Tue·Feb 14, 2023Tuesday·February 14, 2023

1. 01*

   Direct measurement of hexacontatetrapole, $\text{E6}$ {\gamma} decay from ${}^{\text{53m}}$Fe

   T. Palazzo · A. J. Mitchell🇦🇺 · G. J. Lane🇦🇺 · A. E. Stuchbery🇦🇺 · B. A. Brown🇺🇸 · M. W. Reed🇺🇸 · A. Akber · B. J. Coombes🇦🇺 · J. T. H. Dowie🇦🇺 · T. K. Eriksen🇳🇴 · M. S. M. Gerathy🇦🇺 · T. Kibédi🇦🇺 · T. Tornyi🇭🇺 · M. O. de Vries

   The only proposed observation of a discrete, hexacontatetrapole ($E6$) transition in nature occurs from the T${}_{1/2}$ = 2.54(2)-minute decay of ${}^{53m}$Fe. However, there are conflicting claims concerning its $\gamma$-decay branching ratio, and a rigorous interrogation of $\gamma$-ray sum contributions is lacking. Experiments performed at the Australian Heavy Ion Accelerator Facility were used to study the decay of ${}^{53m}$Fe. For the first time, sum-coincidence contributions to the weak $E6$ and $M5$ decay branches have been firmly quantified using complementary experimental and computational methods. Agreement across the different approaches confirms the existence of the real $E6$ transition; the $M5$ branching ratio and transition rate have also been revised. Shell model calculations performed in the full $pf$ model space suggest that the effective proton charge for high-multipole, $E4$ and $E6$, transitions is quenched to approximately two-thirds of the collective $E2$ value. Correlations between nucleons may offer an explanation of this unexpected phenomenon, which is in stark contrast to the collective nature of lower-multipole, electric transitions observed in atomic nuclei.

   nucl-exPRL(2023)·5 citations
2. 02*

   Ordinary muon capture rates on ${}^{100}$Mo and ${}^{\mathrm{nat}}$Mo for astro-antineutrinos and double beta decays

   I. H. Hashim🇲🇾 · H. Ejiri🇯🇵 · N. N. A. M. A. Ghani🇲🇾 · F. Othman🇲🇾 · R. Razali🇲🇾 · Z. W. Ng🇲🇾 · T. Shima🇯🇵 · D. Tomono🇯🇵 · D. Zinatulina🇷🇺 · M. Schirchenko🇷🇺 · S. Kazartsev🇷🇺 · A. Sato🇯🇵 and 3 other authors

   \item[Background] The nuclear responses for antineutrinos associated with double beta decays (DBDs) and astro-antineutrino interactions are studied by measuring ordinary muon capture (OMC) rates. \item[Purpose]The experimental studies of absolute OMC rates and their mass number dependence for ${}^{100}$Mo and the natural Mo are currently of interest in astro-antineutrinos and DBDs. \item[Method]The OMC rates were obtained experimentally by measuring the time spectrum of the trapped muon's decay into electrons to obtain the half-lives of the trapped muons. \item[Results]The OMC rate for the enriched isotope of ${}^{100}$Mo is $\Lambda$(${}^{100}$Mo)=(7.07$\pm$0.32)$\times 10^6$ s${}^{-1}$, while that for the natural Mo is $\Lambda$(${}^{\mathrm{nat}}$Mo)=(9.66$\pm$0.44)$\times 10^6$ s${}^{-1}$, i.e., $\Lambda$(${}^{100}$Mo) is about 27$\%$ of $\Lambda$(${}^{\mathrm{nat}}$Mo), reflecting the blocking effect of the excess neutrons for the proton-to-neutron transformation in OMC. The present experimental observation is consistent with the predictions using Goulard-Primakoff's (GPs) and Primakoff's (Ps) empirical equations. \item[Conclusions] The absolute OMC rates for ${}^{100}$Mo and ${}^{\mathrm{nat}}$Mo were measured. The large neutron excess in ${}^{100}$Mo gives a much lower OMC rate than ${}^{\mathrm{nat}}$Mo. On both ${}^{100}$Mo and ${}^{\mathrm{nat}}$Mo, consistent OMC rates with the GP and P values are observed.

   nucl-exastro-ph.HE0 citations
3. 03*

   Search for resonant neutrinoless double electron capture in Gd-152 and other rare decays in Gd isotopes

   M. Laubenstein🇮🇹 · B. Lehnert🇺🇸 · S. S. Nagorny🇨🇦 · S. Nisi🇮🇹

   A search for rare decays of gadolinium isotopes was performed with an ultra-low background high-purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 198 g Gd${}_2$O${}_3$ powder sample was measured for 63.8 d with a total Gd exposure of 12.6 kg$\times$d. ${}^{152}$Gd is the most promising isotope for resonant neutrinoless double electron capture which could significantly enhance the decay rate over other neutrinoless double beta decay processes. The half-life for this decay was constrained to $>4.2\times 10^{12}$ yr (90\% credibility). This limit is still orders of magnitude away from theoretical predictions but it is the first established limit on the transition paving the way for future experiments. In addition, other rare alpha and double beta decay modes were investigated in ${}^{152}$Gd, ${}^{154}$Gd, and ${}^{160}$Gd with half-life limits in the range of $10^{17-20}$ yr.

   nucl-exEPJC(2023)·6 citations
4. 04*

   Domain-Adversarial Graph Neural Networks for $\Lambda$ Hyperon Identification with CLAS12

   Matthew McEneaney🇺🇸 · Anselm Vossen🇺🇸

   Machine learning methods and in particular Graph Neural Networks (GNNs) have revolutionized many tasks within the high energy physics community. We report on the novel use of GNNs and a domain-adversarial training method to identify $\Lambda$ hyperon events with the CLAS12 experiment at Jefferson Lab. The GNN method we have developed increases the purity of the $\Lambda$ yield by a factor of $1.95$ and by $1.82$ using the domain-adversarial training. This work also provides a good benchmark for developing event tagging machine learning methods for the $\Lambda$ and other channels at CLAS12 and other experiments, such as the planned Electron Ion Collider.

   ↳ hep-exnucl-exJINST(2023)·7 citations
5. 05*

   QCD equation of state at finite chemical potential from unbiased exponential resummation of the lattice QCD Taylor series

   Sabarnya Mitra🇮🇳 · Prasad Hegde🇮🇳

   Exponential resummation of the QCD finite-density Taylor series has been recently introduced as an alternative way of resumming the finite-density lattice QCD Taylor series. Unfortunately the usual exponential resummation formula suffers from stochastic bias which must be subtracted before identifying genuine higher-order contributions. In this paper, we present a new way of subtracting the stochastic bias at the level of each individual gauge configuration, up to a certain order of either the Taylor series or the cumulant expansion, by modifying the argument of the exponential. Retaining the exponential form of the resummation allows us to also calculate the phase factor of the fermion determinant on each gauge configuration. We present our results for the excess pressure, number density, and the average phase factor and show that the new results contain less stochastic bias and are in better agreement with the QCD Taylor series compared to the previous exponential resummation.

   ↳ hep-lathep-phnucl-exnucl-thPRD(2023)·7 citations
6. 06*

   Generation, dynamics, and correlations of the fission fragments' angular momenta

   Guillaume Scamps🇺🇸 · George Bertsch🇺🇸

   The generation of angular momentum in fissioning nuclei is not well understood. The predictions of different models disagree, particularly concerning the correlation between the fragments' angular momenta. In this article, a time-dependent collective Hamiltonian model is proposed to treat the generation of the angular momentum in the fission fragments due to the quantum uncertainty principle as well as the dynamics of the collective wave function during and after scission. The model is constructed in the framework of the frozen Hartree-Fock approximation using a Skyrme energy functional to extract deformations of the fission fragments as well as the interactions in a derived collective Hamiltonian. The fission reactions studied are ${}^{240}$Pu $\to$ ${}^{132}$Sn+${}^{108}$Ru and ${}^{240}$Pu $\to$ ${}^{144}$Ba+${}^{96}$Sr. The model can account for a large part of the angular momentum found in experimental data. The orientation of the angular momentum of each fragment is found to be mainly in the plane perpendicular to the fission axis, in agreement with the experiment. The magnitudes of the angular momenta in the two fragments are nearly uncorrelated, in agreement with the recent experimental data of Wilson et al., Nature (London) 590, 566 (2021). Some of the conclusions of the traditional collective vibration model are supported by the present model but some are not. Surprisingly, it is found that the angular momenta of the fragments are slightly correlated positively as in a wriggling mode. It is also found that the presence of an octupole deformation in a fragment can significantly increase the generated angular momentum.

   ↳ nucl-thnucl-exPRC(2023)·16 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.