21,537 research outputs found
Determining weak phases from B->J/Psi P decays
The decay B -> J/Psi K_S remains the most important source of information for
the B_d mixing phase, determined by the CKM angle beta in the standard model.
When aiming at a precision appropriate for present and coming high luminosity
colliders, the corresponding hadronic matrix elements are a major obstacle, as
their precise calculation is still not feasible with existing methods. Flavour
symmetries offer a possibility to extract them from data, however again with
limited precision. In this article, we propose a framework to take subleading
contributions in B_{u,d,s} -> J/Psi P decays into account, P=(pi,K,(eta_8)),
using an SU(3) analysis, together with the leading corrections to the symmetry
limit. This allows for a model-independent extraction of the B_d mixing phase
adequate for coming high precision data, and additionally yields information on
possible New Physics contributions in these modes. We find the penguin-induced
correction to be small, |Delta S|<~0.01, a limit which can be improved with
coming data on CP asymmetries and branching ratios. Finally, the sensitivity on
the CKM angle gamma from these modes is critically examined, yielding a less
optimistic picture than previously envisaged.Comment: 15+6 pages, 6 figures. Minor changes to v1, conclusions unchanged.
Version accepted for publication in PR
Branching ratio measurements and isospin violation in B-meson decays
The approximate symmetry of the strong interactions under isospin
transformations is among the most precise tools available to control hadronic
matrix elements. It is crucial in extracting fundamental parameters, but also
provides avenues for the search of phenomena beyond the Standard Model. The
precision of the resulting predictions requires special care when determining
the quantities they are to be tested with. Specifically, in the extraction of
branching ratios often isospin symmetry is assumed at one point or another
implicitly, implying a significant bias for precision analyses. We extract a
bias-free value for the production asymmetry between charged and neutral
meson pairs at factories and discuss its consequences for the determination
of branching fractions generally, and isospin-violating observables like the
rate asymmetries in B -> J/psi K or B -> K* gamma decays specifically.Comment: 5 pages. v2: proposal for new measurement of production fractions
added, accepted for publication in PL
A robust limit for the electric dipole moment of the electron
Electric dipole moments constitute a competitive method to search for new
physics, being particularly sensitive to new CP-violating phases. Given the
experimental and theoretical progress in this field and more generally in
particle physics, the necessity for more reliable bounds than the ones usually
employed emerges. We therefore propose an improved extraction of the electric
dipole moment of the electron and the relevant coefficient of the
electron-nucleon coupling, taking into account theoretical uncertainties and
possible cancellations, to be used in model-dependent analyses. Specifically,
we obtain at 95% C.L. |d_e|<=0.14 10^{-26}e cm with present data, which is very
similar to the bound typically quoted from the YbF molecule, but obtained in a
more conservative manner. We examine furthermore in detail the prospects for
improvements and derive upper limits for the dipole moments of several
paramagnetic systems presently under investigation, i.e. Cesium, Rubidium and
Francium.Comment: 8 pages, 2 tables, 4 figures. v2: Extended discussion of the EDM of
Tl, corrected value for the nuclear magnetic moment of Hg (implying small
shifts in the obtained numerical values) and further minor change
Bounds on new physics from electric dipole moments
Electric dipole moments are extremely sensitive probes for additional sources
of CP violation in new physics models. The multi-scale problem of relating the
high-precision measurements with neutrons, atoms and molecules to fundamental
parameters can be approached model-independently to a large extent; however,
care must be taken to include the uncertainties from especially nuclear and QCD
calculations properly. The resulting bounds on fundamental parameters are
illustrated in the context of Two-Higgs-Doublet models.Comment: 9 pages, 1 figure. Prepared for the proceedings of "Flavor Physics &
CP Violation 2015", Nagoya, Japan. arXiv admin note: text overlap with
arXiv:1405.638
Electric Dipole Moments in Two-Higgs-Doublet Models
Electric dipole moments are extremely sensitive probes for additional sources
of CP violation in new physics models. Specifically, they have been argued in
the past to exclude new CP-violating phases in two-Higgs-doublet models. Since
recently models including such phases have been discussed widely, we revisit
the available constraints in the presence of mechanisms which are typically
invoked to evade flavour-changing neutral currents. To that aim, we start by
assessing the necessary calculations on the hadronic, nuclear and
atomic/molecular level, deriving expressions with conservative error estimates.
Their phenomenological analysis in the context of two-Higgs-doublet models
yields strong constraints, in some cases weakened by a cancellation mechanism
among contributions from neutral scalars. While the corresponding parameter
combinations do not yet have to be unnaturally small, the constraints are
likely to preclude large effects in other CP-violating observables.
Nevertheless, the generically expected contributions to electric dipole moments
in this class of models lie within the projected sensitivity of the
next-generation experiments.Comment: 23+8 pages, 6 figures. v2: added new global analysis of the electron
EDM, including the recent ThO result, and additional references. Version
accepted for publication in JHE
- …