43 research outputs found
Measuring of in the forthcoming decade
I first introduce the importance of measuring V_ub precisely. Then, from a
theoretician's point of view, I review (a) past history, (b) present trials,
and (c) possible future alternatives on measuring |V_ub| and/or |V_ub/V_cb|. As
of my main topic, I introduce a model-independent method, which predicts
\Gamma(B -> X_u l \nu) / \Gamma(B -> X_c l \nu) \equiv (\gamma_u / \gamma_c)
\times | V_{ub} / V_{cb}|^2 \simeq (1.83 \pm 0.28) \times |V_ub / V_cb|^2 and
|V_ub/V_cb| \equiv (\gamma_c / \gamma_u)^{1/2} \times [{\cal{B}}(B -> X_u l
\nu)/{\cal{B}}(B -> X_c l \nu)]^{1/2} \simeq (0.74 \pm 0.06) \times
[{\cal{B}}(B -> X_u l \nu)/ {\cal{B}}(B -> X_c l \nu)]^{1/2}, based on the
heavy quark effective theory. I also explore the possible experimental options
to separate B -> X_u l \nu from the dominant B -> X_c l \nu: the measurement of
inclusive hadronic invariant mass distributions, and the `D - \pi' (and `K -
\pi') separation conditions. I also clarify the relevant experimental
backgrounds.Comment: 9 pages(LaTeX), 1 Postscript figur
Exclusive semileptonic rare decays K,K^*) \ell^+ \ell^- in supersymmetric theories
The invariant mass spectrum, forward-backward asymmetry, and lepton
polarizations of the exclusive processes are analyzed under supersymmetric context. Special attention is paid to
the effects of neutral Higgs bosons (NHBs). Our analysis shows that the
branching ratio of the process \bkm can be quite largely modified by the
effects of neutral Higgs bosons and the forward-backward asymmetry would not
vanish. For the process \bksm, the lepton transverse polarization is quite
sensitive to the effects of NHBs, while the invariant mass spectrum,
forward-backward asymmetry, and lepton longitudinal polarization are not. For
both \bkt and \bkst, the effects of NHBs are quite significant. The partial
decay widths of these processes are also analyzed, and our analysis manifest
that even taking into account the theoretical uncertainties in calculating weak
form factors, the effects of NHBs could make SUSY shown up.Comment: Several references are added, typo are correcte
Charm multiplicity and the branching ratios of inclusive charmless b quark decays in the general two-Higgs-doublet models
In the framework of general two-Higgs-doublet models, we calculate the
branching ratios of various inclusive charmless b decays by using the low
energy effective Hamiltonian including next-to-leading order QCD corrections,
and examine the current status and the new physics effects on the determination
of the charm multiplicity and semileptonic branching ratio .
Within the considered parameter space, the enhancement to the ratio due to the charged-Higgs penguins can be as large as a factor of 8 (3) in
the model III (II), while the ratio can be increased from
the standard model prediction of 2.49% to 4.91% (2.99%) in the model III (II).
Consequently, the value of and can be decreased simultaneously
in the model III. The central value of will be lowered slightly by
about 0.003, but the ratio can be reduced significantly from the
theoretical prediction of in the SM to , for GeV, respectively. We find that
the predicted and the measured now agree within roughly one
standard deviation after taking into account the effects of gluonic charged
Higgs penguins in the model III with a relatively light charged Higgs boson.Comment: 25 pages, Latex file, axodraw.sty, 6 figures. Final version to be
published in Phys.Rev.
Weak Phase from
We re-examine the time-dependent rates of \bs(t) \to K^+ K^- and \obs(t)
\to K^+ K^-, including a lifetime difference between neutral \bs mass
eigenstates. The two rates, normalized by the rate of \bs \to \ko \ok, are
used to obtain ambiguity-free information on a strong phase and on the weak
phase . We discuss the sensitivity of extracting to the
measured quantities, and find that an error of in is
possible for a sample of several thousand \bs(t) \to K^+ K^- decays. This
study is complementary to a recent similar analysis of the U-spin related
decays \bo(t) \to \pi^+\pi^- and \ob(t) \to \pi^+\pi^-.Comment: 12 pages, LaTeX, 3 figures, revised version submitted to Phys. Rev.
A Phenomenological Analysis of Heavy Hadron Lifetimes
A phenomenological analysis of lifetimes of bottom and charmed hadrons within
the framework of the heavy quark expansion is performed. The baryon matrix
element is evaluated using the bag model and the nonrelativistic quark model.
We find that bottom-baryon lifetimes follow the pattern
.
However, neither the lifetime ratio nor the
absolute decay rates of the baryon and mesons can be explained.
One way of solving both difficulties is to allow the presence of linear
corrections by scaling the inclusive nonleptonic width with the fifth power of
the hadron mass rather than the heavy quark mass . The hierarchy
of bottom baryon lifetimes is dramatically modified to
: The
longest-lived among bottom baryons in the OPE prescription now
becomes shortest-lived. The replacement of by in nonleptonic
widths is natural and justified in the PQCD-based factorization approach
formulated in terms of hadron-level kinematics. For inclusive charmed baryon
decays, we argue that since the heavy quark expansion does not converge, local
duality cannot be tested in this case. We show that while the ansatz of
substituting the heavy quark mass by the hadron mass provides a much better
description of the charmed-baryon lifetime {\it ratios}, it appears unnatural
and unpredictive for describing the {\it absolute} inclusive decay rates of
charmed baryons, contrary to the bottom case.Comment: 35 pages, to appear in Phys. Rev. The CDF result on the lifetime
ratio of Lambda_b and B_d is discusse
The lifetime of B_c-meson and some relevant problems
The lifetime of the B_c-meson is estimated with consistent considerations on
all of the heavy mesons () and the double
heavy meson B_c. In the estimate, the framework, where the non-spectator
effects for nonleptonic decays are taken into account properly, is adopted, and
the parameters needed to be fixed are treated carefully and determined by
fitting the available data. The bound-state effects in it are also considered.
We find that in decays of the meson B_c, the QCD correction terms of the
penguin diagrams and the main component terms c_1O_1, c_2O_2 of the effective
interaction Lagrangian have direct interference that causes an enhancement
about 3 ~ 4% in the total width of the B_c meson.Comment: 27 pages, 0 figur
Calculation of two-loop virtual corrections to b --> s l+ l- in the standard model
We present in detail the calculation of the virtual O(alpha_s) corrections to
the inclusive semi-leptonic rare decay b --> s l+ l-. We also include those
O(alpha_s) bremsstrahlung contributions which cancel the infrared and mass
singularities showing up in the virtual corrections. In order to avoid large
resonant contributions, we restrict the invariant mass squared s of the lepton
pair to the range 0.05 < s/mb^2 < 0.25. The analytic results are represented as
expansions in the small parameters s/mb^2, z = mc^2/mb^2 and s/(4 mc^2). The
new contributions drastically reduce the renormalization scale dependence of
the decay spectrum. For the corresponding branching ratio (restricted to the
above s-range) the renormalization scale uncertainty gets reduced from +/-13%
to +/-6.5%.Comment: 41 pages including 9 postscript figures; in version 2 some typos and
inconsistent notation correcte
Average Kinetic Energy of Heavy Quark and Virial Theorem
We derive the virial theorem of the relativistic two-body system for the
study of the B-meson physics. It is also shown that the solution of the
variational equation always satisfies the virial theorem. From the virial
theorem we also obtained GeV, which is consistent with the result of the QCD sum rule
calculations of Ball Comment: 13 pages. A lot of parts of the manuscript have been revised. To
appear in Physics Letters
Determination of HQET parameter \lambda_1 from Inclusive Semileptonic B Meson Decay Spectrum
We estimate the heavy quark effective theory parameter \lambda_1 from
inclusive semileptonic B-meson decay spectrum. By using recent CLEO double
lepton tagging data of B -> X e nu, which shows the lepton momentum as low as
0.6 GeV, we extracted \lambda_1 \sim -0.58 GeV^2. We also derived \bar\Lambda
\sim 0.46 GeV and |V_{cb}| = 0.041 \pm 0.002.Comment: 13 pages, 3 figures, LaTeX. Typos are corrected, and added one
commen