2,409 research outputs found
The photon polarization in radiative decays, phenomenologically
We work out the phenomenology of untagged time-dependent analysis with
radiative -decays into CP eigenstates, which allows to probe the photon
polarization by means of the charm mesons' finite width difference. We show
that or decays, which are
SM-dominated, or SM-like, respectively, together with U-spin allow to obtain
chirality-predictions for radiative decay amplitudes. The order of magnitude of
wrong-chirality contributions in the SM can be cross-checked with an up-down
asymmetry in . We explore the
sensitivity to new physics in dipole couplings in the
decays . We point out the possibility to test the SM
with decays.Comment: 15 pages plus references and appendices, 7 figure
Null tests from angular distributions in , decays on and off peak
We systematically analyze the full angular distribution in decays, where , . We identify several null tests
of the standard model (SM). Notably, the angular coefficients ,
driven by the leptons' axial-vector coupling , vanish by
means of a superior GIM-cancellation and are protected by parity invariance
below the weak scale. CP-odd observables related to the angular coefficients
allow to measure CP-asymmetries without -tagging. The
corresponding observables constitute null tests of the SM. Lepton
universality in transitions can be tested by
comparing to decays. Data
for and on muon modes are available from LHCb
and on electron modes from BESIII. Corresponding ratios of dimuon to dielectron
branching fractions are at least about an order of magnitude away from probing
the SM. In the future electron and muon measurements should be made available
for the same cuts as corresponding ratios provide null tests of
--universality. We work out beyond-SM signals model-independently and
in SM extensions with leptoquarks.Comment: 18 pages plus references and appendix, 7 figure
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