Reconstruction of neutrino induced neutral current neutral pion events with the T2K ND280 Tracker and ECAL

T2K is a long baseline neutrino oscillation experiment in Japan. One of the goals is to search for electron neutrino appearance at the far detector (Super Kamiokande) in a muon neutrino beam produced 295 km away, to make a measurement of the unknown neutrino oscillation angle [Symbol appears here. To view, please open pdf attachment]13. A major background to this appearance search is neutral pions (π0) produced in neutral current (NC) neutrino interactions. The π0s decay to photons, which can in cases mimic the electron appearance signal. The near detector of the experiment (ND280) has the capability of measuring the rates of NCπ0 production processes. NCπ0 interactions in the Tracker of the detector (plastic scintillator targets, and time projection chambers for tracking charged particles) can be detected through photon conversions in the electromagnetic calorimeter that surrounds the Tracker. For these types of events, the photon reconstruction in the calorimeter has to have good energy and angular resolutions. This thesis describes the T2K experiment, the ND280 detector and its offline software, and gives details on the ECal reconstruction of photons. The performance of the reconstruction in relation to the π0 decay photons, their energy and angular resolutions, is studied. An analysis is presented for the reconstruction of NC π0s produced in the trackers, with both photons converting in the downstream calorimeter, developed purely with Monte Carlo (with GENIE as the interaction generator), and then applied to the first-year data from ND280. The Monte Carlo expectation is 17.7 ± 1.1(stat) ± 4.9(syst) events, with 37 ± 4% NCπ0 purity; 21 events are seen in the first year data. The MC is consistent with data at the 0.5σ level. As a crosscheck, the same analysis is applied to a different Monte Carlo production (using NEUT as the generator). The expectation from this production is 16.8 ± 1.0(stat) ± 4.7(syst) events, with 30 ± 4% purity. This is consistent with data at the 0.7σ level

A Combined Limit on the Neutrino Mass from Neutrinoless Double-Beta Decay and Constraints on Sterile Majorana Neutrinos

We present a framework to combine data from the latest neutrinoless double-beta decay experiments for multiple isotopes and derive a limit on the effective neutrino mass using the experimental energy distributions. The combined limits on the effective mass range between 130-310 meV, where the spread is due to different model calculations of nuclear matrix elements (NMEs). The statistical consistency (p values) between this result and the signal observation claimed by the Heidelberg-Moscow experiment is derived. The limits on the effective mass are also evaluated in a (3+1) sterile neutrino model, assuming all neutrinos are Majorana particles.Comment: 8 pages, 8 figures. Version accepted by Phys Rev D, including latest CUORE-0 result

A Combined View of Sterile-Neutrino Constraints from CMB and Neutrino Oscillation Measurements

We perform a comparative analysis of constraints on sterile neutrinos from the Planck experiment and from current and future neutrino oscillation experiments (MINOS, IceCube, SBN). For the first time, we express the Planck constraints on $N_{\rm eff}$ and $m_{\rm eff}^{\rm sterile}$ from the Cosmic Microwave Background in the parameter space used by oscillation experiments using both mass-squared differences and mixing angles. In a model with a single sterile neutrino species and using standard assumptions, we find that the Planck data and the oscillation experiments measuring muon-neutrino disappearance have similar sensitivity.Comment: 6 pages, 3 figures, Version accepted by Physics Letters B, minor changes to text, results unchange

Direct comparison of sterile neutrino constraints from cosmological data, νe\nu_{e} disappearance data and νμ→νe\nu_{\mu}\rightarrow\nu_{e} appearance data in a 3+13+1 model

We present a quantitative, direct comparison of constraints on sterile neutrinos derived from neutrino oscillation experiments and from Planck data, interpreted assuming standard cosmological evolution. We extend a $1+1$ model, which is used to compare exclusions contours at the 95% CL derived from Planck data to those from $\nu_{e}$-disappearance measurements, to a $3+1$ model. This allows us to compare the Planck constraints with those obtained through $\nu_{\mu}\rightarrow\nu_{e}$ appearance searches, which are sensitive to more than one active-sterile mixing angle. We find that the cosmological data fully exclude the allowed regions published by the LSND, MiniBooNE and Neutrino-4 collaborations, and those from the gallium and rector anomalies, at the 95% CL. Compared to the exclusion regions from the Daya Bay $\nu_{e}$-disappearance search, the Planck data are more strongly excluding above $|\Delta m^{2}_{41}|\approx 0.1\, \mathrm{eV}^{2}$ and $m_\mathrm{eff}^\mathrm{sterile}\approx 0.2\, \mathrm{eV}$, with the Daya Bay exclusion being stronger below these values. Compared to the combined Daya Bay/Bugey/MINOS exclusion region on $\nu_{\mu}\rightarrow\nu_{e}$ appearance, the Planck data is more strongly excluding above $\Delta m^{2}_{41}\approx 5\times 10^{-2}\,\mathrm{eV}^{2}$, with the exclusion strengths of the Planck data and the Daya Bay/Bugey/MINOS combination becoming comparable below this value.Comment: 9 pages, 4 figures, accepted by Eur. Phys. J.

Search for heavy neutral leptons decaying into muon-pion pairs in the MicroBooNE detector

We present upper limits on the production of heavy neutral leptons (HNLs) decaying to mu p pairs using data collected with the MicroBooNE liquid-argon time projection chamber (TPC) operating at Fermilab. This search is the first of its kind performed in a liquid-argon TPC. We use data collected in 2017 and 2018 corresponding to an exposure of 2.0 x 10(20) protons on target from the Fermilab Booster Neutrino Beam, which produces mainly muon neutrinos with an average energy of approximate to 800 MeV. HNLs with higher mass are expected to have a longer time of flight to the liquid-argon TPC than Standard Model neutrinos. The data are therefore recorded with a dedicated trigger configured to detect HNL decays that occur after the neutrino spill reaches the detector. We set upper limits at the 90% confidence level on the element vertical bar U-mu 4 vertical bar(2) of the extended PMNS mixing matrix in the range vertical bar U-mu 4 vertical bar(2) <(6.6-0.9) x 10(-7) for Dirac HNLs and vertical bar U-mu 4 vertical bar(2) <(4.7-0.7) x 10(-7) for Majorana HNLs, assuming HNL masses between 260 and 385 MeV and vertical bar U-e4 vertical bar(2) = vertical bar U-tau 4 vertical bar(2) = 0