Abstract
An event topology with two secondary vertices compatible with the decay of short-lived particles was found in the analysis of neutrino interactions in the OPERA target. The observed topology is compatible with tau neutrino charged current (CC) interactions with charm production and neutrino neutral current (NC) interactions with coverline{c} pair production. However, other processes can mimic this topology. A dedicated analysis was implemented to identify the underlying process. A Monte Carlo simulation was developed and complementary procedures were introduced in the kinematic reconstruction. A multivariate analysis technique was used to achieve an optimal separation of signal from background. Most likely, this event is a nu _{tau } CC interaction with charm production, the tau and charm particle decaying into 1 prong and 2 prongs, respectively. The significance of this observation is evaluated.
Highlights
1 Introduction discovery of ντ appearance in a muon neutrino beam [11], later extended to a significance of 6.1 σ with its final data sample [12]
The significance of the ντ charged current (CC) interaction with charm production observation is based on a frequentist hypothesis test using a likelihood ratio as a test statistic [38,39]
They depend on 5 nuisance parameters σν: (i) a 20% normalisation factor, dominated by the CERN to Gran Sasso (CNGS) flux uncertainty [10]; (ii) a 20% uncertainty on the cross section of νNC interactions with charm pair production; (iii) a 20% uncertainty on the cross section of ντ CC interactions with single charm; (iv) a 6% uncertainty on ντ CC interactions cross section, for ντ ener-gies in the range of few tens of GeV [40]; (v) a 30% uncer-tainty on the hadronic re-interaction rate, based on test beamresults [27]
Summary
The detector was located at the LNGS underground laboratory and was exposed to the CNGS beam. The experiment profited from a 730 km long baseline and the average neutrino energy was 17 GeV. The beam exposure started in 2008 and ended in 2012, 1.8 × 1020 protons on target were collected. 19 505 neutrino interactions were recorded in the fiducial volume of the detector target The beam exposure started in 2008 and ended in 2012, 1.8 × 1020 protons on target were collected. 19 505 neutrino interactions were recorded in the fiducial volume of the detector target
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