It’s a tight race to the finish in the BSR Spring 2011 Reader’s Choice Award! Voting ends next Friday, June 17, so hurry up and cast your vote here to help your favorite article rise to the top spot.
If you haven’t gotten around to reading the current issue yet (it’s available online here or in print at multiple campus locations), consider getting started with the excerpt posted below, from “What’s the Antimatter” by Denia Djokic (p. 8). This week, the stunning experimental results featured in Denia’s article were published in the journal Nature Physics. Remember, you heard it here first!
For many, the word “antimatter” elicits images of the Starship Enterprise ripping through space faster than the speed of light, or canisters of tiny glowing balls threatening to obliterate Vatican City. Scientific inaccuracies in popular culture aside, the prospect of isolating antimatter, which annihilates in a burst of light upon contact with matter, has eluded physicists for decades. And yet, this is just what a group of scientists working at CERN, the European Organization for Nuclear Research, recently succeeded in doing. Several months ago, the international ALPHA (Antihydrogen Laser Physics Apparatus) collaboration, which includes many researchers from UC Berkeley and Lawrence Berkeley National Laboratory, managed to create and, more importantly, capture 38 antihydrogen atoms for about one sixth of a second—an eternity in the world of subatomic particles. This exciting breakthrough will allow physicists to study matter’s counterpart in detail and will ultimately deepen, and possibly fundamentally change, our understanding of the origins of the universe. The first question at hand: why is our universe made almost entirely of matter and not antimatter?
A particle of matter and its antimatter complement have the same mass but opposite charges. While hydrogen is composed of a proton and an electron, an antihydrogen atom consists of an antiproton, the proton’s negatively charged counterpart, and a positron, the positively charged analog of the electron. Though scientists at CERN have been creating antihydrogen atoms from positrons and antiprotons for several years now, they have not been able to contain them for a significant period of time. The net neutral charge makes the anti-atom impossible to confine with an electric field, and its kinetic energy makes it challenging to control with a magnetic field.
Joel Fajans, UC Berkeley physics professor and one of the lead scientists of the ALPHA collaboration, explains the experiment starting with the process of creating antihydrogen atoms: “It’s not actually that hard—you essentially just need to throw together a lot of positrons and low-energy antiprotons, and eventually you get antihydrogen atoms.” Just like UC Berkeley’s own Bevatron, where antiprotons were first discovered in the 1950s, the CERN laboratory creates antiprotons for a variety of scientific experiments. Unlike the Bevatron, CERN is unique in its capability not only to produce these particles, which are byproducts of high energy particle interactions, but also to slow them down. Once cooled to low energies, the plasma of antiprotons is introduced to a cloud of positrons, letting pairs of particles combine to form bound systems—antihydrogen atoms. The real difficulty lies in trapping the antihydrogen atom, which Fajans’ group can do with remarkable finesse. The ALPHA trap consists of a complex system of repulsive magnets that takes advantage of antihydrogen’s magnetic moment to suspend the atom in space. However, despite state-of-the-art technology, this is a very weak magnetic trap.
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Andresen, G., Ashkezari, M., Baquero-Ruiz, M., Bertsche, W., Bowe, P., Butler, E., Cesar, C., Charlton, M., Deller, A., Eriksson, S., Fajans, J., Friesen, T., Fujiwara, M., Gill, D., Gutierrez, A., Hangst, J., Hardy, W., Hayano, R., Hayden, M., Humphries, A., Hydomako, R., Jonsell, S., Kemp, S., Kurchaninov, L., Madsen, N., Menary, S., Nolan, P., Olchanski, K., Olin, A., Pusa, P., Rasmussen, C., Robicheaux, F., Sarid, E., Silveira, D., So, C., Storey, J., Thompson, R., van der Werf, D., Wurtele, J., & Yamazaki, Y. (2011). Confinement of antihydrogen for 1,000 seconds Nature Physics DOI: 10.1038/nphys2025