4,762 research outputs found
Higher-order estimates of the chromomagnetic moment of a heavy quark
The leading beta_0^(n-1) alpha_s^n terms in the Wilson coefficient and
anomalous dimension of the chromomagnetic operator in the heavy-quark effective
Lagrangian are summed to all orders of perturbation theory. The perturbation
series for the anomalous dimension is well behaved, while that for the Wilson
coefficient exhibits a divergent behaviour already in low orders, caused by a
nearby infrared renormalon singularity. The resulting ambiguity is commensurate
with terms of order 1/m^2 in the effective Lagrangian, whose corresponding
ultraviolet renormalons are identified. An excellent approximation for the
scheme-invariant Wilson coefficient at next-to-next-to-leading order in
renormalization-group improved perturbation theory is obtained.Comment: 16 pages, 3 figures embedde
Simply Modeling Meson HQET
A simple relativistic model of heavy-quark-light-quark mesons is proposed. In
an expansion in inverse powers of the heavy quark mass we find that all zeroth
and first order heavy quark symmetry relations are satisfied. The main results
are: - the difference between the meson mass and the heavy quark mass plays a
significant role even at zeroth order; - the slope of the Isgur-Wise function
at the zero recoil point is typically less than ; - the first order
correction to the pseudoscalar decay constant is large and negative; - the four
universal functions describing the first order corrections to the semileptonic
decay form factors are small; - these latter corrections are quite insensitive
to the choice of model parameters, and in particular to the effects of
hyperfine mass splitting.Comment: 17 pages, LaTeX, 3 LaTeX figures in separate file, UTPT-92-16. This
is the version published long ago but not previously archive
Phenomenology of B -> pi pi, pi K Decays at O(alpha^2 beta_0) in QCD Factorization
We study O(alpha^2 beta_0) perturbative corrections to matrix elements
entering two-body exclusive decays of the form B -> pi pi, pi K in the QCD
factorization formalism, including chirally enhanced power corrections, and
discuss the effect of these corrections on direct CP asymmetries, which receive
their first contribution at O(alpha). We find that the O(alpha^2 beta_0)
corrections are often as large as the O(alpha) corrections. We find large
uncertainties due to renormalization scale dependence as well as poor knowledge
of the non-perturbative parameters. We assess the effect of the perturbative
corrections on the direct CP violation parameters of B -> pi^+ pi^-.Comment: 27 pages, 5 figures. Updated input parameters and added citations;
expanded discussio
Exploring CP Violation through B Decays
The B-meson system provides many strategies to perform stringent tests of the
Standard-Model description of CP violation. In this brief review, we discuss
implications of the currently available B-factory data on the angles alpha,
beta and gamma of the unitarity triangle, emphasize the importance of Bs
studies at hadronic B experiments, and discuss new, theoretically clean
strategies to determine gamma.Comment: 22 pages, 4 figures, invited brief review for Modern Physics Letters
Hadronic Spectral Moments in Semileptonic B Decays With a Lepton Energy Cut
We compute the first two moments of the final hadronic invariant mass in
inclusive semileptonic B decay, in the presence of a cut on the charged lepton
energy. These moments may be measured directly by experiments at the
Upsilon(4S) using the neutrino reconstruction technique, which requires such a
cut. Measurement of these moments will place constraints on the nonperturbative
parameters \bar\Lambda and \lambda_1, which are relevant for extracting the
quark masses m_b and m_c, as well as the CKM angle V_cb. We include terms of
order \alpha_s^2\beta_0 and 1/m_b^3 in the operator product expansion, and use
the latter to estimate the theoretical uncertainty in the extraction of
\bar\Lambda and \lambda_1.Comment: 13 pages, 5 figures, REVTe
Long-range two-body final-state interactions and direct CP asymmetry in {B}^{+}\to{\pi}^{+} {K}^{0} decay
We present a calculation of the direct CP asymmetry, , for the
process including the effects of long-range inelastic
final-state interactions (FSI). We admit three channels in our calculation:
, and . The strong
scattering is described in terms of Pomeron and Regge exchanges. We find that
the direct CP asymmetry is enhanced by a factor of as a result of FSI,
but remains well short of the claims of (10 - 20)% in recent literature. A
critical assessment of papers claiming large CP asymmetries is also presented.Comment: 21 pages, latex, no figures. Added the charge-exchange channel
{B}^{+}\to {\pi}^{0} {K}^{+}. Expanded the discussion section. To be
published in Phys. Rev.
A Consistent Calculation of Heavy Meson Decay Constants and Transition Wave Functions in the Complete HQEFT
Within the complete heavy quark effective field theory (HQEFT), the QCD sum
rule approach is used to evaluate the decay constants including 1/m_Q
corrections and the Isgur-Wise function and other additional important wave
functions concerned at 1/m_Q for the heavy-light mesons. The 1/m_Q corrections
to the scaling law f_M \sim F/\sqrt{m_M} are found to be small in HQEFT, which
demonstrates again the validity of 1/m_Q expansion in HQEFT. It is also shown
that the residual momentum v.k of heavy quark within hadrons does be around the
binding energy \bar{\Lambda} of the heavy hadrons. The calculations presented
in this paper provide a consistent check on the HQEFT and shows that the HQEFT
is more reliable than the usual HQET for describing a slightly off-mass shell
heavy quark within hadron as the usual HQET seems to lead to the breakdown of
1/m_Q expansion in evaluating the meson decay constants. It is emphasized that
the introduction of the `dressed heavy quark' mass is useful for the
heavy-light mesons (Qq) with m_Q >> \bar{\Lambda} >> m_q, while for heavy-heavy
bound states (\psi_1\psi_2) with masses m_1, m_2 >> \bar{\Lambda}, like
bottom-charm hadrons or similarly for muonium in QED, one needs to treat both
particles as heavy effective particles via 1/m_1 and 1/m_2 expansions and
redefine the effective bound states and modified `dressed heavy quark' masses
within the HQEFT.Comment: 20 pages, revtex, 22 figures, axodraw.sty, two irrelevant figures are
moved awa
A priori mixing of mesons and the |Delta I|=1/2 rule in K\to\pi\pi
We consider the hypothesis of a priori mixings in the mass eigenstates of
mesons to obtain the |Delta I|=1/2 rule in K\to\pi\pi. The Hamiltonian
responsible for the transition is the strong interacting one. The experimental
data are described using the isospin symmetry relations between the strong
coupling constants
Large electroweak penguin contribution in B -> K pi and pi pi decay modes
We discuss about a possibility of large electroweak penguin contribution in B
-> K pi and pi pi from recent experimental data. The experimental data may be
suggesting that there are some discrepancies between the data and theoretical
estimation in the branching ratios of them. In B -> K pi decays, to explain it,
a large electroweak penguin contribution and large strong phase differences
seem to be needed. The contributions should appear also in B -> pi pi. We show,
as an example, a solution to solve the discrepancies in both B -> K pi and B ->
pi pi. However the magnitude of the parameters and the strong phase estimated
from experimental data are quite large compared with the theoretical
estimations. It may be suggesting some new physics effects are including in
these processes. We will have to discuss about the dependence of the new
physics. To explain both modes at once, we may need large electroweak penguin
contribution with new weak phases and some SU(3) breaking effects by new
physics in both QCD and electroweak penguin type processes.Comment: 23 pages, 9 figure
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