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Register a new userRecent results of the OPERA experiment
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Fabio Pupilli
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The OPERA experiment aims at the direct confirmation of the leading oscillation mechanism in the atmospheric sector looking for the appearance of $ u_{tau}$ in an almost pure $ u_{mu}$ beam (the CERN CNGS beam). In five years of physics run the experiment collected $17.97 times 10^{19}$ p.o.t. The detection of $tau$s produced in $ u_{tau}$ CC interactions and of their decays is accomplished exploiting the high spatial resolution of nuclear emulsions. Furthermore OPERA has good capabilities in detecting electron neutrino interactions, setting limits on the $ u_{mu} rightarrow u_{e}$ oscillation channel. In this talk the status of the analysis will be presented together with updated results on both oscillation channels.
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DANSS is a one cubic meter highly segmented plastic scintillator detector. Its 2500 one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS detector is placed under an industrial 3.1GW reactor of the Kalinin Nuclear Power plant 350km NW from Moscow. The distance to the core ia varied on-line from 10.7m to 12.7m. Recent results on searches for a sterile neutrino are presented as well as measurements of the antineutrino spectrum dependence on the fuel composition. All results are preliminary. PACS: 14.60.Pq, 14.60.St
We present new results of the DANSS experiment on the searches for sterile neutrinos. They are based on 2.1 million of inverse beta decay events collected at 10.7, 11.7 and 12.7 meters from the reactor core of the 3.1 GW Kalinin Nuclear Power Plant in Russia. This data sample is 2.5 times larger than the data sample in the previous DANSS publication. The search for the sterile neutrinos is performed using the ratio of $bar u_e$ spectra at two distances. This method is very robust against systematic uncertainties in the $bar u_e$ spectrum and the detector efficiency. We do not see any statistically significant sign for the $bar u_e$ oscillations. This allows us to exclude further a large and interesting part of the sterile neutrino parameter space. All results are preliminary.
OPERA is a long-baseline experiment designed to search for $ u_{mu}to u_{tau}$ oscillations in appearance mode. It was based at the INFN Gran Sasso laboratory (LNGS) and took data from 2008 to 2012 with the CNGS neutrino beam from CERN. After the discovery of $ u_tau$ appearance in 2015, with $5.1sigma$ significance, the criteria to select $ u_tau$ candidates have been extended and a multivariate approach has been used for events identification. In this way the statistical uncertainty in the measurement of the oscillation parameters and of $ u_tau$ properties has been improved. Results are reported.
The OPERA experiment has conclusively observed the appearance of tau neutrinos in the muon neutrino CNGS beam. Exploiting the OPERA detector capabilities, it was possible to isolate high purity samples of $ u_{e}$, $ u_{mu}$ and $ u_{tau}$ charged current weak neutrino interactions, as well as neutral current weak interactions. In this Letter, the full dataset is used for the first time to test the three-flavor neutrino oscillation model and to derive constraints on the existence of a light sterile neutrino within the framework of the $3+1$ neutrino model. For the first time, tau and electron neutrino appearance channels are jointly used to test the sterile neutrino hypothesis. A significant fraction of the sterile neutrino parameter space allowed by LSND and MiniBooNE experiments is excluded at 90% C.L. In particular, the best-fit values obtained by MiniBooNE combining neutrino and antineutrino data are excluded at 3.3 $sigma$ significance.
The OPERA neutrino experiment is designed to perform the first observation of neutrino oscillations in direct appearance mode in the $ u_mu to u_tau$ channel, via the detection of the $tau$-leptons created in charged current $ u_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 $ u_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 $ u_tau$ candidate has been observed. The significance of the two events in terms of a $ u_mu to u_tau$ oscillation signal is of 2.40 $sigma$.
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