11 research outputs found
Key Distributions for Charmless Semileptonic B Decay
We present theoretical predictions for a few phenomenologically interesting
distributions in the semileptonic b->u decays which are affected by Fermi
motion. The perturbative effects are incorporated at the one-loop level and
appear to be very moderate. Our treatment of Fermi motion is based directly on
QCD, being encoded in the universal distribution function F(x). The decay
distributions in the charged lepton energy, invariant mass of hadrons, hadron
energy, and q^2 are given. We note that typically about 90% of all decay events
are expected to have M_X < M_D; this feature can be exploited in determination
of |V_ub|.Comment: 9 pages, 6 figures (incorporated in the LaTeX file); plain LaTe
Anathematizing the Guralnik and Manohar Inequality for \bar{\Lambda}
There is a recent claim by Guralnik and Manohar \cite{GM} to have established
a rigorous lower bound on , the asymptotic difference between the
mass of a heavy flavour {\em hadron} and that of the heavy flavour {\em quark}.
We point out the flaw in their reasoning and discuss the underlying physical
problem. An explicit counterexample to the GM bound is given; one can therefore
not count on a refined proof to re-establish this bound. *********** Uses LaTeX
No figures No macros file used.Comment: 7 pages Preprint UND-HEP-93-BIG07, CERN-TH.7091/9
Nonperturbative Corrections to Inclusive Beauty and Charm Decays: QCD versus Phenomenological Models
We present a selfconsistent method for treating nonperturbative effects in
inclusive nonleptonic and semileptonic decays of heavy flavour hadrons. These
effects give rise to powerlike corrections , with
denoting the heavy quark mass.The leading correction to the semileptonic
branching ratio occurs for n=2. It is expressed in terms of the
vector-pseudoscalar mass splitting: \delta BR\ind{sl}/BR\ind{sl} \simeq
BR\ind{nl}\, \cdot \,6\,(\,(M_V^2-M_P^2)/m_Q^2)\cdot (c_+^2 - c_-^2)/2N_c and
yields a {\it reduction} of BR\ind{sl}. This nonperturbative correction
contributes to the nonleptonic width with a sign opposite to that of the
perturbative terms that are non-leading in . In beauty decays the former
reduces the latter by 20 \% whereas in charm decays they more or less cancel.
This leads to a {\it reduction} of BR\ind{sl} by no more than 10 \% in beauty
decays and by a factor of roughly two in charm decays. We confront these
results with those obtained from phenomenological models of heavy flavour
decays and find that such models are unable to mimic these leading corrections
by a specific choice of quark masses or by invoking Fermi motion.Comment: 11 pages (2 figs are not included), Latex file, FERMILAB-PUB-92/158-T
UND-HEP-92-BIG04 TPI-MINN-92/30-
Are IR Renormalons a Good Probe for the Strong Interaction Domain?
We study the origin of non-analyticity in \alpha_s of a short-distance QCD
observable to demonstrate that the infrared renormalons, the same-sign
factorial growth of the perturbative expansion, is a universal phenomenon that
originates entirely from the small coupling domain. In particular, both the
position and the nature of the singularity of the Borel transform of the
perturbative series prove to be independent of whether the running coupling
\alpha(k^2) becomes singular at some finite scale ("Landau pole"), or stays
finite down to k^2=0. We argue that getting hold of the infrared renormalons
per se can help next to nothing in quantifying non-perturbative effects.Comment: 12 pages, one figure put separately as uuencoded PS file. LaTe
D^0 - D^0-bar Oscillations as a Probe of Quark-Hadron Duality
It is usually argued that the Standard Model predicts slow D^0-\bar D^0
oscillations with \Delta M_D, \Delta \Gamma_D < 10^{-3}*\Gamma_D$ and that New
Physics can reveal itself through \Delta M_D exceeding 10^{-3}*\Gamma_D. It is
believed that the bulk of the effect is due to long distance dynamics that
cannot be described at the quark level. We point out that in general the OPE
yields soft GIM suppression scaling only like (m_s/\mu_{hadr})^2 and even like
m_s/\mu_{hadr} rather than m_s^4/m_c^4 of the simple quark box diagram. Such
contributions can actually yield \Delta M_D, \Delta \Gamma_D \sim
O(10^{-3})*\Gamma_D without invoking additional long distance effects. They are
reasonably suppressed as long as the OPE and local duality are qualitatively
applicable in the 1/m_c expansion. We stress the importance of improving the
sensitivity on \Delta \Gamma_D as well as \Delta M_D in a dedicated fashion as
a laboratory for analyzing the onset of quark-hadron duality and comment on the
recent preliminary study on \Delta \Gamma_D by the FOCUS group.Comment: 15 pages, LaTeX. Revised: A reference and a few clarifications in the
text are added. A few inconsistencies in equations are eliminated. We found
the standard contribution to Delta M_D to differ from the expression usually
quoted in the literatur
How to Measure Kinetic Energy of the Heavy Quark Inside B Mesons?
We discuss how one can determine the average kinetic energy of the heavy
quark inside heavy mesons from differential distributions in decays. A new,
so-called third, sum rule for the transition is derived in the
small velocity (SV) limit. Using this sum rule and the existing data on the
momentum dependence in the transition (the slope of the
Isgur-Wise function) we obtain a new lower bound on the parameter proportional to the
average kinetic energy of quark inside meson. The existing data suggest
~GeV and (from the ``optical'' sum rule)
MeV, albeit with some numerical uncertainties.Comment: LaTex, 12 pages, no figures, Preprint TPI-MINN-94/25-T,
UMN-TH-1263-94, UND-HEP-94-BIG07, OUT-4102-5
On the Problem of Boosting Nonleptonic b Baryon Decays
The constituent picture of hadrons implies certain quantum mechanical
inequalities which must hold in the potential models. Basing on this
qualitative consideration I argue that it is not easy to increase significantly
the scale of the flavor-dependent 1/m_b^3 effects within the heavy quark
expansion preserving the conventional constituent picture of heavy flavor
hadrons. I briefly address the physical consequences one might expect if the
effects of weak scattering and interference are attempted to be pushed above
the 10% level within 1/m_b expansion not invoking qualitatively different
mechanisms including violations of duality.Comment: 8 pages, one figure. LaTeX. Revised: More general inequality is
stated which applies to in baryons as well. Explicit expression for the
hybrid renormalization used is quote
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
CP-violation in rare Bs0-meson decays
Translated from Russian; originally published in Pis'ma Zh. Ehksp. Teor. Fiz. v. 43(7) p. 317-318SIGLEAvailable from Deutsches Elektronen-Synchrotron (DESY), Hamburg (DE) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Structure of the Higgs sector and the vertex Z WH
Translated from Russian; originally published in: PISMA JETF, (1982) v. 35(3) p. 125-127.SIGLEDEGerman