Death of a b quark

1 April 1998

Click here to zoom out.

The b-quark (or bottom quark) is the second heaviest of the six basic building blocks of matter known as quarks. Like the other quarks, it is never detected on its own, but only as part of more complex particles (hadrons) held together by the strong force. This week's image shows the brief life of a particle containing a b quark - the particle is known as the Bs meson, and it is built from a b-quark bound with an s (strange) antiquark. The Bs meson has been produced by the annihilation of an electron and a positron at the point marked IP. It lives for only about 10-12s - a million millionths of a second - before it decays in a process akin to radioactive beta-decay. The b quark changes into a c (charm) quark, emitting an electron (e-) and an unseen neutrino. The c-quark and the s-antiquark carry on together as the particle known as the Ds+ meson, which then itself decays to three other mesons - a pion and two kaons (K+ and K-). This all happens WITHIN the beam pipe that carries the colliding beams in the Large Electron Positron collider at CERN, Geneva. The Bs meson here travels about 2 mm before it decays - its decay point is inferred by extrapolating back tracks detected beyond the beam pipe in the ALEPH detector. (Click on the interaction point IP to zoom out.)

Credit: CERN /ALEPH

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