New results on $\nu_\mu \to \nu_\tau$ appearance with the OPERA experiment in the CNGS beam

TL;DR

This paper reports on improved analysis techniques and new data from the OPERA experiment, providing evidence for muon neutrino to tau neutrino oscillations with a significance of 2.40 sigma.

Contribution

It introduces enhanced simulation and analysis methods and extends the dataset, leading to additional candidate events and stronger evidence for neutrino oscillations.

Findings

Observation of two $ u_ au$ candidate events.

Oscillation signal significance of 2.40 sigma.

Improved detection efficiency and background estimation.

Abstract

The OPERA neutrino experiment is designed to perform the first observation of neutrino oscillations in direct appearance mode in the $\nu_\mu \to \nu_\tau$ channel, via the detection of the $\tau$-leptons created in charged current $\nu_\tau$ interactions. The detector, located in the underground Gran Sasso Laboratory, consists of an emulsion/lead target with an average mass of about 1.2 kt, complemented by electronic detectors. It is exposed to the CERN Neutrinos to Gran Sasso beam, with a baseline of 730 km and a mean energy of 17 GeV. The observation of the first $\nu_\tau$ candidate event and the analysis of the 2008-2009 neutrino sample have been reported in previous publications. This work describes substantial improvements in the analysis and in the evaluation of the detection efficiencies and backgrounds using new simulation tools. The analysis is extended to a sub-sample of 2010 and 2011 data, resulting from an electronic detector-based pre-selection, in which an additional $\nu_\tau$ candidate has been observed. The significance of the two events in terms of a $\nu_\mu \to \nu_\tau$ oscillation signal is of 2.40 $\sigma$.