Precise calorimetric reconstruction of 5–50 MeV electrons in liquid argon time projection chambers (LArTPCs) will enable the study of astrophysical neutrinos in DUNE and could enhance the physics ...reach of oscillation analyses. Liquid argon scintillation light has the potential to improve energy reconstruction for low-energy electrons over charge-based measurements alone. Here we demonstrate light-augmented calorimetry for low-energy electrons in a single-phase LArTPC using a sample of Michel electrons from decays of stopping cosmic muons in the LArIAT experiment at Fermilab. Michel electron energy spectra are reconstructed using both a traditional charge-based approach as well as a more holistic approach that incorporates both charge and light. A maximum-likelihood fitter, using LArIAT's well-tuned simulation, is developed for combining these quantities to achieve optimal energy resolution. A sample of isolated electrons is simulated to better determine the energy resolution expected for astrophysical electron-neutrino charged-current interaction final states. In LArIAT, which has very low wire noise and an average light yield of 18 pe / MeV , an energy resolution of σ / E ≃ 9.3 % / √ E ⊕ 1.3 % is achieved. Samples are then generated with varying wire noise levels and light yields to gauge the impact of light-augmented calorimetry in larger LArTPCs. At a charge-readout signal-to-noise of S / N ≃ 30 , for example, the energy resolution for electrons below 40 MeV is improved by ≈ 10 % , ≈ 20 % , and ≈ 40 % over charge-only calorimetry for average light yields of 10 pe / MeV , 20 pe / MeV , and 100 pe / MeV , respectively.
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New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter θ23. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a ...data set corresponding to 6.57×10(20) protons on target, T2K has fit the energy-dependent νμ oscillation probability to determine oscillation parameters. The 68% confidence limit on sin(2)(θ23) is 0.514(-0.056)(+0.055) (0.511±0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Δm32(2)=(2.51±0.10)×10(-3) eV(2)/c(4) (inverted hierarchy: Δm13(2)=(2.48±0.10)×10(-3) eV(2)/c(4)). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.
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Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520 kt, with the first one in Japan at 295 km from the J-PARC neutrino beam with 2.5 degrees off-axis angles (OAAs), and ...the second one possibly in Korea at a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics, mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1000-1300 km and OAAs of 1 degrees-3 degrees. We conducted sensitivity studies on neutrino oscillation physics for a second detector, either in Japan (JD x 2) or Korea (JD + KD), and compared the results with a single detector in Japan. Leptonic charge-parity (CP) symmetry violation sensitivity is improved, especially when the CP is non-maximally violated. The larger matter effect at Korean candidate sites significantly enhances sensitivities to non-standard interactions of neutrinos and mass ordering determination. Current studies indicate the best sensitivity is obtained at Mt. Bisul (1088 km baseline, 1.3 degrees OAA). Thanks to a larger (1000 m) overburden than the first detector site, clear improvements to sensitivities for solar and supernova relic neutrino searches are expected.
Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ...ability of the detector to identify neutrons. A core-collapse supernova (CCSN) will be preceded by an increasing flux of neutrinos and antineutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent CCSN, hours earlier than the detection of the neutrinos from core collapse. Electron antineutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximizing detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hr before core collapse for a 15-25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, -Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hr before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading.
We report the results of a neutrino search in Super-Kamiokande (SK) for coincident signals with the first detected gravitational wave (GW) produced by a binary neutron-star merger, GW170817, which ...was followed by a short gamma-ray burst, GRB170817A, and a kilonova/macronova. We searched for coincident neutrino events in the range from 3.5 MeV to ∼100 PeV, in a time window 500 s around the gravitational wave detection time, as well as during a 14-day period after the detection. No significant neutrino signal was observed for either time window. We calculated 90% confidence level upper limits on the neutrino fluence for GW170817. From the upward-going-muon events in the energy region above 1.6 GeV, the neutrino fluence limit is 16.0 − 0.6 + 0.7 ( 21.3 − 0.8 + 1.1 ) cm−2 for muon neutrinos (muon antineutrinos), with an error range of 5° around the zenith angle of NGC4993, and the energy spectrum is under the assumption of an index of −2. The fluence limit for neutrino energies less than 100 MeV, for which the emission mechanism would be different than for higher-energy neutrinos, is also calculated. It is 6.6 × 107 cm−2 for anti-electron neutrinos under the assumption of a Fermi-Dirac spectrum with average energy of 20 MeV.
A search for boosted dark matter using 161.9 kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with ...a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.
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As a baryon number violating process with ΔB = 2, neutron-antineutron oscillation (n → n) provides a unique test of baryon number conservation. We have performed a search for n → n oscillation with ...bound neutrons in Super-Kamiokande, with the full dataset from its first four run periods, representing an exposure of 0.37 Mton − years. The search used a multivariate analysis trained on simulated n → n events and atmospheric neutrino backgrounds and resulted in 11 candidate events with an expected background of 9.3 events. In the absence of statistically significant excess, we derived a lower limit on n appearance lifetime in 16O nuclei of 3.6 × 1032 years and on the neutron-antineutron oscillation time of τn→n > 4.7 × 108 s at 90% C.L.
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We present a search for an excess of neutrino interactions due to dark matter in the form of weakly interacting massive particles (WIMPs) annihilating in the Galactic center or halo based on the data ...set of Super-Kamiokande-I, -II, -III and -IV taken from 1996 to 2016. We model the neutrino flux, energy, and flavor distributions assuming WIMP self-annihilation is dominant to νν¯, μ+μ−, bb¯, or W+W−. The excess is in comparison to atmospheric neutrino interactions which are modeled in detail and fit to data. Limits on the self-annihilation cross section 〈σAV〉 are derived for WIMP masses in the range 1 GeV to 10 TeV, reaching as low as 9.6 × 10−23 cm3 s−1 for 5 GeV WIMPs in bb¯ mode and 1.2 × 10−24 cm3 s−1 for 1 GeV WIMPs in νν¯ mode. The obtained sensitivity of the Super-Kamiokande detector to WIMP masses below several tens of GeV is the best among similar indirect searches to date.
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Abstract
The Super-Kamiokande detector can be used to search for neutrinos in time coincidence with gravitational waves detected by the LIGO–Virgo Collaboration (LVC). Both low-energy (7–100 MeV) and ...high-energy (0.1–10
5
GeV) samples were analyzed in order to cover a very wide neutrino spectrum. Follow-ups of 36 (out of 39) gravitational waves reported in the GWTC-2 catalog were examined; no significant excess above the background was observed, with 10 (24) observed neutrinos compared with 4.8 (25.0) expected events in the high-energy (low-energy) samples. A statistical approach was used to compute the significance of potential coincidences. For each observation,
p
-values were estimated using neutrino direction and LVC sky map; the most significant event (GW190602_175927) is associated with a post-trial
p
-value of 7.8% (1.4
σ
). Additionally, flux limits were computed independently for each sample and by combining the samples. The energy emitted as neutrinos by the identified gravitational wave sources was constrained, both for given flavors and for all flavors assuming equipartition between the different flavors, independently for each trigger and by combining sources of the same nature.
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