116 research outputs found
Extracting |V_{ub}| from the Hadronic Mass Spectrum of Inclusive B decays
Following a strategy introduced earlier by the authors, we show that it is
possible to extract |V_{ub}| from the cut hadronic mass spectrum of B decays
without large systematic errors which usually arise from having to model the
Fermi motion of the heavy quark. We present a closed form expression for
|V_{ub}|/|V_{ts}| which is accurate up to corrections of order \alpha_s^2,
\alpha_s \rho, (\Lambda/m_b)^2/\rho, where \rho is the experimental cut
(s_c/m_b^2) on the hadronic mass used to veto charmed decays. Modulo duality
violation errors, which are intrinsic to all inclusive predictions, we estimate
the theoretical error in the extraction to be at the 5% level.Comment: 11 pages, 1 figur
Semileptonic Lambda_b decay to excited Lambda_c baryons at order Lambda_{QCD}/m_Q
Exclusive semileptonic Lambda_b decays to excited charmed Lambda_c baryons
are investigated at order Lambda_{QCD}/m_Q in the heavy quark effective theory.
The differential decay rates are analyzed for the J^\pi=1/2^- Lambda_c(2593)
and the J^\pi=3/2^- \Lambda_c(2625). They receive 1/m_{c,b} corrections at zero
recoil that are determined by mass splittings and the leading order Isgur-Wise
function. With some assumptions, we find that the branching fraction for
Lambda_b decays to these states is 2.5-3.3%. The decay rate to the helicity \pm
3/2 states, which vanishes for m_Q \to \infty, remains small at order
Lambda_{QCD}/m_Q since 1/m_c corrections do not contribute. Matrix elements of
weak currents between a Lambda_b and other excited Lambda_c states are analyzed
at zero-recoil to order Lambda_{QCD}/m_Q. Applications to baryonic heavy quark
sum-rules are explored.Comment: 27 pages, 1 fig., minor changes, version to appear in Phys.Rev.
Radiation reaction at 3.5 post-Newtonian order in effective field theory
We derive the radiation reaction forces on a compact binary inspiral through 3.5 order in the post-Newtonian expansion using the effective field theory approach. We utilize a recent formulation of Hamilton’s variational principle that rigorously extends the usual Lagrangian and Hamiltonian formalisms to dissipative systems, including the inspiral of a compact binary from the emission of gravitational waves. We find agreement with previous results, which thus provides a non-trivial confirmation of the extended variational principle. The results from this work nearly complete the equations of motion for the generic inspiral of a compact binary with spinning constituents through 3.5 post-Newtonian order, as derived entirely with effective field theory, with only the spin-orbit corrections to the potential at 3.5 post-Newtonian remaining
The color-singlet contribution to e^+ e^- ->J/psi + X at the endpoint
Recent observations of the J/psi spectrum produced in e^+e^- collisions at
the Upsilon(4S) resonance are in conflict with fixed-order calculations using
Non-Relativsitic QCD effective theory (NRQCD). One problem is an enhancement in
the cross section when the J/psi has maximal energy, due to large perturbative
corrections (Sudakov logarithms). In a recent paper, the Sudakov logarithms in
the color-octet contribution were summed by combining NRQCD with the
Soft-Collinear Effective Theory. However to be consistent, the color-singlet
contributions must also be summed in the endpoint region which was not done in
that paper. In this paper, we sum the leading and next-to-leading logarithms in
the color-singlet contribution to the J/psi production cross section. We find
that the color-singlet cross section is suppressed near endpoint compared to
the fixed order NRQCD prediction.Comment: 17 pages, 7 figure
Quark mass effects in the soft-collinear effective theory and B -> X_s + photon in the endpoint region
We consider the effects of a light quark mass in the soft-collinear effective
theory (SCET) and we apply them to B -> X_s gamma in the endpoint region. We
find that the reparameterization invariance can be extended by including the
collinear quark mass in the SCET Lagrangian. This symmetry constrains the
theory with the quark mass terms, and we present explicit results at one loop.
It also relates the Wilson coefficients of some mass operators to those of the
leading operators, which are useful in organizing the subleading effects due to
the quark mass in B -> X_s gamma. We present strange quark mass corrections to
B -> X_s gamma in the endpoint region as an application. The forward scattering
amplitude from the mass corrections is factorized, and it can be expressed as a
convolution of the m_s^2/p_X^2-suppressed jet function and the leading-order
shape function of the B meson. This contribution should be added to the
existing subleading contributions from the B meson shape functions to obtain
complete subleading corrections.Comment: 30 pages, 6 figures; some errors are corrected and numerical
estimates are adde
A Comment on the Extractions of V_{ub} from Radiative Decays
We present a model independent closed form expression for |V_{ub}|^2/|V_{tb}
V_{ts}^*|^2, which includes the resummation of large endpoint logarithms as
well as the interference effects from the operators and . We
demonstrate that the method to extract |V_{ub}| presented by the authors in
hep-ph/9909404, and modified in this letter to include interference effects, is
not just a refinement of the method introduced in hep-ph/9312311. We also
discuss the model dependence of the latter proposal. Furthermore, we show that
the resummation is not negligible and that the Landau pole does not introduce
any significant uncertainties.Comment: 10 pages, 3 figures; one figure added, one reference added, expanded
discussion
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