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Register a new userFirst measurement of electron neutrino appearance in NOvA
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Added by
Christopher Backhouse
Publication date
2016
fields
Physics
and research's language is
English
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We report results from the first search for $ u_muto u_e$ transitions by the NOvA experiment. In an exposure equivalent to $2.74times10^{20}$ protons-on-target in the upgraded NuMI beam at Fermilab, we observe 6 events in the Far Detector, compared to a background expectation of $0.99pm0.11$ (syst.) events based on the Near Detector measurement. A secondary analysis observes 11 events with a background of $1.07pm0.14$ (syst.). The $3.3sigma$ excess of events observed in the primary analysis disfavors $0.1pi < delta_{CP} < 0.5pi$ in the inverted mass hierarchy at the 90% C.L.
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This paper reports the first measurement using the NOvA detectors of $ u_mu$ disappearance in a $ u_mu$ beam. The analysis uses a 14 kton-equivalent exposure of $2.74 times 10^{20}$ protons-on-target from the Fermilab NuMI beam. Assuming the normal neutrino mass hierarchy, we measure $Delta m^{2}_{32}=(2.52^{+0.20}_{-0.18})times 10^{-3}$ eV$^{2}$ and $sin^2theta_{23}$ in the range 0.38-0.65, both at the 68% confidence level, with two statistically-degenerate best fit points at $sin^2theta_{23} = $ 0.43 and 0.60. Results for the inverted mass hierarchy are also presented.
We present the first measurement of the single-differential $ u_e + bar{ u}_e$ charged-current inclusive cross sections on argon in electron or positron energy and in electron or positron scattering cosine over the full angular range. Data were collected using the MicroBooNE liquid argon time projection chamber located off-axis from the Fermilab Neutrinos at the Main Injector beam over an exposure of $2.0times10^{20}$ protons on target. The signal definition includes a 60 MeV threshold on the $ u_e$ or $bar{ u}_e$ energy and a 120 MeV threshold on the electron or positron energy. The measured total and differential cross sections are found to be in agreement with the GENIE, NuWro, and GiBUU neutrino generators.
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 is designed to search for $ u_{mu} rightarrow u_{tau}$ oscillations in appearance mode i.e. through the direct observation of the $tau$ lepton in $ u_{tau}$ charged current interactions. The experiment has taken data for five years, since 2008, with the CERN Neutrino to Gran Sasso beam. Previously, two $ u_{tau}$ candidates with a $tau$ decaying into hadrons were observed in a sub-sample of data of the 2008-2011 runs. Here we report the observation of a third $ u_tau$ candidate in the $tau^-tomu^-$ decay channel coming from the analysis of a sub-sample of the 2012 run. Taking into account the estimated background, the absence of $ u_{mu} rightarrow u_{tau}$ oscillations is excluded at the 3.4 $sigma$ level.
Neutrino oscillations have been probed during the last few decades using multiple neutrino sources and experimental set-ups. In the recent years, very large volume neutrino telescopes have started contributing to the field. First ANTARES and then IceCube have relied on large and sparsely instrumented volumes to observe atmospheric neutrinos for combinations of baselines and energies inaccessible to other experiments. Using this advantage, the latest result from IceCube starts approaching the precision of other established technologies, and is paving the way for future detectors, such as ORCA and PINGU. These new projects seek to provide better measurements of neutrino oscillation parameters, and eventually determine the neutrino mass ordering. The results from running experiments and the potential from proposed projects are discussed in this review, emphasizing the experimental challenges involved in the measurements.
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