1,275 research outputs found
Time-of-arrival distribution for arbitrary potentials and Wigner's time-energy uncertainty relation
A realization of the concept of "crossing state" invoked, but not
implemented, by Wigner, allows to advance in two important aspects of the time
of arrival in quantum mechanics: (i) For free motion, we find that the
limitations described by Aharonov et al. in Phys. Rev. A 57, 4130 (1998) for
the time-of-arrival uncertainty at low energies for certain mesurement models
are in fact already present in the intrinsic time-of-arrival distribution of
Kijowski; (ii) We have also found a covariant generalization of this
distribution for arbitrary potentials and positions.Comment: 4 pages, revtex, 2 eps figures include
Novel Polypyridyl Ruthenium(II) Complexes Containing Oxalamidines as Ligands.
The complexes [Ru(bpy)2(H2TPOA)](PF6)2 ⋅ 4H2O, (1); [Ru(Me-bpy)2(H2TPOA)](PF6)2
⋅ 2H2O, (2); [Ru(bpy)2(H2TTOA)](PF6)2 ⋅ 2H2O, (3); [Ru(Me-bpy)2(H2TTOA)](PF6)2 ⋅ 2H2O,
(4) and {[Ru(bpy)2]2(TPOA)}(PF6)2 ⋅ 2H2O, (5) (where bpy is 2,2´bipyridine; Me-bpy is 4,4´-
dimethyl-2,2´-bipyridine; H2TPOA is N, N´, N´´, N´´´- tetraphenyloxalamidine; H2TTOA is
N, N´, N´´, N´´´- tetratolyloxalamidine) have been synthesized and characterized by 1H-NMR,
FAB-MS, infrared spectroscopy and elemental analysis. The X-ray investigation shows the
coordination of the still protonated oxalamidine moiety via the 1,2−diimine unit. The dimeric
compound (5) could be separated in its diastereoisomers (5´) and (5´´) by repeated
recrystallisation. The diastereomeric forms exhibit different 1H-NMR spectra and slightly
shifted electronic spectra. Compared with the model compound [Ru(bpy)3]2+, the absorption
maxima of (1)–(5) are shifted to lower energies. The mononuclear complexes show Ru(III/II)-
couples at about 0.9 V vs SCE, while for the dinuclear complex two well defined metal based
redox couples are observed at 0.45 and 0.65 V indicating substantial interaction between the
two metal centres
PMS74 Developing and Implementing Patient-Resource Use Diaries for a Clinical Trial Assessing Spinal Stenosis Interventions in the Elderly
Nonleptonic Cabibbo Favoured -Decays and -Asymmetries for Charmed Final Hadron States in Isgur and Wise Theory
The Cabibbo allowed non-leptonic -decays in two hadrons are studied,
within the factorization hypothesis, in the framework of Isgur and Wise theory
for the matrix elements of the weak currents. The
symmetry relates to currents, which
have been measured in the semileptonic strange decays of charmed particles. By
assuming colour screening and allowing for invariant contributions from
the annihilation terms with charmed final states one is able to comply with the
present experimental knowledge.\\ The violating asymmetries in neutral
decays are given for charmed final states in terms of the angles. With
the central values found for the annihilation parameters there is a destructive
(constructive) interference between the direct and annihilation terms in the
Cabibbo allowed (doubly forbidden) amplitudes for the decays into
and so that they may be of the same order.
This would imply large asymmetries, for which however our present knowledge on
the amplitudes does not allow to predict even their sign.\\ We have better
confidence in our predictions for the charged final states than the neutral
ones and can draw the conclusion that the detection of the corresponding
asymmetries requires, at least, tagged neutral -particles.Comment: CERNTEX, 17 pages, DSF-92/23, INFN-NA-IV-92/2
Nonleptonic Weak Decays of Bottom Baryons
Cabibbo-allowed two-body hadronic weak decays of bottom baryons are analyzed.
Contrary to the charmed baryon sector, many channels of bottom baryon decays
proceed only through the external or internal W-emission diagrams. Moreover,
W-exchange is likely to be suppressed in the bottom baryon sector.
Consequently, the factorization approach suffices to describe most of the
Cabibbo-allowed bottom baryon decays. We use the nonrelativistic quark model to
evaluate heavy-to-heavy and heavy-to-light baryon form factors at zero recoil.
When applied to the heavy quark limit, the quark model results do satisfy all
the constraints imposed by heavy quark symmetry. The decay rates and up-down
asymmetries for bottom baryons decaying into and
are calculated. It is found that the up-down asymmetry is negative except for
decay and for decay modes with in the final
state. The prediction for
is consistent with the recent CDF measurement. We also present
estimates for decays and compare with various model
calculations.Comment: 24 pages, to appear in Phys. Rev. Uncertainties with form factor q^2
dependence are discusse
Applicability of perturbative QCD to decays
We develop perturbative QCD factorization theorem for the semileptonic heavy
baryon decay , whose form factors are
expressed as the convolutions of hard quark decay amplitudes with universal
and baryon wave functions. Large logarithmic
corrections are organized to all orders by the Sudakov resummation, which
renders perturbative expansions more reliable. It is observed that perturbative
QCD is applicable to decays for velocity transfer
greater than 1.2. Under requirement of heavy quark symmetry, we predict the
branching ratio , and determine
the and baryon wave functions.Comment: 12 pages in Latex file, 3 figures in postscript files, some results
are changed, but the conclusion is the sam
A perturbative approach to decays into two mesons
The modified perturbative approach in which transverse degrees of freedom as
well as Sudakov suppressions are taken into account, is applied to decays
into two mesons. The influence of various model parameters (CKM matrix
elements, decay constant, mesonic wave functions) on the results as well as
short distance corrections to the weak Hamiltonian are discussed in some
detail. The perturbative contributions to the decays yield branching ratios
of the order of which values are well below the upper
limit for the branching ratio as measured by CLEO.Comment: 26 pages, RevTex, 6 figures appended (compressed and uuencode using
'uufiles'
Hadronic B Decays to Charmed Baryons
We study exclusive B decays to final states containing a charmed baryon
within the pole model framework. Since the strong coupling for is larger than that for , the two-body charmful decay
has a rate larger than
as the former proceeds via the pole while the latter via the
pole. By the same token, the three-body decay receives less baryon-pole contribution than
. However, because the important charmed-meson
pole diagrams contribute constructively to the former and destructively to the
latter, has a rate slightly larger than
. It is found that one quarter of the rate comes from the resonant contributions. We discuss
the decays and
and stress that they are not color suppressed even though they can only proceed
via an internal W emission.Comment: 25 pages, 6 figure
B -> J/psi K^* Decays in QCD Factorization
The hadronic decay B -> J K^* is analyzed within the framework of QCD
factorization. The spin amplitudes A_0, A_\parallel and A_\perp in the
transversity basis and their relative phases are studied using various
different form-factor models for B-K^* transition. The effective parameters
a_2^h for helicity h=0,+,- states receive different nonfactorizable
contributions and hence they are helicity dependent, contrary to naive
factorization where a_2^h are universal and polarization independent. QCD
factorization breaks down even at the twist-2 level for transverse hard
spectator interactions. Although a nontrivial strong phase for the A_\parallel
amplitude can be achieved by adjusting the phase of an infrared divergent
contribution, the present QCD factorization calculation cannot say anything
definite about the phase phi_\parallel. Unlike B -> J/psi K decays, the
longitudinal parameter a_2^0 for B -> J/psi K^* does not receive twist-3
corrections and is not large enough to account for the observed branching ratio
and the fraction of longitudinal polarization. Possible enhancement mechanisms
for a_2^0 are discussed.Comment: 21 pages, 1 figure, a table and a reference added, some typos
correcte
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
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