The precision measurement of the tritium beta-decay spectrum performed by the KATRIN experiment provides a unique way to search for general neutrino interactions (GNIs). All theoretically allowed GNI terms at dimension 6 involving neutrinos are incorporated into a low-energy effective field theory, and can be identified by specific signatures in the measured tritium beta spectrum. In this Letter an effective description of the impact of GNIs on the beta spectrum is formulated and the first constraints on the effective GNI parameters are derived based on the 4 x 10(6) electrons collected in the second measurement campaign of KATRIN in 2019. In addition, constraints on selected types of interactions are investigated, thereby exploring the potential of KATRIN to search for more specific new physics cases, including a right-handed W boson, a charged Higgs boson, or leptoquarks.

Sterile neutrinos are hypothetical particles in the minimal extension of the Standard Model of Particle Physics. They could be viable dark matter candidates if they have a mass in the keV range. The Karlsruhe tritium neutrino (KATRIN) experiment, extended with a silicon drift detector focal plane array (TRISTAN), has the potential to search for keV-scale sterile neutrinos by measuring the kinematics of the tritium beta-decay. The collaboration targets a sensitivity of 10-6 on the mixing amplitude sine Theta. For this challenging target, a precise understanding of the detector response is necessary. In this work, we report on the characterization of electron backscattering from the detector surface, which is one of the main effects that influence the shape of the observed energy spectrum. Measurements were performed with a tandem silicon drift detector system and a custom-designed electron source. The measured detector response and backscattering probability are in good agreement with dedicated backscattering simulations using the GEANT4 simulation toolkit.

Abstract The projected sensitivity of the effective electron neutrino-mass measurement with the KATRIN experiment is below 0.3 eV (90 % CL) after 5 years of data acquisition. The sensitivity is affected by the increased rate of the background electrons from KATRIN’s main spectrometer. A special shifted-analysing-plane (SAP) configuration was developed to reduce this background by a factor of two. The complex layout of electromagnetic fields in the SAP configuration requires a robust method of estimating these fields. We present in this paper a dedicated calibration measurement of the fields using conversion electrons of gaseous $$^\textrm{83m}$$ 83m Kr, which enables the neutrino-mass measurements in the SAP configuration.

The TRISTAN detector is a new detector for electron spectroscopy at the Karlsruhe Tritium Neutrino (KATRIN) experiment. The semiconductor detector utilizes the silicon drift detector technology and will enable the precise measurement of the entire tritium beta decay electron spectrum. Thus, a significant fraction of the parameter space of potential neutrino mass eigenstates in the keV-mass regime can be probed. We developed a custom electron gun based on the effect of thermionic emission to characterize the TRISTAN detector modules with mono-energetic electrons before installation into the KATRIN beamline. The electron gun provides an electron beam with up to 25 keV kinetic energy and an electron rate in the order of 1E5 electrons per second. This manuscript gives an overview of the design and commissioning of the electron gun. In addition, we will shortly discuss a first measurement with the electron gun to characterize the electron response of the TRISTAN detector.

Sterile neutrinos in the keV mass range present a viable candidate for dark matter. They can be detected through single β -decay, where they cause small spectral distortions. The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to search for keV-scale sterile neutrinos with high sensitivity. To achieve this, the KATRIN beamline will be equipped with a novel multi-pixel silicon drift detector focal plane array named TRISTAN. In this study, we present the performance of a TRISTAN detector module, a component of the eventual 9-module system. Our investigation encompasses spectroscopic aspects such as noise performance, energy resolution, linearity, and stability.

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.

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 $(a_{\text{of}}^{(3)})_{10}$.

We report on the characterization of a monolithic array of 166 Silicon Drift Detectors (SDD) with integrated JFET. This high-density detection module (4 cm by 4 cm) was designed and assembled within the TRISTAN development of the KATRIN experiment for search of sterile neutrinos in the keV mass range by means of beta spectroscopy. The detector was commissioned in the KATRIN monitor spectrometer and was exposed both to X-ray photons (at 5.9 keV of Fe55) and electrons (at 32.2 keV energy of Kr83m) reaching state-of-the-art homogeneity and energy resolution: 157 eV and 352.8 eV FWHM respectively (with 2 us shaping time and -33°C cooling).

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.

Sterile neutrinos are a minimal extension of the standard model of particle physics. A laboratory-based approach to search for this particle is via tritium beta-decay, where a sterile neutrino would cause a kink-like spectral distortion. The Karlsruhe Tritium Neutrino (KATRIN) experiment extended by a multi-pixel Silicon Drift Detector system has the potential to reach an unprecedented sensitivity to the keV-scale sterile neutrino in a lab-based experiment. The new detector system combines good spectroscopic performance with a high rate capability. In this work, we report about the characterization of charge-sharing between pixels and the commissioning of a 47-pixel prototype detector in a MAC-E filter.

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.

This work presents the design and preliminary X-ray characterization of a module designed for high-precision beta-decay measurements. The module is based on a large 166-pixel monolithic Silicon Drift Detector (SDD) matrix with a total active area of 11.6 cm 2 . The detection system is developed in the context of the TRISTAN project that aims at proving the existence of a keV-mass sterile neutrino via the tritium beta-decay spectrum measurement with unprecedented accuracy. We present a 166-pixel module with all functioning channels, the fundamental milestone towards the final TRISTAN focal plane array that will employ multiple monolithic tiles for a total of 3486 pixels.

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}.

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 24 ≲ 1000 eV 2 and to active-to-sterile neutrino mixing down to j U e 4 j 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 24 ≲ 1000 eV 2 and improve the Troitsk bound for m 24 < 30 eV 2 . The reactor and gallium anomalies are constrained for 100 < Δ m 241 < 1000 eV 2 .

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.

A multi-channel data processing and acquisition system based on an analog ASIC (SFERA) has been designed and realized. The platform, called Kerberos, is suitable for the readout of large arrays of Silicon Drift Detector (SDD) for X-ray, γ-ray and electron spectroscopy applications. Each one of its 48 inputs is equipped with a 9 th order semi-Gaussian shaping amplifier with programmable peaking time (0.5, 1, 2, 3, 4 and 6 ). The pulse amplitudes are multiplexed into three 16-bit high linearity SAR ADCs and digitized into an Artix-7 FPGA module. Kerberos will be used for the characterization of monolithic SDD matrices for the TRISTAN project. Many different readout strategies can be selected on Kerberos Graphic User Interface: for TRISTAN it has been decided to use a full detector readout strategy, with maximum input throughput of about 166 kcount/s. This work presents a full characterization of this scalable platform and its use with several detectors types (SDD, micro-strips) in X-ray, gamma and beta spectroscopy.

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).