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[en] The study of νμ→ντ oscillations and the explicit observation of ντ through the identification of the final-state τ lepton ('direct appearance search') represent the most straightforward test of the oscillation phenomenon. It is, nonetheless, the most challenging from the experimental point of view. In this paper, we discuss current empirical evidence for the direct appearance of tau neutrinos at the atmospheric scale and the perspectives for the next few years, up to the completion of the CNGS physics programme. We investigate the relevance of this specific oscillation channel for gaining insights into neutrino physics within the standard three-family framework. Finally, we discuss the opportunities offered by precision studies of νμ→ντ transitions for the occurrence of more exotic scenarios, emerging from additional sterile neutrinos or non-standard interactions.
[en] An updated limit on the mντ has been derived from 295,000 η decays observed in the ALEPH detector at LEP between 1991 and 1994. The result is obtained from a maximum likelihood fit in the hadronic total energy vs hadronic invariant mass plane for a sample of selected 5π(π0) candidates consisting of 39 τ → 5πντ and 3 τ → 5ππ0ντ. A comparison of the invariant mass spectrum with 5π phase space and a a1 + 2π model favors the latter τ decay mechanism. The τ neutrino mass limit of 23.1 MeV at 95 % confidence level is slightly more restrictive that the published value. (author)
[en] TAUWER is a proposed astroparticle experiment to detect ultrahigh energy TAU neutrinos, using detector towers arrayed on a mountainside looking down into a valley. This test is to study the possibility of replacing Hamamatsu miniature PMTs with SiPMs for readout by determining the response of scintillation detectors with SiPM readout to low energy electrons, 2 GeV or lower, as the beam will provide. The detector itself is a compact package shown in the picture on the cover. it was used in a parasitic test beam run on December 15, 2010, to compare the relative timing of the signals from three counters for MIPs. The only change for this new run is the insertion of 1.5 cm of Pb in front of counter 2 or counter 3 during most of the running. The experiment takes some electron data without Pb for calibration purposes. The apparatus will be mounted on the moving table in MT6.2B.
[en] It has been considered that the τ-neutrino is probably the neutrino with the largest mass - if the neutrinos have masses at all. This mass can be either of Dirac or of Majorana type (because the τ neutrino is a charge less object) and the question is how to distinguish between the two possibilities. As an answer to this question it is proposed to carry out a certain high energy experiment. This bound has been ignored because it is always good to check cosmological considerations by an earth experiment. (author). 4 refs., 3 figs
[en] A new long-range interaction between heavy neutrinos may solve some current problems in large-scale structure, if the new interaction mimics gravity. Assuming that the dark matter is dominated by ∼100 eV τ neutrinos, we investigate whether time delay measurements on supernova neutrinos can test this possibility. We find that such experiments can rule out or detect specific forms of the new interaction potential. In addition, we find the exact dispersive nature of the interacting medium to be critical in determining the time delay: even small corrections to the potential can dramatically alter the magnitude of the effect
[en] We report the first observational search for tau neutrinos (ντ) from gamma-ray bursts (GRBs) using one of the Ashra light collectors. The Earth-skimming ντ technique of imaging Cherenkov τ showers was applied as a detection method. We set stringent upper limits on the ντ fluence in PeV-EeV region for 3780 s (between 2.83 and 1.78 hr before) and another 3780 s (between 21.2 and 22.2 hr after) surrounding GRB081203A triggered by the Swift satellite. This first search for PeV-EeV ντ complements other experiments in energy range and methodology, and suggests the prologue of 'multi-particle astronomy' with a precise determination of time and location.