67 research outputs found
Phenomenology of V_ub from Ratios of Inclusive B Decay Rates
We explore the theoretical feasibility of extracting V_ub from two ratios
built from B meson inclusive partial decays,
R_1 = Gamma(b-> u cbar s)/3Gamma(b -> c l nu), and
R_2 = [Gamma(b -> c X) - Gamma(b -> cbar X)]/Gamma(b -> c ubar d).
We discuss contributions to these quantities from perturbative and
nonperturbative physics, and show that they can be computed with overall
uncertainties at the level of 10%.Comment: 19 pages, 8 embedded EPS figures, uses REVTe
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
Experimental Tests of Factorization in Charmless Non-Leptonic Two-Body B Decays
Using a theoretical framework based on the next-to-leading order QCD-improved
effective Hamiltonian and a factorization Ansatz for the hadronic matrix
elements of the four-quark operators, we reassess branching fractions in
two-body non-leptonic decays , involving the lowest lying
light pseudoscalar and vector mesons in the standard model. Using
the sensitivity of the decay rates on the effective number of colors, , as
a criterion of theoretical predictivity, we classify all the current-current
(tree) and penguin transitions in five different classes. The recently measured
charmless two-body decays and charge conjugates) are
dominated by the -stable QCD penguins (class-IV transitions) and their
estimates are consistent with data. The measured charmless and transition ,
on the other hand, belong to the penguin (class-V) and tree (class-III)
transitions. The class-V penguin transitions are in general more difficult to
predict. We propose a number of tests of the factorization framework in terms
of the ratios of branching ratios for some selected decays
involving light hadrons and , which depend only moderately on the
form factors. We also propose a set of measurements to determine the effective
coefficients of the current-current and QCD penguin operators. The potential
impact of decays on the CKM phenomenology is emphasized by
analyzing a number of decay rates in the factorization framework.Comment: 64 pages (LaTex) including 13 figures, requires epsfig.sty; submitted
to Phys. Rev.
Rare Charm Decays in the Standard Model and Beyond
We perform a comprehensive study of a number of rare charm decays,
incorporating the first evaluation of the QCD corrections to the short distance
contributions, as well as examining the long range effects. For processes
mediated by the transitions, we show that sensitivity to
short distance physics exists in kinematic regions away from the vector meson
resonances that dominate the total rate. In particular, we find that
and are sensitive to non-universal
soft-breaking effects in the Minimal Supersymmetric Standard Model with
R-parity conservation. We separately study the sensitivity of these modes to
R-parity violating effects and derive new bounds on R-parity violating
couplings. We also obtain predictions for these decays within extensions of the
Standard Model, including extensions of the Higgs, gauge and fermion sectors,
as well as models of dynamical electroweak symmetry breaking.Comment: 45 pages, typos fixed, discussions adde
Semileptonic Meson Decays in the Quark Model: An Update
We present the predictions of ISGW2, an update of the ISGW quark model for
semileptonic meson decays. The updated model incorporates a number of features
which should make it more reliable, including the constraints imposed by Heavy
Quark Symmetry, hyperfine distortions of wavefunctions, and form factors with
more realistic high recoil behaviors.Comment: All text and tables contained in the ".latex" file and all figures
(14) contained in the ".uu" file
Zinc Single Crystal Deformation Experiments using a "6 Degrees of Freedom" Apparatus
A new experimental technique to study crystallographic slip system activity in metallic single crystals deformed under a condition of uniaxial stress is applied to study the behavior of Zn single crystals. The experimental apparatus allows essentially unconstrained shape change of inherently anisotropic materials under a condition of uniaxial stress by allowing 3 translational and 3 rotational degrees of freedom during compression; hence we have named the experiment 6 degrees of freedom (6DOF). The experiments also utilize a 3-D digital image correlation system to measure full-field displacement fields, which are used to calculate strain and make direct observations of slip system activity. We show that the experimental results associated with a pristine zinc single crystal are precisely consistent with the theoretical predicted shape change (sample distortion) assuming that the most favored slip system on the basal plane is the only one that is active. Another experiment was performed on a processed and annealed Zn single crystal to investigate slip that is inconsistent with the critical resolved shear stress (CRSS) theory. These experiments on zinc illustrate the ability of the 6DOF experiment, together with image correlation (IC) data, to measure slip system activity with a high degree of fidelity
Coherent π0 photoproduction on the deuteron up to 4 GeV
The differential cross section for 2H(γ,d)π0 has been measured at deuteron center-of-mass angles of 90° and 136°. This work reports the first data for this reaction above a photon energy of 1 GeV, and permits a test of the apparent constituent counting rule and reduced nuclear amplitude behavior as observed in elastic ed scattering. Measurements were performed up to a photon energy of 4.0 GeV, and are in good agreement with previous lower energy measurements. Overall, the data are inconsistent with both constituent-counting rule and reduced nuclear amplitude predictions
Perspectives in Global Helioseismology, and the Road Ahead
We review the impact of global helioseismology on key questions concerning
the internal structure and dynamics of the Sun, and consider the exciting
challenges the field faces as it enters a fourth decade of science
exploitation. We do so with an eye on the past, looking at the perspectives
global helioseismology offered in its earlier phases, in particular the
mid-to-late 1970s and the 1980s. We look at how modern, higher-quality, longer
datasets coupled with new developments in analysis, have altered, refined, and
changed some of those perspectives, and opened others that were not previously
available for study. We finish by discussing outstanding challenges and
questions for the field.Comment: Invited review; to appear in Solar Physics (24 pages, 6 figures
- …