Fri·Jun 5, 2020Friday·June 5, 2020

1. 01*

   First high-precision direct determination of the atomic mass of a superheavy nuclide

   P. Schury🇯🇵 · T. Niwase🇯🇵 · M. Wada🇺🇸 · P. Brionnet🇫🇷 · S. Chen🇺🇸 · T. Hashimoto · H. Haba🇯🇵 · H. Hirayama🇯🇵 · D.S. Hou · S. Iimura · H. Ishiyama · S. Ishizawa🇯🇵 and 16 other authors

   We present the first direct measurement of the atomic mass of a superheavy nuclide. Atoms of ${}^{257}$Db ($Z$=105) were produced online at the RIKEN Nishina Center for Accelerator-Based Science using the fusion-evaporation reaction ${}^{208}$Pb(${}^{51}$V, 2n)${}^{257}$Db. The gas-filled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and some transfer products, prior to delivering the energetic beam of ${}^{257}$Db ions to a helium gas-filled ion stopping cell wherein they were thermalized. Thermalized ${}^{257}$Db${}^{3+}$ ions were then transferred to a multi-reflection time-of-flight mass spectrograph for mass analysis. An alpha particle detector embedded in the ion time-of-flight detector allowed disambiguation of the rare ${}^{257}$Db${}^{3+}$ time-of-flight detection events from background by means of correlation with characteristic $\alpha$-decays. The extreme sensitivity of this technique allowed a precision atomic mass determination from 11 events. The mass excess was determined to be $100063(231{)}_{\text{stat}}(132{)}_{\text{sys}}$~keV/c${}^2$. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as $Z$=105 and should allow similar evaluations for heavier species in future work.

   nucl-exPRC(2021)·16 citations
2. 02*

   Examining the $N$ = 28 shell closure through high-precision mass measurements of ${}^{46-48}$Ar

   Maxime Mougeot🇫🇷 · Dinko Atanasov🇩🇪 · Carlo Barbieri🇬🇧 · Klaus Blaum🇩🇪 · Martin Breitenfeld🇨🇭 · Antoine de Roubin🇩🇪 · Thomas Duguet🇫🇷 · Sebastian George🇩🇪 · Frank Herfurth🇩🇪 · Alexander Herlert🇩🇪 · Jason D. Holt🇨🇦 · Jonas Karthein🇨🇭 and 12 other authors

   The strength of the $N$ = 28 magic number in neutron-rich argon isotopes is examined through high-precision mass measurements of ${}^{46-48}$Ar, performed with the ISOLTRAP mass spectrometer at ISOLDE/CERN. The new mass values are up to 90 times more precise than previous measurements. While they suggest the persistence of the $N$ = 28 shell closure for argon, we show that this conclusion has to be nuanced in light of the wealth of spectroscopic data and theoretical investigations performed with the \emph{SDPF-U} phenomenological shell model interaction. Our results are also compared with \emph{ab initio} calculations using the Valence Space In-Medium Similarity Renormalization Group and the Self-Consistent Green's Function approaches. Both calculations provide a very good account of mass systematics at and around $Z$ = 18 and, generally, a consistent description of the physics in this region. This combined analysis indicates that ${}^{46}$Ar is the transition between the closed-shell ${}^{48}$Ca and collective ${}^{44}$S.

   nucl-exnucl-thPRC(2020)·15 citations
3. 03*

   Comment on "Search for ${\eta }^{\prime }$ Bound Nuclei in the ${}^{12}\mathrm{C}(\gamma ,p)$ Reaction with Simultaneous Detection of Decay Products"

   H. Fujioka🇯🇵 · K. Itahashi🇯🇵 · V. Metag🇩🇪 · M. Nanova🇩🇪 · Y.K. Tanaka🇩🇪

   We comment on a recent paper by the LEPS2/BGOegg Collaboration [Phys. Rev. Lett. 124, 202501 (2020), arXiv:2005.03449].

   nucl-exnucl-thPRL(2021)·5 citations
4. 04*

   Neutron flux and spectrum in the Dresden Felsenkeller underground facility studied by moderated ${}^3$He counters

   M. Grieger🇩🇪 · T. Hensel🇩🇪 · J. Agramunt🇪🇸 · D. Bemmerer🇩🇪 · D. Degering · I. Dillmann🇩🇪 · L.M. Fraile🇪🇸 · D. Jordan🇪🇸 · U. Köster🇫🇷 · M. Marta🇩🇪 · S.E. Müller🇩🇪 · T. Szücs🇩🇪 · J.L. Taín🇪🇸 · K. Zuber

   Ambient neutrons may cause significant background for underground experiments. Therefore, it is necessary to investigate their flux and energy spectrum in order to devise a proper shielding. Here, two sets of altogether ten moderated ${}^3$He neutron counters are used for a detailed study of the ambient neutron background in tunnel IV of the Felsenkeller facility, underground below 45 meters of rock in Dresden/Germany. One of the moderators is lined with lead and thus sensitive to neutrons of energies higher than 10 MeV. For each ${}^3$He counter-moderator assembly, the energy dependent neutron sensitivity was calculated with the FLUKA code. The count rates of the ten detectors were then fitted with the MAXED and GRAVEL packages. As a result, both the neutron energy spectrum from 10${}^{-9}$ MeV to 300 MeV and the flux integrated over the same energy range were determined experimentally. The data show that at a given depth, both the flux and the spectrum vary significantly depending on local conditions. Energy integrated fluxes of $(0.61\pm 0.05)$, $(1.96\pm 0.15)$, and $(4.6\pm 0.4)\times 10^{-4}$ cm${}^{-2}$ s${}^{-1}$, respectively, are measured for three sites within Felsenkeller tunnel IV which have similar muon flux but different shielding wall configurations. The integrated neutron flux data and the obtained spectra for the three sites are matched reasonably well by FLUKA Monte Carlo calculations that are based on the known muon flux and composition of the measurement room walls.

   ↳ physics.ins-dethep-exnucl-exPRD(2020)·21 citations
5. 05*

   Factorial cumulants from global baryon number conservation

   Michał Barej🇵🇱 · Adam Bzdak🇵🇱

   The proton, antiproton and mixed proton-antiproton factorial cumulants originating from the global conservation of baryon number are calculated analytically up to the sixth order. Our results can be directly tested in experiments.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2020)·10 citations
6. 06*

   Polarized electron-deuteron deep-inelastic scattering with spectator nucleon tagging

   W. Cosyn🇺🇸 · C. Weiss🇺🇸

   Background: DIS on the polarized deuteron with detection of a proton in the nuclear breakup region (spectator tagging) represents a unique method for extracting the neutron spin structure functions and studying nuclear modifications. The tagged proton momentum controls the nuclear configuration during the DIS process and enables a differential analysis of nuclear effects. Such measurements could be performed with the future electron-ion collider (EIC) and forward proton detectors if deuteron beam polarization could be achieved. Purpose: Develop theoretical framework for polarized deuteron DIS with spectator tagging. Formulate procedures for neutron spin structure extraction. Methods: A covariant spin density matrix formalism is used to describe general deuteron polarization in collider experiments (vector/tensor, pure/mixed). Light-front (LF) quantum mechanics is employed to factorize nuclear and nucleonic structure in the DIS process. A 4-dimensional representation of LF spin structure is used to construct the polarized deuteron LF wave function and efficiently evaluate the spin sums. Free neutron structure is extracted using the impulse approximation and analyticity in the tagged proton momentum (pole extrapolation). Results: General expressions of the polarized tagged DIS observables in collider experiments. Analytic and numerical study of the polarized deuteron LF spectral function and nucleon momentum distributions. Practical procedures for neutron spin structure extraction from the tagged deuteron spin asymmetries. Conclusions: Spectator tagging provides new tools for precise neutron spin structure measurements. D-wave depolarization and nuclear binding effects can be eliminated through the tagged proton momentum dependence. The methods can be extended to tensor-polarized observables, spin-orbit effects, and diffractive processes.

   ↳ hep-phnucl-exnucl-thPRC(2020)·31 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.