149 research outputs found
Interference Between Cabibbo Allowed and Doubly Forbidden Transitions in D\ra K_{S,L} + \pi 's Decays
Both Cabibbo allowed and doubly forbidden transitions contribute coherently
to decays. This leads to several intriguing and
even quantitatively significant consequences, among them: (i) A difference
between and and between and of roughly 10\% ; similarly , and more generally . (ii) A
change in the relative phase between the isospin 3/2 and 1/2 amplitudes as
extracted from the observed branching ratios for ,
. (iii) If New Physics intervenes to
provide the required {\em weak} phase, then CP asymmetries of up to a few per
cent can arise in vs. ,
vs. , vs. , etc.; an
asymmetry of the same size, but opposite in sign occurs when the is
replaced by a in the final state.Comment: 6 pages, latex, no figure
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
On Extracting Heavy Quark Parameters from Moments with Cuts
We point out that applying the photon energy cut significantly modifies the
moments of energy spectrum in B->X_s+gamma decays, with a certain class of
effects not accounted for in the mostly used OPE expressions. This leads to a
systematic bias in the extracted values of the b quark mass and other heavy
quark parameters. The apparent b quark mass increases typically by 70MeV or
more, together with an even more dramatic downward shift in the kinetic
expectation value. Accounting for these cut-related shifts brings different
measurements into a good agreement, when the OPE-based theory employs the
robust approach. These nonperturbative effects are exponential in the effective
hardness severely lowered by high cuts, and do not signify a breakdown of the
1/m_b expansion itself. Similar effects in semileptonic b->c decays are briefly
addressed. We stress the utility of the second moment of E_gamma once these
effects are incorporated.Comment: 8 pages, LaTeX, two figure. Contributed to the Lepton-Photon
Conference, 2003, FNA
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
B decay shape variables and the precision determination of |Vcb| and mb
We present expressions for shape variables of B decay distributions in
several different mass schemes, to order and
(Lambda_{QCD}/mb)^3. Such observables are sensitive to the b quark mass and
matrix elements in the heavy quark effective theory, and recent measurements
allow precision determinations of some of these parameters. We perform a
combined fit to recent experimental results from CLEO, BABAR, and DELPHI, and
discuss the theoretical uncertainties due to nonperturbative and perturbative
effects. We discuss the possible discrepancy between the OPE prediction, recent
BABAR results and the measured branching fraction to D and D* states. We find
|Vcb| = (40.8 +- 0.9) x 10^{-3} and mb^{1S} = 4.74 +- 0.10 GeV, where the
errors are dominated by experimental uncertainties.Comment: 23 pages, 3 figures, Version to appear in PR
Inclusive Decays As A QCD Lab
Phenomenological models of heavy flavour decays differ significantly in their
predictions of global features of decays, like the lifetime or the
relative weight of c\ra s and b\ra c transitions. The expansion
which is directly based on QCD allows predictions on the pattern to be
expected, namely to lie well below 1 psec with c\ra s dominating
over b\ra c and a reduced semileptonic branching ratio. Due to interference
effects one also predicts a lower charm content in the final states of
decays than naively anticipated. The numerical aspect of the predictions,
however, has to be viewed with considerable caution since one cannot expect the
expansion to converge readily for transitions.Comment: 9 pages; LATEX, no figures; submitted for publicatio
Hadron Spectra for Semileptonic Heavy Quark Decay
We calculate the leading perturbative and power corrections to the hadronic
invariant mass and energy spectra in semileptonic heavy hadron decays. We apply
our results to the system. Moments of the invariant mass spectrum, which
vanish in the parton model, probe gluon bremsstrahlung and nonperturbative
effects. Combining our results with recent data on meson branching ratios,
we obtain a lower bound and an upper bound
GeV. The Brodsky-Lepage-Mackenzie scale setting
procedure suggests that higher order perturbative corrections are small for
bottom decay, and even tractable for charm decay.Comment: 24 pages, uses REVTeX, 5 EPS figures embedded with epsf.sty, slightly
modified version to appear in Phys. Rev.
CP Violation and the Cathedral Builders' Paradigm
Pointing out the profound and unique nature of CP violation, I sketch its
basic phenomenology, its CKM prescription and QCD technologies relevant for
heavy flavour physics. After emphasizing the paradigmatic character of the
establishment of direct CP violation I turn to the future, namely indirect
searches for New Physics in electric dipole moments, decays and
charm transitions on one hand and in beauty decays on the other; these are
described as exciting adventures with novel challenges not encountered before.Comment: 20 pages, LaTex, Introductory Lecture given at CPconf2000, Intern.
Conf. on CP Violation Physics, Sept. 18 - 22, 2000, Ferrara, Italy; few
additions, in particular one reference to an early paper by Mohapatra on CP
violatio
CP violation for neutral charmed meson decays to CP eigenstates
CP asymmetries for neutral charmed meson decays to CP eigenstates are
carefully studied. The formulas and numerical results are presented. The impact
on experiments is briefly discussed.Comment: 7 pages, 1 figure, 1 table, Revte
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-
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