Neutrinos Have No Business Being This Freaking Small

Physicists person placed a caller bounds connected however large the elusive neutrino tin be—one of the universe’s smallest known particles—a bounds that makes different subatomic particles look arsenic large arsenic achromatic holes by comparison.

In a caller effect published this week successful Science, researchers person enactment a caller precocious bounds connected the wide of this itsy-bitsy particle: nary much than 0.45 electron volts (eV). For context, that’s little than one-millionth the wide of an electron, which clocks successful astatine a comparatively gargantuan 511,000 eV. So, yeah—neutrinos are ridiculously lightweight.

Trillions of neutrinos walk done your assemblage each second, but they are truthful tiny and truthful weakly interacting that you don’t consciousness a thing.

Neutrinos are the lone known simple particles whose wide remains unknown, though questions stay astir however good those simple particles cooperate with the Standard Model.  Determining the neutrino’s wide with precision could connection profound insights into the universe’s laws. Are neutrinos getting their wide from the Higgs boson, arsenic different particles do? Or is determination immoderate wholly caller mechanics astatine play?

Enter the Karlsruhe Tritium Neutrino Experiment, oregon KATRIN, a 75-foot-long (23-meter-long) blimp-shaped vacuum chamber. Scientists show the radioactive decay of tritium wrong the vacuum chamber; arsenic the tritium decays, it spits retired electrons and antineutrinos. Researchers can’t measurement the antineutrinos straight (they shade done substance similar it’s nothing), but they tin (and do) survey the leftover electron’s vigor to marque inferences astir the wide of the missing particles.

After analyzing 259 days of data, the KATRIN squad was capable to chopped their erstwhile champion estimation for the neutrino’s wide (0.8 eV) astir successful half. But they’re not finished; by the clip the afloat 1,000-day dataset is crunched, the squad hopes to propulsion that wide bounds down to 0.3 eV, possibly adjacent 0.2 eV.

Neutrinos inactive person plentifulness of tricks up their subatomic sleeves. As physicist Susanne Mertens from the Max Planck Institute puts it, the KATRIN Collaboration’s measurement could beryllium a backdoor into caller physics—and perchance a amended knowing of however the aboriginal beingness evolved.

In February, a antithetic squad detected the most energetic neutrino (also called “ghost particles” for their enigmatic nature) heavy successful the Mediterranean Sea, indicating that the particles whitethorn beryllium emitted by interactions betwixt substance and the cosmic microwave background—the oldest disposable airy successful the universe.

If the neutrino wide were more—around 1 electronvolt—KATRIN could person recovered its existent value. But with the particle being truthful freaking small, a caller and improved detector—KATRIN++—may beryllium required to measurement its wide with precision.

Few things successful beingness are certain, but among the things we tin reliably expect are death, taxes, and the neutrino being smaller than ever.