Mon·May 4, 2020Monday·May 4, 2020

1. 01*

   Precision measurement of the magnetic octupole moment in ${}^{45}$Sc as a test for state-of-the-art atomic- and nuclear-structure theory

   R. P. de Groote · J. Moreno · J. Dobaczewski · I. Moore · M. Reponen · B. K. Sahoo · C. Yuan

   We report on measurements of the hyperfine $A,B$ and $C$-constants of the $3d4s^2{}^2{D}_{5/2}$ and $3d4s^2{}^2{D}_{3/2}$ atomic states in ${}^{45}$Sc. High-precision atomic calculations of the hyperfine fields of these states and second-order corrections are performed, and are used to extract $C_{5/2}=-0.06(6)$ kHz and $C_{3/2}=+0.04(3)$ kHz from the data. These results are one order of magnitude more precise than the available literature. From the combined analysis of both atomic states, we infer the nuclear magnetic octupole moment $\Omega =-0.07(53){\mu }_{N}b$, including experimental and atomic structure-related uncertainties. With a single valence proton outside of a magic calcium core, scandium is ideally suited to test a variety of nuclear models, and to investigate in-depth the many intriguing nuclear structure phenomena observed within the neighboring isotopes of calcium. We perform nuclear shell-model calculations of $\Omega$, and furthermore explore the use of Density Functional Theory for evaluating $\Omega$. From this, mutually consistent theoretical values of $\Omega$ are obtained, which are in agreement with the experimental value. This confirms atomic structure calculations possess the accuracy and precision required for magnetic octupole moment measurements, and shows that modern nuclear theory is capable of providing meaningful insight into this largely unexplored observable.

   nucl-exnucl-thPLB(2022)·14 citations
2. 02*

   Ab initio Leading Order Effective Potentials for Elastic Nucleon-Nucleus Scattering

   M. Burrows🇺🇸 · R. B. Baker🇺🇸 · Ch. Elster🇺🇸 · S. P. Weppner · K.D. Launey🇺🇸 · P. Maris🇺🇸 · G. Popa

   Background: Calculating microscopic effective interactions (optical potentials) for elastic nucleon-nucleus scattering has already in the past led to a large body of work. For first-order calculations a nucleon-nucleon (\textit{NN}) interaction and a one-body density of the nucleus were taken as input to rigorous calculations of microscopic full-folding calculations. Purpose: Based on the spectator expansion of the multiple scattering series we employ a chiral next-to-next-to-leading order (NNLO) nucleon-nucleon interaction on the same footing in the structure as well as in the reaction calculation to obtain an in leading-order consistent effective potential for nucleon-nucleus elastic scattering, which includes the spin of the struck target nucleon. Methods: The first order effective folding potential is computed by first deriving a nonlocal scalar density as well as a spin-projected momentum distribution. Those are then integrated with the off-shell Wolfenstein amplitudes $A$, $C$, and $M$. The resulting nonlocal potential serves as input to a momentum-space Lippmann-Schwinger equation, whose solutions are summed to obtain the nucleon-nucleus scattering observables. Results: We calculate elastic scattering observables for ${}^4$He, ${}^6$He, ${}^8$He, ${}^{12}$C, and ${}^{16}$O in the energy regime between 100 and 200 MeV projectile kinetic energy, and compare to available data. We also explore the extension down to about 70 MeV, and study the effect of ignoring the spin of the struck nucleon in the nucleus. Conclusions: In our calculations we contrast elastic scattering off closed-shell and open-shell nuclei. We find that for closed-shell nuclei the approximation of ignoring the spin of the struck target nucleon is excellent. We only see effects of the spin of the struck target nucleon when considering ${}^6$He and ${}^8$He, which are nuclei with a $N/Z$ ratio larger than 1.

   ↳ nucl-thnucl-exPRC(2020)·38 citations
3. 03*

   Novel ansatz for charge radii in density functional theories

   Rong An · Li-Sheng Geng🇨🇳 · Shi-Sheng Zhang🇨🇳

   Charge radii are one of the most fundamental properties of atomic nuclei characterizing their charge distributions. Though the general trend as a function of the mass number is well described by the $A^{1/3}$ rule, some fine structures, such as the evolution along the calcium isotopic chain and the corresponding odd-even staggerings, are notoriously difficult to describe both in density functional theories and ab initio methods. In this letter, we propose a novel ansatz to describe the charge radii of calcium isotopes, by adding a correction term, proportional to the number of Cooper pairs, and determined by the BCS amplitudes and a single parameter, to the charge radii calculated in the relativistic mean field model with the pairing interaction treated with the BCS method. The new ansatz yields results consistent with data not only for calcium isotopes, but also for ten other isotopic chains, including oxygen, neon, magnesium, chromium, nickel, germanium, zirconium, cadmium, tin, and lead. It is remarkable that this ansatz with a single parameter can describe nuclear charge radii throughout the periodic table, particularly the odd-even staggerings and parabolic behavior. We hope that the present study can stimulate more discussions about its nature and relation with other effects proposed to explain the odd-even staggerings of charge radii.

   ↳ nucl-thnucl-exPRC(2020)·39 citations
4. 04*

   Weak charge and weak radius of ${}^{12}$C

   Oleksandr Koshchii🇩🇪 · Jens Erler🇩🇪 · Mikhail Gorchtein🇩🇪 · Charles J. Horowitz🇺🇸 · Jorge Piekarewicz🇺🇸 · Xavier Roca-Maza🇮🇹 · Chien-Yeah Seng🇩🇪 · Hubert Spiesberger🇩🇪

   We present a feasibility study of a simultaneous sub-percent extraction of the weak charge and the weak radius of the ${}^{12}$C nucleus using parity-violating electron scattering, based on a largely model-independent assessment of the uncertainties. The corresponding measurement is considered to be carried out at the future MESA facility in Mainz with $E_{\mathrm{beam}}=155$ MeV. We find that a combination of a $0.3\%$ precise measurement of the parity-violating asymmetry at forward angles with a $10\%$ measurement at backward angles will allow to determine the weak charge and the weak radius of ${}^{12}$C with $0.4\%$ and $0.5\%$ precision, respectively. These values could be improved to $0.3\%$ and $0.2\%$ for a $3\%$ backward measurement. This experimental program will have impact on precision low-energy tests in the electroweak sector and nuclear structure.

   ↳ nucl-thhep-phnucl-exPRC(2020)·14 citations
5. 05*

   Removal of ${}^{210}$Pb by Etch of Crystalline Detector Sidewalls

   Joseph Street🇺🇸 · Rupak Mahapatra🇺🇸 · Eric Morrison🇺🇸 · Mark Platt🇺🇸 · Richard Schnee🇺🇸

   A potential source of dominant backgrounds for many rare-event searches or screening detectors is from radon daughters, specifically ${}^{210}$Pb, deposited on detector surfaces, often during detector fabrication. Performing a late-stage etch is challenging because it may damage the detector. This paper describes a late-stage etching technique that reduces surface ${}^{210}$Pb and ${}^{210}$Po by $>99\times$ at 90% C.L.

   ↳ physics.ins-detastro-ph.IMnucl-exNucl.Instrum.Meth.A(2020)·4 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.