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We report the first measurement of the forward-backward asymmetry and the ratios of Wilson coefficients and in A9/A7 and A10/A7 in B --> K*l+l-, where l represents an electron or a muon. We find evidence for the forward-backward asymmetry with a significance of 3.4sigma. The results are obtained from a data sample containing 386 x 10(6) BB pairs that were collected on the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.  相似文献   

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We present evidence for the flavor-changing neutral current decay B-->K*l+l- and a measurement of the branching fraction for the related process B-->K l+l-, where l+l- is either an epsilon+epsilon- or a mu+mu- pair. These decays are highly suppressed in the standard model, and they are sensitive to contributions from new particles in the intermediate state. The data sample comprises 123 x 10(6) Upsilon(4S)-->B(-)B decays collected with the BABAR detector at the SLAC PEP-II epsilon+epsilon- storage ring. Averaging over K(*) isospin and lepton flavor, we obtain the branching fractions B(B-->Kl+l-)=(0.65(+0.14)(-0.13)+/-0.04)x10(-6) and B(B-->K*l+l-)=(0.88(+0.33)(-0.29)+/-0.10)x10(-6), where the uncertainties are statistical and systematic, respectively. The significance of the B-->Kl+l- signal is over 8sigma, while for B-->K*l+l- it is 3.3sigma.  相似文献   

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We report on a mature experimental program to measure the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from unpolarized 1H, 2H and 4He targets. The focus is the measurement of the nucleon neutral weak form factors at intermediate four-momentum transfer (0.1 < Q 2 < 1) (GeV/c)2 which provide information about the impact of virtual strange quarks on the charge and current distributions inside nucleons. We report on recent technical progress in the design and scope of the experimental techniques. The physics implications of the published measurements are discussed and the current status and anticipated results from experiments under construction are summarized.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.15.Mm Neutral Currents - 14.20.Dh Protons and Neutrons  相似文献   

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