No abstract

Three events for the decay K+-->pi+ nunu have been observed in the pion momentum region below the K+-->pi+pi0 peak, 140 < Ppi < 199 MeV/c, with an estimated background of 0.93+/-0.17(stat.) -0.24+0.32(syst.) events. Combining this observation with previously reported results yields a branching ratio of B(K+-->pi+ nunu) = (1.73(-1.05)+1.15) x 10(-10) consistent with the standard model prediction.

An additional event near the upper kinematic limit for K+-->pi(+)nunu; has been observed by experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+-->pi(+)nunu;)=(1.47(+1.30)(-0.89))x10(-10) based on three events observed in the pion momentum region 211

Additional evidence for the rare kaon decay K + → π + νν has been found in a new data set with comparable sensitivity to the previously reported result. One new event was observed in the pion momentum region examined, 211 < P < 229 MeV/c, bringing the total for the combined data set to two. Including all data taken, the backgrounds were estimated to contribute 0.15 ± 0.05 events.The branching ratio is B(K + → π + νν)= 1.57 +1.75 −0.82 × 10 −10 .

Experiment E949 at Brookhaven National Laboratory studied the rare decay K ! and other processes with an exposure of 1:77 10 12 K 's. The data were analyzed using a blind analysis technique yielding one candidate event with an estimated background of 0:30 0:03 events. Combining this result with the observation of two candidate events by the predecessor experiment E787 gave the branching ratio