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Register a new userImperfect World of $betabeta$-decay Nuclear Data Sets?
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B. Pritychenko
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The precision of double-beta ($betabeta$) decay experimental half-lives and their uncertainties is reevaluated. A complementary analysis of the decay uncertainties indicates deficiencies due to small size of statistical samples, and incomplete collection of experimental information. Further experimental and theoretical efforts would lead toward more precise values of $betabeta$-decay half-lives and nuclear matrix elements.
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We study double gamma ($gammagamma$) decay nuclear matrix elements (NMEs) for a wide range of nuclei from titanium to xenon, and explore their relation to neutrinoless double-beta ($0 ubetabeta$) NMEs. To favor the comparison, we focus on double-magnetic dipole transitions in the final $betabeta$ nuclei, in particular the $gammagamma$ decay of the double isobaric analog of the initial $betabeta$ state into the ground state. For the most probable decay with equal-energy photons, our large-scale nuclear shell model results show a good linear correlation between the $gammagamma$ and $0 ubetabeta$ NMEs. Our analysis reveals that the correlation holds for $gammagamma$ transitions driven by the spin or orbital angular momentum due to the dominance of zero-coupled nucleon pairs, a feature common to $0 ubetabeta$ decay. Our findings point out the potential of future $gammagamma$ decay measurements to constrain $0 ubetabeta$ NMEs, which are key to answer fundamental physics questions based on $0 ubetabeta$ experiments.
Precise measurement of $gamma$-rays following ordinary (non-radiative) capture of negative muons by natural Se, Kr, Cd and Sm, as well as isotopically enriched $^{48}$Ti, $^{76}$Se, $^{82}$Kr, $^{106}$Cd and $^{150}$Sm targets was performed by means of HPGe detectors. Energy and time distributions were investigated and total life time of negative muon in different isotopes was deduced. Detailed analysis of $gamma$-lines intensity allows to extract relative yield of several daughter nuclei and partial rates of ($mu$,$ u$) capture to numerous excited levels of the $^{48}$Sc, $^{76}$As, $^{82}$Br, $^{106}$Ag and $^{150}$Tc isotopes which are considered to be virtual states of an intermediate odd-odd nucleus in 2$beta$-decay of $^{48}$Ca, $^{76}$Ge, $^{82}$Se, $^{106}$Cd and $^{150}$Nd, respectively. These rates are important as an experimental input for the theoretical calculation of the nuclear matrix elements of 2$beta$-decay.
In a separate paper we have discussed the possibility that six quark clusters can affect the rate of double-beta decay. In this article we develop the formalism needed in the evaluation of the energy of all six-quark cluster configurations, which can arise in a harmonic oscillator basis up to $2 hbar omega$ excitations. The symmetries that were found useful for this purpose were the combined spin color symmetry $SU_{cs}(6)$, the orbital symmetry $SU_{o}(6)$ and the isospin symmetry $SU_I(2)$.
A search for neutrinoless $betabeta$ decay processes accompanied with Majoron emission has been performed using data collected during Phase I of the GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del Gran Sasso of INFN (Italy). Processes with spectral indices n = 1, 2, 3, 7 were searched for. No signals were found and lower limits of the order of 10$^{23}$ yr on their half-lives were derived, yielding substantially improved results compared to previous experiments with $^{76}$Ge. A new result for the half-life of the neutrino-accompanied $betabeta$ decay of $^{76}$Ge with significantly reduced uncertainties is also given, resulting in $T^{2 u}_{1/2} = (1.926 pm 0.095)cdot10^{21}$ yr.
We used a high-resolution magnetic spectrograph to study neutron pair-correlated $0^+$ states in $^{136}$Ba, produced via the $^{138}{rm Ba}(p,t)$ reaction. In conjunction with state-of-the-art shell model calculations, these data benchmark part of the dominant Gamow-Teller component of the nuclear matrix element (NME) for $^{136}$Xe neutrinoless double beta ($0 ubetabeta$) decay. We demonstrate for the first time an evaluation of part of a $0 ubetabeta$ decay NME by use of an experimental observable, presenting a new avenue of approach for more accurate calculations of $0 ubetabeta$ decay matrix elements.
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