arXiv subjects

Julian C. Berengut

Publications and source records attributed to Julian C. Berengut.

At least 19 recordsLinked to original sources

arXiv2025

Second-order hyperfine structure and its impact on new physics searches using isotope shift spectroscopy

Recent precision isotope shift spectroscopy experiments have reported King plot non-linearities that may uncover previously hidden nuclear properties or hint at new force-carrying bosons. Interpreting the data requires many isotope pairs, but sufficient stable spin-zero nuclei are not always available. In this paper we consider the use of isotopes with non-zero nuclear spin for these studies. We confirm that observed King plot non-linearity in strontium is explained by second-order hyperfine shift in the fermionic nucleus, and we discuss the limitations of using Yb isotopes with non-zero spin in King plot studies. By introducing a specific difference of two isotopes with nuclear spin, we allow for a promising addition to future experimental schemes.

physics.atom-ph↗

arXiv2025

Probing new bosons and nuclear structure with ytterbium isotope shifts

In this Letter, we present mass-ratio measurements on highly charged Yb$^{42+}$ ions with a precision of $4\times 10^{-12}$ and isotope-shift measurements on Yb$^{+}$ on the $^{2}$S$_{1/2}$ $\to$ $^{2}$D$_{5/2}$ and $^{2}$S$_{1/2}$ $\to$ $^{2}$F$_{7/2}$ transitions with a precision of $4\times 10^{-9}$ for the isotopes $^{168,170,172,174,176}$Yb. We present a new method that allows us to extract higher-order changes in the nuclear charge distribution along the Yb isotope chain, benchmarking ab-initio nuclear structure calculations. Additionally, we perform a King plot analysis to set bounds on a fifth force in the keV$/c^2$ to MeV$/c^2$ range coupling to electrons and neutrons.

physics.atom-ph↗

arXiv2024

Systematic-free limit on new light scalar bosons via isotope shift spectroscopy in Ca$^+$

We report a precise measurement of the isotope shifts in the $4^2$S$_{1/2} \rightarrow 3^2$D$_{3/2}$ electric quadrupole transition at 732~nm in $^{40 - 42,44,48}$Ca$^+$ via high-resolution laser spectroscopy of co-trapped ions, finding measured shifts of 2,775,392,374.8(6.0), 5,347,679,835.1(5.9), and 10,003,129,115.1(5.7)\,Hz between $^{42,44,48}$Ca$^+$and $^{40}$Ca$^+$, respectively. When combined with prior measurements on the $4^2$S$_{1/2} \rightarrow 3^2$D$_{5/2}$ transition [Phys. Rev. A 100, 022514 (2019), https://journals.aps.org/pra/abstract/10.1103/PhysRevA.100.022514] a King Plot analysis shows the data to be consistent with linearity below the level of parts per billion. This observed linearity, which is free of nuclear systematics, improves the previous isotope-shift based limits of Ca$^+$ for couplings of a scalar boson beyond the Standard Model to electrons and neutrons by a factor of 3. Our new limit excludes part of the coupling range remaining for a new physics interpretation after accounting for one higher-order nuclear term in the nonlinear King plot of Yb/Yb$^+$.

physics.atom-ph↗

arXiv2023

Narrow and ultra-narrow transitions in highly charged Xe ions as probes of fifth forces

Optical frequency metrology in atoms and ions can probe hypothetical fifth-forces between electrons and neutrons by sensing minute perturbations of the electronic wave function induced by them. A generalized King plot has been proposed to distinguish them from possible Standard Model effects arising from, e.g., finite nuclear size and electronic correlations. Additional isotopes and transitions are required for this approach. Xenon is an excellent candidate, with seven stable isotopes with zero nuclear spin, however it has no known visible ground-state transitions for high resolution spectroscopy. To address this, we have found and measured twelve magnetic-dipole lines in its highly charged ions and theoretically studied their sensitivity to fifth-forces as well as the suppression of spurious higher-order Standard Model effects. Moreover, we identified at 764.8753(16) nm a E2-type ground-state transition with 500 s excited state lifetime as a potential clock candidate further enhancing our proposed scheme.

physics.atom-ph↗

arXiv2023

Nuclear charge radii of silicon isotopes

The nuclear charge radius of $^{32}$Si was determined using collinear laser spectroscopy. The experimental result was confronted with ab initio nuclear lattice effective field theory, valence-space in-medium similarity renormalization group, and mean field calculations, highlighting important achievements and challenges of modern many-body methods. The charge radius of $^{32}$Si completes the radii of the mirror pair $^{32}$Ar - $^{32}$Si, whose difference was correlated to the slope $L$ of the symmetry energy in the nuclear equation of state. Our result suggests $L \leq 60$\,MeV, which agrees with complementary observables.

nucl-ex↗

arXiv2023

Comment on "Nuclear Excitation by Free Muon Capture"

In the paper [1] the process of free muon capture with simultaneous excitation of a nuclear isomer has been suggested, claiming that ``the effect can be detectable for selected isotopes". Here, we argue that this claim can not be confirmed. Briefly, the process is far from the dominant mechanism for nuclear excitation; it excites high energy nuclear levels that will not generally decay to the isomer; the proposal assumes all incident muons will fulfil energy criteria, ignoring dominant capture paths; and nuclei excited by muons will have a shortened lifetime due to muonic capture.

nucl-th↗

arXiv2022

Evidence of Two-Source King Plot Nonlinearity in Spectroscopic Search for New Boson

Optical precision spectroscopy of isotope shifts can be used to test for new forces beyond the Standard Model, and to determine basic properties of atomic nuclei. We measure isotope shifts on the highly forbidden ${}^2S_{1/2} \rightarrow {}^2F_{7/2}$ octupole transition of trapped $^{168,170,172,174,176}$Yb ions. When combined with previous measurements in Yb$^+$ and very recent measurements in Yb, the data reveal a King plot nonlinearity of up to 240$σ$. The trends exhibited by experimental data are explained by nuclear density functional theory calculations with the Fayans functional. We also find, with 4.3$σ$ confidence, that there is a second distinct source of nonlinearity, and discuss its possible origin.

physics.atom-ph↗

arXiv2021

Effects of variation of the fine structure constant $α$ and quark mass $m_q$ in Mössbauer nuclear transitions

High accuracy measurements in Mössbauer transitions open up the possibility to use them in the search for temporal and spatial variation of the fine-structure constant $α$, quark mass $m_q$, and dark matter field which may lead to the variation of $α$ and $m_q$. We calculate the sensitivity of nuclear transitions to variation of $α$ and $m_q$. Mössbauer transitions have high sensitivity to variation of quark mass $m_q$ and the strong interaction scale $Λ_{QCD}$, to which atomic optical clocks are not sensitive. The enhancement factors $K$, defined by $\frac{δf}{f} =K_{α}\frac{δα}α$ and $\frac{δf}{f} =K_{q }\frac{δm_q}{m_q}$ where $f$ is the transition energy, may be large in some transitions. The 8~eV nuclear clock transition in $^{229}$Th ($K_q \approx 10^4$) and 76~eV transition in $^{235}$U ($K_α\approx K_q \approx 10^3$) may be investigated using laser spectroscopy methods.

nucl-th↗

arXiv2021

Expanding Nuclear Physics Horizons with the Gamma Factory

The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to $\approx 400\,$MeV and photon fluxes (up to $\approx 10^{17}$ photons per second) exceeding those of the currently available gamma sources by orders of magnitude. The high-energy (secondary) photons are produced via resonant scattering of the primary laser photons by highly relativistic partially-stripped ions circulating in the accelerator. The secondary photons are emitted in a narrow cone and the energy of the beam can be monochromatized, eventually down to the $\approx1$ ppm level, via collimation, at the expense of the photon flux. This paper surveys the new opportunities that may be afforded by the GF in nuclear physics and related fields.

nucl-ex↗

arXiv2021

Sensitivity to New Physics of Isotope Shift Studies using the Coronal Lines of Highly Charged Calcium Ions

Promising searches for new physics beyond the current Standard Model (SM) of particle physics are feasible through isotope-shift spectroscopy, which is sensitive to a hypothetical fifth force between the neutrons of the nucleus and the electrons of the shell. Such an interaction would be mediated by a new particle which could in principle be associated with dark matter. In so-called King plots, the mass-scaled frequency shifts of two optical transitions are plotted against each other for a series of isotopes. Subtle deviations from the expected linearity could reveal such a fifth force. Here, we study experimentally and theoretically six transitions in highly charged ions of Ca, an element with five stable isotopes of zero nuclear spin. Some of the transitions are suitable for upcoming high-precision coherent laser spectroscopy and optical clocks. Our results provide a sufficient number of clock transitions for -- in combination with those of singly charged Ca$^+$ -- application of the generalized King plot method. This will allow future high-precision measurements to remove higher-order SM-related nonlinearities and open a new door to yet more sensitive searches for unknown forces and particles.

physics.atom-ph↗

arXiv2021

Sensitivity of $^{229}$Th nuclear clock transition to variation of the fine-structure constant

Peik and Tamm [Europhys. Lett. 61, 181 (2003)] proposed a nuclear clock based on the isomeric transition between the ground state and the first excited state of thorium-229. This transition was recognized as a potentially sensitive probe of possible temporal variation of the fine-structure constant, $α$. The sensitivity to such a variation can be determined from measurements of the mean-square charge radius and quadrupole moment of the different isomers. However, current measurements of the quadrupole moment are yet to achieve an accuracy high enough to resolve non-zero sensitivity. Here we determine this sensitivity using existing measurements of the change in the mean-square charge radius, coupled with the ansatz of constant nuclear density. The enhancement factor for $α$ variation is $K = -(0.82 \pm 0.25) \times 10^4$. For the current experimental limit, $δα/α\lesssim 10^{-17}$ per year, the corresponding frequency shift is $\sim\!200$ Hz per year. This shift is six orders of magnitude larger than the projected accuracy of the nuclear clock, paving the way for increased accuracy of the determination of $δα$ and interaction strength with low-mass scalar dark matter. We verify that the constant-nuclear-density ansatz is supported by nuclear theory and propose how to verify it experimentally. We also consider a possible effect of the octupole deformation on the sensitivity to $α$ variation, and calculate the effects of $α$ variation in a number of Mössbauer transitions.

physics.atom-ph↗

arXiv2020

Power-law intensity distribution in $γ$-decay cascades -- Nuclear Structure as a Scale-Free Random Network

By modeling the transition paths of the nuclear $γ$-decay cascade using a scale-free random network, we uncover a universal power-law distribution of $γ$-ray intensity $ρ_I(I) \propto I^{-2}$, with $I$ the $γ$-ray intensity of each transition. This property is consistently observed for all datasets with a sufficient number of $γ$-ray intensity entries in the National Nuclear Data Center database, regardless of the reaction type or nuclei involved. In addition, we perform numerical simulations which support the model's predictions of level population density.

nucl-th↗

arXiv2020

Population kinetics of many-electron atoms in ionizing plasmas studied using a continuous collisional radiative model

Collisional--radiative (CR) models based on \textit{ab initio} atomic structure calculation have been utilized over 20 years to analyze many-electron atomic and ionic spectra. Although the population distribution of the excited states in plasmas and their emission spectra are computed using the CR models, systematic and analytical understanding of the population kinetics are still lacking. % In this work, we present a reduced model of the population dynamics in many-electron atomic ions, in which we approximate the dense energy structure of complex many-electron atoms by a continuum, a continuous CR model (CCRM). Using this simplification, we show an analytical population distribution of many-electron atoms in plasmas and its electron-density and temperature dependence. % In particular, the CCRM shows that the population distribution of highly excited states of many-electron atoms in plasmas resembles a Boltzmann distribution but with an effective excitation temperature. We also show the existence of three typical electron-density regions and two electron-temperature regions where the parameter dependence of the excitation temperature is different. Analytical representations of the effective excitation temperature and the boundaries of these phases are also presented.

physics.atom-ph↗

arXiv2020

High Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength Problem

For more than 40 years, most astrophysical observations and laboratory studies of two key soft x-ray diagnostic $2p-3d$ transitions, $3C$ and $3D$, in Fe XVII ions found oscillator strength ratios $f(3C)/f(3D)$ disagreeing with theory, but uncertainties had precluded definitive statements on this much studied conundrum. Here, we resonantly excite these lines using synchrotron radiation at PETRA III, and reach, at a millionfold lower photon intensities, a 10 times higher spectral resolution, and 3 times smaller uncertainty than earlier work. Our final result of $f(3C)/f(3D) = 3.09(8)(6)$ supports many of the earlier clean astrophysical and laboratory observations, while departing by five sigmas from our own newest large-scale ab initio calculations, and excluding all proposed explanations, including those invoking nonlinear effects and population transfers.

physics.atom-ph↗

arXiv2020

Generalized King linearity and new physics searches with isotope shifts

Atomic spectral lines for different isotopes are shifted, revealing a change in the properties of the nucleus. For spinless nuclei such isotope shifts for two distinct transitions are expected to be linearly related, at least at leading order in a change of the nuclear mass and charge distribution. Looking for a breaking of linearity in so-called King plots was proposed as a novel method to search for physics beyond the standard model. In the light of the recent experimental progress in isotope shift spectroscopy, the sensitivity of these searches will become limited by the determination of the isotope masses and/or by nuclear effects which may induce nonlinearities at an observable level. In this work, we propose two possible generalizations of the traditional King plot that overcome these limitations by including additional isotope shift measurements, thus significantly extending the new physics reach of King plots in a purely spectroscopy-driven approach.

hep-ph↗

arXiv2020

Improved isotope-shift-based bounds on bosons beyond the Standard Model through measurements of the $^2$D$_{3/2} - ^2$D$_{5/2}$ interval in Ca$^+$

We perform high-resolution spectroscopy of the $3$d$~^2$D$_{3/2} - 3$d$~^2$D$_{5/2}$ interval in all stable even isotopes of $^A$Ca$^+$ (A = 40, 42, 44, 46 and 48) with an accuracy of $\sim$ 20 Hz using direct frequency-comb Raman spectroscopy. Combining these data with isotope shift measurements of the 4s$~^2$S$_{1/2} \leftrightarrow 3$d$~^2$D$_{5/2}$ transition, we carry out a King plot analysis with unprecedented sensitivity to coupling between electrons and neutrons by bosons beyond the Standard Model. Furthermore, we estimate the sensitivity to such bosons from equivalent spectroscopy in Ba$^+$ and Yb$^+$. Finally, the data yield isotope shifts of the 4s$~^2$S$_{1/2} \leftrightarrow 3$d$~^2$D$_{3/2}$ transition at 10 part-per-billion through combination with recent data of Knollmann et al (2019).

physics.atom-ph↗

arXiv2020

A Simple Explanation for the Observed Power Law Distribution of Line Intensity in Complex Many-Electron Atoms

It has long been observed that the number of weak lines from many-electron atoms follows a power law distribution of intensity. While computer simulations have reproduced this dependence, its origin has not yet been clarified. Here we report that the combination of two statistical models -- an exponential increase in the level density of many-electron atoms and local thermal equilibrium of the excited state population -- produces a surprisingly simple analytical explanation for this power law dependence. We find that the exponent of the power law is proportional to the electron temperature. This dependence may provide a useful diagnostic tool to extract the temperature of plasmas of complex atoms without the need to assign lines.

physics.atom-ph↗

arXiv2017

Probing new light force-mediators by isotope shift spectroscopy

In this Letter we explore the potential of probing new light force-carriers, with spin-independent couplings to the electron and the neutron, using precision isotope shift spectroscopy. We develop a formalism to interpret linear King plots as bounds on new physics with minimal theory inputs. We focus only on bounding the new physics contributions that can be calculated independently of the Standard Model nuclear effects. We apply our method to existing Ca+ data and project its sensitivity to possibly existing new bosons using narrow transitions in other atoms and ions (specifically, Sr and Yb). Future measurements are expected to improve the relative precision by five orders of magnitude, and can potentially lead to an unprecedented sensitivity for bosons within the 10 keV to 10 MeV mass range.

hep-ph↗