We present the results of the light sterile neutrino search from the second KATRIN measurement campaign in 2019. Approaching nominal activity, \(3.76 \times 10^6\) tritium \(\beta\)-electrons are ...analyzed in an energy window extending down to \(40\,\)eV below the tritium endpoint at \(E_0 = 18.57\,\)keV. We consider the \(3\nu+1\) framework with three active and one sterile neutrino flavor. The analysis is sensitive to a fourth mass eigenstate \(m_4^2\lesssim1600\,\)eV\(^2\) and active-to-sterile mixing \(|U_{e4}|^2 \gtrsim 6 \times 10^{-3}\). 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 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.
The 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 \(\beta\)-decay ...endpoint region with a sensitivity on \(m_\nu\) of 0.2\(\,\)eV/c\(^2\) (90% CL). For this purpose, the \(\beta\)-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 \(\beta\)-electrons from elastic and inelastic scattering off tritium molecules within the source. We determined the \linebreak 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% T\(_2\) gas mixture at 30\(\,\)K, as used in the first KATRIN neutrino mass analyses, as well as a 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 \(\sigma(m_\nu^2)<10^{-2}\,\mathrm{eV}^2\) arXiv:2101.05253 in the KATRIN neutrino-mass measurement to a subdominant level.
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 of mass \(m_{4}\). The analysis is sensitive to a fourth mass state \(m^2_{4} \lesssim\) 1000 eV\(^2\) and to active-to-sterile neutrino mixing down to \(|U_{e4}|^2 \gtrsim 2\cdot10^{-2}\). No significant spectral distortion is observed and exclusion bounds on the sterile mass and mixing are reported. These new limits supersede the Mainz results and improve the Troitsk bound for \(m^2_{4} <\) 30 eV\(^2\). The reactor and gallium anomalies are constrained for \( 100 < \Delta{m}^2_{41} < 1000\) eV\(^2\).
In this work, we present the first spectroscopic measurements of conversion
electrons originating from the decay of metastable gaseous $^\mathrm{83m}$Kr
with the Karlsruhe Tritium Neutrino (KATRIN) ...experiment. The results obtained
in this calibration measurement represent a major commissioning milestone for
the upcoming direct neutrino mass measurement with KATRIN. The successful
campaign demonstrates the functionalities of the full KATRIN beamline. The
KATRIN main spectrometer's excellent energy resolution of ~ 1 eV made it
possible to determine the narrow K-32 and L$_3$-32 conversion electron line
widths with an unprecedented precision of ~ 1 %.
The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c\(^{2}\). It investigates ...the kinematics of \(\beta\)-particles from tritium \(\beta\)-decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about \(12\%\) of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than \(17\%\) (\(90\%\) confidence level) of the overall MS background.
The Karlsruhe Tritium Neutrino (KATRIN) experiment is a large-scale effort to probe the absolute neutrino mass scale with a sensitivity of 0.2 eV (90% confidence level), via a precise measurement of ...the endpoint spectrum of tritium beta decay. This work documents several KATRIN commissioning milestones: the complete assembly of the experimental beamline, the successful transmission of electrons from three sources through the beamline to the primary detector, and tests of ion transport and retention. In the First Light commissioning campaign of Autumn 2016, photoelectrons were generated at the rear wall and ions were created by a dedicated ion source attached to the rear section; in July 2017, gaseous Kr-83m was injected into the KATRIN source section, and a condensed Kr-83m source was deployed in the transport section. In this paper we describe the technical details of the apparatus and the configuration for each measurement, and give first results on source and system performance. We have successfully achieved transmission from all four sources, established system stability, and characterized many aspects of the apparatus.
The KATRIN experiment aims for the determination of the effective electron anti-neutrino mass from the tritium beta-decay with an unprecedented sub-eV sensitivity. The strong magnetic fields, ...designed for up to 6~T, adiabatically guide \(\beta\)-electrons from the source to the detector within a magnetic flux of 191~Tcm\(^2\). A chain of ten single solenoid magnets and two larger superconducting magnet systems have been designed, constructed, and installed in the 70-m-long KATRIN beam line. The beam diameter for the magnetic flux varies from 0.064~m to 9~m, depending on the magnetic flux density along the beam line. Two transport and tritium pumping sections are assembled with chicane beam tubes to avoid direct "line-of-sight" molecular beaming effect of gaseous tritium molecules into the next beam sections. The sophisticated beam alignment has been successfully cross-checked by electron sources. In addition, magnet safety systems were developed to protect the complex magnet systems against coil quenches or other system failures. The main functionality of the magnet safety systems has been successfully tested with the two large magnet systems. The complete chain of the magnets was operated for several weeks at 70\(\%\) of the design fields for the first test measurements with radioactive krypton gas. The stability of the magnetic fields of the source magnets has been shown to be better than 0.01\(\%\) per month at 70\(\%\) of the design fields. This paper gives an overview of the KATRIN superconducting magnets and reports on the first performance results of the magnets.
The neutrino mass experiment KATRIN requires a stability of 3 ppm for the retarding potential at -18.6 kV of the main spectrometer. To monitor the stability, two custom-made ultra-precise ...high-voltage dividers were developed and built in cooperation with the German national metrology institute Physikalisch-Technische Bundesanstalt (PTB). Until now, regular absolute calibration of the voltage dividers required bringing the equipment to the specialised metrology laboratory. Here we present a new method based on measuring the energy difference of two \(^{83\mathrm{m}}\)Kr conversion electron lines with the KATRIN setup, which was demonstrated during KATRIN's commissioning measurements in July 2017. The measured scale factor \(M=1972.449(10)\) of the high-voltage divider K35 is in agreement with the last PTB calibration four years ago. This result demonstrates the utility of the calibration method, as well as the long-term stability of the voltage divider.
The KATRIN experiment aims to determine the effective electron neutrino mass with a sensitivity of \(0.2\,{\text{eV}/c^2}\) (90\% C.L.) by precision measurement of the shape of the tritium ...\textbeta-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. A common background source in this setup is the decay of short-lived isotopes, such as \(\textsuperscript{219}\)Rn and \(\textsuperscript{220}\)Rn, in the spectrometer volume. Active and passive countermeasures have been implemented and tested at the KATRIN main spectrometer. One of these is the magnetic pulse method, which employs the existing air coil system to reduce the magnetic guiding field in the spectrometer on a short timescale in order to remove low- and high-energy stored electrons. Here we describe the working principle of this method and present results from commissioning measurements at the main spectrometer. Simulations with the particle-tracking software Kassiopeia were carried out to gain a detailed understanding of the electron storage conditions and removal processes.
