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We report the results of the second measurement campaign of the Karlsruhe Tritium Neutrino (KATRIN) experiment. KATRIN probes the effective electron anti-neutrino mass, $m_{ u}$, via a high-precision measurement of the tritium $beta$-decay spectrum close to its endpoint at $18.6,mathrm{keV}$. In the second physics run presented here, the source activity was increased by a factor of 3.8 and the background was reduced by $25,%$ with respect to the first campaign. A sensitivity on $m_{ u}$ of $0.7,mathrm{eV/c^2}$ at $90,%$ confidence level (CL) was reached. This is the first sub-eV sensitivity from a direct neutrino-mass experiment. The best fit to the spectral data yields $m_{ u}^2 = (0.26pm0.34),mathrm{eV^4/c^4}$, resulting in an upper limit of $m_{ u}<0.9,mathrm{eV/c^2}$ ($90,%$ CL). By combining this result with the first neutrino mass campaign, we find an upper limit of $m_{ u}<0.8,mathrm{eV/c^2}$ ($90,%$ CL).
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The European Research Council has recently funded HOLMES, a new experiment to directly measure the neutrino mass. HOLMES will perform a calorimetric measurement of the energy released in the decay of 163Ho. The calorimetric measurement eliminates systematic uncertainties arising from the use of external beta sources, as in experiments with beta spectrometers. This measurement was proposed in 1982 by A. De Rujula and M. Lusignoli, but only recently the detector technological progress allowed to design a sensitive experiment. HOLMES will deploy a large array of low temperature microcalorimeters with implanted 163Ho nuclei. The resulting mass sensitivity will be as low as 0.4 eV. HOLMES will be an important step forward in the direct neutrino mass measurement with a calorimetric approach as an alternative to spectrometry. It will also establish the potential of this approach to extend the sensitivity down to 0.1 eV. We outline here the project with its technical challenges and perspectives.
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We report a search result for a light sterile neutrino oscillation with roughly 2200 live days of data in the RENO experiment. The search is performed by electron antineutrino ($overline{ u}_e$) disappearance taking place between six 2.8 GW$_{text{th}}$ reactors and two identical detectors located at 294 m (near) and 1383 m (far) from the center of reactor array. A spectral comparison between near and far detectors can explore reactor $overline{ u}_e$ oscillations to a light sterile neutrino. An observed spectral difference is found to be consistent with that of the three-flavor oscillation model. This yields limits on $sin^{2} 2theta_{14}$ in the $10^{-4} lesssim |Delta m_{41}^2| lesssim 0.5$ eV$^2$ region, free from reactor $overline{ u}_e$ flux and spectrum uncertainties. The RENO result provides the most stringent limits on sterile neutrino mixing at $|Delta m^2_{41}| lesssim 0.002$ eV$^2$ using the $overline{ u}_e$ disappearance channel.
We report on the first cross section measurements for charged current coherent pion production by neutrinos and antineutrinos on argon. These measurements are performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The cross sections are measured to be $2.6^{+1.2}_{-1.0}(stat)^{+0.3}_{-0.4}(syst) times 10^{-38} textrm{cm}^{2}/textrm{Ar}$ for neutrinos at a mean energy of $9.6$ GeV and $5.5^{+2.6}_{-2.1}(stat)^{+0.6}_{-0.7}(syst) times 10^{-39} textrm{cm}^{2}/textrm{Ar}$ for antineutrinos at a mean energy of $3.6$ GeV.
We report on the data set, data handling, and detailed analysis techniques of the first neutrino-mass measurement by the Karlsruhe Tritium Neutrino (KATRIN) experiment, which probes the absolute neutrino-mass scale via the $beta$-decay kinematics of molecular tritium. The source is highly pure, cryogenic T$_2$ gas. The $beta$ electrons are guided along magnetic field lines toward a high-resolution, integrating spectrometer for energy analysis. A silicon detector counts $beta$ electrons above the energy threshold of the spectrometer, so that a scan of the thresholds produces a precise measurement of the high-energy spectral tail. After detailed theoretical studies, simulations, and commissioning measurements, extending from the molecular final-state distribution to inelastic scattering in the source to subtleties of the electromagnetic fields, our independent, blind analyses allow us to set an upper limit of 1.1 eV on the neutrino-mass scale at a 90% confidence level. This first result, based on a few weeks of running at a reduced source intensity and dominated by statistical uncertainty, improves on prior limits by nearly a factor of two. This result establishes an analysis framework for future KATRIN measurements, and provides important input to both particle theory and cosmology.
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