326 research outputs found

    Bhabha vs. Moller scattering as a contact-interaction analyzer at a polarized Linear Collider

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    We discuss electron-electron contact-interaction searches in the Bhabha and Moller processes at planned Linear Colliders run in the electron-positron and electron-electron modes, with longitudinally polarized beams. Our analysis is based on the measurement, for the two processes, of polarized differential cross sections that allow to disentangle the different, independent, four-fermion couplings. We evaluate by a model-independent analysis the sensitivities to the contact coupling constants, emphasizing the role of the available beam polarization and the complementarity of the two processes in giving the best limits. We also make a comparison with the potential of e+eμ+μe^+e^-\to\mu^+\mu^- at the same energy and beams polarization.Comment: 18 latex pages, 15 eps figs., some misprints corrected and added ref

    On meson dominance in the `second class' tau \to eta pi nu_tau decay

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    Motivated by recent estimates of the isospin-violating process tau \to eta pi nu_tau, mostly relying on the rho and a_0 dominance of the relevant form factors near threshold, we present an assessment for the branching ratio that accounts for additional, potential, effects from the lowest radial excitations rho(1450) and a_0(1450), respectively, also lying in the decay phase space.Comment: 8 page

    Semileptonic charm meson decays and the matrix elements |Vcs| and |Vcd|

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    Abstract Using QCD sum rules for a two-point function involving charmed vector currents we determine the Dl3 form factor: ƒ + (0)=0.75±0.05 . This result, combined with the Dl3 decay widths, leads to a prediction for the quark mixing matrix elements |Vcs| and |Vcd|. We find: |Vcs|=0.96±0.12 and Γ( D →πl ν l )=(0.76±0.24)×10 11 [ |V cd | (0.21±0.03) ] 2 s −1 . Our estimate is reliable to the extent that employing the same technique for Kl3 decay we obtain: ƒ + (0)| Kl3 =0.96+-0.13