Tue·Jan 18, 2022Tuesday·January 18, 2022

1. 01*

   Longitudinal Spin Transfer to $\Lambda$ Hyperons in CLAS12

   Matthew McEneaney (for the CLAS Collaboration)🇺🇸

   Using the self-analyzing decay of the $\Lambda$, the longitudinal spin transfer $D_{L{L}^{\prime }}$ to the hyperon from a polarized electron beam scattering off an unpolarized proton target can be determined. For $\Lambda$s produced in the current fragmentation region, this quantity is proportional to the helicity dependent fragmentation function $G_1^{\Lambda }$ and can provide insight into the spin structure of the $\Lambda$. Currently, limited experimental data on $D_{L{L}^{\prime }}$ cannot discriminate between different models of $\Lambda$ spin structure. This contribution reports on the status of the ongoing analysis of the longitudinal spin transfer using data taken by the CLAS12 spectrometer at Jefferson Lab with a 10.6 GeV polarized electron beam. We also report on the novel use of Graph Neural Networks (GNNs) to identify signal events.

   nucl-exhep-exJPS Conf.Proc.(2022)·8 citations
2. 02*

   New limits on double-beta decay of ${}^{190}$Pt and ${}^{198}$Pt

   F.A. Danevich🇺🇦 · M. Hult🇧🇪 · A. Junghans🇩🇪 · D.V. Kasperovych🇺🇦 · B.N. Kropivyansky🇺🇦 · G. Lutter🇧🇪 · G. Marissens🇧🇪 · O.G. Polischuk🇺🇦 · M.V. Romaniuk🇺🇦 · H. Stroh🇧🇪 · S. Tessalina🇦🇺 · V.I. Tretyak🇺🇦 · B. Ware🇦🇺

   A search for double-beta decay of ${}^{190}$Pt and ${}^{198}$Pt with emission of $\gamma$-ray quanta was realized at the HADES underground laboratory with a 148 g platinum sample measured by two ultralow-background HPGe detectors over 8946 h. The isotopic composition of the platinum sample has been measured with high precision using inductively coupled plasma mass spectrometry. New lower limits for the half-lives of ${}^{190}$Pt relative to different channels and modes of the decays were set on the level of $\lim T_{1/2}\sim 10^{14}-10^{16}$ yr. A possible exact resonant $0\nu KN$ transition to the 1,2 1326.9 keV level of ${}^{190}$Os is limited for the first time as $T_{1/2}\ge 2.5\times 10^{16}$ yr. A new lower limit on the double-beta decay of ${}^{198}$Pt to the first excited level of ${}^{198}$Hg was set as $T_{1/2}\ge 3.2\times 10^{19}$ yr, one order of magnitude higher than the limit obtained in the previous experiment.

   nucl-exEPJC(2022)·2 citations
3. 03*

   ${\rm Y}$ and ${\eta }_b$ nuclear bound states

   J. J. Cobos-Martínez🇲🇽 · G. N. Zeminiani🇧🇷 · K. Tsushima🇧🇷

   ${\rm Y}$ and ${\eta }_b$ nuclear bound state energies are calculated for various nuclei neglecting any possible effects of the widths. Essential input for the calculations, namely the medium-modified $B$ and $B^{\ast }$ meson masses, as well as the density distributions in nuclei, are calculated within the quark-meson coupling (QMC) model. The attractive potentials for the ${\rm Y}$ and ${\eta }_b$ mesons in nuclei are calculated from the mass shifts of these mesons in nuclear matter in the local density approximation. These potentials originate from the in-medium enhanced $B\overline{B}$ and $B{B}^{\ast }$ loops in their respective self energy. After an extensive analysis we conclude that our results suggest that the ${\rm Y}$ and ${\eta }_b$ mesons should form bound states with all the nuclei considered.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2022)·15 citations
4. 04*

   Erosion of N = 28 shell closure: Shape coexistence and monopole transition

   Y. Suzuki🇯🇵 · W. Horiuchi🇯🇵 · M. Kimura🇯🇵

   Background: In neutron-rich nuclei neighboring 42Si, the quenching of the N = 28 shell gap occurs and is expected to induce the shape coexistence in their excitation spectra. Purpose: We show that different nuclear shapes coexist in N = 28 isotones 40Mg, 42Si, and 44S, and investigate observables to probe it. Method: Antisymmetrized molecular dynamics with Gogny D1S density functional is applied to describe the shape coexistence phenomena without ad hoc assumption of the nuclear shape. Results: We find that rigid shapes with different deformations coexist in the ground and the first excited 0+ states of 40Mg and 42Si, while in 44S the states exhibit large-amplitude collective motion, which does not have any particular shape. These characteristics are reflected well in the monopole transition strengths. Conclusion: The quenching of the N = 28 shell gap leads to the unique shape coexistence in the N = 28 isotones, which can be probed by the monopole transition strengths.

   ↳ nucl-thnucl-exPTEP(2022)·9 citations
5. 05*

   Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals

   Igor Strakovsky (GWU)🇺🇸 · Simon Širca (University of Ljubljana)🇸🇮 · William J. Briscoe (GWU)🇺🇸 · Alexandre Deur (JLab)🇺🇸 · Axel Schmidt (GWU)🇺🇸 · Ron L. Workman (GWU)🇺🇸

   Phenomenological amplitudes obtained in partial-wave analyses (PWA) of single-pion photoproduction are used to evaluate the contribution of this process to the Gerasimov-Drell-Hearn (GDH), Baldin and Gell-Mann-Goldberger-Thirring (GGT) sum rules, by integrating up to 2 GeV in photon energy. Our study confirms that the single-pion contribution to all these sum rules converges even before the highest considered photon energy, but the levels of saturation are very different in the three cases. Single-pion production almost saturates the GDH sum rule for the proton, while a large fraction is missing in the neutron case. The Baldin integrals for the proton and the neutron are both saturated to about four fifths of the predicted total strength. For the GGT sum rule, the wide variability in predictions precludes any definitive statement.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2022)·12 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.