Fermilab is America’s leading particle physics laboratory.
On this, I think you’ll agree.
People ask me which is Fermilab’s most important experiment, and that’s a little harder to
answer, as the laboratory’s scientific staff is involved in many world-class efforts to
understand the secrets of the universe.
However, there is no doubt that the laboratory has a large and robust neutrino research effort
and there is also no denying that the laboratory’s long term and flagship experiment is called
DUNE, short for Deep Underground Neutrino Experiment.
In what might be a case of stating the very obvious, the DUNE detector will be located
deep underground and will search for neutrino interactions.
That sounds obvious enough.
But, when you dig into the details, reality is a bit more complex.
DUNE actually consists of a couple of detectors: a smallish one located on the Fermilab campus
and a much larger one located 800 miles away in Lead, South Dakota.
Fermilab will shoot the world’s most intense beams of neutrinos and antimatter neutrinos
through both detectors to better understand a fascinating behavior called neutrino oscillation.
One of the key goals is to see if neutrinos and antimatter neutrinos oscillate identically.
If they don’t, this will be an absolutely crucial discovery which will help explain
why the universe exists as we know it.
I’ve made a couple of videos that talk in detail about neutrinos and neutrino oscillation,
but I can give you the thumbnail description here.
Neutrinos are the ghosts of the subatomic world and are very hard to detect.
Because they experience only the weak nuclear force, they can easily pass through matter.
For instance, neutrinos can pass through the entire Earth, with only a very tiny probability
of interacting.
In fact, that happens all of the time with neutrinos produced in the Sun.
There are three different types of neutrinos, each denoted by the Greek letter nu and a
subscript that identifies which kind they are.
The three types are the electron-type, the muon-type, and the tau-type.
Each type has a special affinity for a specific charged lepton, like the electron-type neutrino
is produced at the same time as an electron and so on.
These three types of neutrinos are similar, but different- like a cat, a jaguar, and a
tiger.
Neutrino oscillation is the phenomenon where neutrinos change their identity going from
one to another and back again.
It’s like a cat morphing into a jaguar and then a tiger and then back to a cat.
Researchers have suspected neutrinos oscillated since the early 1970s and data recorded in
the late 1990s proved that it’s true.
We’ve spent the last two decades studying the phenomenon in detail.
The DUNE experiment is designed to study neutrino oscillation and compare it to antineutrino
oscillation.
A beam of nearly-pure muon neutrinos or antineutrinos will be shot from Fermilab to western South
Dakota.
The detector on the Fermilab campus will characterize the beam when it leaves the site and the distant
detector will study it when it arrives, 800 miles away.
These two measurements will allow researchers to determine how much oscillation occurred
while the particles were in flight.
So, oscillation measurements like those are the bread and butter of the DUNE research
program, but it’s not the driving point of the experiment.
There are a couple of topics that are worth calling out.
The first one I’ll mention is the most persuasive reason to build the DUNE experiment, but the
others are pretty cool too.
The first one has to deal with a very serious mystery of modern physics, specifically the
seemingly silly question of why our universe is made of matter.
That question just seems very peculiar- I mean- of course the universe is made of matter.
But it turns out that that ‘of course’ isn’t so obvious.
For instance, we know of a substance called antimatter which is a cousin of matter.
Take matter and antimatter and combine them and they convert into energy.
The converse is also true.
Energy can convert into matter and antimatter.
You can combine that observation with the theory of the Big Bang and you encounter a
mystery.
And if you’re wondering how I could touch antimatter, you’ll have to speak up a bit.
I’m a trifle deaf in my left ear.
The Big Bang says that the universe was once smaller and hotter and full of energy.
As the universe expanded and cooled, that energy should have turned into equal amounts
of matter and antimatter.
And yet, our universe consists entirely of matter.
So where did the antimatter go?
We don’t know the answer to that, but we believe that there was a very tiny imbalance
in the early universe, so that for every three billion antimatter particles, there were three
billion and one matter particles.
The three billions cancelled each other out and the one left over is what made us.
I said that we don’t know how that happens, but we have found some small indications that
the universe slightly favors matter over antimatter, but not enough to explain the mystery.
So that’s where neutrinos and the DUNE experiment comes in.
The DUNE experiment will study neutrino oscillation using both neutrinos and antimatter neutrinos.
If we find that they oscillate to a different degree, that could be the crucial clue that
explains, well, the whole mystery.
Or not.
That’s why we do the experiment- to help us find out if this line of thinking is true.
So this study of matter and antimatter neutrinos is the biggest reason to build the DUNE detector,
but there are a couple of others.
Another reason is because there are theories that say that ordinary protons will decay.
Now our best theory of physics says that protons are stable and we’ve measured their lifetime
and determined that if they decay they live for ten to the thirty fourth power years.
That’s ten billion, trillion, trillion years- which is enormously longer than the measly
14 billion year lifetime of the universe.
The DUNE experiment will be able to achieve comparable performance to the best existing
measurements.
And, for certain decays, it will be able to do better than any other detector.
And, if DUNE actually observes proton decay, that will completely rewrite the textbooks.
There is a third neat thing that DUNE can do and that is to look for neutrinos emitted
from a supernova, which is the explosion of a star.
Using different apparatus, we’ve seen one such example before.
In 1987, a star blew up in the Larger Magellanic Cloud, which is a small galaxy orbiting the
Milky Way.
The biggest detector at the time, called Kamiokande II, saw a grand total of 12 neutrinos.
If you combine the neutrinos from all detectors that were active at the time, a total of 25
were seen.
If the DUNE experiment were running back in 1987, it would have measured 120 neutrinos
by itself.
Such a measurement would help us better understand the dynamics of just what happens when a star
collapses.
Supernovae are pretty rare, with only about one per galaxy per century, and the DUNE detector
will only see supernovae in the galaxies closer than Andromeda, so DUNE researchers will have
to get lucky to see one.
But since the detector is being built anyway, it would be foolish to not use it to do some
astrophysics as well.
I’ve talked about why DUNE is very interesting scientifically, but it's also interesting
both technologically and sociologically.
The detector in Lead, South Dakota will be buried nearly a mile under the Earth’s surface
in the Sanford Underground Research Facility.
The detector will consist of almost seventy thousand tons of liquid argon, housed in four
gigantic caverns.
Each cavern will contain a detector 45 feet square and 200 feet long.
Liquid argon was chosen as a technology because it allows researchers to record in detail
the particles originating in collisions of neutrinos with atoms in the detector.
And we know that approach works, because a prototype version of DUNE has been built and
tested.
The prototype is called ProtoDUNE and this is what it looks like before it's filled with
liquid argon.
It’s really quite beautiful.
And researchers have already used ProtoDUNE to look at particles passing through the detector.
It’s just a lovely detector, both aesthetically and scientifically and it bodes very well
for the future of the DUNE project.
DUNE is an international collaboration, involving researchers at institutions from 32 countries
and CERN.
CERN isn’t a country, but as the world’s other powerhouse particle physics institution,
it gets special mention.
Fermilab and CERN have collaborated before, but this is the first time CERN has invested
in infrastructure outside of Europe.
The DUNE collaboration really does have some of the world’s foremost neutrino experimenters
among its collaborators.
So what’s the status of DUNE, you ask?
Well, it’s being built.
The first of the caverns should have an operational detector by the mid 2020s.
The others will follow shortly thereafter.
I know that sounds like quite a ways away, but it’s not a lot of time to build a world
class beamline and facility.
We’ll be buried in neutrino data before you know it.
Okay.
That’s the end of the video.
Did you like, subscribe and share?
If not, why not?
It's really is hard to pick out just one of Fermilab’s dozens of research efforts, when
so much good science is going on, but DUNE is definitely the biggest in terms of both
manpower and resources.
It’s going to dominate the neutrino landscape for decades, resulting in fascinating physics.
And that makes it very important because, as you know, physics is everything.