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Nuclear Experiment

New submissions

[ total of 9 entries: 1-9 ]

New submissions for Fri, 5 Jun 20

[1]  arXiv:2006.02605 [pdf, other]
Title: First high-precision direct determination of the atomic mass of a superheavy nuclide evinces a new means to unambiguously determine atomic numbers
Comments: Sumitted to PRL, 5 pages, 5 figures
Subjects: Nuclear Experiment (nucl-ex)

Atoms of the superheavy element isotope $^{257}$Db ($Z$=105) were produced online in 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 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. Using 11 events where $\alpha$-decay and time-of-flight could be correlated to $^{257}$Db, a mass excess of $100\,063(231)_\textrm{stat}(2)_\textrm{sys}$~keV/c$^2$ could be determined. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as $Z$=105.

[2]  arXiv:2006.02712 [pdf, other]
Title: Examining the $N$ = 28 shell closure through high-precision mass measurements of $^{46-48}$Ar
Comments: 17 pages, 14 figures

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.

[3]  arXiv:2006.02912 [pdf, ps, other]
Title: Comment on "Search for η' Bound Nuclei in the $^{12}\mathrm{C}(γ,p)$ Reaction with Simultaneous Detection of Decay Products"
Comments: submitted to Physical Review Letters
Subjects: Nuclear Experiment (nucl-ex)

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

Cross-lists for Fri, 5 Jun 20

[4]  arXiv:2006.01151 (cross-list from hep-ph) [pdf, other]
Title: Dynamical Evidence For a Fifth Force Explanation of the ATOMKI Nuclear Anomalies
Comments: 32 pages, 6 figures

Recent anomalies in $^8$Be and $^4$He nuclear decays can be explained by postulating a fifth force mediated by a new boson $X$. The distributions of both transitions are consistent with the same $X$ mass, 17 MeV, providing kinematic evidence for a single new particle explanation. In this work, we examine whether the new results also provide dynamical evidence for a new particle explanation, that is, whether the observed decay rates of both anomalies can be described by a single hypothesis for the $X$ boson's interactions. We consider the observed $^8$Be and $^4$He excited nuclei, as well as a $^{12}$C excited nucleus; together these span the possible $J^P$ quantum numbers up to spin 1. For each transition, we determine whether scalar, pseudoscalar, vector, or axial vector $X$ particles can mediate the decay, and we construct the leading operators in a nuclear physics effective field theory that describes them. Assuming parity conservation, the scalar case is excluded and the pseudoscalar case is highly disfavored. Remarkably, however, the protophobic vector gauge boson, first proposed to explain only the $^8$Be anomaly, also explains the $^4$He anomaly within experimental uncertainties. We predict signal rates for other closely related nuclear measurements, which, if confirmed, will provide overwhelming evidence that a fifth force has been discovered.

[5]  arXiv:2006.02696 (cross-list from physics.ins-det) [pdf, other]
Title: Neutron flux and spectrum in the Dresden Felsenkeller underground facility studied by moderated $^3$He counters
Comments: 10 figures, 4 tables; to be published in Phys. Rev. D

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.

[6]  arXiv:2006.02836 (cross-list from nucl-th) [pdf, other]
Title: Factorial cumulants from global baryon number conservation
Comments: 15 pages, 3 figures
Subjects: Nuclear Theory (nucl-th); High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)

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.

[7]  arXiv:2006.03033 (cross-list from hep-ph) [pdf, other]
Title: Polarized electron-deuteron deep-inelastic scattering with spectator nucleon tagging
Authors: W. Cosyn, C. Weiss
Comments: 52 pages, 19 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)

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.

Replacements for Fri, 5 Jun 20

[8]  arXiv:2005.06909 (replaced) [pdf, other]
Title: Two-pole structures in QCD: Facts, not fantasy!
Authors: Ulf-G. Meißner
Comments: 22 pages, 10 figures, invited article for the special issue in "Symmetry" on "Chiral Symmetry in Physics", D. Klabucar (ed.), accepted version
[9]  arXiv:2005.13542 (replaced) [pdf, other]
Title: Explaining $b\to s\ell^+\ell^-$ and the Cabibbo Angle Anomaly with a Vector Triplet
Comments: 11 pages, 4 figures, 2 tables; references added, typos corrected
[ total of 9 entries: 1-9 ]

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