Short news items of interest to the RHIC/AGS community.
The E949 Collaboration at the AGS
The E949 collaboration at the AGS has observed three new events of the rare kaon decay K → π+νν. This brings the total number observed to seven, four of which were found by E949 and three by its predecessors E787. The branching ratio from all seven candidate events is 1.73 +1.15/–1.05 ×1010, which is consistent with the Standard Model prediction of (0.85 ±0.07) ×10−10.
K → π+νν is one of the rarest and most challenging particle decays ever observed, and is highly sensitive to physics beyond the Standard Model (SM). The uncertainty of the SM prediction, which involves second-order weak interactions- that is, the exchange of two weak force carrier bosons-is less than 10%. Any deviations uncovered by a precise measurement of this branching ratio could unambiguously signal the presence of new physics effects that are predicted in extensions to the SM.
The paper appears in the November 7, 2008 issue of
Physical Review Letters (A. V. Artamonov et al., Phys.
Rev. Lett. 101, 191802 (2008)).