17 research outputs found
Phenomenological Analysis of D Meson Lifetimes
The QCD-based operator-product-expansion technique is systematically applied
to the study of charmed meson lifetimes. We stress that it is crucial to take
into account the momentum of the spectator light quark of charmed mesons,
otherwise the destructive Pauli-interference effect in decays will lead
to a negative decay width for the . We have applied the QCD sum rule
approach to estimate the hadronic matrix elements of color-singlet and
color-octet 4-quark operators relevant to nonleptonic inclusive decays. The
lifetime of is found to be longer than that of because the latter
receives a constructive -exchange contribution, whereas the hadronic
annihilation and leptonic contributions to the former are compensated by the
Pauli interference. We obtain the lifetime ratio
, which is larger than some earlier theoretical
estimates, but still smaller than the recent measurements by CLEO and E791.Comment: 14 pages, 3 figure
Further study of the helicity selection rule evading mechanism in , and decaying to baryon anti-baryon pairs
We investigate the long distance contribution via charmed hadron loops in the
processes , and decaying to baryon anti-baryon pairs,
which are supposed to be highly suppressed by the helicity selection rule as a
consequence of the perturbative QCD framework. With an effective Lagrangian
method, our estimation result indicates that such hadron loops play an
important role in these hadronic decays. It is a further test of the evading
mechanism for the helicity selection rule in charmonium baryon-antibaryon
decays.Comment: 9 pages, 7 figures, to appear in J. Phys.
Covariant Light-Front Approach for s-wave and p-wave Mesons: Its Application to Decay Constants and Form Factors
We study the decay constants and form factors of the ground-state s-wave and
low-lying p-wave mesons within a covariant light-front approach. Numerical
results of the form factors for transitions between a heavy pseudoscalar meson
and an s-wave or p-wave meson and their momentum dependence are presented in
detail. In particular, form factors for heavy-to-light and B to D**
transitions, where D** denotes generically a p-wave charmed meson, are compared
with other model calculations. The experimental measurements of the decays B^-
to D** pi^- and B to D D**_s are employed to test the decay constants of D**_s
and the B to D** transition form factors. The heavy quark limit behavior of the
decay constants and form factors is examined and it is found that the
requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW)
functions, one for s-wave to s-wave and two for s-wave to p-wave transitions,
are obtained. The values of IW functions at zero recoil and their slope
parameters can be used to test the Bjorken and Uraltsev sum rules.Comment: 59 pages, 6 figures. Version to appear in Phys. Rev. D. Changes are:
(i) D_s to phi transition form factors are discussed and compared with the
recent FOCUS measurements and (ii) zero mode effects are clarifie
Charmless Exclusive Baryonic B Decays
We present a systematical study of two-body and three-body charmless baryonic
B decays. Branching ratios for two-body modes are in general very small,
typically less than , except that \B(B^-\to p \bar\Delta^{--})\sim
1\times 10^{-6}. In general, due to
the large coupling constant for . For three-body modes we
focus on octet baryon final states. The leading three-dominated modes are with a branching ratio of
order for and
for . The penguin-dominated decays with strangeness
in the meson, e.g., and , have appreciable rates and the mass
spectrum peaks at low mass. The penguin-dominated modes containing a strange
baryon, e.g., , have
branching ratios of order . In contrast, the decay
rate of is smaller. We explain why some of
charmless three-body final states in which baryon-antibaryon pair production is
accompanied by a meson have a larger rate than their two-body counterparts:
either the pole diagrams for the former have an anti-triplet bottom baryon
intermediate state, which has a large coupling to the meson and the
nucleon, or they are dominated by the factorizable external -emission
process.Comment: 46 pages and 3 figures, to appear in Phys. Rev. D. Major changes are:
(i) Calculations of two-body baryonic B decays involving a Delta resonance
are modified, and (ii) Penguin-dominated modes B-> Sigma+N(bar)+p are
discusse
Extraction of and from Decays
Based on the factorization approach, we show that the CLEO data for the ratio
and the CDF measurement of the
fraction of longitudinal polarization in can be accounted for by
the heavy-flavor-symmetry approach for heavy-light form factors provided that
the form factor behaves as a constant, while the dependence is of
the monopole form for , and of the dipole behavior for
and . This extrapolation for form factors is further supported by
data and by a recent QCD-sum-rule analysis. We then apply this
method to decays to extract the parameters and
. It is found that and . Our result thus
significantly improves the previous analysis that leads to . We argue that, contrary to what anticipated from the leading
expansion, the sign of a_2(B\to\psi\K) should be positive and
a_2(B\to\psi\K)~{\large ^>_\sim}~ a_2(B\to D^{(*)}\pi(\rho)).Comment: 14 pages, revised versio
Nonspectator Effects and B Meson Lifetimes from a Field-theoretic Calculation
The B meson lifetime ratios are calculated to the order of in the
heavy quark expansion. The predictions of those ratios are dependent on four
unknown hadronic parameters , , and , where
and parametrize the matrix elements of color singlet-singlet
four-quark operators and and the matrix elements of
color octet-octet operators. We derive the renormalization-group improved QCD
sum rules for these parameters within the framework of heavy quark effective
theory. The results are , ,
, and to zeroth
order in . The resultant meson lifetime ratios are
and in SU(3)
symmetry limit.Comment: 22 pages, 2 figures. (i) Sec.II is shortened, (ii) numerical results
for epslion_i are revised, and (iii) Fig.2 is revise
Recommended from our members
Collective future orientation, group-based emotions, and support for policy
While past studies have demonstrated the role of group-based emotions in intergroup attitudes within the context of intractable conflicts, it is unknown how individual temporal perspectives, namely collective future orientations and political ideology, moderate the relationship between conflict-related emotions and support for policies. In two exploratory studies, we adopted a functional approach to emotions in conflict and examined whether the associations between the three group-based emotions of compassion, hope, and hatred and support for conciliatory versus aggressive policies were moderated by individual perceptions of collective future and by political ideology. The results indicate that the way group-based emotions predict support for policies is moderated by both future and political orientation, such that high collective future orientation reduces the effect of positively-valenced emotions on support for conciliatory policies, and increases the effect of negatively-valenced emotions on support for aggressive policies, but only among leftwingers. We discuss the theoretical and practical implications of this nuanced link between group-based emotions and support for policies, moderated by political ideology and collective future orientation
Six habits to enhance MET performance under stress: A discussion paper reviewing team mechanisms for improved patient outcomes
Effective team decision making has the potential to improve the quality of health care outcomes. Medical Emergency Teams (METs), a specific type of team led by either critical care nurses or physicians, must respond to and improve the outcomes of deteriorating patients. METs routinely make decisions under conditions of uncertainty and sub optimal care outcomes still occur. In response, the development and use of Shared Mental Models (SMMs), which have been shown to promote higher team performance under stress, may enhance patient outcomes. This discussion paper specifically focuses on the development and use of SMMs in the context of METs. Within this process, the psychological mechanisms promoting enhanced team performance are examined and the utility of this model is discussed through the narrative of six habits applied to MET interactions. A two stage, reciprocal model of both non-analytic decision making within the acute care environment and analytic decision making during reflective action learning was developed. These habits are explored within the context of a MET, illustrating how applying SMMs and action learning processes may enhance team-based problem solving under stress. Based on this model, we make recommendations to enhance MET decision making under stress. It is suggested that the corresponding habits embedded within this model could be imparted to MET members and tested by health care researchers to assess the efficacy of this integrated decision making approach in respect to enhanced team performance and patient outcomes