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[ intro ]
Imagine putting a house on a really big scale and weighing the whole thing.
And then you break it down
and weigh all of the individual pieces separately.
And then you find one brick that’s heavier than the whole house.
That can’t be right, that’s impossible.
But in the weird world of subatomic physics
it could totally happen,
and new research has found evidence for it inside protons.
So, if the proton is a proverbial house, that brick is a charm quark,
and learning more about it might help us understand
the biggest mysteries in particle physics.
Every atom in the universe has at least one proton inside of it.
In fact, protons make up most of the regular matter out there.
And thanks to decades of particle physics research,
we know that protons are made of even smaller particles called quarks.
Specifically, protons are made of two fundamental ‘flavors’ of quark:
‘up’ flavored quarks and ‘down’ flavored quarks.
Or at least, that’s what we’ve thought until recently.
Because new research says this may not be the whole story.
Some physicists have proposed that in addition to those quarks,
There is another fundamental component to the proton:
a charm quark.
A charm quark is another flavor of quark, behaving exactly like an up quark,
only with a lot more mass.
A single charm quark is more massive than an entire proton!
So yeah, the idea of protons being built from them sounds a little bizarre.
But it’s physically plausible because of another strange rule.
On this teeny tiny scale of reality, everything comes down to probabilities.
Physicists use equations to describe the possible outcomes
for which quarks they will see when they observe a proton.
They do this by smashing protons together at high speeds
and watching what particles are formed from all that energy.
About 99.5% of the time, when they observe a proton in these situations,
they see it’s made of up quarks and down quarks as expected.
But the other 0.5% of the time,
they see it’s made of a charm quark, too.
Because the charm quarks are there so infrequently and they’re short-lived,
they only contribute a small amount of their enormous mass
to the overall mass of the proton in the equations that describe these things.
That is how the brick can weigh more than the house.
So, physicists do see short-lived charm quarks come out of protons all the time.
But they call them extrinsic charm quarks,
because they’re not thought to be a component of protons
when we’re not smashing them together and creating all kinds of new particles.
Some physicists, however, have theorized
that there are also intrinsic charm quarks
fundamental building blocks
that exist whether we are tinkering with protons in a particle accelerator or not.
And finding evidence that protons are really made of charm quarks
turns out to be a lot more difficult.
Physicists have been chasing
after subtle hints of intrinsic charm quarks for decades,
but there’s a big effect that may be masking it.
Every proton also has a roiling ‘sea’ of particles popping in and out of existence,
buzzing around at all times.
Physicists have to hunt through that noise to find intrinsic charm quarks.
If you don’t go into the data analysis with a particular model in mind,
you can’t really wade through all that noise.
And there are lots of plausible models of intrinsic charm,
so generally physicists have to go through each model
one at a time to see if the data match.
But research published in August 2022 used a new trick:
machine learning.
The team fed 30 years of particle collision data into a computer,
including hot-off-the-press data from the Large Hadron Collider in Switzerland.
Then they told the computer to look for evidence of intrinsic charm quarks,
using whatever model it needed to.
But it was also allowed to assume there was no intrinsic charm quark.
Because that’s always a possibility, too.
By looking at loads of different models at once,
it could identify which ones fit the data best way more effectively than previous attempts.
And sure enough, the researchers did find evidence for intrinsic charm quarks.
They even calculated the probability of spotting one of them: around 0.6%.
But is this evidence actual proof?
The team says there’s only a one in one thousand chance they’re wrong.
But in the world of particle physics,
that is not good enough.
Before anyone can actually claim a discovery has been made,
they have to show there’s only a one in three million chance they’re wrong.
I mean we are talking about the fundamental rules of reality here.
The standards should be pretty high!
Whether or not protons really do have this intrinsic charm quark,
these sorts of ultra-precise tests are crucial for the future of particle physics.
Researchers are probing ever-deeper into the smallest parts of reality,
and that requires an extreme level of accuracy…
both in the experimental design,
and the understanding of laws of nature.
That way, if experiments don’t match what those laws predict will happen,
they can be sure it’s because of something new and exciting,
not some kind of accounting error.
And if this new evidence holds up,
then we’ve learned a new fact about the nature of reality…
and about a particle that we are all made of.
That’s an idea that really has some intrinsic charm.
You made it to the end of the video, so you probably think quantum objects have some merit.
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[ outro ]