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The Sciences

PANICking in Santa Fe and Antiprotons in San Francisco

Cosmic VarianceBy Mark TroddenNovember 1, 2005 11:39 AM

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I'm starting to write this post in the United Airlines Red Carpet Club at Philadelphia airport, as I wait for a flight to Syracuse that is delayed for (I hope only) 35 minutes. I've been traveling since Wednesday and have had a truly enjoyable time at two different conferences. Extremely early Wednesday morning, I left Syracuse to head to Santa Fe. I flew into Albuquerque, rented a car and drove the final hour to Santa Fe. It is a remarkably beautiful drive that impresses me each time I do it. The landscape is just so very different from the Northeast and England. I always think of the landscapes in old Western movies when I drive through it. I went to Santa Fe to give a plenary talk at the Particles and Nuclei International Conference (PANIC-05). Because of previous plans, which I'll get to in a while, I could only be there for a couple of days. But it was enough to have a great time. I spent most of Wednesday afternoon recovering from getting up so early and putting the finishing touches to the talk - Connecting the Dark Side and Fundamental Physics - that I was to deliver first thing on Thursday morning. In the evening, I got together with my friend and co-blogger JoAnne, and with my other friends, Daniel Holz (from Los Alamos National Laboratory) and his [strike]wife[/strike] partner Jessica, for dinner. We went to an outstanding restaurant in Santa Fe (Geronimo, for those of you interested in a recommendation for next time you're there), and enjoyed wonderful food, good wine and great conversation. It's a pleasant fringe benefit of traveling to conferences that one can meet up with good friends who live so far away. My talk on Thursday morning seemed to go well (although you'd have to ask someone who was in the audience for an unbiased opinion). This was pretty much a standard discussion of how particle physics and cosmology must work together if we are to understand the mysterious components (dark matter and dark energy) that seem to make up 95% of the universe. I also discussed the mystery of the baryon asymmetry of the universe - why the observable universe contains essentially all matter, with negligible primordial antimatter. Speaking after me was another very good friend who I haven't seen for a long time - Dan Akerib from Case Western Reserve University. Dan is an experimentalist who works on the Cryogenic Dark Matter Search (CDMS) experiment, and we know each other from when I was a postdoc in Cleveland. Dan gave a very nice overview of the different attempts to detect dark matter directly, by detecting nuclear recoils as the experiment collides with dark matter particles as the Earth flies through the galaxy. These are very cool experiments, which have been steadily pushing down the limits on the cross-section of dark matter particles, and there are high hopes for a detection in the not-too-distant future. Dan and I had a few drinks after the conference banquet that evening, and then I got a reasonably early night because I needed to get up early Friday morning to drive back to Albuquerque and fly to San Francisco. I was headed to San Francisco to spend Friday and Saturday at Lawrence Berkeley National Laboratory (LBNL) at a symposium to celebrate the fiftieth anniversary of the discovery of the antiproton. This discovery was announced in a paper titled Observation of antiprotons, by Owen Chamberlain, Emilio Segrè, Clyde Wiegand, and Thomas Ypsilantis, which appeared in the November 1, 1955 issue of Physical Review Letters, making today the perfect day to mention it. The antiproton was found at a brand spanking new accelerator, the Bevatron. LBL has a nice discussion of the prehistory, the machine and the discovery, in which they write

Even with Ernest O. Lawrence's invention of the cyclotron in 1931, earthbound accelerators weren't up to the task. Physicists knew that the creation of an antiproton would necessitate the simultaneous creation of a proton or a neutron. Since the energy required to produce a particle is proportional to its mass, the creation of a proton-antiproton pair would require twice the proton rest energy, or about 2 billion electron volts. Given the fixed-target collision technology of the times, the best approach for making 2 billion electron volts available would be to strike a stationary target of neutrons with a beam of protons accelerated to about 6 billion electron volts of energy. In 1954, Lawrence commissioned the Bevatron accelerator at his Rad Lab. (Upon Lawrence's death in 1958, the lab was renamed Lawrence Berkeley Laboratory in his honor.) This weak-focusing proton synchrotron was designed to accelerate protons up to energies of 6.5 billion electron volts. At the time, around Berkeley, a billion electron volts was designated BeV; it's now universally known as GeV. Though this was never its officially stated purpose, the Bevatron was built to go after the antiproton. As Chamberlain noted in his Nobel lecture, Lawrence and his close colleague, Edwin McMillan, who codiscovered the principle behind synchronized acceleration and coined the term "synchrotron," were well aware of the 6 billion electron volts needed to produce antiprotons, and they made certain the Bevatron would be able to get there.

The symposium was fantastic; attended mostly by elderly men and women who are among the great physicists of the last fifty or more years. Owen Chamberlain who, along with Segrè, won the 1959 Nobel Prize for the discovery, was there, even though he is not in great health. Another speaker was Carlo Rubbia, who won the Nobel prize for the discovery of the W and Z bosons at the European Center for Nuclear Research (CERN) in 1984. I spent a wonderful couple of days listening to and talking with these great scientists. My talk was close to the end of the symposium, in the part called "The Future". My assigned title was The Search for New Particles and Symmetries, and I discussed the roles that both of these may play in understanding some of the mysteries of cosmology, such as dark energy, dark matter and baryogenesis. This entire five day trip was a lot of fun, although it was also exhausting and a huge amount of work. I learned a lot - not only physics but physics history as well (If you don't know the drama behind this particular Nobel Prize, take a look at this obituary for a clue), but I'm glad to be home again and back to a normal routine (for a short while anyway).

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