Wed·Dec 16, 2020Wednesday·December 16, 2020

1. 01*

   Extensive study of the quality of fission yields from experiment, evaluation and GEF for antineutrino studies and applications

   K.-H. Schmidt (1)🇫🇷 · M. Estienne (1)🇫🇷 · M. Fallot (1)🇫🇷 · S. Cormon (1)🇫🇷 · A. Cucoanes (1)🇫🇷 · B. Jurado (2)🇫🇷 · K. Kern (3)🇵🇦 · Ch. Schmitt (4)🇫🇷 · T. Shiba (1) ((1) SUBATECH, CNRS/IN2P3, Université de Nantes, IMTA, (2) CENBG, CNRS/IN2P3, (3) Prokerno Corp., (4) IPHC, CNRS/IN2P3)

   The understanding of the antineutrino production in fission and the theoretical calculation of their energy spectra in different types of fission reactors rely on the application of the summation method, where the individual contributions from the different radioactive nuclides that undergo a beta decay are estimated and summed up. The most accurate estimation of the independent fission-product yields is essential to this calculation. We have coupled for the first time the predictions of the general fission model GEF for the fission yields to fission-product beta-decay data in a summation calculation of reactor antineutrino energy spectra. The first comparisons performed between the spectra from GEF and those obtained with the evaluated nuclear databases exhibited large discrepancies that highlighted the exigency of the modelisation of the antineutrino spectra and showing their usefulness in the evaluation of nuclear data. Additional constraints for the GEF model were thus needed in order to reach the level of accuracy required. The quality of different sources of information on the fission yields has been investigated with GEF, and the benefit of a combined analysis is demonstrated. The quality of fission yields emerging from different experimental techniques has been analyzed and indications for shortcomings of mass yields for some of the studied fissioning systems were provided. The combination of a careful study of the independent isotopic yields and the adjunction of the LOHENGRIN fission-yield data as additional constraints led to a substantially improved agreement between the antineutrino spectra computed with GEF and with the evaluated data. The comparison of inverse beta-decay yields computed with GEF with those measured by the Daya Bay experiment shows the excellent level of predictiveness of the GEF model for the fundamental or applied antineutrino physics.

   nucl-exNucl.Data Sheets(2021)·8 citations
2. 02*

   A search for rare and induced nuclear decays in hafnium

   B. Broerman🇨🇦 · M. Laubenstein🇮🇹 · S. Nagorny🇨🇦 · N. Song🇨🇦 · A.C. Vincent🇨🇦

   A measurement of hafnium foil using a modified ultra-low-background high purity detector with optimized sample-to-detector geometry was performed at Laboratori Nazionale del Gran Sasso. Radiopurity of the stock Hf foil was studied in detail, in addition to an analysis of data collected over 310 days to search for rare processes that can occur in natural Hf isotopes. Firstly, limits on alpha decays of all natural Hf isotopes to the first excited state of the daughter nuclides were established in the range of $10^{16}$-$10^{18}$a (90% C.L.). Secondly, a search for modes of double electron capture and electron capture with positron emission in ${}^{174}$Hf was performed, yielding half-life limits $10^{16}$-$10^{18}$a (90% C.L.). Lastly, novel dark matter-induced nuclear excitations in hafnium isotopes were investigated. For dark matter with 1 TeV/$c^2$ mass, leading limits on the inelastic dark matter--nucleon cross section are set for mass splittings in the range 428 keV $<\delta <$ 473 keV.

   nucl-exNPA(2021)·13 citations
3. 03*

   Evidence against the Efimov effect in ${}^{12}\mathrm{C}$ from spectroscopy and astrophysics

   J. Bishop · G.V. Rogachev · S. Ahn · E. Aboud · M. Barbui · A. Bosh · J. Hooker · C. Hunt · J. Hooker · H. Jayatissa · E. Koshchiy · R. Malecek and 8 other authors

   Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body sub-systems. A hypothetical state in ${}^{12}\mathrm{C}$ at 7.458 MeV excitation energy, comprising of a loose structure of three $\alpha$-particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally. Method: Using the combined data sets from two recent experiments, one with the TexAT TPC to measure $\alpha$-decay and the other with Gammasphere to measure $\gamma$-decay of states in ${}^{12}\mathrm{C}$ populated by ${}^{12}\mathrm{N}$ and ${}^{12}\mathrm{B}$ $\beta$-decay respectively, we achieve high sensitivity to states in close-proximity to the $\alpha$-threshold in ${}^{12}\mathrm{C}$. Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95\% C.L. $\gamma$-decay branching ratio is determined as a function of the $\beta$-decay feeding strength relative to the Hoyle state. In parallel, calculations of the triple-alpha reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around $5\times 10^7$ K. Conclusion: From decay spectroscopy - at the 95\% C.L., the Efimov state cannot exist at 7.458 MeV with any $\gamma$-decay branching ratio unless the $\beta$-strength is less than 0.7\% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in ${}^{12}\mathrm{C}$. Furthermore, the triple-alpha reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.

   nucl-exPRC(2021)·13 citations
4. 04*

   Almost medium-free measurement of the Hoyle state direct-decay component with a TPC

   J. Bishop🇺🇸 · G.V. Rogachev🇺🇸 · S. Ahn🇺🇸 · E. Aboud🇺🇸 · M. Barbui🇺🇸 · A. Bosh🇺🇸 · C. Hunt🇺🇸 · H. Jayatissa🇺🇸 · E. Koshchiy🇺🇸 · R. Malecek🇺🇸 · S.T. Marley🇺🇸 · E.C. Pollacco🇫🇷 and 5 other authors

   Background: The structure of the Hoyle state, a highly $\alpha$-clustered state at 7.65 MeV in ${}^{12}\mathrm{C}$, has long been the subject of debate. Understanding if the system comprises of three weakly-interacting $\alpha$-particles in the 0s orbital, known as an $\alpha$-condensate state, is possible by studying the decay branches of the Hoyle state. Purpose: The direct decay of the Hoyle state into three $\alpha$-particles, rather than through the ${}^8\mathrm{Be}$ ground state, can be identified by studying the energy partition of the 3 $\alpha$-particles arising from the decay. This paper provides details on the break-up mechanism of the Hoyle stating using a new experimental technique. Method: By using beta-delayed charged-particle spectroscopy of ${}^{12}\mathrm{N}$ using the TexAT (Texas Active Target) TPC, a high-sensitivity measurement of the direct 3 $\alpha$ decay ratio can be performed without contributions from pile-up events. Results: A Bayesian approach to understanding the contribution of the direct components via a likelihood function shows that the direct component is $<0.043\%$ at the 95\% confidence level (C.L.). This value is in agreement with several other studies and here we can demonstrate that a small non-sequential component with a decay fraction of about $10^{-4}$ is most likely. Conclusion: The measurement of the non-sequential component of the Hoyle state decay is performed in an almost medium-free reaction for the first time. The derived upper-limit is in agreement with previous studies and demonstrates sensitivity to the absolute branching ratio. Further experimental studies would need to be combined with robust microscopic theoretical understanding of the decay dynamics to provide additional insight into the idea of the Hoyle state as an $\alpha$-condensate.

   nucl-exPRC(2020)·21 citations
5. 05*

   $D^{\pm }{D}^{\ast \mp }$ Hadronic Atom as a Key to Revealing the $X(3872)$ Mystery

   Zhen-Hua Zhang🇨🇳 · Feng-Kun Guo🇨🇳

   The $X(3872)$, whose mass coincides with the $D^0{\bar{D}}^{\ast 0}$ threshold, is the most extended hadron object. Since its discovery in 2003, debates have never stopped regarding its internal structure. We propose a new object, the $X$ atom, which is the $D^{\pm }{D}^{\ast \mp }$ composite system with positive charge parity and a mass of $(3879.89\pm 0.07)$ MeV, formed mainly due to the Coulomb force. We show that a null signal of the $X$ atom can be used to put a lower limit on the binding energy of the $X(3872)$. From the current knowledge of the $X(3872)$ properties, the production rate for the $X$ atom relative to the $X(3872)$ in $B$ decays and at hadron colliders should be at least $1\times 10^{-3}$. New insights into the $X(3872)$ will be obtained through studying the $X$ atom.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2021)·19 citations
6. 06*

   Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis

   Alex Gnech🇮🇹

   Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of ${}^7$Li and ${}^6$Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to ${}^6$Li abundance and recently the $\alpha$+d$\to$ ${}^6$Li + $\gamma$ and the p+${}^6$Li$\to$${}^7$Be+$\gamma$ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the ${}^6$Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and ${}^6$Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

   ↳ nucl-thnucl-ex0 citations
7. 07*

   New data acquisition system of the Lintott magnetic spectrometer at the S-DALINAC

   M. Singer · U. Bonnes🇩🇪 · A. D'Alessio · M. Hilcker · P. von Neumann-Cosel🇩🇪 · N. Pietralla (Institut für Kernphysik, Technische Universität Darmstadt, Darmstdt, Germany)🇩🇪

   A new data acquisition system for the high resolution magnetic spectrometer Lintott at the superconducting Darmstadt electron linear accelerator S-DALINAC was developed. It allows inclusive and coincidence electron scattering experiments with event rates up to 10 kHz.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·2 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.