381 research outputs found
On the branching ratio of the "second class" tau --> eta' pi nu_tau decay
We present an assessment of the standard model expectations for the branching
ratio of the isotopic spin and G-parity violating decay tau --> eta' pi nu_tau.
The estimate is based on a vector and scalar meson dominance parametrization of
the relevant form factors, that explicitly accounts for pi^0-eta-eta' mixing.
The numerical results obtained in this framework indicate a branching ratio one
order of magnitude (or more) below the current experimental limit, and suggest
the possibility of evidencing some novel interaction in high statistics studies
of this decay.Comment: 8 page
Positron Polarization at the International Linear Collider
We review some recent arguments supporting the upgrade of the International
Linear Collider by a polarized positron beam, in addition to the polarized
electron beam. The examples presented here mainly focus on the impact of
positron polarization on items relevant to new physics searches, such as the
identification of novel interactions in fermion-pair production and the
formulation of new CP-sensitive observables. In particular, in addition to the
benefits from positron and electron longitudinal polarizations, the advantages
in this field of having transverse polarization of both beams are emphasized.Comment: Invited talk at 2005 International Linear Collider Workshop, Stanford
Ca (LCWS05) 6 pages, LaTeX, 2 eps figure
Bhabha vs. Moller scattering as a contact-interaction analyzer at a polarized Linear Collider
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
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
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
Flavour symmetry breaking in quark vacuum condensates
Abstract We study SU(3) and SU(2) flavour symmetry violations in the vacuum from the viewpoint of nonperturbative quark mass generation and independently from charge symmetry-breaking considerations. The results for the ratios of quark condensates of different flavours are compatible with those of QCD sum rules. However, we find that very large SU(3) violating effects, suggested by some sum rule analyses, are barely accommodated in the present nonperturbative approach
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