Measuring tau neutrino appearance probability via unitarity

We propose a unitarity method for determining tau neutrino appearance probability P(nu mu -> nu tau) in longbaseline (LBL) accelerator experiments and atmospheric neutrino observations. When simultaneous in situ measurements of P(nu mu -> nu mu) and P(nu mu -> nu e) proceed, as is typical in the LBL experiments, one can use unitarity to measure P(nu mu -> nu tau). A theorists' toy analysis for the model-independent determination of P(nu mu -> nu mu) and P(nu mu -> nu e) is presented by using the NOvA data. It is shown in our analysis that less than or similar to 5% (8%) measurement of tau neutrino appearance probability in neutrino (antineutrino) mode is possible in the peak region 1.5 less than or similar to E nu less than or similar to 2.5 GeV. The nu SM-independent nature of determination of the probabilities is emphasized.

Automated summary

A unitarity method is proposed for determining tau neutrino appearance probability in LBL accelerator experiments and atmospheric neutrino observations. Toy analysis using NOvA data demonstrates the feasibility of measuring these probabilities with less than 5% accuracy in certain energy ranges, emphasizing the SM-independent nature of the determination.