The Large Hadron Collider is just as exciting as it sounds—it’s the world’s largest
and most powerful particle accelerator.
It helps us discover brand new subatomic particles!
One of the most recent newbies is called uhhhhhh...this.
And it’s a...pentaquark, which is a kind of exotic hadron...which means what, exactly?
And how does it fit into—or potentially break—our modern understanding of quantum
physics?
To get there, we need to start with the basics: the good ol’ Standard Model.
It’s the set of mathematical principles that, over time and with experimental verification,
has resulted in a widely-accepted physics theory.
It’s an organized way of looking at the elementary particles and fundamental forces
of the universe, much in the same way that the periodic table has organized chemical
elements.
Fermions are the smallest unit of matter we currently know of —we cannot
break them down into anything smaller.
The fundamental forces are what act on the universe: the strong force, the weak force,
the electromagnetic force, and the gravitational force.
All of the forces except gravity have a carrier particle, and these are called bosons.
Within the fermions are another two categories: quarks and leptons.
Quarks are fast-moving points of energy—and so far we’ve identified 6 kinds, 3 pairs
of two.
The stable matter in the universe is made up of the first generation of quarks, the
up and down quarks.
And for context—all protons are made up of one down and two up quarks, and neutrons
are made of two down and one up quark, held together by the strong force.
In the next generation, we have the charm quark and strange quark, and the last delightfully
named pair is the top (or truth) and bottom (or beauty) quarks.
Then we have the other big chunk within the fermions—the leptons.
Quarks make up protons and neutrons, while the leptons are a class of particles that
includes the electron.
Just like with quarks, we’ve got six particles here, three pairs of two: the electron and
its pair the electron neutrino, the muon and the muon neutrino, and the tau and tau neutrino.
The electron, muon, and tau particles all have mass, while their neutrino counterparts
are like their ghosts, with no charge, almost no mass, hardly interacting with any other
matter at all!
WHOO ok we made it through the fermions.Then we have the bosons—the particles that carry
the universe’s fundamental forces.
The gluon carries the strong force, which is what binds the nucleus of an atom—you
could say it glues things together.
The friendly and familiar photon is what carries the electromagnetic force, and the W and Z
bosons carry the weak force—the force responsible for radioactive decay, among other things.
To finish off our current Standard Model, which is undeniably incomplete, and I promise
we’re working our way up to that particle I mentioned at the beginning—we’ve got
the Higgs Boson.
This name may ring a few bells as it's been featured all over the news in recent years.
It’s famous!
But why?
Well, one important part of the Standard Model is a hypothetical quantum field that is what
gives the particles their mass.
It’s called the Higgs field, which--because the field behaves with wave-particle duality--is
carried by the Higgs boson, much like the fundamental forces are carried by their bosons.
The experimental confirmation of the Higgs Boson by the LHC in 2012 was a Nobel-prize
winning breakthrough--now that we know this particle exists and how to find it, we’re
able to learn more about it and how it behaves WITH other particles, like fermions, helping
us understand how the Higgs field imparts mass onto the other particles.
It’s totally fine if your brain is breaking at this point.
A saying attributed to Richard Feynman, one of the most renowned theoretical physicists
of the 20th century, is anyone who claims to understand quantum mechanics does not.
There’s so much more detail here that we’re not going into, like color charge and spin
dynamics, that we could talk about for literally years--so if that’s something you’re interested
in, let us know in the comments below.
But since the discovery of the Higgs boson, no new fundamental particles have come out
of the work at the LHC.
So what are these new discoveries?
Well the pentaquark just discovered is what’s called a composite particle--specifically,
an exotic hadron.
Hadrons are the class of subatomic particles made up of clusters of quarks--the proton,
for example is a hadron.
The Large Hadron Collider is so named because it smashes together protons or other ions
that all belong to the hadron family.
Hadrons come in different configurations, either in quark-antiquark pairs, which are
known as mesons, or groups of three quarks, known as baryons, all held together by the
strong force.
There are a few rebels however, that don’t fit into this model, and these are called
exotic hadrons.
Predicted decades ago, they were experimentally discovered in 2014–and are made up configurations
of quarks that don’t fit into the conventional hadron blueprint.
This new pentaquark is one such exotic hadron and, as its name suggests, is made up of 5
quarks.
While it may not necessarily add another dot to the Standard Model, studying its formation,
decay, and how all the quarks within the particle interact with each other tells us a lot about
the behavior of both hadrons and quarks.
These kinds of unstable, short-lived particles may not be ones we interact with on a daily
basis, but they are very similar to matter and energy interactions that exist inside
extreme astrophysical environments, like neutron stars.
Studying these particles here on earth helps us better understand those kinds of events.
The Standard Model is our best way of organizing our existing understanding of the quantum
world.
In using the best facilities in the world, like the LHC, we push the boundaries of how
much of this behavior we can actually see, in our attempts to experimentally verify the
Standard Model.
You may notice, however, that gravity, the fourth fundamental force, is conspicuously
absent from the Standard Model as a force-carrying particle.
The current Standard Model of quantum physics and the theory of general relativity are fundamentally
at odds with one another—if one is correct, our understanding of the other shifts.
Like we’re trying to fill out the structure of the Standard Model with experimental data,
new astrophysics research aims to support Einstein’s theory of general relativity,
which could make us rethink physics as a whole, including the quantum stuff.
Besides the excitement of actually finding the particles we’ve been looking for, for
decades because their existence is predicted by the Standard Model, new experimental evidence
of particles like this tells us more about how all the particles in the standard model
interact with each other, why they have the properties they have, and could clue us in
on how to look for the stuff we’re still missing.
All just by smashing stuff together.
If you want more mind-breaking quantum physics, check out my video on string theory here,
and let us know in the comments below what else you’d like us to cover in the quantum
realm.
Make sure you subscribe to Seeker for all your particle breakthrough updates, and as
always, thanks for watching.