KATRIN Sets Stricter Limit on Neutrino Mass

Context

The Karlsruhe Tritium Neutrino (KATRIN) Experiment, a major international collaboration in astroparticle physics, has released a new result setting the most precise upper limit yet on the mass of neutrinos.
About KATRIN Experiment

• Objective: To determine the mass of the neutrino by studying the beta decay of molecular tritium.
• Collaboration: Over 150 researchers from 12 institutions across Germany, the UK, Czech Republic, and the USA.
• Data Collection: Between March 2019 and June 2021, KATRIN recorded around 36 million electron events over 259 days.

Key Findings

• KATRIN has set a new upper limit on the combined mass of the three neutrino types:
  ≤ 8.8 × 10⁻⁷ times the mass of an electron.
• This is twice as precise as the previous best direct measurement, making it the most stringent constraint yet on neutrino mass from direct detection experiments.

Neutrinos

Feature	Details
Nature	Electrically neutral, extremely light particles (hence called ghost particles)
Interactions	Interact only via weak nuclear force and gravity
Abundance	Most abundant massive particles in the universe
Detection	Difficult due to weak interaction with matter

Types of Neutrinos

1. Electron neutrino
2. Muon neutrino
3. Tau neutrino

Sources of Neutrinos

• Solar fusion reactions
• Cosmic ray interactions with Earth’s atmosphere
• Nuclear reactors
• Supernovae
• Big Bang (relic neutrinos)

Why are Neutrinos Important?

1. Cosmic Messengers:
   Neutrinos can escape from the dense interiors of stars and supernovae, carrying unique information about these objects that light or other particles cannot.
2. Physics Beyond the Standard Model:
   • Neutrinos having mass contradicts the original Standard Model of Particle Physics, suggesting the existence of new physics.
   • Understanding their properties may provide insights into dark matter, early universe evolution, and the matter-antimatter asymmetry.

Why is Measuring Neutrino Mass So Difficult?

• Extremely Low Mass:
  Neutrino mass is likely over a million times smaller than the electron, making direct measurement very challenging.
• Weak Interaction:
  Neutrinos rarely interact with matter, making them elusive and hard to detect.
• Current Measurement Limitations:
  • Neutrino oscillation experiments (which won the 2015 Nobel Prize) confirm that neutrinos have mass.
  • However, they only reveal the differences in the squares of masses, not the absolute mass of any neutrino.