My hardcore science geeks out there probably know about Super-Kamiokande, or Super-K, as
its friends call it.
The 15-story tall tank of water buried 1,000 meters under a mountain in Japan has been
instrumental for detecting and studying neutrinos, reshaping the standard model of particle physics
while it was at it.
Now the Japanese government has approved Hyper-Kamiokande which will be,
you guessed it, even bigger. So big that it may rewrite the standard model yet again.
Before we get to the particle physics-changing event that Hyper-K could detect in theory,
let’s first talk about what it’s being designed to detect.
Hyper-K, like Super-K before it, will hunt for neutrinos.
Neutrinos are incredibly elusive and hard to spot, because they very rarely interact
with anything.
Billions and trillions of the ultra-lightweight and chargeless particles pass through us at
nearly the speed of light every second , and honestly I’ve never noticed.
But here’s the beauty of the word “almost.”
Neutrinos almost never interact with other matter, which is another way of saying they
sometimes do!
So if you can get a lot of matter and just stare at it for awhile, and I mean all
of it, eventually you should see the telltale sign of a neutrino interaction.
The telltale sign in question is something known as Cherenkov Radiation.
Cherenkov radiation occurs when a charged particle travels faster than the speed of
light through a dielectric medium like water.
Think of it almost like a sonic boom, but instead of a conical shock wave of air, the
moving charged particle generates a cone of blue light.
If you were paying very close attention, you noticed that I said Cherenkov radiation is
generated by charged particles, but neutrinos have no charge.
However, neutrinos come in three types or “flavors”; electron, muon, and tau.
On the rare occasion that a neutrino does interact with water, it will convert into
one of these other subatomic particles based on its flavor.
Electrons, muons, and tau particles are charged, and will briefly emit a cone of Cherenkov
light until they slow down below the speed of light in water.
The end result sensors can detect is a faint flash of a blue ring of light.
Super-K uses 50,000 metric tons of ultra-pure water watched by 11,000 golden bulbs called
Photo Multiplier Tubes that take that faint light and convert it into an electrical current. Thanks
to its huge size and sensitivity, it can detect neutrinos from the sun, our atmosphere, or
even from a particle accelerator on the other side of Honshu that shoots neutrinos at it
from hundreds of kilometers away.
In 1998, just two years after it began operating, it observed that neutrinos oscillate, meaning
they switch between their three flavors as they travel.
This discovery altered the standard model and won one Japanese researcher the Nobel prize.
Super-K has achieved so much, so what could an even bigger detector with over five times the
water and four times the Photo Multiplier Tubes hope to accomplish?
How about explaining why stuff is here at all.
Scientists believe Hyper-K will be able to make more precise measurements that will reveal
the different speeds neutrinos and their antimatter counterparts, anti-neutrinos, cycle through
their three flavors.
This difference could be the key to explaining why more matter than antimatter was created
when the universe began, instead of being made in equal parts that annihilated each
other completely.
And if physicists are really, really, really lucky, Hyper-K will observe the decay of a
proton.
Right now the standard model says it’s impossible, but if Hyper-Kamiokande does observe a proton
decay, then our understanding of the entire universe changes.
It would mean that three of the four fundamental forces stem from a single fundamental force
when time began.
It would be the final piece that’s been missing from the puzzle of grand unified theories
that otherwise seem to fit together so perfectly.
Hyper-K should be able to see a proton decay if their average lifetime is 10^34 years.
That’s a 1 with 34 zeros after it.
Hopefully it does, because if the ultra-huge Hyper-K doesn’t detect it, that means the
average life of a proton must be at least 10 times longer.
But we’re getting ahead of ourselves, Hyper-K isn’t even built yet.
Let’s let them actually construct it, then pull up a chair and stare at 260,000 metric
tons of water.
Or as I call it, Tuesday.
Fun fact: while Super-K used ultra-pure water for decades, in 2019, researchers added gadolinium
to make it more sensitive to antineutrinos.
To test the water filtration with the new element, scientists made two testbeds with
the acronyms EGADS and GADZOOKS! because scientists cannot resist cheesy acronyms.
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Point on the international race to find the ghost particle.
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