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Acceleration of polarized protons at RHIC requires fast and reliable measurements of proton beam polarization. There are not many physical processes which could be used to measure polarization of protons with momentum larger than 10 GeV. Elastic scattering with very small momentum transferred is one of these processes. Its advantages are large cross section, which gives large figure of merit, and weak energy dependence of the analyzing power. CNI polarimeter with ultra thin carbon ribbon target and silicon detectors for recoiled nuclei was successfully tested with internal polarized beam at AGS. Then the polarimeter consisting of 4 silicon detectors was used for RHIC polarized beam commissioning in the blue ring. This year polarimeters of 6 silicon detectors each are to work in both rings to ensure RHIC polarized beam collisions.

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.

Based on results of a search for the lepton-family-number-violating decay \\(K^+ \\to \\pi^+\\mu^+ e^-\\) 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 \\(2.1 \\times 10^{-11}\\) (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 \\(1.3 \\times 10^{-11}\\) (90% C.L.) is obtained.

The reaction anti-proton + proton -> anti-\\Lambda + \\Lambda -> anti-proton + \\pi^+ + proton + \\pi^- has been measured with high statistics at anti-proton beam momentum of 1.637 GeV/c. The use of a transversely-polarized frozen-spin target combined with the self-analyzing property of \\Lambda/anti-\\Lambda decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of eleven real parameters for each bin of scattering angle, each of these parameters is determined with reasonable precision. From these results all conceivable spin-correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables in anti-proton + proton -> anti-\\Lambda + \\Lambda near this energy. Existing theoretical models do not give good predictions for those spin-observables that had not been previously measured.

E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+(e3) events with the purpose of measuring the relative K+(e3) branching ratio. The pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e-gamma decay and no photons were required. Using the Particle Data Group branching ratios for the normalization decays we obtain BR(K+(e3(gamma))=(5.13+/-0.02(stat)+/-0.09(sys)+/-0.04(norm))%, where \\(K+(e3(gamma)) includes the effect of virtual and real photons. This result is 2.3 sigma higher than the current Particle Data Group value. The implications of this result for the \\)V_{us}$ element of the CKM matrix, and the matrix's unitarity are discussed.

Experiment 865 at the Brookhaven AGS obtained 410 K+ -> e+ nu e+e- and 2679 K+ -> mu+ nu e+e- events including 10% and 19% background. The branching ratios were measured to be (2.48+-0.14(stat.)+-0.14(syst.))x10^-8 (m_ee>150 MeV) and (7.06+-0.16+-0.26)x10^-8 (m_ee>145 MeV), respectively. Results for the decay form factors are presented.