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Every second greater than 10 25 antineutrinos radiate to space from Earth, shining like a faint antineutrino star. Underground antineutrino detectors have revealed the rapidly decaying fission products inside nuclear reactors, verified the long-lived radioactivity inside our planet and informed sensitive experiments for probing fundamental physics. Mapping the anisotropic antineutrino flux and energy spectrum advance geoscience by defining the amount and distribution of radioactive power within Earth while critically evaluating competing compositional models of the planet. We present the Antineutrino Global Map 2015 (AGM2015), an experimentally informed model of Earth’s surface antineutrino flux over the 0 to 11 MeV energy spectrum, along with an assessment of systematic errors. The open source AGM2015 provides fundamental predictions for experiments, assists in strategic detector placement to determine neutrino mass hierarchy and aids in identifying undeclared nuclear reactors. We use cosmochemically and seismologically informed models of the radiogenic lithosphere/mantle combined with the estimated antineutrino flux, as measured by KamLAND and Borexino, to determine the Earth’s total antineutrino luminosity at . We find a dominant flux of geo-neutrinos, predict sub-equal crust and mantle contributions, with ~1% of the total flux from man-made nuclear reactors.

We consider the detector size, location, depth, background, and radio-purity required of a mid-Pacific deep-ocean instrument to accomplish the twin goals of making a definitive measurement of the electron anti-neutrino flux due to uranium and thorium decays from Earth’s mantle and core, and of testing the hypothesis for a natural nuclear reactor at the core of Earth. We take the experience with the KamLAND detector in Japan as our baseline for sensitivity and background estimates. We conclude that an instrument adequate to accomplish these tasks should have an exposure of at least 10 kilotonne-years (kT-y), should be placed at least at 4 km depth, may be located close to the Hawaiian Islands (no significant background from them), and should aim for KamLAND radio-purity levels, except for radon where it should be improved by a factor of at least 100. With an exposure of 10 kT-y we should achieve a 25% measurement of the flux of U/Th neutrinos from the mantle plus core. Exposure at multiple ocean locations for testing lateral heterogeneity is possible.

New developments in liquid scintillators, high-efficiency, fast photon detectors, and chromatic photon sorting have opened up the possibility for building a large-scale detector that can discriminate between Cherenkov and scintillation signals. Such a detector could reconstruct particle direction and species using Cherenkov light while also having the excellent energy resolution and low threshold of a scintillator detector. Situated deep underground, and utilizing new techniques in computing and reconstruction, this detector could achieve unprecedented levels of background rejection, enabling a rich physics program spanning topics in nuclear, high-energy, and astrophysics, and across a dynamic range from hundreds of keV to many GeV. The scientific program would include observations of low- and high-energy solar neutrinos, determination of neutrino mass ordering and measurement of the neutrino CP-violating phase δ , observations of diffuse supernova neutrinos and neutrinos from a supernova burst, sensitive searches for nucleon decay and, ultimately, a search for neutrinoless double beta decay, with sensitivity reaching the normal ordering regime of neutrino mass phase space. This paper describes Theia , a detector design that incorporates these new technologies in a practical and affordable way to accomplish the science goals described above.

The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet’s interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2±1.0 TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute  TW to Earth’s heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4 TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth’s total heat flux. We therefore conclude that Earth’s primordial heat supply has not yet been exhausted. Relative contributions to Earth’s total heat flux from the radioactive decay of isotopes versus primordial heat are debated. Measurements of geoneutrino particles emitted during radioactive decay in the Earth’s interior indicate that radiogenic isotopes contribute only about half of the total heat flux.

Particle dark matter could belong to a multiplet that includes an electrically charged state. WIMP dark matter (\\(\\chi^{0}\\)) accompanied by a negatively charged excited state (\\(\\chi^{-}\\)) with a small mass difference (e.g. \\(<\\) 20 MeV) can form a bound-state with a nucleus such as xenon. This bound-state formation is rare and the released energy is \\(\\mathcal{O}(1-10\\)) MeV depending on the nucleus, making large liquid scintillator detectors suitable for detection. We searched for bound-state formation events with xenon in two experimental phases of the KamLAND-Zen experiment, a xenon-doped liquid scintillator detector. No statistically significant events were observed. For a benchmark parameter set of WIMP mass \\(m_{\\chi^{0}} = 1\\) TeV and mass difference \\(\\Delta m = 17\\) MeV, we set the most stringent upper limits on the recombination cross section times velocity \\(\\langle\\sigma v\\rangle\\) and the decay-width of \\(\\chi^{-}\\) to \\(9.2 \\times 10^{-30}\\) \\({\\rm cm^3/s}\\) and \\(8.7 \\times 10^{-14}\\) GeV, respectively at 90% confidence level.

We report initial results of the Antarctic Impulsive Transient Antenna (ANITA) 2006-2007 Long Duration Balloon flight, which searched for evidence of the flux of cosmogenic neutrinos. ANITA flew for 35 days looking for radio impulses that might be due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. In our initial high-threshold robust analysis, no neutrino candidates are seen, with no physics background. In a non-signal horizontal-polarization channel, we do detect 6 events consistent with radio impulses from extensive air showers, which helps to validate the effectiveness of our method. Upper limits derived from our analysis now begin to eliminate the highest cosmogenic neutrino models.

We report a measurement of the strange axial coupling constant \\(g_A^s\\) using atmospheric neutrino data at KamLAND. This constant is a component of the axial form factor of the neutral-current quasielastic (NCQE) interaction. The value of \\(g_A^s\\) significantly changes the ratio of proton and neutron NCQE cross sections. KamLAND is suitable for measuring NCQE interactions as it can detect nucleon recoils with low-energy thresholds and measure neutron multiplicity with high efficiency. KamLAND data, including the information on neutron multiplicity associated with the NCQE interactions, makes it possible to measure \\(g_A^s\\) with a suppressed dependence on the axial mass \\(M_A\\), which has not yet been determined. For a comprehensive prediction of the neutron emission associated with neutrino interactions, we establish a simulation of particle emission via nuclear deexcitation of \\(^{12}\\)C, a process not considered in existing neutrino Monte Carlo event generators. Energy spectrum fitting for each neutron multiplicity gives \\(g_A^s =-0.14^{+0.25}_{-0.26}\\), which is the most stringent limit obtained using NCQE interactions without \\(M_A\\) constraints. The two-body current contribution considered in this analysis relies on a theoretically effective model and electron scattering experiments and requires future verification by direct measurements and future model improvement.

The Single-Volume Scatter Camera (SVSC) approach to kinematic neutron imaging, in which an incident neutron’s direction is reconstructed via multiple neutron-proton scattering events, potentially offers much greater efficiency and portability than current systems. In our first design of an Optically-Segmented (OS) SVSC, the detector consists of an 8 × 8 array of 5 × 5 × 200 mm 3 bars of EJ-204 scintillator wrapped in Teflon tape, optically coupled with SensL J-series 6 × 6 mm Silicon Photomultiplier (SiPM) arrays, all inside an aluminum frame that serves as a dark box. The SiPMs are read out using custom (multi-GSPS) waveform sampling electronics. In this work, construction, characterization, and electronics updates are reported. The position, time, and energy resolutions of individual bars were obtained by measuring different scintillators with different reflectors. This work was carried out in parallel at the University of Hawaii and at Sandia National Laboratories and resulted in the preliminary design of the camera. Monte-Carlo simulations using the Geant4 toolkit were carried out for individual scintillator bars, as well as the array setup. A custom analysis using ROOT libraries in C++ simulated the SiPM response from Geant4 photon hits. This analysis framework is under development and will allow for seamless comparisons between experimental and simulated data.

The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (\\(0\\nu\\beta\\beta\\)) decay half-life in \\(^{136}\\)Xe using a xenon-loaded liquid scintillator. We report an improved search using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of \\(^{136}\\)Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the \\(0\\nu\\beta\\beta\\) decay half-life of \\(T_{1/2}^{0\\nu} > 2.3 \\times 10^{26}\\) yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.