arXiv subjects

Renu Bala

Publications and source records attributed to Renu Bala.

At least 19 recordsLinked to original sources

arXiv2026

Isotopic effect on collisional widths and shifts of Hg clock transition induced by cold Rb atoms

We study the isotopic dependence of collisional widths and shifts of the Hg clock transition $^1$S$_0$-$^3$P$_0$ perturbed by the Rb atoms in the temperature range from 1 nK to 1 K. For this purpose, we model the Born-Oppenheimer effective interaction potential by including the leading long-range van der Waals coefficients. For elastic collisions, we show the connection between the dependence of collision line shape parameters on the reduced mass of colliding partners as well as the variation of the scattering length in the excited and ground states of the Hg-Rb system in the $\upmu$K temperature range. We confront the full quantum scattering calculations with a semi-classical approximation for collisional widths and shifts. We show that the shape resonances in excited and ground scattering states lead to significant variations of collisional line shape parameters with the change of the reduced mass of colliding atoms. We also indicate the possible influence of inelastic collisions, which could lead to universal behavior and significantly affect the dependence of collisional broadening and shifting on the isotopic combination of colliding atoms.

physics.atom-ph↗

arXiv2026

Relativistic KRCI calculations of symmetry violating interaction constants for YbX (X: Cu, Ag and Au) molecules

The present work reports the parity ($\mathcal{P}$)-odd and time-reversal ($\mathcal{T}$)-odd interaction constants for the ground electronic state, X$^2\Sigma^{+}_{1/2}$, of YbX, X: Cu, Ag and Au molecules. The reported results have been calculated using the Kramers-restricted configuration interaction method limited to single and double excitations, in conjunction with relativistic core-valence double-, triple-, and quadruple-zeta quality basis sets, within a four-component relativistic framework. The computed results for the symmetry violating properties have been compared with the available results in the literature. Further, the parallel and perpendicular components of the hyperfine structure constants for the constituent atoms in YbX molecules are reported here for the first time.

physics.atom-ph↗

arXiv2025

Study of ground state electronic structure of XH$^+$ (X : Cd, Hg and Yb) molecular ions via coupled-cluster approach

The present work reports the spectroscopic parameters and molecular properties for the ground electronic state, $^1\Sigma^+$, of CdH$^+$, HgH$^{+}$, and YbH$^{+}$ molecular ions. We have used the state-of-the-art relativistic coupled cluster method together with the relativistic core-valence triple- and quadruple zeta quality basis sets for the calculation of structural parameters. The computed results have been extrapolated to the complete basis set limit using a two-point polynomial fit. The reliability of the results has been confirmed by their remarkable agreement with existing experimental and theoretical values. Further, we have calculated the relevant vibrational parameters by solving the vibrational Schr\"odinger equation using the potential energy curve and the permanent dipole moment curve of the electronic ground state. Subsequently, the lifetimes of the vibrational states have been determined by calculating the spontaneous and black-body radiation (BBR) induced transition rates. At room temperature, the lifetimes of the lowest ro-vibrational state ($v$ = $0$, $J$ = $0$) due to BBR-induced transitions are estimated to be $98.48$\,s for CdH$^+$, $204.85$\,s for HgH$^+$, and $1250.28$\,s for YbH$^+$. Additionally, the rotational energies within each vibrational state are also calculated in this work.

physics.atom-ph↗

arXiv2025

Charm production and fragmentation fractions at midrapidity in pp collisions at the LHC with ALICE

Heavy quarks, such as charm and beauty, possess masses significantly larger than the characteristic energy scale of Quantum Chromodynamics (QCD), and are thus predominantly produced in hard-scattering processes with large momentum transfer ($Q^{2}$). This makes them effective probes for verifying QCD calculations and investigating heavy-quark hadronization processes across various collision systems. Recent measurements of charm meson and baryon production in proton--proton (pp) collisions at the LHC have enabled, for the first time, a determination of the total charm production cross section, including contributions from all ground-state charm hadrons.Additionally, the fragmentation fractions of charm quarks into hadrons in pp collisions have been quantified.

hep-ex↗

arXiv2025

Ab initio calculations of diatomic constants and ro-vibrational parameters for the ground state of singly charged aluminium monohalides

We report electronic, vibrational, and rotational spectroscopic parameters for the ground state, X$^2\Sigma^{+}$, of singly charged aluminium monohalides, employing single-reference coupled-cluster theory with single and double excitations (CCSD) together with the relativistic basis sets. Higher order correlation effects coming from triple excitations are treated using perturbative CCSD(T) approach. Most of the molecular ions in the AlX$^+$ series, particularly barring the first two, have been studied here for the first time for their ground state electronic and vibrational structure. The vibrational parameters have been calculated by solving the vibrational Schr\"odinger equation utilizing potential energy curves and permanent dipole moment curves. Further, spontaneous and black-body radiation induced lifetimes have also been computed using relative energy separation and the transition dipole moments between the vibrational levels. The lifetimes of the lowest ro-vibrational states are found to be 10.63 s, 40.39 s, 23.13 s, 31.26 s, 13.43 s, and 8.08 s for the AlF$^+$, AlCl$^+$, AlBr$^+$, AlI$^+$, AlAt$^+$, and AlTs$^+$ ions, respectively. Furthermore, the rotational parameters such as Einstein coefficients and Franck-Condon factors for the lowest six vibrational states are also computed and reported in this work.

physics.atom-ph↗

arXiv2024

Relativistic coupled-cluster calculations for the molecular properties of AlX$^+$ (X: F, Cl, Br, I, At and Ts) ions

In this article, the molecular permanent electric dipole moments and components of static dipole polarizabilities for the electronic ground state of singly charged aluminum monohalides are reported. The coupled-cluster method by considering single and double excitations (CCSD) together with relativistic Dyall basis sets have been used to carry out these molecular property calculations. The contribution from triple excitations are incorporated through perturbative triples (CCSD(T)). The results from a series of progressively larger basis sets are extrapolated to the complete basis set limit. Further, the role of correlation and relativistic effects, and also the effect of augmentation over the considered basis sets on the valence molecular properties are studied. Our results are compared with those available in the literature.

physics.atom-ph↗

arXiv2024

Relativistic VQE calculations of molecular electric dipole moments on trapped ion quantum hardware

The quantum-classical hybrid variational quantum eigensolver (VQE) algorithm is among the most actively studied topics in atomic and molecular calculations on quantum computers, yet few studies address properties other than energies or account for relativistic effects. This work presents high-precision 18-qubit relativistic VQE simulations for calculating the permanent electric dipole moments (PDMs) of BeH to RaH molecules on traditional computers, and 6- and 12-qubit PDM computations for SrH on IonQ quantum devices. To achieve high precision on current noisy intermediate scale era quantum hardware, we apply various resource reduction methods, including Reinforcement Learning and causal flow preserving ZX-Calculus routines, along with error mitigation and post-selection techniques. Our approach reduces the two-qubit gate count in our 12-qubit circuit by 99.71%, with only a 2.35% trade-off in precision for PDM when evaluated classically within a suitably chosen active space. On the current generation IonQ Forte-I hardware, the error in PDM is -1.17% relative to classical calculations and only 1.21% compared to the unoptimized circuit.

physics.atom-ph↗

arXiv2019

Calculations of P and T -odd interaction constants of alkaline-earth monofluorides using KRCI method

We have reported the results of ab initio calculations of parity- and time- reversal -odd interaction constants for the ground state of alkaline-earth monofluorides. The Kramers-restricted configuration interaction method limited to single and double excitations in conjunction with the quadruple zeta quality basis sets have been employed to perform these 4-component relativistic calculations. The results are compared with the existing semi-empirical and other theoretical results, wherever available.

physics.atom-ph↗

arXiv2019

Exact ground-state properties of one-dimensional electron gas at high density

The dynamical response theory is used to obtain an analytical expression for the exchange energy of a quantum wire for arbitrary polarization and width. It reproduces the known form of exchange energy for 1D electron gas in the limit of infinitely thin cylindrical and harmonic wires. The structure factor for these wires are also obtained analytically in the high-density or small $r_s$ limit. This structure factor enables us to get the {\it exact} correlation energy for both the wires and demonstrates that there are at least two methods to get the ideal Coulomb limit in one dimension. The structure factor and the correlation energy are found to be independent of the way the one-dimensional Coulomb potential is regularized. The analytical expression for the pair correlation function is also presented for small distances and provides a justification for the small $r_s$ expansion as long as $r_s< \frac{3}{2} \left(\frac{π^2}{π^2+3} \right)=1.15$.

cond-mat.str-el↗

arXiv2018

Ab initio calculations of permanent dipole moments and dipole polarizabilities of alkaline-earth monofluorides

The ground-state permanent dipole moments (PDMs) and molecular dipole polarizabilities (DPs) of open-shell alkaline-earth monofluorides, and atomic DPs of alkaline-earth- and fluorine atoms are reported at the Kramers-restricted configuration interaction level of theory limited to single- and double excitations (KRCISD), using the finite-field approach. Sufficiently large basis sets such as quadruple-zeta (QZ) and augmented-QZ basis sets together with the generalized active space technique is employed to carry out the field dependent energy calculations at the KRCISD level. The PDMs and the components of DPs are extracted from the linear- and quadratic fit of energies against perturbative electric field, respectively. Accuracy of the present calculations for the electronic properties is examined by comparison with the measurements and calculations where ever available.

physics.atom-ph↗

arXiv2018

Calculations of electronic properties and vibrational parameters of alkaline-earth lithides: MgLi^+ and CaLi^+

The ^1Σ^+ electronic ground states of MgLi^+ and CaLi^+ molecular ions are investigated for their spectroscopic constants and properties such as the dipole- and quadrupole moments, and static dipole polarizabilities. The quadrupole moments and the static dipole polarizabilities for these ions have been calculated and reported here, for the first time. The maximum possible error bars, arising due to the finite basis set and the exclusion of higher correlation effects beyond partial triples, are quoted for reliability. Further, the adiabatic effects such as diagonal Born-Oppenheimer corrections are also calculated for these molecules. The vibrational energies, the wavefunctions, and the relevant vibrational parameters are obtained by solving the vibrational Schrödinger equation using the potential energy curve and the permanent dipole moment curve of the molecular electronic ground state. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the lifetimes of the vibrational states. The lifetime of rovibronic ground state for MgLi^+ , at room temperature, is found to be 2.81 s and for CaLi^+ it is 3.19 s. It has been observed that the lifetime of the highly excited vibrational state is several times larger than (comparable to) that of the vibrational ground state of MgLi^+ (CaLi^+ ). In addition, a few low-lying electronic excited states of Σ and Π symmetries have been investigated for their electronic and vibrational properties, using EOM-CCSD method together with the QZ basis sets.

physics.atom-ph↗

arXiv2018

Conditions where RPA becomes exact in the high-density limit

It is shown that in $d$-dimensional systems, the vertex corrections beyond the random phase approximation (RPA) or GW approximation scales with the power $d-β-α$ of the Fermi momentum if the relation between Fermi energy and Fermi momentum is $ε_{\rm f}\sim p_{\rm f}^β$ and the interacting potential possesses a momentum-power-law of $\sim p^{-α}$. The condition $d-β-α<0$ specifies systems where RPA is exact in the high-density limit. The one-dimensional structure factor is found to be the interaction-free one in the high-density limit for contact interaction. A cancellation of RPA and vertex corrections render this result valid up to second-order in contact interaction. For finite-range potentials of cylindrical wires a large-scale cancellation appears and found to be independent of the width parameter of the wire. The proposed high-density expansion agrees with the Quantum Monte Carlo simulations.

cond-mat.str-el↗

arXiv2017

Dependence of structure factor and correlation energy on the width of electron wires

The structure factor and correlation energy of a quantum wire of thickness $b\ll a_B$ are studied in random phase approximation and for the less investigated region $r_s<1$. Using the single-loop approximation, analytical expressions of the structure factor have been obtained. The exact expressions for the exchange energy are also derived for a cylindrical and harmonic wire. The correlation energy $ε_c$ is found to be represented by $ε_c (b,r_s)= \frac{α(r_s)}{b} + β(r_s)\; ln(b) + η(r_s)$, for small $b$ and high densities. For a pragmatic width of the wire, the correlation energy is in agreement with the quantum Monte Carlo simulation data.

cond-mat.quant-gas↗

arXiv2017

Ab initio calculations of spectroscopic constants and properties of BeLi +

We have calculated the ground state spectroscopic constants and the molecular properties, of a molecular ion BeLi + , such as dipole moment, quadrupole moment and dipole polarizability at different levels of correlation: many-body perturbation theory (MP2), coupled cluster method with single and double excitations (CCSD) and CCSD with perturbative triples (CCSD(T)). The correlation consistent polarized valence cc-pVXZ (X=D, T, Q) basis sets and also their augmented counterparts are used together with the non-relativistic and relativistic Hamiltonians. The results are extrapolated to the complete basis set limit (CBS) using exponential-Gaussian function. Thus, accurate and reliable results for BeLi + with the most conservative error estimates on them are reported.

physics.atom-ph↗

arXiv2016

Heavy-ion physics at the LHC: Review of Run I results

In this work we review what we consider are, some of the most relevant results of heavy-ion physics at the LHC. This paper is not intended to cover all the many important results of the experiments, instead we present a brief overview of the current status on the characterization of the hot and dense QCD medium produced in the heavy-ion collisions. Recent exciting results which are still under debate are discussed too, leading to intriguing questions like whether we have a real or fake QGP formation in small systems.

hep-ex↗

arXiv2013

Open-charm production as a function of charged particle multiplicity in pp collisions at \sqrt{s}=7 TeV with ALICE

Heavy quarks (charm and beauty) are an effective tool to investigate the properties of the Quark-Gluon Plasma created in heavy-ion collisions as they are produced in initial hard scattering processes and as they experience all the stages of the medium evolution. The measurement of heavy-flavour production cross sections in pp collisions at the LHC, besides providing a reference for heavy-ion studies, allows one to test perturbative QCD calculations. A brief review of ALICE results on the production of heavy-flavoured hadrons measured from fully reconstructed hadronic decay topologies in pp collisions at \sqrt{s} = 7 TeV is presented. Furthermore, heavy-flavour production was also studied as a function of the particle multiplicity in pp collisions. This could provide insight into multi-parton scatterings. A measurement of the inclusive J/ψ yield as a function of the charged-particle pseudorapidity density was performed by the ALICE Collaboration at the LHC in pp collisions at \sqrt{s} = 7 TeV. An increase of the J/ψ yield with increasing multiplicity was observed. In this context, the study of the yield of D mesons as a function of the charged-particle multiplicity could provide a deeper insight into charm-quark production in pp collisions. We will present the first results obtained for prompt D0, D+, and D*+ mesons using hadronic decay channels at midrapidity in pp collisions \sqrt{s}=7 TeV as a function of the charged-particle multiplicity. The prompt D-meson yields as a function of multiplicity are measured in different pT intervals. These yields will be compared to the results obtained for inclusive and non-prompt J/ψ.

nucl-ex↗

arXiv2012

Heavy flavour and quarkonia production measurement in pp and Pb-Pb collisions at LHC energies with the ALICE detector

ALICE is the dedicated heavy-ion experiment at the LHC. Its main physics goal is to study the properties of strongly-interacting matter at conditions of high energy density and high temperature expected to be reached in central Pb--Pb collisions. Charm and beauty quarks are well-suited tools to investigate this state of matter since they are produced in initial hard scatterings and are therefore generated early in the system evolution and probe its hottest, densest stage. ALICE recorded pp data at $\rm \sqrt{s}$ = 7 TeV and 2.76 TeV and Pb--Pb data at $\rm \sqrt{s}_{\rm NN}$=2.76 TeV in 2010 and 2011. We present the latest results on heavy flavour and J/$ψ$ production at both central and forward rapidity.

nucl-ex↗

arXiv2012

Inclusive Open Charm Production in pp and Pb-Pb collisions with the ALICE Detector

ALICE is the dedicated heavy-ion experiment at the LHC. Its main physics goal is to study the properties of strongly-interacting matter at conditions of high energy density (>10 GeV/ fm^3) and high temperature (> 0.5 GeV) expected to be reached in central Pb-Pb collisions. Charm and beauty quarks are powerful tools to investigate this high density and strongly interacting state of matter since they are produced in initial hard scatterings that are therefore generated early in the system evolution and probe its hottest, densest stage. The measurement of the charm production cross sections in pp collisions provides an interesting insight into QCD processes and is crucial as a reference for heavy ion studies. We present open charm cross section measurements in pp collisions at \sqrt{s} = 7 TeV and \sqrt{s}=2.76 TeV in the central rapidity region. In addition, the first measurement of nuclear modification factor of D-meson in Pb-Pb collisions at \sqrt{s}= 2.76 TeV is shown.

nucl-ex↗