That neutrinos carry a nonvanishing rest mass is evidence of physics beyond the Standard Model of elementary particles. Their absolute mass holds relevance in fields from particle physics to cosmology. We report on the search for the effective electron antineutrino mass with the KATRIN experiment. KATRIN performs precision spectroscopy of the tritium β-decay close to the kinematic endpoint. On the basis of the first five measurement campaigns, we derived a best-fit value of m ν 2 = − 0.14 − 0.15 + 0.13 eV ² , resulting in an upper limit of m _ν < 0.45 eV at 90% confidence level. Stemming from 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.

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 β-decay. The collaboration targets a sensitivity of 10^-6 on the mixing amplitude sin²Θ. 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.

The ASPECT-BET project, or An sdd-SPECTrometer for BETa decay studies, aims to develop a novel technique for the precise measurement of forbidden beta spectra in the 10 keV–1 MeV range. This technique employs a Silicon Drift Detector (SDD) as the main spectrometer with the option of a veto system to reject events exhibiting only partial energy deposition in the SDD. A precise understanding of the spectrometer’s response to electrons is crucial for accurately reconstructing the theoretical shape of the beta spectrum. To compute this response, GEANT4 simulations optimized for low-energy electron interactions are used and validated with a custom-made electron gun. In this article we present the performance of these simulations in reconstructing the electron spectra measured with SDDs of a ¹⁰⁹Cd monochromatic source, both in vacuum and in air. The allowed beta spectrum of a ¹⁴C source was also measured and analyzed, proving that this system is suitable for the application in ASPECT-BET.

Precision spectroscopy of the electron spectrum of the tritium $$\upbeta $$ β -decay near the kinematic endpoint is a direct method to determine the effective electron antineutrino mass. The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to determine this quantity with a sensitivity of better than $${0.3}{\hbox { eV}}$$ 0.3 eV ( $$90\%$$ 90 % C.L.). An inhomogeneous electric potential in the tritium source of KATRIN can lead to distortions of the $$\upbeta $$ β -spectrum, which directly impact the neutrino-mass observable. This effect can be quantified through precision spectroscopy of the conversion-electrons of co-circulated metastable $$^{83\text {m}}\text {Kr}$$ 83 m Kr . Therefore, dedicated, several-weeks long measurement campaigns have been performed within the KATRIN data taking schedule. In this work, we infer the tritium source potential observables from these measurements, and present their implications for the neutrino-mass determination.

KATRIN (Karlsruhe Tritium Neutrino Experiment) aims to measure the neutrino mass by analyzing the endpoint region of a Tritium spectrum using a high-luminosity source and a high-resolution MAC-E filter technique. KATRIN holds the current best limit on the neutrino mass of 0.8 eV, coming from the joint analysis of the first two measurement campaigns. After KATRIN’s data taking, a detector upgrade, called TRISTAN, is planned. The choice for this new detector is a matrix of Silicon Drift Detectors (SDDs) made of 9 modules with 166 pixels each. SDDs, able to sustain a high count rate, will allow a high-statistics measurement of the whole Tritium spectrum, and thus the search for new physics, like sterile neutrinos with mass in the keV-range, candidates to be Dark Matter particles. A model for the measured Tritium spectrum is therefore needed. In this work, I will present the status of such a model, together with experimental tests of one of its parts, the detector response.