BaBar reveals a "golden event"

23 August 2000



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The BaBar experiment at the Stanford Linear Accelerator Center (SLAC) in California has recently presented its first results. In the collision show here, an electron and a positron have annihilated at the centre of the detector, to produce a B meson and an anti-B meson. One of them has decayed into a particle called the J/psi together with a neutral kaon, and each of these has soon decayed to give the particles visible through the tracks coloured gold. The J/psi decayed almost instantly into a pair of muons (m); some time later (nearly a tenth of a nanosecond!) the neutral kaon (a "K-short") decayed into a pair of pions (p), which emerge at some distance from the initial annihilation point. The other B decays into a kaon (K) and three pions, producing the tracks coloured red. So-called "golden events" of this kind are playing a key role in BaBar's studies of the the subtle difference between matter and antimatter known as CP violation.

Credit: SLAC / BaBar