Experiment 865 at the Brookhaven AGS has observed the decay K + → e + νeµ + µ − . The branching ratio extracted is (1.72±0.37(stat)±0.17(syst)±0.19(model))×10 −8 where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.

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Erratum: High statistics measurement of K e4 decay properties [Phys. Rev. D 67, 072004 (2003)]

The MINOS CollaborationArgonne -Athens -Caltech -Chicago -Dubna -Fermilab -Harvard IHEP-Beijing -Indiana -ITEP-Moscow -Lebedev Livermore VCL-London Minnesota -Oxford -Pittsburgh -Protvino -Rutherford -Stanford -SussexTexas A&M -Texas-Austin -Tufts -Western Washington - Executive summaryThe MINOS (Main Injector Neutrino Oscillation Search) experiment is designed to search for neutrino oscillations with a sensitivity significantly greater than has been achieved to date. The phenomenon of neutrino oscillations, whose existence has not been proven convincingly so far, allows neutrinos of one "flavor" (type) to slowly transform themselves into another flavor, and then back again to the original flavor, as they propagate through space or matter.The MINOS experiment is optimized to explore the region of neutrino oscillation "para meter space" (values of the !:l.m 2 and sin 2 29 parameters) suggested by previous investigations of atmospheric neutrinos: the Kamiokande, 1MB, Super-Kamiokande and Soudan 2 experi ments. The study of oscillations in this region with a neutrino beam from the Main Injector requires measurements of the beam after a very long flight path. This in turn requires an intense neutrino beam and a massive detector in order to have an adequate event rate at a great distance from the source.We propose to enhance significantly the physics capabilities of the MINOS experiment by the addition of a Hybrid Emulsion Detector at Soudan, capable of unambigous identification of the neutrino flavor. Recent developments in emulsion experiments make such a detector possible, although significant technological challenges must be overcome. We propose to initiate an R&D effort to identify major potential problems and to develop practical solutions to them.In addition to this primary motivation for this R&D work, we note that the strong and growing interest in studies of neutrino oscillations using neutrino beams from future muon storage rings provides another potential application. These beams will offer significantly higher intensities, albeit of mixed 1I1J-and lie, beams. In order to take full advantage of these beams for neutrino oscillation studies it will be necessary that the detector be capable of determination of the flavor of the final state lepton, and the lepton's charge in a significant fraction of the interactions. At present, an emulsion detector in an external magnetic field appears best suited to offer such capabilities. The R&D effort discussed here will be an important step towards a design of such a future detector. This document is organized as follows:• Chapter 1 summarizes the physics motivation for the proposed emulsion detector,• Chapter 2 briefly reviews the status of the emulsion technology and its aplication to particle physics experiments,• Chapter 3 discusses design considerations for an emulsion detector,• Chapter 4 describes some of the details of a possible detector as well as results from the work up to date,• Chapter 5 outlines the proposed R&D program and summarizes the resources req...

A new measurement of the properties of the rare decay K + → π + e + e − R. Appel 6,3 , G.S. A large low-background sample of events (10300) has been collected for the rare decay of kaons in flight K + → π + e + e − by experiment E865 at the Brookhaven AGS. The decay products were accepted by a broad band high-resolution charged particle spectrometer with particle identification. The branching ratio (2.94 ± 0.05 (stat.) ± 0.13 (syst.) ± 0.05 (model)) × 10 −7 was determined normalizing to events from the decay chain K + → π + π 0 ; π 0 → e + e − γ. From the analysis of the decay distributions the vector nature of this decay is firmly established now, and limits on scalar and tensor contributions are deduced. From the e + e − invariant mass distribution the decay form factor f (z) = f0(1 + δz) (z = M 2 ee /m 2 K ) is determined with δ = 2.14 ± 0.13 ± 0.15. Chiral QCD perturbation theory predictions for the form factor are also tested, and terms beyond leading order O(p 4 ) are found to be important. 13.20Eb