P. Truöl

High statistics measurement ofKe4decay properties

We report experimental details and results of a new measurement of the decay K+ -> pi+pi-e+nue (Ke4}. A sample of more than 400,000 Ke4 events with low background has been collected by Experiment 865 at the Brookhaven Alternate Gradient Synchrotron. From these data, the branching ratio (4.11+-0.01+-0.11)*10**(-5) and the pi-pi invariant mass dependence of the form factors F, G, and H of the weak hadronic current as well as the phase shift difference delta00-delta11 for pi-pi-scattering were extracted. Using constraints based on analyticity and chiral symmetry, a new value with considerably improved accuracy for the s-wave pi-pi-scattering length a00 has been obtained also: a00=0.216+-0.013 (stat.)+-0.002(syst.)+-0.002(theor.).

New, high statistics measurement of the K+ ---> pi0 e+ nu (K+(e3)) branching ratio

E865 at the Brookhaven National Laboratory AGS collected about 70 000 K(+)(e3) events to measure the K(+)(e3) branching ratio relative to the observed K+-->pi(+)pi(0), K+-->pi(0)micro(+)nu, and K+-->pi(+)pi(0)pi(0) decays. The pi(0) in all the decays was detected using the e(+)e(-) pair from pi(0)-->e(+)e(-)gamma decay and no photons were required. Using the 2002 Particle Data Group branching ratios for the normalization decays, we obtain BR(K(+)(e3(gamma)))=(5.13+/-0.02(stat)+/-0.09(syst)+/-0.04(norm))%, where K(+)(e3(gamma)) includes the effect of virtual and real photons. This result is approximately 2.3sigma higher than the current Particle Data Group value. Implications for the V(us) element of the CKM matrix, and the matrixs unitarity are discussed.

New Measurement of the Properties of the Rare Decay K{sup +}{yields}{pi}{sup +} e{sup +}e{sup -}

A large low-background sample of events (10300) has been collected for the rare decay of kaons in flight K+ ->pi+ 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+ ->pi+ pi0; pi0 ->e+ e- gamma. 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+ delta*z) (z=M(ee)**2/m(K)**2) is determined with delta=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.

A large acceptance, high-resolution detector for rare K+-decay experiments

Abstract The detector of the E865-collaboration at the Brookhaven-AGS described here combines a magnetic spectrometer for the charged decay products of 6 GeV /c K + with excellent electromagnetic calorimetry and efficient particle identification for electrons and muons. Its high-resolution, large acceptance and high rate capability made it well suited for the study of extremely rare or forbidden decays with multi-leptonic final states such as K+→π+μ+e−, K+→π+l+l−, K+→l+νle−e+ and K+→π+π−e+νe down to branching ratios below 10−11 in an intense K+ beam (≈108 per AGS spill).

First observation of the decayK+→e+νeμ+μ−

Experiment 865 at the Brookhaven AGS has observed the decay K{sup +}{yields}e{sup +}{nu}{sub e}{mu}{sup +}{mu}{sup -}. The branching ratio extracted is (1.72{+-}0.37(stat){+-}0.17(syst){+-}0.19(model))x10{sup -8} where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.Experiment 865 at the Brookhaven AGS has observed the decay K^+ -> e^+ nu mu^+ mu^-. The branching ratio extracted is (1.72 +/- 0.37(stat) +/- 0.17(syst) +/- 0.19(model)) x 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.

Improved upper limit on the decayK+→π+μ+e−

Based on results of a search for the lepton-family-number-violating decay

New Measurement ofKe4+Decay and thes-Waveππ-Scattering Lengtha00

K^+ \to \pi^+\mu^+ e^-

Search for Lepton Flavor Violation in K + Decays

with data collected by experiment E865 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an upper limit on the branching ratio at

Erratum: New Measurement ofKe4+Decay and thes-WaveππScattering Lengtha00[Phys. Rev. Lett.87, 221801 (2001)]

2.1 \times 10^{-11}

Erratum: High statistics measurement ofKe4decay properties [Phys. Rev. D67, 072004 (2003)]

(90% C.L.). Combining the results with earlier E865 data and those of a previous experiment, E777, an upper limit on the branching ratio of