Fri·Nov 27, 2020Friday·November 27, 2020

1. 01*

   Sub-threshold states in ${}^{19}$Ne relevant to ${}^{18}$F(p,$\alpha$)${}^{15}$O

   J. E. Riley🇬🇧 · A. M. Laird🇬🇧 · N. de Séréville🇫🇷 · A. Parikh🇪🇸 · S. P. Fox🇬🇧 · F. Hammache🇫🇷 · I. Stefan🇫🇷 · P. Adsley🇫🇷 · M. Assié🇫🇷 · B. Bastin🇫🇷 · F. Boulay🇫🇷 · A. Coc🇫🇷 and 15 other authors

   Classical novae result from thermonuclear explosions producing several $\gamma$-ray emitters which are prime targets for satellites observing in the MeV range. The early 511 keV gamma-ray emission depends critically on the ${}^{18}$F(p,$\alpha$)${}^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the ${}^{18}$F(p,$\alpha$)${}^{15}$O reaction rate is the contribution in the Gamow window of interference between sub-threshold ${}^{19}$Ne states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states. States in the ${}^{19}$Ne compound nucleus were studied at the Tandem-ALTO facility using the ${}^{19}$F(${}^3$He,t)${}^{19}$Ne charge exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or $\alpha$-particles from unbound ${}^{19}$Ne states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high spin and low spin components. Evidence for a broad, low spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold. The levels schemes of ${}^{19}$Ne and ${}^{19}$F are still not sufficiently well known and further studies of the analogue assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

   nucl-exastro-ph.SRPRC(2021)·4 citations
2. 02*

   New Limit for Neutrinoless Double-Beta Decay of ${}^{100}$Mo from the CUPID-Mo Experiment

   E. Armengaud🇫🇷 · C. Augier🇫🇷 · A. S. Barabash🇷🇺 · F. Bellini🇮🇹 · G. Benato🇮🇹 · A. Benoît🇫🇷 · M. Beretta🇺🇸 · L. Bergé🇫🇷 · J. Billard🇫🇷 · Yu. A. Borovlev🇷🇺 · Ch. Bourgeois🇫🇷 · V. B. Brudanin🇷🇺 and 82 other authors

   The CUPID-Mo experiment at the Laboratoire Souterrain de Modane (France) is a demonstrator for CUPID, the next-generation ton-scale cryogenic $0\nu \beta \beta$ experiment. It consists of a 4.2 kg array of 20 enriched Li${}_2$${}^{100}$MoO${}_4$ scintillating bolometers to search for the lepton number violating process of $0\nu \beta \beta$ decay in ${}^{100}$Mo. With more than one year of operation (2.16 kg$\times$yr of physics data), no event in the region of interest and hence no evidence for $0\nu \beta \beta$ is observed. We report a new limit on the half-life of $0\nu \beta \beta$ decay in ${}^{100}$Mo of $T_{1/2}>1.5\times 10^{24}$yr at 90 % C.I. The limit corresponds to an effective Majorana neutrino mass $⟨m_{\beta \beta }⟩$ $<$ (0.31--0.54)eV, dependent on the nuclear matrix element in the light Majorana neutrino exchange interpretation.

   nucl-exPRL(2021)·124 citations
3. 03*

   Search for explanation of the neutron lifetime anomaly

   A.P.Serebrov🇷🇺 · M.E. Chaikovskii🇷🇺 · G.N. Klyushnikov🇷🇺 · O.M. Zherebtsov🇷🇺 · A.V. Chechkin🇷🇺

   All results of the neutron lifetime measurements performed in the last 20 years with the UCN storage method are in a good agreement. These results are consistent with the latest most accurate measurements of the neutron decay asymmetry within the Standard Model. However, there is a significant discrepancy at $3.6\sigma$ (1% of the decay probability) level between the averaged result of the storage method experiments and the most accurate measurements performed with the beam method. This article addresses the possible causes of such discrepancy. We focused on finding the spectrum of possible systematic corrections in the beam experiment. Four separate sources of the systematic errors which had not been properly addressed in articles dedicated to the beam technique were considered. Two of those sources are related with the motion of protons in an electromagnetic field and the elastic scattering by the residual gas. The third error concerns proton loss in the dead layer of the detector. It is shown the corresponding correction requires a more detailed analysis than that given in the papers describing the beam measurement method. The fourth source of the systematic error is the charge exchange process on the residual gas. The influence of that process was neglected in the beam method experiments. We present arguments that careful analysis of this issue is necessary since the proposed proton losses correction decreases the measured lifetime. For the problem of proton charge exchange on a residual gas, the spectrum of possible corrections is investigated. It is shown that for an accurate calculation of the correction, it is necessary to directly measure the concentration and composition of the residual gas inside the proton trap. The analysis reveals that even presence of only $H_2$ molecules can lead to the significant correction which is the most probable explanation of the neutron anomaly.

   nucl-exPRD(2021)·27 citations
4. 04*

   Mass measurements of As, Se and Br nuclei and their implication on the proton-neutron interaction strength towards the N=Z line

   I. Mardor (1 and 2)🇮🇱 · S. Ayet San Andres (3)🇩🇪 · T. Dickel (3 and 4)🇩🇪 · D. Amanbayev (4)🇩🇪 · S. Beck (3 and 4)🇮🇱 · J. Bergmann (4)🇩🇪 · H. Geissel (3 and 4)🇩🇪 · L. Grof (4)🇩🇪 · E. Haettner (3)🇩🇪 · C. Hornung (4)🇩🇪 · N. Kalantar-Nayestanaki (5)🇳🇱 · G. Kripko-Koncz (4)🇩🇪 and 44 other authors

   Mass measurements of the ${}^{69}$As, ${}^{70,71}$Se and ${}^{71}$Br isotopes, produced via fragmentation of a ${}^{124}$Xe primary beam at the FRS at GSI, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost 1,000,000. For the ${}^{69}$As isotope, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only 10 events. For the ${}^{70}$Se isotope, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of $\delta$m/m = 4.0$\times 10^{-8}$, with less than 500 events. The masses of the ${}^{71}$Se and ${}^{71}$Br isotopes were measured with an uncertainty of 23 and 16 keV, respectively. Our results for the ${}^{70,71}$Se and ${}^{71}$Br isotopes agree with the 2016 Atomic Mass Evaluation, and our result for the ${}^{69}$As isotope resolves the discrepancy between previous indirect measurements. We measured also the mass of ${}^{14}$N${}^{15}$N${}^{40}$Ar (A=69) with a relative accuracy of $\delta$m/m = 1.7$\times 10^{-8}$, the highest yet achieved with a MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction ($\delta$V${}_{pn}$) for odd-odd nuclei at the N=Z line above Z=29 (recently extended to Z=37) is hardly evident at N-Z=2, and not evident at N-Z=4. Nevertheless, detailed structure of $\delta$V${}_{pn}$ along the N-Z=2 and N-Z=4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing $\approx$500 keV discrepancy in the mass value of the ${}^{70}$Br isotope, which prevents including it in the world average of $Ft$-value for superallowed 0${}^{+}\to$ 0${}^{+}$ $\beta$ decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the N=Z line in the same region of the nuclear chart, including the ${}^{70}$Br isotope.

   nucl-exnucl-thPRC(2021)·28 citations
5. 05*

   Nucleon axial and pseudoscalar form factors from lattice QCD at the physical point

   C. Alexandrou (Univ. of Cyprus and The Cyprus Inst.)🇨🇾 · S. Bacchio (The Cyprus Inst.)🇨🇾 · M. Constantinou (Temple Univ.)🇺🇸 · P. Dimopoulos (Univ. of Parma and INFN)🇮🇹 · J. Finkenrath (The Cyprus Inst.)🇨🇾 · K. Hadjiyiannakou (Univ. of Cyprus and The Cyprus Inst.)🇨🇾 · K. Jansen (DESY-Zeuthen)🇩🇪 · G. Koutsou (The Cyprus Inst.)🇨🇾 · B. Kostrzewa (Univ. of Bonn)🇩🇪 · T. Leontiou (Frederick Univ.)🇨🇾 · C. Urbach (Univ. of Bonn)🇩🇪

   We compute the nucleon axial and induced pseudoscalar form factors using three ensembles of gauge configurations, generated with dynamical light quarks with mass tuned to approximately their physical value. One of the ensembles also includes the strange and charm quarks with their mass close to physical. The latter ensemble has large statistics and finer lattice spacing and it is used to obtain final results, while the other two are used for assessing volume effects. The pseudoscalar form factor is also computed using these ensembles. We examine the momentum dependence of these form factors as well as relations based on pion pole dominance and the partially conserved axial-vector current hypothesis.

   ↳ hep-lathep-phnucl-exnucl-thPRD(2021)·87 citations
6. 06*

   Two-Neutrino Double Beta Decay with Sterile Neutrinos

   Patrick D. Bolton🇬🇧 · Frank F. Deppisch🇬🇧 · Lukáš Gráf🇩🇪 · Fedor Šimkovic🇸🇰

   Usually considered a background for experimental searches for the hypothetical neutrinoless double beta decay process, two-neutrino double beta decay nevertheless provides a complementary probe of physics beyond the Standard Model. In this paper we investigate how the presence of a sterile neutrino, coupled to the Standard Model either via a left-handed or right-handed current, affects the energy distribution and angular correlation of the outgoing electrons in two-neutrino double beta decay. We pay particular attention on the behaviour of the energy distribution at the kinematic endpoint and we estimate the current limits on the active-sterile mixing and effective right-handed coupling using current experimental data as a function of the sterile neutrino mass. We also investigate the sensitivities of future experiments. Our results complement the corresponding constraints on sterile neutrinos from single beta decay measurements in the 0.1 - 10 MeV mass range.

   ↳ hep-phhep-exnucl-exPRD(2021)·49 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.