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January 10, 2002

Electronic newsroom


Background on the Search for Rare Kaon Decays

K+ => pi+,nu,nubar event in the E787 apparatus

In the upper left a K+ enters near the center of the concentric circles representing a cylindrical tracking chamber. It loses energy and stops in a segmented target of scintillating plastic counters, then decays to a pi+, which leaves the target and is tracked through the chambers (small circles indicate the path) into an array of large scintillation counters surrounding the chamber. The counters in the path of the pi+ are shown. It stops in the 15th counter on the path. On the upper right is a blowup of the stopping target region. The filled red squares indicate target elements hit by the K+, the blue outlines are those hit by the pi+ leaving the target. The curved element indicates a trigger scintillation counter adjacent to the target which the pi+ also hit on its way out. The curve on the lower right is the pulse of energy left by the K+ in the target element in which it stoped. The curve on the lower left shows the pattern of energy deposition in the last counter on the pi+ trajectory. The pulse of energy left by the stopping pion is shown by the muon to which it decayed after about 15 billionths of a second. The lack of other tracks or significant energy depositions indicates that the pi+ was unaccompanied by any detectable particles (neutrinos are not detectable in this apparatus).

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The U.S. Department of Energy's Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.