29 research outputs found
Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation Îł rays
Neutrino- and antineutrino-oxygen neutral-current quasielastic-like
interactions are measured at Super-Kamiokande using nuclear de-excitation
-rays to identify signal-like interactions in data from a $14.94 \
(16.35)\times 10^{20}\langle \sigma_{\nu {\rm -NCQE}} \rangle = 1.70 \pm 0.17 ({\rm stat.}) ^{+
{\rm 0.51}}_{- {\rm 0.38}} ({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}\langle \sigma_{\bar{\nu} {\rm
-NCQE}} \rangle = 0.98 \pm 0.16 ({\rm stat.}) ^{+ {\rm 0.26}}_{- {\rm 0.19}}
({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}$ with a flux-averaged energy
of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are
the most precise to date, and the antineutrino result is the first cross
section measurement of this channel. They are compared with various theoretical
predictions. The impact on evaluation of backgrounds to searches for supernova
relic neutrinos at present and future water Cherenkov detectors is also
discussed
Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors
We report a measurement of the flux-integrated ΜΌ charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are ÏH2OCC=(0.840±0.010(stat.)+0.10â0.08(syst.))Ă10â38cm2/nucleon, ÏCHCC=(0.817±0.007(stat.)+0.11â0.08(syst.))Ă10â38cm2/nucleon, and ÏFeCC=(0.859±0.003(stat.)+0.12â0.10(syst.))Ă10â38cm2/nucleon, respectively, for a restricted phase space of induced muons: ΞΌ0.4 GeV/c in the laboratory frame. The measured cross section ratios are ÏH2OCC/ÏCHCC=1.028±0.016(stat.)±0.053(syst.)â , ÏFeCC/ÏH2OCC=1.023±0.012(stat.)±0.058(syst.)â , and ÏFeCC/ÏCHCC=1.049±0.010(stat.)±0.043(syst.)â . These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses
Constraint on the matter-antimatter symmetry-violating phase in neutrino oscillations
The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matterâantimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard modelâs charged current interactions5,6, provides a potential source of CP violation through a complex phase ÎŽCP, which is required by some theoretical models of leptogenesis7,8,9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of ÎŽCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of ÎŽCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3Ï). The 3Ï confidence interval for ÎŽCP, which is cyclic and repeats every 2Ï, is [â3.41, â0.03] for the so-called normal mass ordering and [â2.54, â0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matterâantimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks