Search for Lepton Flavor Violating Processes in Neutrino Interactions
Neutrino oscillations are the only known, so far, examples of the lepton flavor violating processes. Two neutrino mass differences induce the neutrino flavour changing in the whenever the sin(Deltamsq*L/E) significantly deviates from zero. The relative probablilities of the appearance of the neutrino flavors different from the original neutrino beam is given by the neutrino mixing matrix MNS.

The interactions responsible for the oscillations-induced lepton flovor violation are the same as the ones responsible for the neutrino masses and they are likely to operate at very high energies, similar to the GUT scale. On the other hand it is quite possible that there are other processes, beyond the minimal standard model, which operate at much lower energies and which induce lepton flavor violations.  The examples of mechanisms include:
  • Non-untitarity of the neutrino mxing matrix: TeV scale see-saw, inverse see-saw could be a typical example
  • Leptoquarks mediated interactions
  • R-parity SUSY particles violating interactions
  • Charged Higgs mediated interactions

Neutrino oscillations constitute an irreducible background for such possible rare processes, hence the search for the non-standard interactions ought to be conducted at the short baseline, where oscillations probability is known to be very small. Muon neutrino to tau neutrino appears to be particularily promising proposition. The existng limit provided by the shprt-baseline neutrino oscillations experiments NOMAD and CHORUS is of the order of ~10-^4.

The next generation of the short-baseline tau appearance experiments with the sensitiivity improved by up to two orders of magnitude was well developed, but abandoned shortly after the discovery of the neutrino oscillations by the SuperK experiment and a determination that the atmosperic neutrino oscillations are induced by the mass differnece of the order or 3x10-^3 eV^2. This discovery has demonstrated that the oscillation probability is xtremely low at the short-baseline oscillations.

What was a fatal blow for the neutrino oscillations search is a great advantage for the search for non-standard neutrino oscillations: signatures for potential new physics may appear on top the extremely low or no backgrond. The proposals for the next generation short baseline oscillation searh offered a major improvement of the sensitivity event with the detector technology of the late 90's. Advances in the experimental techniques in conjunction with modern high intensity neutrino beams offer an attractive prospect of discovery of the non-standard neutrino interactions or a signficant improvement of the limits on the strength of such interactions. Such a search is complementary to tha direct searches conducted at the LHC and it has somewhat different sensitivities.

These studies are focused on the establishing of a potential case for a tau appearance experiment at the short distance in the NUMI beam with a target sensitivity better than 10-^6. The directions pursued include:
  • development of the physics case: are the potential interaction at such a level allowed by the body of limits on various rare process, like lepton flavor viotating tau decays? Are there theoretical models allowing or predicting the processes leading to the tau appearance? What are the levels of experimental sensitivity necessary to confirm or refute these models?
  • development of a design of a detector with adequate sentivity and necessary background rejection capability. The desired sensitive detector mass is the range of several tonnes, whereas the background rejection power must exceed 10^6.
  • evaluation of the rates, energy spectra and potential backgrounds for the improved NUMI beams
Expressions of interest, corrections and suggestions of improvement and especially constructive contributions are extremely welcome and should be direted to the temporary webmaster.