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StanfordAround the Bay |
Attobarns: Not for Your Average Size CowToday, BaBar collaborators are holding an all-day workshop on "1/ab." Not familiar with the term? It stands for inverse attobarns, which means big things for BaBar. An inverse attobarn corresponds to one billion pairs of B and anti-B particles produced by the PEP-II accelerator. More data means more physics. For BaBar, this number will be 10 years in the making, from when the experiment turned on in 1999 to when it ends in September 2008. To date, the experiment has generated almost half an inverse attobarn. "To put that in perspective, when BaBar turned on the total number of B, anti-B pairs collected by previous electron-position colliders operating at this energy was roughly 10 million. Now we are less than two years from achieving one billion pairs collected," said Jim Olsen, BaBar's physics analysis coordinator. A "barn" is a unit of area—10^{-24} cm^{2}—used to measure the chance that something will happen when two particles collide, that is, the interaction cross section. An inverse barn is the total number of collisions in a given period of time, also called integrated luminosity. The prefix "atto" stands for 10^{-18}, which seems small, but an inverse attobarn, 10^{18}, is big: a billion times a billion. When you multiply your inverse attobarns by your cross section size, you get the total number of events. The workshop participants are examining how best to quarry the wealth of data that resides in 1/ab.
—Heather Rock Woods Above image courtesy of Alan Chou. |