Muons on the Move

Big science is a massively collaborative endeavor. From the initial theoretical puzzles to the brilliant engineers that build on-of-a-kind machinery, experts come together to make discoveries happen. Case in point: We’re  moving this 50-foot-wide physics experiment over 3,200 miles of land, sea, and river, starting on Long Island, NY and ending in Batavia, IL. Sometimes understanding the fabric of the universe requires a very technical and very long journey.

The muon ring assembled at Brookhaven Lab.

The 50-foot-wide muon ring assembled at Brookhaven Lab.

The experiment is called Muon g-2 (pronounced gee-minus-two), and will study the properties of muons — tiny subatomic particles that exist for only 2.2 millionths of a second. The core of the experiment is the massive machine built at Brookhaven in the 1990s (assembled above), and a circular electromagnet made of steel and aluminum filled with superconducting cable is its centerpiece. These powerful cables produce a field of 1.45 Tesla, or about 30,000 times magnetic field of our planet.

Back when we ran the experiment, our scientists caught a tantalizing glimpse of physics beyond the Standard Model. But they could only claim a 3-sigma result, which is insufficient to announce a physics-shaking discovery. Clearly, you can’t just leave a question about the nature of the not-so-empty vacuum unanswered.

Our friends at Fermilab are giving this instrument a second life. As they explain on the experiment website:

A muon has an internal magnet, sort of like a miniature bar magnet. It also has an angular momentum, much like a spinning top. One way to study as yet unobserved particles and forces residing in the vacuum is to study the behavior of muons in a magnetic field. The Muon g-2 experiment aims to do just that.

Fermilab can produce a more pure and energetic muon beam than we could back in the day, so they can explore particle puzzles with even greater precision. But we can’t take that giant ring apart, so we have to move the whole thing very, very carefully. This beastly project includes installing a custom-built suspension system, slowly rolling along multiple lanes of highway (watch the animation!), traveling by barge around the tip of Florida, and then floating up the Mississippi River before arriving in Illinois.

We’ve had some great coverage from the media, including local outlets that will see this big ring float or drive by. Our favorite headline has to be this gem from CleanTechnica: Honk If You Love Muons. More updates to come after the move begins this Sunday, June 16!

Comments

  1. #1 Ignacio Gallo
    pofume.org
    June 11, 2013

    If it’s big, it must be meaningful!

  2. #2 Patrick M. Dennis
    June 11, 2013

    The first paragraph reads as if you are conducting a new test of translational invariance!

  3. #3 G.
    California USA
    June 13, 2013

    Hi Justin-

    Re. this: “Back when we ran the experiment, our scientists caught a tantalizing glimpse of physics beyond the Standard Model. But they could only claim a 3-sigma result, which is insufficient to announce a physics-shaking discovery.”

    Dude, don’t just keep us in suspense until 2016 or later! ;-) Seriously, say more. Understood that the results aren’t up to the normal standards, and speculation is speculation. But it would be most interesting to have a glimpse, so we (laypeople) know what to watch out for in the science news.

    Does whatever-it-is extend the Standard Model, or does it call some of it into question?

    I read the material here:
    http://muon-g-2.fnal.gov/1-muon-g-2-collaboration-to-solve-mystery.shtml

    and here:
    http://muon-g-2.fnal.gov/3-how-does-muon-g-2-work.shtml

    It suggests the possibility of new particles that aren’t yet understood.

    Would that be because the new particles were too short-lived for the previous apparatus to catch unequivocally? Or because they have different properties than what the system was designed for? Or something else?

    (The articles at Fermilab describe muons as decay products of pions, each composed of an electron and two neutrinos. But elsewhere, they say that muons break down into neutrinos and positrons. In either case, is there any theoretical or practical reversibility to the breakdown of muons into neutrinos and positrons or electrons?)

    As I understand it, the vacuum is basically a froth of virtual particles that pop into and out of existence, and average to a net value of zero. Is there any theoretical lower limit to the longevity or other values of those particles?

    • #4 Justin Eure
      June 13, 2013

      Thanks, G, for the excellent questions. I’ll do another post later on about the physics behind g-2 (both past and future), but in the mean time one of our experts weighed in on your comment. Physicist Bill Morse worked on the experiment here at Brookhaven, and he’ll stay involved with it at Fermi. He gets technical, but I’ll flesh out some of the finer points in a future post.

      On the anomaly seen when the experiment ran at Brookhaven Lab:

      A charged spin ½ particle creates a tiny magnetic field. That magnetic field is given by the magnetic moment = egS/2m. All the physics is in g, the rest just makes the units come out right, well except for the 2. The Dirac equation predicted g=2 for spin ½ point particles. The electron has g = 2.002…, where the 0.002… is the anomalous magnetic moment (g-2) due to virtual particles. However, the proton g value was measured in the 1930s to be 5.6! This was finally explained in the 1960s by the quark model. So maybe the muon is made up of other stuff also (predicted by some models called prions). There is another muon anomaly found at the PSI Lab. Muonic hydrogen (bound state of a muon and a proton) gives different spectroscopy from what you would expect from hydrogen (bound state of an electron and a proton). There are models about a new force that couples to muons, but not electrons. Other models go by the names Super-symmetry, and Dark Light.

      Does whatever-it-is extend the Standard Model, or does it call some of it into question?

      Great question! Some theorists say the former, and some the latter.

      On the possibility of new particles:

      The LHC discovered the Higgs, the last particle predicted by the Standard Model, but didn’t see Super-symmetry. However, the g-2 interpretation would predict that they wouldn’t have seen Super-symmetry, until they double the LHC energy (specifically for large tan (beta) models). The LHC is now off for two years in order to double their beam energy.

      The articles at Fermilab describe muons as decay products of pions, each composed of an electron and two neutrinos. But elsewhere, they say that muons break down into neutrinos and positrons. In either case, is there any theoretical or practical reversibility to the breakdown of muons into neutrinos and positrons or electrons?

      Great question! Some theories say yes, and some say no. So far none have been discovered. I actually did one of those experiments, before I joined g-2. That’s a very interesting, but different, story.

      As I understand it, the vacuum is basically a froth of virtual particles that pop into and out of existence, and average to a net value of zero. Is there any theoretical lower limit to the longevity or other values of those particles?

      This is due to Quantum Mechanics. Bohr said that anyone who thinks they understand Quantum Mechanics, and is not deeply disturbed by it, doesn’t understand Quantum Mechanics. Anyway, the quantum fluctuations in the vacuum go as (dE) (dt) = Planck’s constant. dE is the energy fluctuation. dt is the time it does it. The average value is close to zero; however, the muon’s spin is precessing due to the magnetic moment egS/2m. Suppose the muon briefly turns into a W particle (500 times more massive than the muon with S=1, and a neutrino). The mass and spin are very different, for this very brief time. The TOTAL angle the muon’s spin has precessed will be different, i.e., we don’t have to “catch it in the act” for this extremely short dt, we just know it did it. It’s like you are driving from NY to LA on a paved highway at 65mph, but briefly go over a rubble strip at 64mph. The time it takes to get to LA will be different!