KATRIN Experiment and the Hunt for Neutrino Mass

What is KATRIN?

• The Karlsruhe Tritium Neutrino Experiment (KATRIN) in Germany aims to measure the mass of neutrinos, the lightest and most elusive subatomic particles.

• The massive 200-tonne spectrometer was transported via a global sea and river route due to its size and sensitivity.

Recent Achievement:

• KATRIN set a new upper limit on the sum of the masses of the three known neutrino types:
  Less than 8.8 × 10⁻⁷ times the mass of an electron (2× improvement from earlier).

• This was based on 259 days of data and 36 million electron measurements from tritium decay.

How It Works:

• KATRIN studies beta decay of tritium, focusing on the maximum energy of emitted electrons to infer the neutrino’s mass.

• The precision method does not rely on theoretical assumptions, making it experimentally robust.

Why Neutrino Mass Matters:

1. Neutrinos have mass, but the Standard Model predicts them to be massless.

2. Their masses are extremely small and unknown — only differences in squared masses are measurable via oscillation.

3. Measuring exact masses may point to new physics beyond the Standard Model, including unknown forces or particles.

4. Neutrinos might be their own antiparticles (Majorana particles) — if proven, it would revolutionize particle physics.

Comparison with Other Methods:

• Cosmology-based limits suggest an even tighter cap, but are model-dependent.

• Neutrinoless double beta decay could confirm if neutrinos are Majorana particles but assumes self-conjugacy.

Significance:

• KATRIN’s result is a major step in neutrino physics, offering a model-independent upper bound.

• It continues a legacy of efforts since 1991 and affirms the experimental challenge posed by neutrinos due to their elusive nature.