PHYSICISTS have discovered a mysterious new subatomic particle. But they are unsure what it is, as it doesn鈥檛 fit theories that describe nuclear forces.
The particle, dubbed Ds (2317), is thought to be a 鈥渃harm-strange meson鈥�. There are supposed to be eight such particles, which are combinations of charm and strange quarks and their antimatter counterparts. Four have been discovered so far, each with their predicted properties. But the fifth, the Ds, has too small a mass.
The Ds particle is thought to be a charm quark paired with an anti-strange quark. This ought to have a mass of about 2500 megaelectronvolts, says Marcello Giorgi from the University of Pisa in Italy, who is the leader of the BaBar detector project at Stanford that made the discovery. But the particle they have found is 10 per cent lighter.
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