Bound on 3+1 Active-Sterile Neutrino Mixing from the First Four-Week Science Run of KATRIN

Area of Science:

• Particle Physics
• Neutrino Physics
• Cosmology

Background:

• The existence of sterile neutrinos is hypothesized to explain anomalies in neutrino oscillations and cosmological observations.
• Searches for light sterile neutrinos are crucial for understanding neutrino mass and beyond-Standard-Model physics.

Purpose of the Study:

• To search for evidence of a light sterile neutrino using high-precision beta-decay spectroscopy.
• To set exclusion limits on the mass and mixing parameters of a potential fourth sterile neutrino state.

Main Methods:

• Analysis of beta-decay electron spectra from a high-purity gaseous molecular tritium source.
• Utilizing the KATRIN experiment's high-resolution MAC-E filter spectrometer.
• Comparing observed spectra to predictions within a 3+1 neutrino model framework.

Main Results:

• No significant spectral distortion indicative of a light sterile neutrino was observed.
• Exclusion limits were placed on the sterile neutrino mass squared (m_{4}^{2}≲1000 eV^{2}) and active-to-sterile mixing (|U_{e4}|^{2}≳2×10^{-2}).
• New limits supersede previous results from Mainz and improve upon the Troitsk bound.

Conclusions:

• The KATRIN experiment's first science run provides stringent constraints on light sterile neutrino properties.
• The results constrain parameters relevant to the reactor and gallium neutrino anomalies.
• Further data collection will enhance sensitivity to sterile neutrino searches.