The fact that neutrinos carry a non-vanishing rest mass is evidence of physics beyond the Standard Model of elementary particles. Their absolute mass bears important relevance from particle physics to cosmology. In this work, we report on the search for the effective electron antineutrino mass with the KATRIN experiment. KATRIN performs precision spectroscopy of the tritium $\beta$-decay close to the kinematic endpoint. Based on the first five neutrino-mass measurement campaigns, we derive a best-fit value of $m_\nu^{2} = {-0.14^{+0.13}_{-0.15}}~\mathrm{eV^2}$, resulting in an upper limit of $m_\nu < {0.45}~\mathrm{eV}$ at 90 % confidence level. With six times the statistics of previous data sets, amounting to 36 million electrons collected in 259 measurement days, a substantial reduction of the background level and improved systematic uncertainties, this result tightens KATRIN's previous bound by a factor of almost two.

In this work we present a keV-scale sterile-neutrino search with a low-tritium-activity data set of the KATRIN experiment, acquired in a commissioning run in 2018. KATRIN performs a spectroscopic measurement of the tritium -decay spectrum with the main goal of directly determining the effective electron anti-neutrino mass. During this commissioning phase a lower tritium activity facilitated the measurement of a wider part of the tritium spectrum and thus the search for sterile neutrinos with a mass of up to 1.6 keV . We do not find a signal and set an exclusion limit on the sterile-to-active mixing amplitude of sin ^2θ < 5× 10^-4 ( 95% C.L.) at a mass of 0.3 keV. This result improves current laboratory-based bounds in the sterile-neutrino mass range between 0.1 and 1.0 keV.

An energy value of 9406.3(5) eV was determined for the 9.4 keV (M1+E2) nuclear transition in 83Kr by the internal conversion electron spectrometry method. This value agrees within 1σ with the most precise values determined previously for which their weighted mean amounts to 9405.9(2) eV. A value of 22745.3(2) eV was obtained directly from our experimental data for the energy difference between the 32.1 keV and 9.4 keV transitions in 83Kr. Electron binding energies (related to the Fermi level) on the K, L, and M1,2,3 subshells of Kr implanted into a polycrystalline Pt matrix were also derived. They were found to be lower by weighted mean values of 11.6(4) and 1.7(6) eV compared to those for free Kr atoms and for Kr in an evaporated 83Rb layer on Al backing, respectively, and higher by a weighted mean value of 2.9(2) eV than the binding energies in Kr in an evaporated layer on polycrystalline Pt backing.

Some extensions of the Standard Model of Particle Physics allow for Lorentz invariance and Charge-Parity-Time (CPT)-invariance violations. In the neutrino sector strong constraints have been set by neutrino-oscillation and time-of-flight experiments. However, some Lorentz-invariance-violating parameters are not accessible via these probes. In this work, we focus on the parameters $(a_{\text{of}}^{(3)})_{00}$, $(a_{\text{of}}^{(3)})_{10}$ and $(a_{\text{of}}^{(3)})_{11}$ which would manifest themselves in a non-isotropic beta-decaying source as a sidereal oscillation and an overall shift of the spectral endpoint. Based on the data of the first scientific run of the KATRIN experiment, we set the first limit on $\left|(a_{\text{of}}^{(3)})_{11}\right|$ of $<3.7\cdot10^{-6}$ GeV at 90\% confidence level. Moreover, we derive new constraints on $(a_{\text{of}}^{(3)})_{00}$ and $(a_{\text{of}}^{(3)})_{10}$.

The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to measure a high-precision integral spectrum of the endpoint region of T-2 beta decay, with the primary goal of probing the absolute mass scale of the neutrino. After a first tritium commissioning campaign in 2018, the experiment has been regularly running since 2019, and in its first two measurement campaigns has already achieved a sub-eV sensitivity. After 1000 days of data-taking, KATRIN's design sensitivity is 0.2 eV at the 90% confidence level. In this white paper we describe the current status of KATRIN; explore prospects for measuring the neutrino mass and other physics observables, including sterile neutrinos and other beyond-Standard-Model hypotheses; and discuss research-and-development projects that may further improve the KATRIN sensitivity.

We present the results of the light sterile neutrino search from the second Karlsruhe Tritium Neutrino (KATRIN) measurement campaign in 2019. Approaching nominal activity, 3.76 x 10(6) tritium ss-electrons are analyzed in an energy window extending down to 40 eV below the tritium end point at E-0 = 18.57 keV. We consider the 3 nu + 1 framework with three active and one sterile neutrino flavors. The analysis is sensitive to a fourth mass eigenstate m(4)(2) less than or similar to 1600 eV(2) and active-to-sterile mixing |U-e4|(2) greater than or similar to 6 x 10(-3). As no sterile-neutrino signal was observed, we provide improved exclusion contours on m(4)(2) and |U-e4|(2) at 95% C.L. Our results supersede the limits from the Mainz and Troitsk experiments. Furthermore, we are able to exclude the large Delta m(41)(2) solutions of the reactor antineutrino and gallium anomalies to a great extent. The latter has recently been reaffirmed by the BEST Collaboration and could be explained by a sterile neutrino with large mixing. While the remaining solutions at small Delta m(41)(2) are mostly excluded by short-baseline reactor experiments, KATRIN is the only ongoing laboratory experiment to be sensitive to relevant solutions at large Delta m(41)(2) through a robust spectral shape analysis.

We report on the direct search for cosmic relic neutrinos using data acquired during the first two science campaigns of the KATRIN experiment in 2019. Beta-decay electrons from a high-purity molecular tritium gas source are analyzed by a high-resolution MAC-E filter around the end point at 18.57 keV. The analysis is sensitive to a local relic neutrino overdensity ratio of η<9.7×10^{10}/α (1.1×10^{11}/α) at a 90% (95%) confidence level with α=1 (0.5) for Majorana (Dirac) neutrinos. A fit of the integrated electron spectrum over a narrow interval around the end point accounting for relic neutrino captures in the tritium source reveals no significant overdensity. This work improves the results obtained by the previous neutrino mass experiments at Los Alamos and Troitsk. We furthermore update the projected final sensitivity of the KATRIN experiment to η<1×10^{10}/α at 90% confidence level, by relying on updated operational conditions.

Author(s): Aker, M; Altenmuller, K; Beglarian, A; Behrens, J; Berlev, A; Besserer, U; Bieringer, B; Blaum, K; Block, F; Bornschein, B; Bornschein, L; Bottcher, M; Brunst, T; Caldwell, TS; La Cascio, L; Chilingaryan, S; Choi, W; Diaz Barrero, D; Debowski, K; Deffert, M; Descher, M; Doe, PJ; Dragoun, O; Drexlin, G; Dyba, S; Edzards, F; Eitel, K; Ellinger, E; Engel, R; Enomoto, S; Fedkevych, M; Felden, A; Formaggio, JA; Frankle, FM; Franklin, GB; Friedel, F; Fulst, A; Gauda, K; Gil, W; Gluck, F; Grossle, R; Gumbsheimer, R; Hohn, T; Hannen, V; Hausmann, N; Helbing, K; Hickford, S; Hiller, R; Hillesheimer, D; Hinz, D; Houdy, T; Huber, A; Jansen, A; Kollenberger, L; Karl, C; Kellerer, J; Kippenbrock, L; Klein, M; Kopmann, A; Korzeczek, M; Kovalik, A; Krasch, B; Krause, H; Lasserre, T; Le, TL; Lebeda, O; Lehnert, B; Lokhov, A; Lopez Poyato, JM; Muller, K; Machatschek, M; Malcherek, E; Mark, M; Marsteller, A; Martin, EL; Melzer, C; Mertens, S; Niemes, S; Oelpmann, P; Osipowicz, A; Parno, DS; Poon, AWP; Priester, F; Rollig, M; Rottele, C | Abstract: We report on the dataset, 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 β-decay kinematics of molecular tritium. The source is highly pure, cryogenic T2 gas. The β electrons are guided along magnetic field lines toward a high-resolution, integrating spectrometer for energy analysis. A silicon detector counts β 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.

We report on the light sterile neutrino search from the first four-week science run of the KATRIN experiment in 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are analyzed by a high-resolution MAC-E filter down to 40 eV below the endpoint at 18.57 keV. We consider the framework with three active neutrinos and one sterile neutrino. The analysis is sensitive to the mass, m_{4}, of the fourth mass state for m_{4}^{2}≲1000  eV^{2} and to active-to-sterile neutrino mixing down to |U_{e4}|^{2}≳2×10^{-2}. No significant spectral distortion is observed and exclusion bounds on the sterile mass and mixing are reported. These new limits supersede the Mainz results for m_{4}^{2}≲1000  eV^{2} and improve the Troitsk bound for m_{4}^{2}<30  eV^{2}. The reactor and gallium anomalies are constrained for 100<Δm_{41}^{2}<1000  eV^{2}.

The 9.2 keV nuclear transition in 227Th was studied in the β−-decay of 227Ac by means of the internal conversion electron spectroscopy to clarify the spin-parity assignment of the ground state and the two lowest excited states of 227Th. The transition multipolarity was proved to be of mixed character M1 + E2 and the spectroscopic admixture parameter δ2(E2/M1)=0.695±0.248 (|δ(E2/M1)|=0.834±0.149) was determined. Nonzero value of δ(E2/M1) questioned the present theoretical interpretation of low-lying levels of 227Th. Calculations performed prefer the 1/2+, 3/2+, and 3/2+ sequence instead of the adopted 1/2+, 5/2+ and 3/2+ one for the 0.0, 9.2, and 24.3 keV levels, respectively.

The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns.

AbstractThe KATRIN experiment is designed for a direct and model-independent determination of the effective electron anti-neutrino mass via a high-precision measurement of the tritium $$\upbeta $$ β -decay endpoint region with a sensitivity on $$m_\nu $$ m ν of 0.2 $$\hbox {eV}/\hbox {c}^2$$ eV / c 2 (90% CL). For this purpose, the $$\upbeta $$ β -electrons from a high-luminosity windowless gaseous tritium source traversing an electrostatic retarding spectrometer are counted to obtain an integral spectrum around the endpoint energy of 18.6 keV. A dominant systematic effect of the response of the experimental setup is the energy loss of $$\upbeta $$ β -electrons from elastic and inelastic scattering off tritium molecules within the source. We determined the energy-loss function in-situ with a pulsed angular-selective and monoenergetic photoelectron source at various tritium-source densities. The data was recorded in integral and differential modes; the latter was achieved by using a novel time-of-flight technique. We developed a semi-empirical parametrization for the energy-loss function for the scattering of 18.6-keV electrons from hydrogen isotopologs. This model was fit to measurement data with a 95% $$\hbox {T}_2$$ T 2 gas mixture at 30 K, as used in the first KATRIN neutrino-mass analyses, as well as a $$\hbox {D}_2$$ D 2 gas mixture of 96% purity used in KATRIN commissioning runs. The achieved precision on the energy-loss function has abated the corresponding uncertainty of $$\sigma (m_\nu ^2)< {{10}^{-2}}{\hbox {eV}^{2}}$$ σ ( m ν 2 ) < 10 - 2 eV 2 [1] in the KATRIN neutrino-mass measurement to a subdominant level.

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 ν , via a high-precision measurement of the tritium β-decay spectrum close to its endpoint at 18.6 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 ν of 0.7 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 ν 2 =(0.26±0.34) eV 2 /c 4 , resulting in an upper limit of m ν <0.9 eV/c 2 (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 (90% CL).

In this work, we present the first spectroscopic measurements of conversion electrons originating from the decay of metastable gaseous Kr-83m with the Karlsruhe Tritium Neutrino (KATRIN) experiment. The obtained results represent one of the major commissioning milestones for the subsequent direct neutrino mass measurement with KATRIN. The successful campaign demonstrates the functionalities of the KATRIN beamline. Precise measurement of the narrow K-32, L-3-32, and N-2,N-3-32 conversion electron lines allowed to verify the eV-scale energy resolution of the KATRIN main spectrometer necessary for competitive measurement of the absolute neutrino mass scale.

AbstractThe KArlsruhe TRItium Neutrino experiment (KATRIN) aims to determine the effective electron (anti)-neutrino mass with a sensitivity of 0.2eV/c$$^2$$ 2 by precisely measuring the endpoint region of the tritium $$\beta $$ β -decay spectrum. It uses a tandem of electrostatic spectrometers working as magnetic adiabatic collimation combined with an electrostatic (MAC-E) filters. In the space between the pre-spectrometer and the main spectrometer, creating a Penning trap is unavoidable when the superconducting magnet between the two spectrometers, biased at their respective nominal potentials, is energized. The electrons accumulated in this trap can lead to discharges, which create additional background electrons and endanger the spectrometer and detector section downstream. To counteract this problem, “electron catchers” were installed in the beamline inside the magnet bore between the two spectrometers. These catchers can be moved across the magnetic-flux tube and intercept on a sub-ms time scale the stored electrons along their magnetron motion paths. In this paper, we report on the design and the successful commissioning of the electron catchers and present results on their efficiency in reducing the experimental background.

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.

The energy scale of the main spectrometer in the KATRIN tritium project is required to remain stable within ±60 meV at an electron energy of 18.6 keV for two months in order to reach the intended sensitivity of 0.2 eV for the rest mass of the electron antineutrino. A natural source of reference electrons with an energy of 17824.3 ± 0.5 eV based on K-conversion electrons of the 32-keV nuclear γ-transition in 83mKr from the decay of parent 83Rb was developed for this purpose using precision low-energy nuclear electron spectrometry. The spectroscopic parameters of 83mKr/83Rb sources fabricated by ion implantation into polycrystalline platinum foils were significantly better than the parameters of vacuum-deposited sources. A large-scale study of the influence of the physicochemical environment of atoms of different radioisotopes in various matrices of vacuum-deposited and implanted radioactive sources on the energy of emitted conversion and Auger electrons and on the structure of the corresponding energy spectra was conducted in the process. The possibility of application of photoelectron sources with a metallic converter as sources of reference electrons for the KATRIN project was also considered.

Using the internal conversion electron spectroscopy, the energy of the 15.1 keV $ M1+E2$ nuclear transition in 227Th populated in the $ \beta^{-}$ decay of 227Ac was determined to be $ 15098.6 \pm 1.0$ eV. This value is more accurate than the present accepted one by a factor of 200. The present uncertainty in the transition multipolarity was removed and it was found to be $ M1+E2$ with the admixture $ \vert\delta (E2/M1)\vert = 0.035 \pm 0.006$.

Abstract The KATRIN experiment aims to measure the effective electron antineutrino mass $$m_{\overline{\nu }_e}$$ mν¯e with a sensitivity of $${0.2}\,{\hbox {eV}/\hbox {c}^2}$$ 0.2eV/c2 using a gaseous tritium source combined with the MAC-E filter technique. A low background rate is crucial to achieving the proposed sensitivity, and dedicated measurements have been performed to study possible sources of background electrons. In this work, we test the hypothesis that gamma radiation from external radioactive sources significantly increases the rate of background events created in the main spectrometer (MS) and observed in the focal-plane detector. Using detailed simulations of the gamma flux in the experimental hall, combined with a series of experimental tests that artificially increased or decreased the local gamma flux to the MS, we set an upper limit of $${0.006}\,{\hbox {count}/\hbox {s}}$$ 0.006count/s (90% C.L.) from this mechanism. Our results indicate the effectiveness of the electrostatic and magnetic shielding used to block secondary electrons emitted from the inner surface of the MS.