This paper describes the design and construction of the MicroBooNE liquid argon time projection chamber and associated systems. MicroBooNE is the first phase of the Short Baseline Neutrino program, located at Fermilab, and will utilize the capabilities of liquid argon detectors to examine a rich assortment of physics topics. In this document details of design specifications, assembly procedures, and acceptance tests are reported.
We present new constraints on the neutrino oscillation parameters ∆m 2 21 , θ12, and θ13 from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of 3.49 × 10 32 target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis (θ13 = 0) of the KamLAND and solar data yields the best-fit values tan 2 θ12 = 0.444 −0.016 . This θ13 interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global θ13 analysis, incorporating the CHOOZ, atmospheric and accelerator data, which indicates sin 2 θ13 = 0.009 +0.013 −0.007 . A nonzero value is suggested, but only at the 79% C.L.
Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in ν detectors, double-β-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of 11 C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be Y n = (2.8 ± 0.3) × 10 −4 µ −1 g −1 cm 2 . For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment.
We present the results of a search for extraterrestrial electron antineutrinos (ν e 's) in the energy range 8.3 MeV < E ν e < 31.8 MeV using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of 8 B solar ν e 's converting into ν e 's at 5.3 × 10 −5 (90% CL), if we assume an undistorted ν e shape. This limit corresponds to a solar ν e flux of 93 cmor an event rate of 1.6 events (kton-year) −1 above the energy threshold (E ν e 8.3 MeV). The present data also allows us to set more stringent limits on the diffuse supernova neutrino flux and on the annihilation rates for light dark matter particles.
Determination of the neutrino mass hierarchy using a reactor neutrino experiment at ∼60 km is analyzed. Such a measurement is challenging due to the finite detector resolution, the absolute energy scale calibration, as well as the degeneracies caused by current experimental uncertainty of |∆m 2 32 |. The standard χ 2 method is compared with a proposed Fourier transformation method. In addition, we show that for such a measurement to succeed, one must understand the non-linearity of the detector energy scale at the level of a few tenths of percent.
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