Sunday, November 20, 2011

Muons, Electrons, and Quarks, Oh My!!

We had a great program Saturday! (I always say that, but it's true.)

My song was called "Quarks and Electrons." Everything we can touch or see in the universe is made of quarks and electrons. Yet that represents only 4% of what we know is out there!

For the first hour Dr. Flera Rizatdinova spoke with us about the Large Hadron Collider - the world's largest machine! - and the Atlas Detector. We also explored the Standard Model of particle physics and learned about some mysteries of the universe such as: What is dark matter? and How do particles get their mass? These are questions the LHC was designed to help answer.

Dr. Rizatdinova describes the superconducting magnets inside the ATLAS detector.
Then we took a break to look for muons! Muons are elementary particles similar to electrons, but heavier. They are formed when high energy protons (cosmic rays) smash into the Earth's upper atmosphere. A shower of particles are created. This is basically the same thing that happens inside the ATLAS detector! Muons happen to live a relatively long time, so they are the ones that make it all the way down to the Earth's surface. There are thousands of muons passing through your body every second. They are way to small for us to see or feel them.

Peering into the cloud chamber looking for muon trails!
So if they are too small to see, how were we looking for them? With a detector of our own - a cloud chamber. This is a tank filled with alcohol vapor. The vapor is cooled at the bottom of the tank by dry ice until it's almost ready to condense. The cooled vapor is so unstable that a muon passing through it triggers the condensation. What you see then is a cloud of alcohol droplets. Each cloud appears spontaneously, taking the shape of the path of the muon that triggered it - usually a straight line - then drifting to the bottom of the tank.

It takes a while for your eyes to adjust their focus to the right area of the tank, near the bottom.

We could see two or three events happening every second or so!

It isn't hard to make your own cloud chamber. You can find instructions on YouTube.

After our break, for those who were interested in learning more, Dr. Rizatdinova spoke about her particular role in the LHC and the research that's being done there. The ATLAS detector is like a giant camera that records each proton collision, tracking all the hundreds of particles that fly out. There are about six hundred million collisions per second to record, and the data fills 15 million gigs of hard drive space every year!

Dr. Rizatdinova's team designed a piece of electronics that converts electric signals from passing particles into light, which is piped out of the detector in fiber optic cables and then converted back to electric signals. Why is this necessary? There are 80 million channels of data coming out of each pixel module! If these were each carried out by wire, well you can imagine the mess - there isn't room for it!

Dr. Rizatdinova's team also wrote the software to interpret these signals, determining whether top quarks are present. Top quarks are heavy particles that might indicate the presence of a Higg's Boson.

The Higg's Boson is one of the reasons the LHC was built. It's the last of the fundamental particles in our Standard Model of the universe that hasn't actually been observed yet. If it really exists, as we think it does, the LHC will find it. The Higg's is important because it is thought to explain how particles get their particular masses.

Here's how the searching works. The LHC accelerates protons to very close to the speed of light and then smashes the together and records all the particles that come out. Even though protons are relatively lightweight, much heavier particles can pop out when you collide them at such high energies. This is due to the conversion of that energy into mass.

The heavy particles that are formed don't stay around very long at all - nearly instantly they decay into a shower of smaller particles, which also decay into showers and on down the line. The detector isn't fast enough to actually "see" a Higg's Boson before it decays, but it can see the top quarks and other particles that it decays into. If the right pattern is detected, we'll know the Higg's was there!

As I said, it was a great program! Everybody's head got stretched a bit, and many great questions were asked. As I reminded the audience several times, it's natural to have trouble picturing all this! Sub-atomic particles are unlike anything in our human-scale experience. Even particle physicists have trouble visualizing what's going on down there in the quantum world! I sure enjoy trying, though, and I think the kids yesterday did as well.

Our next program is about something almost as difficult to fathom: Teenager Psychology!! Please join us December 17!


  1. Amazingly cool! I'm sorry my kids missed it!

  2. Hi Reagan,
    I'm sorry you missed it, too! Is Saturday morning not a good time for you? We may do a survey or something to see if there's a better time for the programs.