This week, scientists from the National Fermi Acceleration Laboratory in Batavia, Illinois, announced progress that could improve particle physics. It turns out that when you expose particles known as muons – called “fat electrons” – to intense magnetic fields, they behave in a way that physics cannot explain as we know it, suggesting that a bunch of things are happening in the quantum for scientists to discover.
The result has long been expected among physicists, and one Fermilab researcher described it to the New York Times as the “moment of Mars rover’s landing,” but for most of us the discovery that depends on the difference between the measurements is 0.00116592040 and the expected 0.00116591810 is a little difficult to break down.
To better understand what muons are, why they do what they do, and what muons do what they do mean to the universe, I spoke with Emily Conover, a Science News reporter who earned her doctorate. from particle physics from the University of Chicago before turning to writing science. Our conversation is edited and concise for clarity.
Joshua Keating: First question: As the saying goes, mew-on or moo-on?
Emily Conover: Mew-na, like the Greek letter μ.
OK, great. What is a moon?
Muons are basically like a heavy version of an electron. They are unstable particles, so their life span is a second after which they disintegrate into other particles. They’re actually always all around us, we just don’t realize it. They are usually produced when a high-energy particle like a proton hits the Earth’s atmosphere. There are these high-energy particles that explode all over space and when they hit the atmosphere, other particles, including muons, interact with the gas there.
I have a picture of an atom model in my head. There is a nucleus with protons inside it, and there are small electrons whistling around on the outside. So, where are the muons?
A great concept that most people are not aware of is that there are a lot of other particles that are not in atoms. Because they are not stable, they do not make a thing that does everything we know.
I got it. But they always are around us?
Yes, there are a lot of muons that rain all the time on the Earth’s surface. In fact, it is a kind of interference for most physical experiments, because most physical experiments do not want to detect muons.
They are weird. There is a famous quote from a scientist when it was discovered: “Who ordered it?” * But in this experiment they do it to do they want to study the muon, so they create them artificially to study them.
So what did we learn about them this week?
Muons have this property where they behave like little magnets. And basically, the strength of that magnet is something you can really well predict using our particle physics theories – the “standard model” is called that. So you can predict how that magnet should react within the magnetic field. People compare their behavior in the field with a spinning top – the axis around which the top rotates, it is a shaky movement.
So the muons were exposed to a large magnet, and then the scientists observed what they were doing?
Yes. So they have this big donut shaped magnet and they send muons u that magnet, and they circulate inside it, and as they circulate around, they do this whole shaky, rotating thing, too.
How do muons enter a magnet?
So, this is done on Fermilab, and they use a particle accelerator to accelerate the protons, and the protons crash into the target and interact with it, and then you have the muons coming out at the end of it. So they accelerate the particles and then convert them into other particles, which continue to move in fast air, and are then able to enclose those around this circular magnet.
They put the muons in a big magnetic tube, and then the muons did something weird. What did they do?
So this magnet [muon] it fluctuated — it nodded a little differently than they expected. This suggests that our theories of particle physics lack something in predicting how much this muon should climate [according to the Standard Model] as opposed to how much he nodded.
Did they expect to discover this deviation or did they honestly have no idea what would happen?
They tried to see if they could confirm the previous deviation. It was an experiment in Brookhaven [National Laboratory] 90s and early 2000s who saw a sign of this strange muon behavior. But it wasn’t a strong enough signature to be really sure. So a new experiment, the goal of which was to say, “Hey, was that the thing we saw earlier? Or was there some other explanation? “This was a fictional version of an earlier experiment. They used the same magnet, but otherwise improved all the other components of the experiment. And they’ll be able to measure it even better in the coming years. They’ll be better able to figure out if the muons are really weird or there is some other explanation.
The last time everyone was really excited about particle physics was a few years ago, when the Higgs boson was discovered. Does this have anything to do with it?
The Higgs boson is part of the Standard Model. In fact, people talked about it as the last missing part of the Standard Model. The standard model is this theoretical mathematical model that explains how all particles interact, but for this to work and explain how particles in the standard model achieve mass, there had to be this other particle, the Higgs boson. That’s why it was a big deal when it was discovered in 2012, it solidified the image of the Standard Model we had.
Just in time not to stiffen!
It’s interesting. When they discovered the Higgs boson, of course it was very exciting and people were happy. But they also found nothing beyond the Standard Model and many people hoped they would. I think some theoretical physicists felt a little let down that we didn’t find it to be anything further than what we knew. So, if this new experiment is confirmed with more data, it could result from that.
OK, back to the muons. What could make them do weird shaky things?
I will give you a general picture: Muons constantly emit, absorb and communicate with other particles. There are these transient particles that exist in this strange quantum landscape that occurs. The strength of a muon magnet and the way it interacts with the magnetic field is not only a property of the muon itself, but is related to the way the muon interacts with all other particles.
There could be particles there that we don’t know about; they could interact with the muon and change the strength of its magnet. So this could be a sign that there is a particle we have not identified that is even stranger than the strangest particles we know about it.
What does this have to do with the abolition of the Standard Model?
The standard model is really useful for giving really accurate predictions. It explains all the crazy things we saw on the Large Hadron Collider. This is a really well-tested theory. But there are some things that don’t explain it. This does not explain dark matter – this matter is invisible, but it seems to be there in space, because you can see the gravitational effect of it on galaxies, but it cannot be explained by any particle we know in the standard model. And so, physicists are looking for something that is a little outside the Standard Model and think there is a deeper explanation that involves more particles or more forces.
The magnetism of the muons could provide a signature that points us to them. This could lead us to a theory that helps us better understand matter.
Correction, April 8: Due to a transcription error, this article originally attributed a quote to a muon finder said by another scientist.