics was simulated using an initial condition, a pre-equilibrium stage, hydrodynamics and a hadron afterburner. The transverse momentum spectra and rapidity distribution was obtained for light flavored hadrons and compared with the experimental data. The increase in elliptic flow fluctuations indicate breakdown of fluid behavior at $dN/dy \approx 14$ for p-Pb collision at $\sqrt{s_{NN}} =$ 5.02 TeV.

hep-ph↗

arXiv2024

Quark Flavor Balancing in Nuclear Collisions

The notion of charge balance function, originally designed to study the evolution of charge production in heavy-ion collisions, is extended to consider quark flavor balancing. This extension is considered based on simulations performed with the PYTHIA 8 event generator in the context of pp collisions at $\sqrt{s} = 13.6$ TeV but can be trivially applied to any other scenario and implemented in measurements of correlated particle production in pp, pA, and AA collisions at colliders. Correlation of selected flavor balancing pairs are examined as function of the produced charged particle multiplicity. One finds that the amplitude of the correlations increases monotonically with the number of balanced flavors and the actual flavor content of correlated particles.

hep-ph↗

arXiv2024

Monte-Carlo Study Of Higher-Order Cumulants of Net-Particle Distributions in $p+p$ Collisions at $\sqrt{s}$ = 13 TeV

Measurement of higher order cumulants of the distributions of conserved quantities, like net-charge, net-baryon and net-strangeness in heavy-ion collisions, is proposed as a sensitive tool to determine the freeze-out parameters and the nature of phase transitions at the LHC energies. Baseline measurements for heavy-ion collisions are essential to understand the experimental measurements. Recently, several experimental observations have shown some QGP-like scenarios in small systems (pp collisions). We report the first Monte-Carlo study of the measurements of cumulants and their ratios for net-charge, net-hadron, net-kaon, net-baryon, and net-proton distributions in pp collisions at $\sqrt{s}$=13 TeV using pQCD models like Pythia8 and Herwig. We also discuss the effect of different particle production mechanisms on the higher-order cumulants. This simulation study will serve as a baseline for future measurements at the LHC. Furthermore, it will shed more light on the measurement of cumulants and the connection between small systems and heavy-ion collisions at the LHC.

nucl-ex↗

arXiv2024

Study of transport properties of a hot and dense QCD matter using a novel approximation method

We have studied the charge and the heat transport properties of a hot and dense QCD matter by solving the relativistic Boltzmann transport equation using a novel approximation method. Following the recently developed novel relaxation time approximation (RTA) model, we have proposed a novel Bhatnagar-Gross-Krook (BGK) model with a modified collision integral to carry out the aforementioned study. We have also compared our findings with the results of the novel RTA, the standard RTA and the standard BGK models. Our observation shows that the novel collision integrals for both the RTA and BGK models decrease the charge and the heat transport phenomena in the medium, as evidenced by the reduced values of the transport coefficients, such as the electrical conductivity and the thermal conductivity, when compared to the standard RTA and standard BGK models. Furthermore, certain observables, such as the thermal diffusion constant and the Lorenz number have been explored using the novel approaches of the aforesaid models. We have found an overall decreasing trend of the thermal diffusion constant with the temperature in the novel BGK model, similar to the novel RTA model, but the magnitude remains higher throughout the temperature range. However, the magnitude of the thermal diffusion constant in the proposed novel BGK model remains lower than its value in the standard BGK model. The magnitude of the Lorenz number in the novel BGK model remains higher than that in the standard BGK model, but it is lower than that in the novel RTA model. We have also observed that the Lorenz number in all cases has an increasing trend at low temperatures, showing a violation of the Wiedemann-Franz law, whereas at high temperatures, it becomes saturated. The Lorenz number remaining above unity indicates that the thermal conductivity prevails over the electrical conductivity in the aforesaid models.

hep-ph↗

arXiv2024

Charged particle multiplicity fluctuation in $A-A$ collisions at RHIC and LHC energies using Angantyr model

Event-by-event fluctuations of the charged particle multiplicity are studied for a wide range of centralities for Au$-$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, Pb$-$Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV and 5.02 TeV using the Pythia 8 Angantyr model. The centrality dependence of $ω_{ch}$ observable, which quantifies the fluctuations in terms of scaled variance is studied for different pseudorapidity ranges and has been compared with those obtained from a simple participant superposition model. The $ω_{ch}$ was found to be lower than the expectations from the participant model. The estimate would act like a baseline for current and future measurements of event-by-event fluctuations in the charged particle multiplicities in systems at LHC energies where no de-confined medium of quarks and gluons are formed.

hep-ph↗

arXiv2024

Study of identified particle production as a function of transverse event activity classifier, $S_{T}$ in p$-$p collisions

A new observable, $S_{T}$, is introduced in terms of the sum of the transverse momentum of charged particles ($\sum_{i} p_{T_{i}}$ ) produced in proton proton (p$-$p) collisions at LHC energies to probe the underlying events (UE). The UE are defined as those aspects of proton-proton collisions that are not attributed to the primary hard scattering process, but rather to the accompanying interactions of the rest of the proton. The conventional approach of studying underlying events is usually carried out by defining topological regions with respect to the leading particle in an event. The transverse region is generally sensitive to UE and various classifiers have been used to discriminate the extent of UE activity regions. The production of identified particles like $π^{\pm}$, $K^{\pm}$, p , $K_{S}^{0}$, and $Λ^{0}$ are studied in different ranges of transverse activity classifier in p$-$p collisions at $\sqrt{s} = 13 $ TeV using pQCD inspired PYTHIA 8 event generator. A comparative analysis of the identified particle spectra, mean multiplicity and mean transverse momentum has been carried out with respect to $S_{T}$ and the performance of this new observable is gauged by comparing the results with previously defined $R_{T}$ observable.

hep-ph↗

arXiv2024

Analyzing the transport coefficients and observables of a rotating QGP medium in kinetic theory framework with a novel approach to the collision integral

In the present work, we have studied how the rotation of the QGP medium affects the transport coefficients and observables in heavy ion collisions. For the noncentral collisions, although most of the angular momentum gets carried away by the spectators, there still remains a finite angular momentum with a finite range of angular velocity, which thus incites rotation in the produced matter. As a result, various properties of the QGP medium including its transport properties are most likely to be modulated by the rotation. We have calculated the transport coefficients and observables, such as the electrical conductivity, the thermal conductivity, the Knudsen number, the elliptic flow, the specific heat at constant pressure, the specific heat at constant volume, the trace anomaly, the thermal diffusion constant and the isothermal compressibility using the kinetic theory to see the effect of rotation on them. In particular, we have used the novel relaxation time approximation for the collision integral in the relativistic Boltzmann transport equation to derive the transport coefficients and compared them with their values in the relaxation time approximation within the kinetic theory approach in conjunction with the finite angular velocity. We have found that the emergence of angular velocity enhances the flow of charge and heat in the medium. Further, as compared to the relaxation time approximation, the electrical and the thermal conductivities have smaller values in the novel relaxation time approximation and these differences between the conductivities in the said approximations are more pronounced at high temperatures than at low temperatures. Furthermore, all the aforesaid observables are found to be sensitive to the rotation of the QGP medium.

hep-ph↗