Physics · the experiment
Track down the neutrino background
A giant tank of water, 5,003 days of data, barely a few events a year. Four questions, from beginner to expert, on what Super-Kamiokande saw, and on what it has not seen yet.
1 · Weigh the result
Beginner
What did Super-Kamiokande find on the diffuse supernova neutrino background?
2 · Turn the flux into events
With the reference signal shape, a flux of 3.6 antineutrinos per square centimetre per second corresponds to 4.8 events per year in Super-Kamiokande. Fitted alone, the gadolinium phases give a flux of 3.9.
Intermediate
How many events per year does that flux correspond to?
3 · Compare the two halves of the data
The gadolinium phases last 1,653.7 days, half as long as the pure-water phases, 3,349.3 days.
Expert
Which of the two weighs more in the hint, and why?
4 · Unmask lithium-9
Cosmic muons create radioactive isotopes in the water up to a million times more common than the signal. Requiring a neutron removes most of them.
Expert
Why is that requirement not enough against lithium-9?
Neutrino background tracked
—