Rare Kaon Decay from E949 at Bnl: K+ -> π + ν bar {ν }

In the first year of physics run, the E949 experiment at Brookhaven National Laboratory has already collected 1.8 × 10^l2 kaons stopping in the target. Additional evidence for the rare charged kaon decay K⁺ -> π ⁺ ν bar {ν } has been observed. Combined with previous results from the E787 experiment, the branching ratio is measured to be Br(K⁺ -> π ⁺ ν bar {ν }) = (1.47_-0.89^+1.30) × 10^-10.