Final NOMAD results on nu_mu->nu_tau and nu_e->nu_tau oscillations including a new search for nu_tau appearance using hadronic tau decays

TL;DR

This paper reports on the NOMAD experiment's search for nu_tau appearance via neutrino oscillations, unifying hadronic tau decay channels, and setting new limits on oscillation parameters and tau couplings, with no evidence of oscillations found.

Contribution

It introduces a comprehensive analysis of all hadronic tau decays in NOMAD, significantly enhancing sensitivity to neutrino oscillations and providing updated limits on oscillation parameters.

Findings

No evidence for nu_tau oscillations was observed.

Set 90% confidence level limits on oscillation parameters.

Derived new constraints on tau lepton couplings to neutrinos.

Abstract

Results from the nu_tau appearance search in a neutrino beam using the full NOMAD data sample are reported. A new analysis unifies all the hadronic tau decays, significantly improving the overall sensitivity of the experiment to oscillations. The "blind analysis" of all topologies yields no evidence for an oscillation signal. In the two-family oscillation scenario, this sets a 90% C.L. allowed region in the sin^2(2theta)-Delta m^2 plane which includes sin^2(2theta)<3.3 x 10^{-4} at large Delta m^2 and Delta m^2 < 0.7 eV^2/c^4 at sin^2(2theta)=1. The corresponding contour in the nu_e->nu_tau oscillation hypothesis results in sin^2(2theta)<1.5 x 10^{-2} at large Delta m^2 and Delta m^2 < 5.9 eV^2/c^4 at sin^2(2theta)=1. We also derive limits on effective couplings of the tau lepton to nu_mu or nu_e.