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  • More than 20 years ago, a team at Brookhaven National Lab detected a missing piece in the Standard Model.

  • A measurement they had taken to better understand the effects of the forces that shape our universe

  • So, the international physics community came up with a plan: Take the measurement again with much more powerful instruments and see what sticks.

  • Fast forward to April 7th, 2021, that highly anticipated measurement is finally in

  • and it seems like the Brookhaven results weren't a fluke.

  • This means that our current understanding of the universe may not account for every particle and force within it,

  • and therefore, may need to be entirely reworked.

  • So, this experiment is looking at little elementary particles called muons.

  • And what we really care about muons for this experiment is that they're like little spinning tops. They're like little magnets.

  • As it turns out, muons are one of the most precise ways for scientists to probe the quantum world.

  • The muon is one of 12 elementary particles described by the Standard Model.

  • This model aims to understand how each of these particles is affected by the universe's four known forces:

  • the strong, weak, gravitational, and electromagnetic.

  • These twelve particles are divided into quarks and leptons, which are each further divided into six distinctflavors.”

  • Like electrons, muons are just oneflavorof leptons.

  • They also spin like a top and have a negative charge, meaning they're able to generate their own magnetic field.

  • So, when a muon's internalmagnetis exposed to a strong external magnetic field

  • like one produced by, say, a particle accelerator

  • the muon starts to wobble.

  • The rate of this wobble is what physicists call its “g-factor,” or magnetic moment.

  • This is an experiment that allows us to see from the wobble of the muons, what's an otherwise invisible quantum world

  • that contains all kinds of stuff that we'd like to know about.

  • So, it's basically, it's pointing us to something that we don't understand. And this is why it's very interesting.

  • Muons are around 200 times heavier than electrons,

  • which means the moment they become 'magnetic' is 200 times smaller...

  • and therefore way more sensitive to all of the virtual particles swimming around in the quantum realm.

  • So, to measure this moment, precision is everything.

  • Which is exactly what physicists from around the world have been after.

  • Which brings us back to the Brookhaven experiment.

  • In 2001, the team published some surprising findings.

  • Their measurement of the muon's g-factor deviated from the Standard Models' prediction,

  • and nothing could account for the difference.

  • Instead of finding a g-factor slightly above 2 as the Standard Model had predicted,

  • they'd found a g-factor that was off by nearly 3 standard deviations.

  • The Brookhaven experiment was a big surprise.

  • It made a lot of people think that maybe there's something we really don't understand either about particle physics,

  • or about how to do these kinds of experiments.

  • So, the physics community decided that the only way to confirm these findings was to take that measurement again.

  • Led by Fermilab, the Muon g-2 experiment cast its first beam of particles back in 2017

  • and has been searching for the muon's g-factor ever since.

  • We decided to combine the experimental techniques by moving the magnetic ring from Brookhaven National Lab,

  • all the way to Fermilab.

  • Fermilab's accelerators first blast particles into a giant ring where they decay into muons.

  • These muons then travel to a second ring, where they spin and start to wobble in reaction to the ring's powerful magnets.

  • By comparing measurements of this wobble with the ring's magnetic field,

  • the team is able to walk away with a measurement of the magnetic momentwith a precision of 0.14 parts per million.

  • At this level of precision, we get a window into the world of muons that we've never had before...

  • and a more specific number to compare our theoretical predictions with.

  • It's taken 20 years of effort by theorists like me to actually make these very, very precise predictions that we're checking.

  • And it's the difference between that theory prediction and what the experiment sees, that could be something new

  • some new force of nature, or something that we just didn't know about.

  • After years of intense efforts on the part of the team and the muon beam, the first round of results are finally ready.

  • So, the new measurement agrees amazingly well with the Brookhaven measurement from 20 years ago,

  • and the fact that now you have two different experiments, including this much more modern version,

  • getting the same answer to me says that the experiments are probably right.

  • This is the kind of breakthrough that you live for when you're doing science.

  • The team still has to analyze more data from this experiment,

  • so there's a chance that they'd stumble on some answers in those numbers.

  • But one thing is for sure: The team's search for muon's magnetic moment definitely isn't over.

  • To me, what's exciting is that we don't know what it is that they're seeing.

  • But whatever it is, it would have to be something fundamentally new.

  • It's not just a little bit different, it would be something that I think would revolutionize our thinking, whatever it turns out to be.

  • We've actually covered Fermilab's work on the channel beforecheck that video out here.

  • Let us know what you think is lurking out there in the universe that could explain the g-2's latest findings.

  • And make sure to subscribe to Seeker to hopefully, one day, find out.

  • Thanks for watching and I'll see you next time!

More than 20 years ago, a team at Brookhaven National Lab detected a missing piece in the Standard Model.

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B1 US muon measurement magnetic experiment wobble standard model

Scientists Just Discovered a Major “Hole” in the Standard Model of Particle Physics

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    joey joey posted on 2021/04/16
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