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Register a new userSearch for an admixture of sterile neutrino in the electron spectrum from tritium $beta$-decay
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We propose an experiment intended for search for an admixture of sterile neutrino with mass m$_s$ in the range of 1-8 keV that may be detected as specific distortion of the electron energy spectrum during tritium decay. The distortion is spread over large part of the spectrum so to reveal it one can use a detector with relatively poor (near 10-15%) energy resolution. A classic proportional counter is a simple natural choice for a tritium $beta$-decay detector. The method we are proposing is original in two respects. First, the counter is produced as a whole from fully-fused quartz tube allowing to measure current pulse directly from anode while providing high stability for a long time. Second, a modern digital acquisition technique can be used in measurements at ultrahigh count rate - up to 10$^6$ Hz. As a result an energy spectrum of tritium electrons containing up to 10$^{12}$ counts may be collected in a month of live time measurements. Due to high statistics an upper limit down to 10$^{-3}$..10$^{-5}$ can be put on sterile neutrino mixing at 95% CL for m$_s$ in the range of 1-8 keV, that will be 1..2 orders of magnitude better then bounds published up to now.
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The paper reviews recent experiments on tritium beta spectroscopy searching for the absolute value of the electron neutrino mass $m( u_e)$. By use of dedicated electrostatic filters with high acceptance and resolution, the uncertainty on the observable $m^2( u_e)$ has been pushed down to about 3 eV$^2$. The new upper limit of the mass is $m( u_e) < 2$ eV at 95% C.L. In view of erroneous and unphysical mass results obtained by some earlier experiments in beta decay, particular attention is paid to systematic effects. The mass limit is discussed in the context of current neutrino research in particle- and astrophysics. A preview is given of the next generation of beta spectroscopy experiments currently under development and construction; they aim at lowering the $m^2( u_e)$-uncertainty by another factor of 100, reaching a sensitivity limit $m( u_e) < 0.2$ eV.
The investigation of the endpoint region of the tritium beta decay spectrum is still the most sensitive direct method to determine the neutrino mass scale. In the nineties and the beginning of this century the tritium beta decay experiments at Mainz and Troitsk have reached a sensitivity on the neutrino mass of 2 eV/c^2 . They were using a new type of high-resolution spectrometer with large sensitivity, the MAC-E-Filter, and were studying the systematics in detail. Currently, the KATRIN experiment is being set up at Forschungszentrum Karlsruhe, Germany. KATRIN will improve the neutrino mass sensitivity by one order of magnitude down to 0.2 eV/c^2, sufficient to cover the degenerate neutrino mass scenarios and the cosmologically relevant neutrino mass range.
The paper reports on the improved Mainz experiment on tritum $beta$ spectroscopy which yields a 10 times higher signal to background ratio than before. The main experimental effects and systematic uncertainties have been investigated in side experiments and possible error sources have been eliminated. Extensive data taking took place in the years 1997 to 2001. A residual analysis of the data sets yields for the square of the electron antineutrino mass the final result of $m^2( u_e)=(-0.6 pm 2.2_{rm{stat}} pm 2.1_{rm{syst}})$ eV$^2$/c$^4$. We derive an upper limit of $m( u_e)leq 2.3$ eV/c$^2$ at 95% confidence level for the mass itself.
The beta decay of tritium in the form of molecular TT is the basis of sensitive experiments to measure neutrino mass. The final-state electronic, vibrational, and rotational excitations modify the beta spectrum significantly, and are obtained from theory. We report measurements of the branching ratios to specific ionization states for the isotopolog HT. Two earlier, concordant measurements gave branching ratios of HT to the bound HHe$^+$ ion of 89.5% and 93.2%, in sharp disagreement with the theoretical prediction of 55-57%, raising concerns about the theorys reliability in neutrino mass experiments. Our result, 56.5(6)%, is compatible with the theoretical expectation and disagrees strongly with the previous measurements.
The MJ Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-beta decay in $^{76}$Ge. The MJ DEM comprises 44.1~kg of Ge detectors (29.7 kg enriched in $^{76}$Ge) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at qval and a very low background with no observed candidate events in 10 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of $1.9times10^{25}$ yr (90% CL). This result constrains the effective Majorana neutrino mass to below 240 to 520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is $4.0_{-2.5}^{+3.1}$ counts/(FWHM t yr).
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