TheQ EC dependence of evidence for a 17-keV neutrino from the55Fe radiative decay

The internal bremsstrahlung spectrum of⁵⁵Fe was studied using HPGe detector in low background and reduced pileup conditions. The data show that the conclusion on the presence of a heavy mass neutrino strongly depends from the experimental decay energy value taken in the analysis. The decay energy was found to beQ _EC =231.37 ± 0.10 keV. The obtained results also show the need for the higher accuracyQ _EC used in the analysis of the existence of a 17-keV neutrino in the⁵⁵Fe decay.The authors would like to thank A. Plochocki and J. ylicz for helpful discussion and assistance.     

Implications of a 17 keV neutrino for baryogenesis

There is some experimental evidence for a 17 keV component of the electron neutrino, in the form of the recent observations of kinks in the beta-decay spectra of tritium, ¹⁴C, ³⁵S and ⁶³Ni. In this paper I show that most particle-physics models consistent with the 17 keV neutrino require a baryogenesis scale below 10⁶ GeV. Furthermore, models with a 17 keV neutrino typically contain new sources of CP violation, and the cosmological baryon asymmetry could be generated by anomalous electroweak interactions during a first-order weak phase transition.     

On the implications of a 17 keV neutrino

We discuss the implications of the recent measurement of a 17 keV mass component in the electron neutrino sector. Such a heavy state must decay in order to be compatible with cosmology; this requires states additional to those of the standard model. The most likely candidates are either majorons, allowing the decay into massless weakly interacting scalars, or single neutrinos, allowing the decay via the Z into light neutrinos. We show that in the latter case there is a lower bound on the lifetime in conflict with the cosmological constraints on this decay channel and on the photon plus neutrino decay channel which is also present. The extensions of the standard model needed to reduce the lifetime are considered. We analyze the mass matrix, playing particular regard to the singlet neutrino case, and discuss how it might be extended to explain the solar neutrino deficit.     

Search for oscillation of the electron-capture decay probability of Pm

We have searched for time modulation of the electron capture decay probability of ¹⁴²Pm in an attempt to confirm a recent claim from a group at the Gesellschaft für Schwerionenforschung (GSI). We produced ¹⁴²Pm via the ¹²⁴Sn(²³Na, 5n)¹⁴²Pm reaction at the Berkeley 88-Inch Cyclotron with a bombardment time short compared to the reported modulation period. Isotope selection by the Berkeley Gas-filled Separator is followed by implantation and a long period of monitoring the ¹⁴²Nd Kα${\text{K}}_{\alpha }$ x-rays from the daughter. The decay time spectrum of the x-rays is well-described by a simple exponential and the measured half-life of 40.68(53) seconds is consistent with the accepted value. We observed no oscillatory modulation at the proposed frequency at a level 31 times smaller than that reported by Litvinov et al. [Y.A. Litvinov, et al., Phys. Lett. B 664 (2008) 162]. A literature search for previous experiments that might have been sensitive to the reported modulation uncovered another example in ¹⁴²Eu electron-capture decay. A reanalysis of the published data shows no oscillatory behavior.     

Investigations into the origin of the spurious 17 keV neutrino signal observed in35S beta decay

An exhaustive study has been made of the β spectrum of³⁵S, recorded with a Si(Li) detector. The object was to identify the origin of a distortion in the³⁵S β spectrum some 17 keV below the end point, reported over three years ago and interpreted then as evidence for a 17 keV neutrino. Measurements with different source-detector spacings and with varied collimation have shown that there is a long range curvature in the Kurie plot which is a sensitive function of configuration, but the principal origin of the distortion is energy loss in the³⁵S sources. The³⁵S sources, prepared by chemical adsorption of Ba³⁵SO₄ on a gold substrate, are clumped and locally thick. Electrons near the end point lose ～0.3 keV in the source material and if this is taken into account the spectra are well fitted without any admixture of 17 keV neutrino. The source thickness has been investigated with a proton microprobe and determined from both source tilting and the yield of bariumK X-rays; these studies are discussed in detail. The uncertainties in and justification for the form of the electron response function employed are also thoroughly discussed. If there is no systematic error common to the majority of 14 independent sets of³⁵S data, the admixture of 17 keV neutrino is <10^?3 (95% CL). A simple search for a kink at 150 keV in the combined data from all 14 runs yielded a limit of 1.8×10^?3 (95% CL). The end point of the³⁵S β spectrum is found to be 167.60±0.05 keV.     

Search for neutrino radiative decay with a prototype Borexino detector

Results of background measurements with a prototype of the Borexino detector were used to obtain bounds on the lifetime of radiative neutrino decay ν_H→ν_L+γ. The new lower limit for the lifetime of pp and ⁷Be neutrinos is τ_c.m.(ν_H→ν_L+γ) /mν≥4.2×10³ s eV^?1(α)= 0). It is more than an order of magnitude stronger than the value obtained in previous experiments using nuclear reactors and accelerators.     

Levels in55Fe from the decay of55Co

The decay of the 18 h⁵⁵Co has been investigated. Twenty-one gamma rays were observed. The following levels in the daughter nucleus⁵⁵Fe were populated in the decay: g.s. (3/2^?), 411.0 keV (1/2^?), 931.5 keV (5/2^?), 1316.7 keV (7/2^?), 1408.7 keV (7/2^?), 2144.1 keV (5/2^?), 2212.5 keV (9/2^?), 2301.4 keV (9/2^?), 2578.2 keV (5/2^±), 2871.9 keV (5/2^?, 7/2^?), 2939.0 keV (5/2^?, 7/2^?) and 3108.6 keV (5/2^?, 7/2^?).     

Does the 17 keV neutrino annihilate in the early universe?

Recent experiments indicate that the electron neutrino contains a heavy 17 keV component. If these experiments and their interpretation are correct then this will require a modification of the minimal standard model. The standard cosmological model gives significant constraints on the properties of a 17 keV neutrino. It is usually assumed that these constraints imply that the 17 keV neutrino must decay rapidly into Goldstone bosons. We construct a class of gauge models which describe the 17 keV neutrino but which do not involve Goldstone bosons. The 17 keV neutrino is long lived, but annihilates sufficiently in the early universe so that its present day abundance is cosmologically acceptable.     

Double internal bremsstrahlung in the electron-capture decay of 55Fe

The energy distribution of photons emitted in double internal bremsstrahlung accompanying the electron-capture decay of ⁵⁵Fe has been investigated. For sum photon energies in the range of 44–230 keV and at an emission angle of 90°, the ratio of transition probabilities of double to single internal bremsstrahlung processes has been found to be (5.6±0.5) × 10^?5. The experimental data are compared with the existing theoretical predictions.     

Search for neutrino oscillations

A search for ν_μ→ν_e and oscillations has been conducted with the AGS wide-band neutrino beam at the Brookhaven National Laboratory. We find more ν_e ( _e) interactions than were expected on the basis of the number of incident ν_e ( _e) calculated as part of the neutrino beam. The excess is about a factor two over the expectation, the statistical significance being about two and a half standard deviations for ν_e and weaker for _e.     

The Internal Bremsstrahlung following the Electron Capture decay of55Fe

The Internal Bremsstrahlung Electron Capture spectrum from⁵⁵Fe was measured with a HPGe detector. The total spectrum was unfolded taking into account the secondary detection effects and agrees with Glauber and Martin calculations. The measured intensity relative to K capture in the range 35 to 231 keV is 3.24(6)·10^?5 while the calculated one is 3.20·10^?5. TheQ value for the electron capture was deduced as 230.7(19) keV.     

On the theory of auto-ionization in electron-capture decay

Existing theories of auto-ionization in electron-capture decay are reviewed. It is proved that the theoretical model recently developed by Law and Campbell is identical with an earlier theory due to the author. Disagreement between the final results obtained from these two theories is traced to additional approximations introduced by Law and Campbell in the course of their calculations. These approximations are critically examined and found to be invalid thus explaining the reported disagreement. The results of various theoretical calculations previously reported by the author are evaluated for several nuclei of interest.