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The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross section is by far the largest of all low-energy neutrino couplings. This mode of interaction offers new opportunities to study neutrino properties and leads to a miniaturization of detector size, with potential technological applications. We observed this process at a 6.7σ̃ confidence level, using a low-background, 14.6-kilogram CsI[Na] scintillator exposed to the neutrino emissions from the Spallation Neutron Source at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the standard model for this process, were observed in high signal-to-background conditions. Improved constraints on nonstandard neutrino interactions with quarks are derived from this initial data set.

The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of 238 U and 232 Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained. Earthly powers The KamLAND experiment located in the Kamioka mine one kilometre beneath the Japanese Alps was primarily designed to detect antineutrinos produced by nuclear reactors. But radioactive elements in the Earth also release antineutrinos — known as geoneutrinos — and KamLAND should be sensitive enough to detect these too. And detect them it has. About 20 antineutrinos with characteristics typical of the products of uranium-238 and thorium-232 decay have so far been recorded. This opens up an exciting new era for geophysicists. Using geoneutrinos it should be possible to build up a three-dimensional image of the Earth's interior, and to establish how much geothermal heat is released by radioactive decay. On the cover, the half-globe to the left gives the neutrino rate at KamLAND from different locations on and beneath the Earth's surface.

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 measured the cross section of coherent elastic neutrino-nucleus scattering (\\cevns{}) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. New data collected before detector decommissioning has more than doubled the dataset since the first observation of \\cevns{}, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision. With these analysis improvements, the COHERENT collaboration determined the cross section to be \\((165^{+30}_{-25})\\times10^{-40}\\)~cm\\(^2\\), consistent with the standard model, giving the most precise measurement of \\cevns{} yet. The timing structure of the neutrino beam has been exploited to compare the \\cevns{} cross section from scattering of different neutrino flavors. This result places leading constraints on neutrino non-standard interactions while testing lepton flavor universality and measures the weak mixing angle as \\(\\sin^2\\theta_{W}=0.220^{+0.028}_{-0.026}\\) at \\(Q^2\\approx(50\\text{ MeV})^2\\)

Differential cross sections for Compton scattering from the proton have been measured at scattering angles of \\(55^\\circ\\), \\(90^\\circ\\), and \\(125^\\circ\\) in the laboratory frame using quasimonoenergetic linearly (circularly) polarized photon beams with a weighted mean energy value of 83.4\\,MeV (81.3\\,MeV). These measurements were performed at the High Intensity Gamma-Ray Source facility at the Triangle Universities Nuclear Laboratory. The results are compared to previous measurements and are interpreted in the chiral effective field theory framework to extract the electromagnetic dipole polarizabilities of the proton, which gives \\(\\alpha_{E1}^p = 13.8\\pm1.2_{\\rm stat}\\pm0.1_{\\rm BSR}\\pm0.3_{\\rm theo}, \\beta_{M1}^p = 0.2\\mp1.2_{\\rm stat}\\pm0.1_{\\rm BSR}\\mp0.3_{\\rm theo}\\) in units of 10\\(^{-4}\\)\\, fm\\(^3\\).

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.

We present the analysis and results of the first dataset collected with the MARS neutron detector deployed at the Oak Ridge National Laboratory Spallation Neutron Source (SNS) for the purpose of monitoring and characterizing the beam-related neutron (BRN) background for the COHERENT collaboration. MARS was positioned next to the COH-CsI coherent elastic neutrino-nucleus scattering detector in the SNS basement corridor. This is the basement location of closest proximity to the SNS target and thus, of highest neutrino flux, but it is also well shielded from the BRN flux by infill concrete and gravel. These data show the detector registered roughly one BRN per day. Using MARS' measured detection efficiency, the incoming BRN flux is estimated to be \\(1.20~\\pm~0.56~\\text{neutrons}/\\text{m}^2/\\text{MWh}\\) for neutron energies above \\(\\sim3.5\\) MeV and up to a few tens of MeV. We compare our results with previous BRN measurements in the SNS basement corridor reported by other neutron detectors.

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.

The decay of the primordial isotopes \\(^{238}\\mathrm{U}\\), \\(^{235}\\mathrm{U}\\), \\(^{232}\\mathrm{Th}\\), and \\(^{40}\\mathrm{K}\\) have contributed to the terrestrial heat budget throughout the Earth's history. Hence the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth model. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid-Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18-year observation time, and improvements in detector background levels mainly by an 8-year almost rector-free period now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. Herein the KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High-Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2\\(\\sigma\\) assuming a homogeneous heat producing element distribution in the mantle.