Posted by: Jamie | June 9, 2009


I stumbled across Symmetry Breaking, the joint Fermilab/SLAC publication. This article absolutely fascinated me!

“We hope that with a variety of technical refinements–such as slowing down the antiprotons as they enter the trap, cooling the positrons more before they interact with the antiprotons, and revising the mixing technique–we can make antihydrogen which is cold enough [to] stay in our shallow trap.”

The day when antihydrogen atoms by the hundreds or thousands are not only created but kept around long enough to study is growing closer.

There’s a lot of technical background to this article, so I’m not entirely sure where would be the best place to start in terms of de-jargon-ing it. Leave comments with your questions and I’ll try my best to clarify (though I’m still a beginner in this field). I’m hoping some posts for the SCI 101 page develop out of this! Most importantly: No question is too trivial.


  1. Well, that’s perfectly thrilling. Thanks for posting the article! The search for CPT violations reminds me of Pasteur’s discoveries re: tartaric and paratartaric acid. One question: how do they detect the anti-hydrogen atoms’ annihilation against the trap walls? I assume they don’t leave teeny little splat marks.

    Also, re: “they have so much extra energy that the positrons are bouncing around the antiprotons in very complicated, high-amplitude orbits” – if you ever run across any articles examining those orbits, I’d love to read more.

  2. One question: how do they detect the anti-hydrogen atoms’ annihilation against the trap walls? I assume they don’t leave teeny little splat marks.

    Sunnyhello, I checked out the ATHENA website (there are often multiple possible ways of detecting particles, but the ALPHA website didn’t specify how they do theirs. They linked to ATHENA, though, so hopefully that explanation will suffice). Based on their explanation, it looks like their detection system is largely the same as the electromagnetic calorimeters used in large particle accelerators. This is good, because it means I have a foggy clue of what’s going on and can try to clarify! It says that they’re specifically using silicon strip detectors, but the silicon detectors in use in the project I’m familiar with are a lot more complicated than the EM calorimeter, and I don’t know as much about them. The premise is going to be fundamentally the same, though. :)

    EM calorimeters generally consist of alternating layers of a dense material (often steel if large quantities are being used) and a “scintillator” – a material which ionizes easily, such as argon gas. When a particle like an electron enters the dense material, the electric fields of the atoms cause the electron to swerve. This makes it release a photon (to conserve energy and momentum). The photon is usually energetic enough to decay into an electron/positron pair, which will then also be moved by the fields. Each of these three particles will produces more photons, resulting in a cascade or a shower of particles in the calorimeter. As each of these particles passes through the gas, the atoms of the scintillator are ionized. These ions drift to the edges of the detector and are turned into voltage pulses, which activate electric circuits that record the presence of the ion. The mere presence of ionization is enough to tell us that something passed through the detector. How much ionization there is tells us something about how energetic that something was.

    In the case of antimatter, such as the antihydrogen, not only do the antiproton and the positron react to the electric field of the atoms in the dense material, but if the anti-particles collide with a regular particle, then they will immediately annihilate. This means that they let out a burst of energy together, usually in the form of other types of energetic particles. This shows up, again, as a bunch of ionization in the detector.

    For the record, I got a bunch of this explanation from here.

    Please feel free to ask me for clarification on any of this. Some things that seem obvious to me might actually not be. :)

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