KOPIO

Fifteen billion years ago the universe was born in a cataclysmic explosion known as the “Big Bang”. In this instant of creation energy was released in the form of all of the postulated fundamental constituents of the universe – now postulated in the so-called Standard Model to be the quarks and leptons, and the force carriers such as photons and gluons. In that first instant matter and anti-matter must have been created equally, and if left to their own devices would have annihilated each other eventually leaving a universe filled only with energy in the form of photons. But some mysterious physical principle intervened and created a small asymmetry between matter and anti-matter, with the result that the universe as we know it today consists almost entirely of matter and energy with few traces of anti-matter left. Today we believe that the principle responsible was CP-violation, discovered in the 1960’s at Brookhaven National Laboratory in the decays of neutral K-mesons (and garnering the Nobel Prize for V. Fitch and J. Cronin). After almost 40 years of study the source of CP-violation is still not understood and although much progress has been made, it is still not even completely characterized. Recently CP-violation has also been observed in the decays of another family of particles – the B-mesons – and is under scrutiny at almost every high-energy laboratory in the world!

CP-violation is not only important for the light it may shed on the early evolution of our universe, but also for the fact that it provides the only known method for distinguishing matter from anti-matter. When neutral K-mesons decay, violating CP, they do so preferentially into anti-electrons (positrons) over electrons by a tiny but measurable amount. Thus we can provide an unambiguous prescription for identifying matter or anti-matter, by observing such decays.

KOPIO seeks to measure a very special decay of the neutral K-meson, which can provide an almost complete characterization of the phenomenon of CP-violation, competitive and complementary to the studies being done on B-mesons. If the results agree it will provide important confirmation of our understanding of CP-violation, however, if they do not agree, it may provide prima facie evidence of new and important physics phenomenon that will shed light on the evolution of the early universe.

> CONTINUE: The Basic Constituents of Matter

Last updated January 24, 2006 by Gary Schroeder.