The \textit{KArlsruhe TRItium Neutrino} (KATRIN) experiment aims to measure the neutrino mass with a sensitivity of \SI{0.2}{\electronvolt} (\SI{90}{\percent} CL). This will be achieved by a ...precision measurement of the endpoint region of the \(\upbeta\)-electron spectrum of tritium decay. The \(\upbeta\)-electrons are produced in the \textit{Windowless Gaseous Tritium Source} (WGTS) and guided magnetically through the beamline. In order to accurately extract the neutrino mass the source activity is required to be stable and known to a high precision. The WGTS therefore undergoes constant extensive monitoring from several measurement systems. The \textit{Forward Beam Monitor} (FBM) is one such monitoring system. The FBM system comprises a complex mechanical setup capable of inserting a detector board into the KATRIN beamline with a positioning precision of better than \SI{0.3}{\milli\metre}. The electron flux density at that position is on the order of \SI{e6}{\per\second\per\milli\metre\squared}. The detector board contains two silicon detector chips of \pin diode type which can measure the \(\upbeta\)-electron flux from the source with a precision of \SI{0.1}{\percent} within \SI{60}{\second} with an energy resolution of FWHM \(=\) \SI{2}{\kilo\electronvolt}. The unique challenge in developing the FBM arise from its designated operating environment inside the Cryogenic Pumping Section which is a potentially tritium contaminated ultra-high vacuum chamber at cryogenic temperatures in the presence of a \SI{1}{\tesla} strong magnetic field. Each of theses parameters do strongly limit the choice of possible materials which e.g. caused difficulties in detector noise reduction, heat dissipation and lubrication. In order to completely remove the FBM from the beam tube a \SI{2}{\meter} long traveling distance into the beamline is needed demanding a robust as well as highly precise moving mechanism.
The most common method to measure direct current high voltage (HV) down to the ppm-level is to use resistive high-voltage dividers. Such devices scale the HV into a range where it can be compared ...with precision digital voltmeters to reference voltages sources, which can be traced back to Josephson voltage standards. So far the calibration of the scale factors of HV dividers for voltages above 1~kV could only be done at metrology institutes and sometimes involves round-robin tests among several institutions to get reliable results. Here we present a novel absolute calibration method based on the measurement of a differential scale factor, which can be performed with commercial equipment and outside metrology institutes. We demonstrate that reproducible measurements up to 35~kV can be performed with relative uncertainties below \(1\cdot10^{-6}\). This method is not restricted to metrology institutes and offers the possibility to determine the linearity of high-voltage dividers for a wide range of applications.
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.
The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to measure a high-precision integral spectrum of the endpoint region of T2 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.
In this work we present a keV-scale sterile-neutrino search with the first
tritium data of the KATRIN experiment, acquired in the commissioning run in
2018. KATRIN performs a spectroscopic ...measurement of the tritium $\beta$-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 search for sterile neutrinos with a mass of up to $1.6\,
\mathrm{keV}$. We do not find a signal and set an exclusion limit on the
sterile-to-active mixing amplitude of down to $\sin^2\theta < 5\cdot10^{-4}$
($95\,\%$ C.L.), improving current laboratory-based bounds in the
sterile-neutrino mass range between 0.1 and $1.0\, \mathrm{keV}$.
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 direct cosmic relic neutrino background search from the first two science runs 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 kinematic endpoint at 18.57 keV. The analysis is sensitive to a local relic neutrino overdensity of 9.7e10 (1.1e11) at a 90% (95%) confidence level. A fit of the integrated electron spectrum over a narrow interval around the kinematic endpoint accounting for relic neutrino captures in the Tritium source reveals no significant overdensity. This work improves the results obtained by the previous kinematic neutrino mass experiments at Los Alamos and Troitsk. We furthermore update the projected final sensitivity of the KATRIN experiment to <1e10 at 90% confidence level, by relying on updated operational conditions.
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.
Sterile neutrinos are a minimal extension of the Standard Model of Particle Physics. A promising model-independent way to search for sterile neutrinos is via high-precision beta spectroscopy. The ...Karlsruhe Tritium Neutrino (KATRIN) experiment, equipped with a novel multi-pixel silicon drift detector focal plane array and read-out system, named the TRISTAN detector, has the potential to supersede the sensitivity of previous laboratory-based searches. In this work we present the characterization of the first silicon drift detector prototypes with electrons and we investigate the impact of uncertainties of the detector's response to electrons on the final sterile neutrino sensitivity.
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.
