Triangle Universities Nuclear Laboratory

KamLAND has measured the flux of ${\overline{\ensuremath{\nu}}}_{e}$'s from distant nuclear reactors. We find fewer ${\overline{\ensuremath{\nu}}}_{e}$ events than expected from standard assumptions about ${\overline{\ensuremath{\nu}}}_{e}$ propagation at the 99.95% C.L. In a $162\text{ }\mathrm{\text{ton}}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{y}\mathrm{r}$ exposure the ratio of the observed inverse $\ensuremath{\beta}$-decay events to the expected number without ${\overline{\ensuremath{\nu}}}_{e}$ disappearance is $0.611\ifmmode\pm\else\textpm\fi{}0.085\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\ifmmode\pm\else\textpm\fi{}0.041\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}$ for ${\overline{\ensuremath{\nu}}}_{e}$ energies $>3.4\text{ }\text{ }\mathrm{M}\mathrm{e}\mathrm{V}$. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the ``large mixing angle'' region are excluded.

We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 ${\overline{\ensuremath{\nu}}}_{e}$ candidate events with energies above 3.4 MeV compared to $365.2\ifmmode\pm\else\textpm\fi{}23.7$ events expected in the absence of neutrino oscillation. Accounting for $17.8\ifmmode\pm\else\textpm\fi{}7.3$ expected background events, the statistical significance for reactor ${\overline{\ensuremath{\nu}}}_{e}$ disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from ${\overline{\ensuremath{\nu}}}_{e}$ oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives $\ensuremath{\Delta}{m}^{2}={7.9}_{\ensuremath{-}0.5}^{+0.6}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{e}\mathrm{V}}^{2}$. A global analysis of data from KamLAND and solar-neutrino experiments yields $\ensuremath{\Delta}{m}^{2}={7.9}_{\ensuremath{-}0.5}^{+0.6}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{e}\mathrm{V}}^{2}$ and ${tan}^{2}\ensuremath{\theta}={0.40}_{\ensuremath{-}0.07}^{+0.10}$, the most precise determination to date.

We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.

The KamLAND experiment has determined a precise value for the neutrino oscillation parameter $\ensuremath{\Delta}{m}_{21}^{2}$ and stringent constraints on ${\ensuremath{\theta}}_{12}$. The exposure to nuclear reactor antineutrinos is increased almost fourfold over previous results to $2.44\ifmmode\times\else\texttimes\fi{}{10}^{32}\text{ }\text{ }\mathrm{proton}\text{ }\mathrm{yr}$ due to longer livetime and an enlarged fiducial volume. An undistorted reactor ${\overline{\ensuremath{\nu}}}_{e}$ energy spectrum is now rejected at $>5\ensuremath{\sigma}$. Analysis of the reactor spectrum above the inverse beta decay energy threshold, and including geoneutrinos, gives a best fit at $\ensuremath{\Delta}{m}_{21}^{2}={7.58}_{\ensuremath{-}0.13}^{+0.14}(\mathrm{stat}{)}_{\ensuremath{-}0.15}^{+0.15}(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$ and ${tan}^{2}{\ensuremath{\theta}}_{12}={0.56}_{\ensuremath{-}0.07}^{+0.10}(\mathrm{stat}{)}_{\ensuremath{-}0.06}^{+0.10}(\mathrm{syst})$. Local $\ensuremath{\Delta}{\ensuremath{\chi}}^{2}$ minima at higher and lower $\ensuremath{\Delta}{m}_{21}^{2}$ are disfavored at $>4\ensuremath{\sigma}$. Combining with solar neutrino data, we obtain $\ensuremath{\Delta}{m}_{21}^{2}={7.59}_{\ensuremath{-}0.21}^{+0.21}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$ and ${tan}^{2}{\ensuremath{\theta}}_{12}={0.47}_{\ensuremath{-}0.05}^{+0.06}$.

A 14.6-kilogram sodium-doped CsI scintillator is used to detect a neutrino scattering process with a 6.7σ confidence level.

Forty years ago Burbidge, Burbidge, Fowler, and Hoyle combined what we would now call fragmentary evidence from nuclear physics, stellar evolution and the abundances of elements and isotopes in the solar system as well as a few stars into a synthesis of remarkable ingenuity. Their review provided a foundation for forty years of research in all of the aspects of low energy nuclear experiments and theory, stellar modeling over a wide range of mass and composition, and abundance studies of many hundreds of stars, many of which have shown distinct evidence of the processes suggested by B${}^{2}$FH. In this review we summarize progress in each of these fields with emphasis on the most recent developments.

We report on the neutrino mass measurement result from the first four-week science run of the Karlsruhe Tritium Neutrino experiment KATRIN in spring 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are energy analyzed by a high-resolution MAC-E filter. A fit of the integrated electron spectrum over a narrow interval around the kinematic end point at 18.57 keV gives an effective neutrino mass square value of (-1.0_{-1.1}^{+0.9}) eV^{2}. From this, we derive an upper limit of 1.1 eV (90% confidence level) on the absolute mass scale of neutrinos. This value coincides with the KATRIN sensitivity. It improves upon previous mass limits from kinematic measurements by almost a factor of 2 and provides model-independent input to cosmological studies of structure formation.

Abstract Since the discovery of neutrino oscillations, we know that neutrinos have non-zero mass. However, the absolute neutrino-mass scale remains unknown. Here we report the upper limits on effective electron anti-neutrino mass, m ν , from the second physics run of the Karlsruhe Tritium Neutrino experiment. In this experiment, m ν is probed via a high-precision measurement of the tritium β -decay spectrum close to its endpoint. This method is independent of any cosmological model and does not rely on assumptions whether the neutrino is a Dirac or Majorana particle. By increasing the source activity and reducing the background with respect to the first physics campaign, we reached a sensitivity on m ν of 0.7 eV c –2 at a 90% confidence level (CL). The best fit to the spectral data yields $${{\mbox{}}}{m}_{\nu }^{2}{{\mbox{}}}$$ m ν 2 = (0.26 ± 0.34) eV 2 c –4 , resulting in an upper limit of m ν < 0.9 eV c –2 at 90% CL. By combining this result with the first neutrino-mass campaign, we find an upper limit of m ν < 0.8 eV c –2 at 90% CL.

We present results from the first phase of the KamLAND-Zen double-beta decay experiment, corresponding to an exposure of 89.5 kg yr of $^{136}\mathrm{Xe}$. We obtain a lower limit for the neutrinoless double-beta decay half-life of ${T}_{1/2}^{0\ensuremath{\nu}}>1.9\ifmmode\times\else\texttimes\fi{}{10}^{25}\text{ }\text{ }\mathrm{yr}$ at 90% C.L. The combined results from KamLAND-Zen and EXO-200 give ${T}_{1/2}^{0\ensuremath{\nu}}>3.4\ifmmode\times\else\texttimes\fi{}{10}^{25}\text{ }\text{ }\mathrm{yr}$ at 90% C.L., which corresponds to a Majorana neutrino mass limit of $⟨{m}_{\ensuremath{\beta}\ensuremath{\beta}}⟩<(120--250)\text{ }\text{ }\mathrm{meV}$ based on a representative range of available matrix element calculations. Using those calculations, this result excludes the Majorana neutrino mass range expected from the neutrinoless double-beta decay detection claim in $^{76}\mathrm{Ge}$, reported by a part of the Heidelberg-Moscow Collaboration, at more than 97.5% C.L.

The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor ${\overline{\ensuremath{\nu}}}_{e}$ flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor ${\overline{\ensuremath{\nu}}}_{e}$ oscillation analysis. The data set also has improved sensitivity for other ${\overline{\ensuremath{\nu}}}_{e}$ signals, in particular ${\overline{\ensuremath{\nu}}}_{e}$'s produced in $\ensuremath{\beta}$-decays from $^{238}\mathrm{U}$ and $^{232}\mathrm{Th}$ within the Earth's interior, whose energy spectrum overlaps with that of reactor ${\overline{\ensuremath{\nu}}}_{e}$'s. Including constraints on ${\ensuremath{\theta}}_{13}$ from accelerator and short-baseline reactor neutrino experiments, a combined three-flavor analysis of solar and KamLAND data gives fit values for the oscillation parameters of ${tan}^{2}{\ensuremath{\theta}}_{12}={0.436}_{\ensuremath{-}0.025}^{+0.029}$, $\ensuremath{\Delta}{m}_{21}^{2}={7.53}_{\ensuremath{-}0.18}^{+0.18}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$, and ${sin}^{2}{\ensuremath{\theta}}_{13}={0.023}_{\ensuremath{-}0.002}^{+0.002}$. Assuming a chondritic Th/U mass ratio, we obtain ${116}_{\ensuremath{-}27}^{+28}$ ${\overline{\ensuremath{\nu}}}_{e}$ events from $^{238}\mathrm{U}$ and $^{232}\mathrm{Th}$, corresponding to a geo ${\overline{\ensuremath{\nu}}}_{e}$ flux of ${3.4}_{\ensuremath{-}0.8}^{+0.8}\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo ${\overline{\ensuremath{\nu}}}_{e}$ rate.

Evidence for the applicability of random-matrix theory to nuclear spectra is reviewed. In analogy to systems with few degrees of freedom, one speaks of chaos (more accurately, quantum chaos) in nuclei whenever random-matrix predictions are fulfilled. An introduction into the basic concepts of random-matrix theory is followed by a survey over the extant experimental information on spectral fluctuations, including a discussion of the violation of a symmetry or invariance property. Chaos in nuclear models is discussed for the spherical shell model, for the deformed shell model, and for the interacting boson model. Evidence for chaos also comes from random-matrix ensembles patterned after the shell model such as the embedded two-body ensemble, the two-body random ensemble, and the constrained ensembles. All this evidence points to the fact that chaos is a generic property of nuclear spectra, except for the ground-state regions of strongly deformed nuclei.

We present new constraints on the neutrino oscillation parameters $\ensuremath{\Delta}{m}_{21}^{2}$, ${\ensuremath{\theta}}_{12}$, and ${\ensuremath{\theta}}_{13}$ 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 $3.49\ifmmode\times\else\texttimes\fi{}{10}^{32}$ target-proton-year. Under the assumption of $CPT$ invariance, a two-flavor analysis (${\ensuremath{\theta}}_{13}=0$) of the KamLAND and solar data yields the best-fit values ${tan}^{2}{\ensuremath{\theta}}_{12}={0.444}_{\ensuremath{-}0.030}^{+0.036}$ and $\ensuremath{\Delta}{m}_{21}^{2}={7.50}_{\ensuremath{-}0.20}^{+0.19}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$; a three-flavor analysis with ${\ensuremath{\theta}}_{13}$ as a free parameter yields the best-fit values ${tan}^{2}{\ensuremath{\theta}}_{12}={0.452}_{\ensuremath{-}0.033}^{+0.035}$, $\ensuremath{\Delta}{m}_{21}^{2}={7.50}_{\ensuremath{-}0.20}^{+0.19}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$, and ${sin}^{2}{\ensuremath{\theta}}_{13}={0.020}_{\ensuremath{-}0.016}^{+0.016}$. This ${\ensuremath{\theta}}_{13}$ interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global ${\ensuremath{\theta}}_{13}$ analysis, incorporating the CHOOZ, atmospheric, and accelerator data, which indicates ${sin}^{2}{\ensuremath{\theta}}_{13}={0.009}_{\ensuremath{-}0.007}^{+0.013}$. A nonzero value is suggested, but only at the 79% C.L.

The axion is a promising dark matter candidate, which was originally proposed to solve the strong-$CP$ problem in particle physics. To date, the available parameter space for axion and axionlike particle dark matter is relatively unexplored, particularly at masses ${m}_{a}\ensuremath{\lesssim}1\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. ABRACADABRA is a new experimental program to search for axion dark matter over a broad range of masses, ${10}^{\ensuremath{-}12}\ensuremath{\lesssim}{m}_{a}\ensuremath{\lesssim}{10}^{\ensuremath{-}6}\text{ }\text{ }\mathrm{eV}$. ABRACADABRA-10 cm is a small-scale prototype for a future detector that could be sensitive to the QCD axion. In this Letter, we present the first results from a 1 month search for axions with ABRACADABRA-10 cm. We find no evidence for axionlike cosmic dark matter and set 95% C.L. upper limits on the axion-photon coupling between ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}<1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ and ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}<3.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ over the mass range $3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}--8.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{eV}$. These results are competitive with the most stringent astrophysical constraints in this mass range.

Proton-induced reaction rates on 26 stable and 29 unstable target nuclei in the mass A = 20–40 region have been evaluated and compiled. Recommended reaction rates, assuming that all interacting nuclei are in the ground state, are presented in tabular form on a temperature grid in the range T = 0.01–10.0 GK. Most reaction rates involving stable targets were normalized to a set of measured standard resonance strengths in the sd shell. For the majority of reaction rates, experimental information from transfer reaction studies has been used consistently. Our results are compared with recent statistical model (Hauser-Feshbach) calculations. Reaction rate uncertainties are presented and amount to several orders of magnitude for many of the reactions. Several of these reaction rates and/or their corresponding uncertainties deviate from results of previous compilations. In most cases, the deviations are explained by the fact that new experimental information became available recently. Examples are given for calculating reaction rates and reverse reaction rates for thermally excited nuclei from the present results. The survey of literature for this review was concluded in 2000 August.

We report the first measurement of coherent elastic neutrino-nucleus scattering (CEvNS) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer CEvNS over the background-only null hypothesis with greater than 3σ significance. The measured cross section, averaged over the incident neutrino flux, is (2.2±0.7)×10^{-39} cm^{2}-consistent with the standard model prediction. The neutron-number dependence of this result, together with that from our previous measurement on CsI, confirms the existence of the CEvNS process and provides improved constraints on nonstandard neutrino interactions.

A search for neutrinoless double-β decay (0νββ) in ^{136}Xe is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββ and background events. Relative to previous analyses, the signal detection efficiency has been raised from 80.8% to 96.4±3.0%, and the energy resolution of the detector at the Q value of ^{136}Xe 0νββ has been improved from σ/E=1.23% to 1.15±0.02% with the upgraded detector. Accounting for the new data, the median 90% confidence level 0νββ half-life sensitivity for this analysis is 5.0×10^{25} yr with a total ^{136}Xe exposure of 234.1 kg yr. No statistically significant evidence for 0νββ is observed, leading to a lower limit on the 0νββ half-life of 3.5×10^{25} yr at the 90% confidence level.

Model surfaces with switchable functionality based on nanopatterned, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) brushes were fabricated using interferometric lithography combined with surface-initiated polymerization. The temperature-triggered hydration and conformational changes of nanopatterned PNIPAAm brushes reversibly modulate the spatial concealment and exposure of molecules that are immobilized in the intervals between nanopatterned brushes. A biocidal quaternary ammonium salt (QAS) was used to demonstrate the utility of nanopatterned PNIPAAm brushes to control biointerfacial interactions with bacteria. QAS was integrated into polymer-free regions of the substrate between nanopatterned PNIPAAm brushes. The biocidal efficacy and release properties of these surfaces were tested against Escherichia coli K12. Above the lower critical solution temperature (LCST) of PNIPAAm, desolvated, collapsed polymer chains facilitate the attachment of bacteria and expose QAS moieties that kill attached bacteria. Upon a reduction of the temperature below the LCST, swollen PNIPAAm chains promote the release of dead bacteria. These results demonstrate that nanopatterned PNIPAAm/QAS hybrid surfaces are model systems that exhibit an ability to undergo noncovalent, dynamic, and reversible changes in structure that can be used to control the attachment, killing, and release of bacteria in response to changes in temperature.

The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (0νββ) 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 0νββ decay half-life of T_{1/2}^{0ν}>2.3×10^{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 application of random-matrix theory (RMT) to compound-nucleus (CN) reactions is reviewed. An introduction into the basic concepts of nuclear scattering theory is followed by a survey of phenomenological approaches to CN scattering. The implementation of a random-matrix approach into scattering theory leads to a statistical theory of CN reactions. Since RMT applies generically to chaotic quantum systems, that theory is, at the same time, a generic theory of quantum chaotic scattering. It uses a minimum of input parameters (average $S$ matrix and mean level spacing of the CN). Predictions of the theory are derived with the help of field-theoretical methods adapted from condensed-matter physics and compared with those of phenomenological approaches. Thorough tests of the theory are reviewed, as are applications in nuclear physics, with special attention given to violation of symmetries (isospin and parity) and time-reversal invariance.

The observation of neutrinoless double-beta decay (0νββ) would show that lepton number is violated, reveal that neu-trinos are Majorana particles, and provide information on neutrino mass. A discovery-capable experiment covering the inverted ordering region, with effective Majorana neutrino masses of 15 − 50 meV, will require a tonne-scale experiment with excellent energy resolution and extremely low backgrounds, at the level of ∼0.1 count /(FWHM·t·yr) in the region of the signal. The current generation 76Ge experiments GERDA and the Majorana Demonstrator, utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the 0νββ signal region of all 0νββ experiments. Building on this success, the LEGEND collaboration has been formed to pursue a tonne-scale 76Ge experiment. The collaboration aims to develop a phased 0νββ experimental program with discovery potential at a half-life approaching or at 1028 years, using existing resources as appropriate to expedite physics results.