448 research outputs found
Extracting short distance information from b-->s[script-l]+[script-l]- effectively
We point out that in inclusive B-->Xs[script-l]+[script-l]- decay an angular decomposition provides a third (q2 dependent) observable sensitive to a different combination of Wilson coefficients than the rate and the forward-backward asymmetry. Since a precise measurement of q2 dependence requires large data sets, it is important to consider the data integrated over regions of q2. We develop a strategy to extract all measurable Wilson coefficients in B-->Xs[script-l]+[script-l]- from a few simple integrated rates in the low q2 region. A similar decomposition in B-->K*[script-l]+[script-l]-, together with the B-->K*gamma rate, also provides a determination of the Wilson coefficients, without reliance on form factor models and without having to measure the zero of the forward-backward asymmetry
Universality and m_X cut effects in B -> Xs l+ l-
The most precise comparison between theory and experiment for the B -> Xs l+
l- rate is in the low q^2 region, but the hadronic uncertainties associated
with an experimentally required cut on m_X potentially spoil the search for new
physics in these decays. We show that a 10-30% reduction of d\Gamma(B -> Xs l+
l-) / dq^2 due to the m_X cut can be accurately computed using the B -> X_s
gamma shape function. The effect is universal for all short distance
contributions in the limit m_X^2 << m_B^2, and this universality is spoiled
neither by realistic values of the m_X cut nor by alpha_s corrections. Both the
differential decay rate and forward-backward asymmetry with an m_X cut are
computed.Comment: 5 pages, journal versio
Constraining CP violation in neutral meson mixing with theory input
There has been a lot of recent interest in the experimental hints of CP
violation in B_{d,s}^0 mixing, which would be a clear signal of beyond the
standard model physics (with higher significance). We derive a new relation for
the mixing parameters, which allows clearer interpretation of the data in
models in which new physics enters in M_12 and/or \Gamma_12. Our results imply
that the central value of the D\O\ measurement of the semileptonic CP asymmetry
in B_{d,s}^0 decay is not only in conflict with the standard model, but in a
stronger tension with data on \Delta\Gamma_s than previously appreciated. This
result can be used to improve the constraint on \Delta\Gamma or A_SL, whichever
is less precisely measured.Comment: 5 pages, 2 figures, informed of prior derivation of eq. (21), title
modifie
B -> K^* gamma from D -> K^* l nu
The B -> K^* gamma branching fraction is predicted using heavy quark spin
symmetry at large recoil to relate the tensor and (axial-)vector form factors,
using heavy quark flavor symmetry to relate the B decay form factors to the
measured D -> K^* l nu form form factors, and extrapolating the semileptonic B
decay form factors to large recoil assuming nearest pole dominance. This
prediction agrees with data surprisingly well, and we comment on its
implications for the extraction of |Vub| from B -> rho l nu.Comment: 10 page
Corrections of Order to Inclusive Rare B Decays
We calculate nonperturbative corrections to
the dilepton invariant mass spectrum and the forward-backward charge asymmetry
in decay using a heavy quark expansion approach. The method
has recently been used to estimate long-distance effects in .
We generalize this analysis to the case of nonvanishing photon invariant mass,
, relevant for the rare decay mode . In the
phenomenologically interesting region away from the resonances,
the heavy quark expansion approach should provide a reasonable description of
possible nonperturbative corrections. In particular this picture is preferable
to the model-dependent approach relying on the tails of Breit-Wigner
resonances, which has been employed so far in the literature to account for
these effects. We find that the corrections
to the dilepton invariant mass spectrum and to the forward-backward asymmetry
in amount to several percent at most for and
. The correction to the
decay rate is also computed and found to be +3%, which agrees
in magnitude with previous calculations. Finally, we comment on long-distance
effects in , which in this case are extremely suppressed
due to the absence of virtual photon contributions.Comment: Latex, 15 pages, 3 figures (included
On The Expected Photon Spectrum in B -> X_s + gamma and Its Uses
Measuring the photon energy spectrum in radiative B decays provides essential
help for gaining theoretical control over semileptonic B transitions. The
hadronic recoil mass distribution in B -> X_u \ell\nu promises the best
environment for determining |V_ub|. The theoretical uncertainties are largest
in the domain of low values of the lepton pair mass q^2. Universality relations
allow to describe this domain reliably in terms of the photon spectrum in B ->
X_s + \gamma. A method is proposed to incorporate 1/m_b corrections into this
relation. The low-E_\gamma tail in radiative decays is important in the context
of extracting |V_ub|. We argue that CLEO's recent fit to the spectrum
underestimates the fraction of the photon spectrum below 2 GeV. Potentially
significant uncertainties enter in the theoretical evaluation of the integrated
end-point lepton spectrum or the B -> X_u \ell\nu width with a too high value
of the lower cut on q^2 in alternative approaches to |V_ub|.Comment: 24 pages, 6 figures, LaTeX. Revised: Complete version. Numerical
predictions are improved and the estimate for the decay fraction revised. The
theoretical expectations for the decay fraction and the spectrum itself are
given on the plot
Lessons from CLEO and FOCUS Measurements of D0-anti-D0 Mixing Parameters
If the true values of the D0-anti-D0 mixing parameters lie within the one
sigma ranges of recent measurements, then there is strong evidence for a large
width difference, y > 0.01, and large SU(3) breaking effects in strong phases,
\delta > pi/4. These constraints are model independent, and would become
stronger if M_{12}/Gamma_{12} << 1 in the D0-anti-D0 system. The interesting
fact that the FOCUS result cannot be explained by a large mass difference is
not trivial and depends on the small D0-anti-D0 production asymmetry in FOCUS
and the bounds on CP violating effects from CLEO. The large value of \delta
might help explain why y ~ sin^2(theta_c).Comment: 15 pages, harvma
Right-Handed New Physics Remains Strangely Beautiful
Current data on CP violation in B_d -> eta' K_S and B_d -> phi K_S, taken
literally, suggest new physics contributions in b -> s transitions. Despite a
claim to the contrary, we point out that right-handed operators with a single
weak phase can account for both deviations thanks to the two-fold ambiguity in
the extraction of the weak phase from the corresponding CP-asymmetry. This
observation is welcome since large mixing in the right-handed sector is favored
by many GUT models and frameworks which address the flavor puzzle. There are
also interesting correlations with the B_s system which provide a way to test
this scenario in the near future.Comment: 7 pages, 9 figures; published version: added 1 reference and 1
clarificatio
Relativistic quantum theories and neutrino oscillations
Neutrino oscillations are examined under the broad requirements of
Poincar\'e-invariant scattering theory in an S-matrix formulation.
This approach can be consistently applied to theories with either field or
particle degrees of freedom. The goal of this paper is to use this general
framework to identify all of the unique physical properties of this problem
that lead to a simple oscillation formula. We discuss what is in principle
observable, and how many factors that are important in principle end up being
negligible in practice.Comment: 21 pages, no figure
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