arXiv subjects

Saraswati Pandey

Publications and source records attributed to Saraswati Pandey.

13 recordsLinked to original sources

arXiv2026

Markov chain Monte Carlo (MCMC) based Likelihood Extraction of Chiral-Odd Compton Form Factors from Deeply Virtual Exclusive Experiments

We present a likelihood analysis of observables in deeply virtual exclusive meson production off the proton. The study uses experimental data for cross sections together with beam and target spin asymmetries measured in the unpolarized beams and unpolarized as well as longitudinally polarized target configurations at Jefferson Lab Halls A and B. For a fixed kinematic bin defined by $(Q^2, x_B, t,ε)$, we derive a joint likelihood for the twist-two chiral-odd helicity amplitudes and the corresponding Compton Form Factors (CFFs), that parameterize the underlying QCD scattering amplitude. The joint likelihood analysis of cross-section and Asymmetry data strongly constrains the CFF parameter space beyond the either of the measurements studied alone. Markov chain Monte Carlo (MCMC) methods are employed to explore the full parameter space, extracting the parameter uncertainties, correlations and credible intervals.

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arXiv2026

Neural Network Representation of Generalized Parton Distributions (NNGPD)

We present a neural-network-based framework for modeling generalized parton distributions, referred to as NNGPD, in which GPDs are represented as flexible functions constrained through physically motivated integral relations. In this approach, experimental and theoretical information is incorporated into the training procedure via loss functions enforcing convolution integrals that define Compton form factors, as well as Mellin moments related to generalized form factors accessible in lattice QCD. This formulation reflects the inverse-problem character of GPD phenomenology without assuming a specific functional ansatz. As a proof of concept, we benchmark the NNGPD framework using a phenomenological spectator-based GPD model, from which synthetic training data for Compton form factors and Mellin moments are generated. The neural network is trained solely on these aggregate observables, and the resulting GPDs are compared directly with the underlying model distributions in a closure-type test. We find that the neural-network representation reproduces the main features of the GPDs over the relevant kinematic domain, despite being constrained only by their integral projections. This study demonstrates the viability of neural-network representations of GPDs constrained by global physical observables and provides a basis for future phenomenological applications combining experimental measurements of deeply virtual Compton scattering, including those anticipated at the Electron Ion Collider, with lattice QCD inputs for Mellin moments and generalized form factors.

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arXiv2025

Connected and disconnected contributions to nucleon form factors and parton distributions

Using the framework of generalized parton distribution, we provide a unified interpretation of the connected and disconnected contributions from the ab-initio Euclidean path-integral formulation of the hadronic tensor in both the nucleon elastic form factors and the parton distribution functions. We develop a phenomenology to elucidate non-perturbative contributions to deep inelastic structure functions, which can be extended to observables in heavy-ion collisions probing baryon junctions.

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arXiv2025

Updated flexible global parametrization of generalized parton distributions from elastic and deep inelastic inclusive scattering data

An updated flexible parametrization of the generalized parton distributions in the quark, antiquark and gluon sectors is presented using constraints from high precision electron nucleon deep inelastic scattering data, as well as from the $u$, $d$ quark and gluonic contributions to the nucleon electromagnetic elastic form factors. The latter include recently updated lattice QCD moment calculations. The generalized parton distributions in the vector sector are $H$ and $E$. We rigorously constrain the partonic components, $H_{u_v}$, $H_{d_v}$, $H_{\bar{u}}$, $H_{\bar{d}}$, $H_{\bar{s}}$ and $H_{g}$, and the analogous quantities for $E$, with proper uncertainty quantification. These distributions obey leading order perturbative QCD evolution equations in $α_S$. Parametric forms at the initial scale, $Q_o^2 = 0.58$ $\mathrm{GeV}^2$, for both quarks and gluon distributions are presented as a function of the relevant kinematic variables, namely, the parton momentum fraction, $x$, the skewness, $ξ$, and the invariant, $t$. We also present the Compton form factors entering the deeply virtual Compton scattering process in the kinematic regimes for both fixed target and electron-ion collider settings.

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arXiv2025

Likelihood and Correlation Analysis of Compton Form Factors for Deeply Virtual Exclusive Scattering on the Nucleon

A likelihood analysis of the observables in deeply virtual exclusive photoproduction off a proton target, $ep \rightarrow e' p' γ'$, is presented. Two processes contribute to the reaction: deeply virtual Compton scattering, where the photon is produced at the proton vertex, and the Bether-Heitler process, where the photon is radiated from the electron. We consider the unpolarized process for which the largest amount of data with all the kinematic dependences are available from corresponding datasets with unpolarized beams and unpolarized targets from Jefferson Lab. We provide and use a method which derives a joint likelihood of the Compton form factors, which parametrize the deeply virtual Compton scattering amplitude in QCD, for each observed combination of the kinematic variables defining the reaction. The unpolarized twist-two cross section likelihood fully constrains only three of the Compton form factors (CFFs). The impact of the twist-three corrections to the analysis is also explored. The derived likelihoods are explored using Markov chain Monte Carlo (MCMC) methods. Using our proposed method we derive CFF error bars and covariances. Additionally, we explore methods which may reduce the magnitude of error bars/contours in the future.

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arXiv2025

Pseudorapidity density, transverse momentum spectra, and elliptic flow studies in Xe-Xe collision systems at $\rm{\sqrt{s_{NN}} = 5.44 TeV}$ using the HYDJET++ model

In this paper, we present a systematic study of Xe--Xe collisions at $\sqrt{s_{\mathrm{NN}}} = 5.44$~TeV center-of-mass energy. We employ the Monte Carlo (hydrodynamics plus jets) HYDJET++ model to calculate the pseudorapidity distribution, transverse momentum ($p_{\mathrm{T}}$) spectra, and the elliptic flow ($v_2$) of charged hadrons with different parameters in two geometrical configurations: body-body and tip-tip types of Xe--Xe collisions. The kinematic ranges $0 < p_{\mathrm{T}} < 50~\mathrm{GeV}/c$ and $|η| < 0.8$ are considered in our study. Results are obtained for seven classes of centrality. For comparison, we have shown results from the AMPT model with the string-melting version. The results obtained for Xe--Xe collision systems for minimum bias at midrapidity match well with the experimental data from the ALICE and CMS Collaborations. We observe that the pseudorapidity density depends on the size and geometry of the colliding system. The centrality dependence of average transverse momentum ($\langle p_{\mathrm{T}} \rangle$) and average elliptic flow ($\langle v_2 \rangle$) is also observed. The charged hadron properties also show clear dependence on the geometrical configuration of the collisions. Our model results have been compared to results obtained from the AMPT model. The HYDJET++ model matches the experimental data more closely than the AMPT model, which tends to overpredict the data.

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arXiv2025

Higher-order anisotropic flow correlations in Xe-Xe collisions at $\mathrm{\sqrt{s_{NN}}= 5.44 TeV}$

By employing the Monte Carlo HYDJET++ model (HYDrodynamics plus JETs), we produce anisotropic harmonic flow coefficients $v_n$ ($n = 4$-$7$) in deformed Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44~\mathrm{TeV}$. These harmonics are measured with respect to a plane constructed using the lower-order Fourier harmonics $v_2$ and $v_3$, produced using the reaction plane method. The cross-talk between elliptic and triangular flows in the model generates both even and odd higher-order harmonics. By combining analyses of higher harmonics with those of $v_2$ and $v_3$, one can eliminate uncertainties in modeling anisotropic flow from initial conditions and define quantities that involve only nonlinear hydrodynamic response coefficients. In this context, we study the individual response of higher-order flow coefficients to the lower-order ones through a power-law scaling technique of the form $v_n / v_m^m$, as a function of collision centrality. We report that the higher-order flow coefficients $v_n$ ($n = 4$-$7$) exhibit strong centrality dependence and are significantly correlated with the elliptic and triangular flow. The results are compared with data from recent ALICE, ATLAS, and CMS experiments at the LHC.

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arXiv2025

Study of octupole deformations in Pb-Pb collisions at 5.02 TeV

In this letter, we present the study of the role of octupole deformation in non-spherical nuclei in most-central Pb--Pb collisions at the LHC energy regime. The sensitivity of octupole deformation $β_3$ to the QGP observables is presented by employing the Monte Carlo HYDJET++ model. Motivated by the discrepancies in the $v_2$-to-$v_3$ puzzle found in Pb--Pb collisions and the low-energy nuclear structure calculations of nuclear deformation, we studied the first basic observables necessary for any study in heavy-ion collisions. Using the HYDJET++ framework, we calculate the pseudorapidity distribution, transverse momentum ($p_{\mathrm{T}}$) spectra, and average anisotropic flow ($v_2$ and $v_3$) of primary charged hadrons with different parameters in two geometrical configurations: body-body and tip-tip types of Pb--Pb collisions. The kinematic ranges $0 < p_{\mathrm{T}} < 20~\mathrm{GeV}/c$ and $|η| < 0.8$ are considered. We observe that the charged hadron multiplicity and transverse momentum spectra are dependent on the strength of the octupole deformation parameter. The $\langle v_2 \rangle$ and $\langle v_3 \rangle$ in body-body collisions show a weak positive correlation with $β_3$, while the average anisotropic flow in tip-tip collisions is weakly correlated with $β_3$ in the most-central collision region.

hep-ph↗

arXiv2025

Beam energy dependence of transverse momentum distribution and elliptic flow in Au-Au collisions using HYDJET++ model

In this work, we present the particle ratios, transverse momentum spectra, and elliptic flow ($v_2$) of $π^\pm,k^\pm,$ $p$, and $\bar{p}$ in Au-Au collisions at $\sqrt{s_{NN}}=$ 62.4, 39.0, 27.0, 19.6 and 11.5 GeV using HYDJET++ model. The particle ratios match the experimental data that validates the Cleymans-Reidlich parameterization of freeze-out parameters at lower beam energies under the HYDJET++ framework. The lower collision energies produce a system of high baryon chemical potential ($μ_B$) and have a lower inelastic cross section. The interplay between these effects affects the overall shape of the $p_T$ spectra. The HYDJET++ model calculations for $p_T$ spectra agree well with the available experimental data. The invariant yield ratio of central and peripheral collisions is independent of beam energy. The elliptic flow is calculated based on the scaling between initial and final azimuthal spatial anisotropy ($k$). This interpretation of $v_2$ successfully describes the experimental data for all the collision energies studied in this work. The positive correlation of $k$ with beam energy leads to a small $v_2$ at lower collision energies. The hadrons containing strange quarks tend to have smaller values of $k$ than the non-strange hadrons.

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arXiv2023

Predicting Quadrupole deformation via anisotropic flow and transverse momentum spectra in isotopic $\mathbf{\prescript{128-135}{54}{\mathrm{Xe}}}$ collisions at LHC

In the hydrodynamical description of heavy-ion collisions, the elliptic flow $\mathrm{v_{2}}$ and triangular flow $\mathrm{v_{3}}$ are sensitive to the quadrupole deformation $\mathrm{β_{2}}$ of the colliding nuclei. We produce $\mathrm{v_{2}}$ and $\mathrm{v_{3}}$ ratios qualitatively and quantitatively in most-central Xe-Xe collisions at 5.44 TeV. By employing HYDJET++ model, we study the sensitivity of anisotropic flow coefficients and mean transverse momentum to the quadrupole deformation and system-size in isotopic Xe-Xe collisions. Flow observables strongly depend on the strength of nucleon-nucleon scattering occuring in even-A and odd-A nuclei. Flow for odd-A nuclei is suppressed in comparison to flow in even-A collisions. There exists a linear inter-dependence between $\mathrm{p_{T}}$ integrated anisotropic flow and nuclear deformation. Mean transverse momentum signifies the fireball temperature in body-body and tip-tip collisions. There exists a negative linear correlation of $\mathrm{\langle p_{T} \rangle}$ with collision system-size and a positive correlation with nuclear deformation. Flow measurements in high-energy, heavy-ion collisions using isotopic collision systems, offer a new precision tool to study nuclear structure physics. Observation of nuclear structure properties like nuclear deformation in a heavy-ion collision such as this would be very interesting.

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arXiv2023

Higher flow harmonics of strange hadrons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV with HYDJET++ model

Using the HYDJET++ model, we measure the higher-order flow harmonics $v_{n}$(n=2,3,4) of (multi-) strange hadrons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. We have compared our model results and experimental data at RHIC and LHC energies. The model reproduces the higher flow harmonics of (multi-) strange hadrons as a function of $p_{T}$, centrality, and quark content. We have studied and discussed mass ordering of flows $v_{n}$(n=2,3,4) among $π^{+}+π^{-}$, $K^{-}+K^{+}$, $K_{s}^{0}$, $p+\overline{p}$, $Λ+\overlineΛ$, $Ξ^{-}+\overlineΞ^{+}$, $Ω^{-}+\overlineΩ^{+}$ at low $p_{T}$ and the baryon-meson grouping at intermediate $p_{T}$. NCQ scaling using the HYDJET++ model and its comparison with experimental results at RHIC and LHC energies have also been discussed. Study of flow harmonics behaviour in RHIC and LHC energy regimes will provide an additional insight into the dynamics of anisotropic flow and the effect of radial flow expansion in the system.

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arXiv2022

Transverse momentum spectra and suppression of charged hadrons in deformed Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV using HYDJET++ model

In this study, we systematically investigate deformed Xe-Xe collisions at 5.44 TeV center of mass energy. We exploit the Monte Carlo HYDJET++ model to compute transverse momentum ($p_{T}$) distribution, nuclear modification factor $R_{AA}$ and relative suppression in terms of $R_{CP}$ as a function of transverse momentum and centrality of collision of charged hadrons in body-body and tip-tip geometrical configurations, respectively. We have compared HYDJET++ model results to those from ALICE experimental data and AMPT model (String-Melting version) results. Minimum bias Xe-Xe collisions show a suitable match with ALICE experimental data at midrapidity. Average transverse momentum ($\langle p_{T} \rangle$) show strong centrality dependence. The contribution of hard parton scatterings to the total charged hadron yield is discussed. Both nuclear modification factor $R_{AA}$ and relative suppression $R_{CP}$ show a clear dependence on centrality as well as transverse momentum. The charged hadron observables show a clear dependence on the geometrical configuration of the collisions. HYDJET++ model justifies experimental data more closely than the AMPT model.

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arXiv2021

Anisotropic flow and correlations between azimuthal anisotropy Fourier harmonics in Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV under HYDJET++ framework

The study of anisotropic harmonic flow coefficients $ v_{n}$(n=2,3,4) is performed in Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV under Monte Carlo HYDJET++ model (HYDrodynamics plus JETs) framework. Anisotropic flow of identified particles and correlation between the azimuthal harmonic flow amplitudes is presented. Here, we have considered body-body and tip-tip type of geometrical configurations for Xe-Xe collision systems. The kinematic ranges $|η|<0.8$, $0 2$ are considered. The results have been shown for seven classes of centrality and compared with the ALICE experimental data. The anisotropic flow of identified charged particles show a strong centrality dependence. Mass ordering is observed for $v_{2},v_{3}$ and $v_{4}$. Mass ordering is different for different ranges of transverse momentum $p_{T}$. Strong correlation is observed between $v_{3}-v_{2}$, $v_{4}-v_{2}$, and $v_{4}-v_{3}$. Such correlation is centrality dependent and is different in different centrality windows. The anisotropic flow coefficients show a clear dependence on the total charged particle multiplicity. HYDJET++ model justifies experimental data well enough.

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