Reconstructed Neutrino Energy Research Articles

Measurement of the neutrino component of an antineutrino beam observed by a nonmagnetized detector

Two independent methods are employed to measure the neutrino flux of the anti-neutrino-mode beam observed by the MiniBooNE detector. The first method compares data to simulated event rates in a high purity $\numu$ induced charged-current single $\pip$ (CC1$\pip$) sample while the second exploits the difference between the angular distributions of muons created in $\numu$ and $\numub$ charged-current quasi-elastic (CCQE) interactions. The results from both analyses indicate the prediction of the neutrino flux component of the pre-dominately anti-neutrino beam is over-estimated - the CC1$\pip$ analysis indicates the predicted $\numu$ flux should be scaled by $0.76 \pm 0.11$, while the CCQE angular fit yields $0.65 \pm 0.23$. The energy spectrum of the flux prediction is checked by repeating the analyses in bins of reconstructed neutrino energy, and the results show that the spectral shape is well modeled. These analyses are a demonstration of techniques for measuring the neutrino contamination of anti-neutrino beams observed by future non-magnetized detectors.

Re-evaluation of the T2KK physics potential with simulations including backgrounds

The Tokai-to-Kamioka-and-Korea (T2KK) neutrino oscillation experiment under examination can have a high sensitivity to determine the neutrino mass hierarchy for a combination of relatively large ( ∼ 3.0°) off-axis angle beam at Super-Kamiokande (SK) and small ( ∼ 0.5°) off-axis angle at L ∼ 1,000 km in Korea. We elaborate previous studies by taking into account smearing of reconstructed neutrino energy due to finite resolution of electron or muon energies, nuclear Fermi motion and resonance production, as well as the neutral current π0 production background to the νμ → νe oscillation signal. It is found that the mass hierarchy pattern can still be determined at 3σ level if sin22θRCT ≡ 4|Ue3|2(1 − |Ue3|2) ≳ 0.08(0.09) when the hierarchy is normal (inverted) with 5 × 1021} POT (protons on target) exposure, or 5 years of the T2K experiment, if a 100 kton water Čerenkov detector is placed in Korea. The π0 backgrounds deteriorate the capability of the mass hierarchy determination, whereas the events from CC nuclear resonance productions contribute positively to the hierarchy discrimination power. We also find that the π0 backgrounds seriously affect the CP phase measurement. Although δMNS can still be constrained with an accuracy of ∼ ±45° (±60°) at 1σ level for the normal (inverted) hierarchy with the above exposure if sin22θRCT ≳ 0.04, CP violation can no longer be established at 3σ level even for δMNS = ±90° and sin22θRCT = 0.1. About four times higher exposure will be needed to measure δMNS with ±30° accuracy.

Unexplained Excess of Electronlike Events from a 1-GeV Neutrino Beam

The MiniBooNE Collaboration observes unexplained electronlike events in the reconstructed neutrino energy range from 200 to 475 MeV. With 6.46x10;{20} protons on target, 544 electronlike events are observed in this energy range, compared to an expectation of 415.2+/-43.4 events, corresponding to an excess of 128.8+/-20.4+/-38.3 events. The shape of the excess in several kinematic variables is consistent with being due to either nu_{e} and nu[over ]_{e} charged-current scattering or nu_{mu} neutral-current scattering with a photon in the final state. No significant excess of events is observed in the reconstructed neutrino energy range from 475 to 1250 MeV, where 408 events are observed compared to an expectation of 385.9+/-35.7 events.

K2K far detector analysis

The far detector analysis for ν μ disappearance in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment is presented. The data used for this analysis is 8.9 × 10 19 protons on target (POT). A total of 107 events are observed in the far detector, Super-Kamiokande (SK), while 151 −10 +12 are expected without ν μ oscillation. Spectral distortion of the reconstructed neutrino energy (E ν ) is also observed, and it is consistent with ν μ − ν τ oscillation. The two-flavor ν μ − ν τ oscillation analysis is evaluated. We obtain an allowed region which is consistent with SK atmospheric neutrino oscillation analysis results. The probability to observe our results from a statistical fluctuation is 0.005% (4.0 σ ) in the case of no oscillation.

Recent results from K2K

The result for ν μ oscillation analysis in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment are presented. The data used for this analysis is 8.9 × 1019 protons on target (POT). A total of 107 events are observed in the far detector, Super-Kamiokande (SK), while 151 −10 +12 expected if ν μ oscillation is not assumed. The spectrum distortion of the reconstructed neutrino energy (Eν) is also observed, and it is consistent with the ν μ − ν τ oscillation. The two-flavor ν μ - ν τ oscillation analysis is evaluated. We obtained the allowed region which is consistent with SK atmospheric neutrino oscillation analysis results. The probability to get these results without neutrino oscillation is 0.005% (4.0σ).