168 research outputs found
Quark-binding effects in inclusive decays of heavy mesons
We present a new approach to the analysis of quark-binding effects in
inclusive decays of heavy mesons within the relativistic dispersion quark
model. Various differential distributions, such as electron energy spectrum,
- and -distributions, are calculated in terms of the meson soft
wave function which also determines long-distance effects in exclusive
transition form factors. Using the quark-model parameters and the meson
wave function previously determined from the description of the exclusive transitions within the same dispersion approach, we provide numerical
results on various distributions in the inclusive decays.Comment: revtex, 18 pages, preprint HD-THEP-99-50 (Heidelberg) and
RM3-TH/99-13 (Roma
Non-local anomaly of the axial-vector current for bound states
We demonstrate that the amplitude does not vanish in the limit of zero quark masses. This
represents a new kind of violation of the classical equation of motion for the
axial current and should be interpreted as the axial anomaly for bound states.
The anomaly emerges in spite of the fact that the one loop integrals are
ultraviolet-finite as guaranteed by the presence of the bound-state wave
function. As a result, the amplitude behaves like in the limit of
a large momentum of the current. This is to be compared with the amplitude
which remains
finite in the limit .
The observed effect leads to the modification of the classical equation of
motion of the axial-vector current in terms of the non-local operator and can
be formulated as a non-local axial anomaly for bound states.Comment: revtex, 4 pages, numerical value for in Eq. (19) is
corrected, Eqs. (22) and (23) are modified. New references added. Results
remain unchange
Bound-state parameters from dispersive sum rules for vacuum-to-vacuum correlators
We study the extraction of the ground-state parameters from vacuum-to-vacuum
correlators. We work in quantum-mechanical potential model which provides the
only possibility to probe the reliability and the actual accuracy of this
method: one obtains the bound-state parameters from the correlators by the
standard procedures adopted in the method of sum rules and compares these
results with the exact values calculated from the Schroedinger equation. We
focus on the crucial ingredient of the method of sum rules - the effective
continuum threshold - and propose a new algorithm to fix this quantity. In a
quantum-mechanical model, our procedure leads to a remarkable improvement of
the accuracy of the extracted ground-state parameters compared to the standard
procedures adopted in the method and used in all previous applications of
dispersive sum rules in QCD. The application of the proposed procedure in QCD
promises a considerable increase of the accuracy of the extracted hadron
parameters.Comment: Introduction modified, comment on analytic properties of dual
correlators adde
Rare exclusive semileptonic b -> s transitions in the Standard Model
We study long-distance effects in rare exclusive semileptonic decays B -> (K,
K*) (l+ l-, nu bar{nu}) and analyze dilepton spectra and asymmetries within the
framework of the Standard Model. The form factors, describing the meson
transition amplitudes of the effective Hamiltonian are calculated within the
lattice-constrained dispersion quark model: the form factors are given by
dispersion representations through the wave functions of the initial and final
mesons, and these wave functions are chosen such that the B -> K* transition
form factors agree with the lattice results at large q**2. We calculate
branching ratios of semileptonic B -> K, K* transition modes and study the
sensitivity of observables to the long-distance contributions. The shape of the
forward-backward asymmetry and the longitudinal lepton polarization asymmetry
are found to be independent of the long-distance effects and mainly determined
by the values of the Wilson coefficients in the Standard Model.Comment: revtex, 17 pp., 5 figures with epsfig.st
Hybrid tracking detector based on semiconductor and gas technologies
New Silicon-Gas Pixel Detector (SiGPD) is the result of the further development already proposed Gas-Pixel Detector (GPD). The only disadvantage of GPD was the uncertainty of the particle arriving time. The problem can be solved by additional silicon pixels implementation inside existed electronic chip epitaxial layer during regular chip production. The cost of new Si-Gas Pixel Detector remains practically the same. The new detectors have self-triggering properties and can be used for a first level trigger generation in the particle physics experiments and for many other applications
The parameters of the fermion-mixing and search restriction on a mass leptoquark.
It is shown that the inclusion of fermion mixing in the framework of fourcolour quark-lepton symmetric model can be greatly reduces the restrictions on the mass vector leptoquark. The lower limit for the mass of the vector leptoquark obtained from processes
K
L
0
→
l
i
+
l
j
−
,
B
0
→
l
i
+
l
j
−
and
B
s
→
l
i
+
l
j
−
can be of the order of 85 TeV
- …