arXiv subjects

Shikha Rathi

Publications and source records attributed to Shikha Rathi.

5 recordsLinked to original sources

arXiv2026

Nuclear Charge Radius of $^9$Be from Muonic Atom Spectroscopy Using a Microcalorimeter

The $2p\to1s$ transition energy in muonic $^9$Be was measured using a metallic magnetic calorimeter, resulting in $E_{2p\to 1s}=33\,391.48(34)\,$eV. The result is 30 times more precise than the previous best measurement and enables the extraction of the corresponding nuclear charge radius $r_c($$^9$Be$)=2.5506(51)\,$fm. It is $2.4$ times more precise than the commonly used value based on electron scattering and differs from it by $2.3$ times the combined uncertainties. This measurement represents the first determination of a nuclear charge radius using muonic x-ray spectroscopy with microcalorimeters.

nucl-ex↗

arXiv2026

Binding Energy of Muonic Beryllium: Perturbative versus All--Order Calculations

We compute the ground-state binding energy of muonic $^9$Be in two ways: first, the fully perturbative treatment of the nuclear-size effect often employed in light systems, and second, an approach that accounts for the finite-nuclear-size to all orders (and is inspired by calculations otherwise employed for heavy muonic ions). The results are compared term by term and show that both approaches agree to better than one part-per-million of the total energy. The objective of this work is twofold. The first is practical: to provide a parametrization that allows the extraction of the $^9$Be charge radius from recent and forthcoming experiments with high precision. The second is more conceptual: to act as a bridge between the community working on calculations for light systems and those focusing on heavy systems, demonstrating that the fully relativistic approach otherwise chosen for heavy systems can be enhanced to cover theoretical predictions for all charge numbers.

physics.atom-ph↗

arXiv2025

Towards Precision Spectroscopy of Antiprotonic Atoms for Probing Strong-field QED

PAX (antiProtonic Atom X-ray spectroscopy) is a new experiment with the aim to test strong-field quantum electrodynamics (QED) effects by performing high-precision x-ray spectroscopy of antiprotonic atoms. By utilizing advanced microcalorimeter detection techniques and a low-energy antiproton beam provided by the ELENA ring at CERN, gaseous targets will be used for the creation of antiprotonic atoms, and the measurement of transitions between circular Rydberg states will be conducted with up to two orders of magnitude improved accuracy over previous studies using high-purity germanium detectors. Our approach eliminates the longstanding issue of nuclear uncertainties that have hindered prior studies using highly charged ions, thus enabling direct and purely QED-focused measurements. By precisely probing atomic systems with electric fields up to two orders of magnitude above the Schwinger limit, PAX will test vacuum polarization and second-order QED corrections, opening new frontiers in fundamental physics and uncovering potential pathways to physics beyond the Standard Model.

physics.atom-ph↗

arXiv2022

Relativistic Calculation of Energies, Transition Parameters Hyperfine Structure, Land\'e g$_J$ and Isotope shifts factors for Ar$^{7+}$, Kr$^{25+}$ and Xe$^{43+}$ ions

In this study a comprehensive calculations of energies, hyperfine structure constants, Land\'e g$_J$ factors and isotope shifts have been performed for the lowest 71 states of Na-like Ar$^{7+}$, Kr$^{25+}$ and Xe$^{43+}$ ions. Radiative parameters viz., transition rates, wavelengths, oscillator strengths and lifetimes are also estimated for the electric and magnetic dipole and quadrupole transitions among these levels. The states under consideration includes $1s^2s^22p^6nl$ where n = 3 to 9 and l = s to i and fully relativistic multiconfiguration Dirac Fock method integrated in the latest version of general purpose relativistic atomic structure package is used. The relativistic calculation viz., Briet interactions and quantum electrodynamics effects are also included and their effects on energies are analysed. To inspect the reliability of MCDF results, we carried out another calculations using many body perturbation theory method integrated in Flexi Atomic code. A thorough comparison between the two obtained calculations and with the previous theoretical and experimental results, wherever available, is carried out and a good agreement is observed. The present calculations will considerably extend the already existing results for these Na-like ions as most of the results are reported for the first time Further, we believe that our results are of high accuracy and will be beneficial for spectral analysis and diagnosis in plasma and astrophysics.

physics.atom-ph↗

arXiv2022

Comprehensive calculations of energy levels, radiative transition parameters, hyperfine structure constants A$_J$-B$_J$, Landé g$_J$ factors and isotope shifts for Sc XX

Large scale calculations for the energy levels, transition rates, oscillator strengths, hyperfine interaction constants, Landé g$_J$ factors and isotope shifts have been performed for $1s^2$ and $1snl \: (n=2-8 $ and $l \leq (n-1) )$ levels of He-like scandium, Sc XX. The GRASP2018 package based on the multi-configurational Dirac-Fock method is used to perform these calculations. The leading quantum electrodynamics corrections, Breit interactions and nuclear recoil effects are also included in the succeeding relativistic configuration interaction calculations. The relativistic isotope shift (RIS4) program is used to determine the mass and field shifts factors. A detailed comparison of the present results with the corresponding values from the NIST database and other theoretical work, wherever available, has been done, and an excellent agreement is achieved. A large section of the results is reported for the first time in the present work.

physics.atom-ph↗