Name: The Quest for Glueballs
Uploaded: 2017-01-15T05:43:53.000Z
Duration: 8 min 18 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

There’s a certain attitude that particle physicists tend to take when it comes to their experiments:

When it comes to the tiniest particles in the universe, there’s a lot we still don’t know.

So physicists study them using particle accelerators, huge machines that get particles -- like protons,

or electrons -- moving almost as fast as the speed of light.

Then they smash them together, and… physics happens. Very explode-y physics.

And sometimes, the researchers can’t predict what’s going to come out of the reaction.

Instead, they have to work backward, looking at the data and using math to figure out what

Which is why, in September, physicists from the Technical University of Vienna announced

that they think they’ve identified a whole new kind of subatomic particle… all because

The particle’s called a glueball, which is, somewhat surprisingly, a pretty accurate name.

It’s a particle of gluons, the sticky particles responsible for keeping an atom’s nucleus

Now that is a weird thing because this particle doesn’t contain any matter -- it’s made

And if they can confirm the discovery, it’ll be another big piece of evidence that The

Standard Model of Physics -- the current understanding of how physics works -- is in fact right.

You might remember the Higgs boson -- the main particle that gives matter its mass -- which

physicists confirmed not too long ago using the same working-backward method.

They bashed together some particles, then sifted through the data.

It can take years to analyze all that information, and new insights can crop up long after the

In the case of Higgs, scientists knew exactly what to look for, but had to analyze years

worth of data before they could confirm the discovery.

With glueballs, they’re not even sure what the thing they’re trying to find looks like

-- though they do know that they’re made of stuck-together gluons.

Now, normally, gluons are the things that hold quarks together.

Quarks join up to form protons and neutrons, the basic components of atoms.

So, no atoms without protons, and no protons without quarks.

And to stick together, the quarks need gluons.

That’s because the protons in an atomic nucleus are all positively charged. If it

were up to the electromagnetic force, those charges would repel each other and atoms would never form.

The protons can all stay inside the nucleus because they have the strong force keeping them there.

The strong force is a fundamental force -- meaning that we describe it separately from other

fundamental forces, like gravity or electromagnetism.

It’s more than a hundred times stronger than the electromagnetic force and many, many

more times stronger than gravity, but it’s mostly important on the scale of an atomic  nucleus.

Each proton or neutron in the nucleus is made of three different quarks, held together by

The strong force holds together not only the three quarks that make up the proton, but

the quarks in the other protons as well, so that electromagnetic force doesn’t send

Every force has a particle to carry it, known, appropriately, as a force carrier. Force carriers

have no mass. The one for electromagnetism, for instance, is the photon.

The same goes for the strong force, which also has a massless force carrier, which is

That’s what gluons are, and where their name comes from -- they glue quarks together.

And gluons are definitely a thing -- researchers discovered them in 1979 using the PETRA particle

But as far back as 1972, physicists were using math to show that gluons might have an odd

property: the ability to stick to each other, forming a glueball.

43 years later, we still haven’t been able to prove they exist.

But scientists really want to, because glueballs are predicted by the Standard Model -- the

best explanation we have for how particles and forces behave.

Almost all of our understanding of science is based on the Standard Model -- so, uh,

it’s kind of important to make sure that it’s right.

And there’s a lot of evidence that it is right -- like when we discovered the Higgs

boson, which the Standard Model said we should.

Until then, there was a chance that the Standard Model was totally wrong about how mass works,

and if it was, we’d have to rethink a LOT of science.

So, since the Standard Model tells us that glueballs should exist, researchers are looking

for them as another way to confirm that our science isn’t totally off track.

And it’s not like glueballs occur in nature. You can’t just walk outside, pull out a

powerful microscope, and find one in a tree.

But the Standard Model does tell us that there are a few different ways to make them in a

particle accelerator, like by smashing together a proton and an antiproton -- which is exactly

I mean, don’t try this at home or anything, but it sounds easy, right?

Trouble is, there’s a lot of stuff that comes out of these glueball-making reactions,

and it’s hard to tell what’s what because we don’t know exactly what we’re looking for.

Things that seem like they could be glueballs have been showing up in particle accelerators for ages.

But nothing’s for sure, because we don’t know some of the properties of a glueball

The idea of a glueball having mass is strange to think about in general, because -- like

we said earlier -- none of the individual gluons that stick together to form the glueball have mass.

And when you add together a bunch of things with zero mass, you’ve got 0 + 0 + 0...that’s 0, right?

Wrong! You don’t, because of a weird property of energy -- it’s related to mass, by a

little equation you might’ve heard of: E = mc^2.

And turns out, the energy that’s holding all those gluons together in the glueball?

It translates to mass… we just don’t know exactly how much.

To make matters worse, glueballs aren’t stable. You couldn’t pick up a handful of

them. They would flit into existence and right back out a moment later.

And when you do create a glueball, it causes quarks -- and their opposites, antiquarks

And whenever a particle and its opposite interact with each other, they both get annihilated.

The blast of energy from a quark and antiquark coming into contact with each other blows

So how do you find a glueball, if you can’t observe one directly?

Physicists have to put on their Sherlock Holmes deerstalker hats and deduce its existence

from the traces it leaves when it’s destroyed.

They look at the data from the experiment, and if any of it looks like it could be a

sign of an unidentified particle, they do the math to see if that particle would match

Which is why every so often, candidate glueballs turn up in the scientific literature. For

the most promising ones, there are usually a dozen or so papers arguing for or against

Two of these are the catchily named f0(1500) and f0(1710).

We’ve known about both of them for a while, discovered in various particle accelerators

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The Quest for Glueballs

weird

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