Brookhaven AGS Experiment 949

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Results (from the first 20% of the running approved by DOE-OHEP)

E949 has observed three additional K⁺→π⁺νν candidate events in the phase space region below the K⁺ → π⁺ π⁰ (K_π2) peak (0808.2459). The new branching ratio, based on seven candidate events in the entire E787+E949 data sample, is BR=1.73^+1.15_-1.05x10^-10. (8/18/2008)
The first E949 K⁺→π⁺ν ν candidate event (The third event ever observed); the new branching ratio remains almost twice the SM level BR=1.47^+1.30_-0.89x10^-10. This result comes from the phase space region above the K_π2 peak. (3/23/2004)
E949 results from the search for K⁺→π⁺γγ near the kinematic endpoint and for K⁺→π⁺γ. (5/24/2005)

Although it is clear that additional running is needed to evaluate consistency with the SM prediction, funding for the completion of E949 is not yet available. (The United States Department of Energy's Office of High Energy Physics has neglected to provide the funding to complete the operations of E949 that they approved in August of 1999.)

Description of the experiment

E949 is a rare kaon decay experiment in the C4 beamline (LESB III) at the AGS.


Introduction to E949 (pdf version of poster for Lepton Photon 2003)	E949 Event

We are seeking to measure the branching ratio of K⁺ → π⁺ ν ν. E949 is a successor experiment to the very successful E787 experiment. E787 was the first experiment to observe this very rare decay. The first event was collected during the 1995 run at the AGS. More information on E787 can be found at the web site, or in the following brief description. The second event was found in the 1998 data set of E787. E949 has substantially upgraded the photon veto system, the trigger, the data acquisition, and several other key detector systems, and plans to run with the full AGS beam intensity (x5 more than was available for the observation of the first event).