Final Results of the OPERA Experiment on ντ Appearance in the CNGS Neutrino Beam

Abstract

The OPERA experiment was designed to study ν_{μ}→ν_{τ} oscillations in the appearance mode in the CERN to Gran Sasso Neutrino beam (CNGS). In this Letter, we report the final analysis of the full data sample collected between 2008 and 2012, corresponding to 17.97×10^{19} protons on target. Selection criteria looser than in previous analyses have produced ten ν_{τ} candidate events, thus reducing the statistical uncertainty in the measurement of the oscillation parameters and of ν_{τ} properties. A multivariate approach for event identification has been applied to the candidate events and the discovery of ν_{τ} appearance is confirmed with an improved significance level of 6.1σ. |Δm_{32}^{2}| has been measured, in appearance mode, with an accuracy of 20%. The measurement of the ν_{τ} charged-current cross section, for the first time with a negligible contamination from ν[over ¯]_{τ}, and the first direct evidence for the ν_{τ} lepton number are also reported.

On the role of the ντ appearance in DUNE in constraining standard neutrino physics and beyond

“…[52]. We observe that a fit to the OPERA ν τ events [32] did in Ref. [46] predicted the bound | µτ | 0.41 (marginalising over all parameters including NSI parameters) which is almost a factor of two larger than the worst limit DUNE can set.…”

Exploring new physics from ν events in OPERA

“…The OPERA detector [15] was located in the underground laboratory at Gran Sasso and exposed to the CERN to Gran Sasso neutrino beam; fluxes for our numerical simulations have been taken from [16] and normalized accordingly to 10 19 proton on target (pot) and a detector mass of 1 Kton. The efficiencies for ν τ identification, as well as the bin-to-bin normalization for both charm and neutral current events, have been extracted from the MonteCarlo expectations of Fig.1 of [1], which refer to the full data sample corresponding to 17.97·10 19 pot and 1.25 Kton mass, and the relevant mixing angles fixed to θ 23 = 45 • and ∆m 2 23 = 2.50 × 10 −3 eV 2 . For the sake of completeness these numbers are reported in Tab.1, grouped in 6 energy bins of variable size in the energy range E ν ∈ [0, 60] GeV; the corresponding total number of ν τ events is 6.8, while for the charm and NC backgrounds we have 0.63 and 1.37 events, respectively.…”

“…In the NSI sector, the relevant new parameter to which OPERA is maximally sensitive is ε µτ on which, using the spectral informations released in [1], can set the 90% CL upper bound |ε µτ | < 0.41, roughly two orders of magnitude worse than the current constraint. Anything can be said on the related CP phase, which remains undetermined in the whole [0, 2π) interval.…”

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We analyze in details the impact of the 10 ν τ events seen in the OPERA experiment [1] in constraining the Non Standard Interaction parameter ε µτ affecting neutrino propagation in matter and the allowed parameter space of models with one sterile neutrino of the 3 + 1 type.

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Probing nonstandard lepton number violating interactions in neutrino oscillations

“…Unlike MINOS, OPERA measured neutrinos from the CNGS beam at CERN that were above the threshold for τ ± production. The main physics goal of the experiment was to confirm ν τ appearance -around 10 τ ± events were recorded over four years of data taking [146]. Unfortunately the experiment was only able to distinguish the charge of one τ − event at 5σ significance, while the other charges were undetermined.…”