696 research outputs found
Exclusive processes in factorization
The exclusive processes , in the region of which the final
state meson momentum is much larger than the hadronic scale ,
are studied in the framework of PQCD approach based on the factorization.
Including the transverse momentum distribution in the light cone wave
functions, our results are consistent with the experimental measurements.
According to our results, many processes have large enough cross sections to be
detected at GeV. The dependence of the cross section has
been directly studied and our result indicates that the scaling is more
favored than . We also find that the gluonic contribution for the
processes involving is tiny.Comment: 17 pages, including 5 figures, Revtex
Weak productions of new charmonium in semi-leptonic decays of B_c
We study the weak productions of novel heavy mesons, such as
, , , , X(3940),
Y(3940), X(3872), and Y(4260), in the semi-leptonic decays. Since there
is still no definite answer for the components of X(3940), Y(3940), X(3872),
Y(4260) so far, we will assign them as excited charmonium states with the
possible quantum numbers constrained by the current experiments. As for the
weak transition form factors, we calculate them in the framework of light-cone
QCD sum rules approach, which is proved to be a powerful tool to deal with the
non-perturbative hadronic matrix element. Our results indicate that different
interpretations of X(3940) can result in remarkable discrepancy of the
production rate in the decays, which would help to clarify the inner
structure of the X(3940) with the forthcoming LHC-b experiments. Besides, the
predicted large weak production rates of X(3872) and Y(3940) in decays
and the small semi-leptonic decay rate for all depend on
their quantum number assignments. Moreover, the mixing of
various vector charmonium states in the weak decay of is also discussed
in this work. The future experimental measurements of these decays will test
the inner structures of these particles, according to our predictions here.Comment: 26 pages, with 7 figures, revTex
The Vertex Including the -Meson Mass
The effective vertex function is calculated in the
QCD hard-scattering approach, taking into account the -meson mass.
We work in the approximation in which only one non-leading Gegenbauer moment
for both the quark-antiquark and the gluonic light-cone distribution amplitudes
for the -meson is kept. The vertex function with one off-shell
gluon is shown to have the form (valid for )
, where is a slowly varying
function, derived analytically in this paper. The resulting vertex function is
in agreement with the phenomenologically inferred form of this vertex obtained
from an analysis of the CLEO data on the -meson energy spectrum in
the decay . We also present an interpolating
formula for the vertex function for the space-like region of the virtuality , which
satisfies the QCD anomaly normalization for on-shell gluons and the
perturbative-QCD result for the gluon virtuality GeV.Comment: 26 pages, 6 figures; use epsfig.sty; submitted to the European
Physical Journal
Spatial distributions in static heavy-light mesons: a comparison of quark models with lattice QCD
Lattice measurements of spatial distributions of the light quark bilinear
densities in static mesons allow to test directly and in detail the wave
functions of quark models. These distributions are gauge invariant quantities
directly related to the spatial distribution of wave functions. We make a
detailed comparison of the recent lattice QCD results with our own quark
models, formulated previously for quite different purposes. We find a striking
agreement not only between our two quark models, but also with the lattice QCD
data for the ground state in an important range of distances up to about 4/GeV.
Moreover the agreement extends to the L=1 states [j^P=(1/2)^+]. An explanation
of several particular features completely at odds with the non-relativistic
approximation is provided. A rather direct, somewhat unexpected and of course
approximate relation between wave functions of certain quark models and QCD has
been established.Comment: 40 pages, 5 figures (version published in PRD
Perturbative QCD of hard and soft processes
We discuss some problems concerning the application of perturbative QCD to
high energy processes. In particular for hard processes, we analyze higher
order and higher twist corrections. It is argued that these effects are of
great importance for understanding the behaviour of pion electromagnetic form
factor at moderately large momentum transfers. For soft processes, we show that
summing the contributions of the lowest twist operators leads to a Regge-like
amplitude.Comment: Reproduction of unpublished JINR Report E2-80-521, Dubna 1980. 22
pages 9 figures. To be published in Modern Physics Letters A. Style file is
include
An Analysis of the Inclusive Decay and Constraints on the -Meson Distribution Amplitudes
We calculate the -meson energy spectrum in the decay in the leading-order perturbative
QCD in the static quark limit for the Orthoquarkonium. Our principal result is
the extraction of parameters of the effective vertex
function (EVF) involving a virtual and a real gluon from the available data on
the hard part of the -meson energy spectrum. The perturbative QCD
based framework provides a good description of the available CLEO data,
allowing to constrain the lowest Gegenbauer coefficients and
of the quark-antiquark and gluonic distribution amplitudes of the
-meson. The resulting constraints are combined with the existing
ones on these coefficients from an analysis of the and
transition form factors and the requirement of positivity
of the EVF, yielding and
for GeV. This reduces
significantly the current uncertainty on these coefficients. The resulting EFV
, including the
-meson mass effects, is presented.Comment: 23 pages, 8 figures; use epsfig.sty; Typos corrected, numerical
analysis further refined; added an equation; to appear in the European
Physical Journal
Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays
According to the heavy-quark flavour symmetry, the transition
form factors could be related to the corresponding ones of D-meson decays near
the zero recoil point. With the recent precisely measured exclusive
semileptonic decays and , we perform a
phenomenological study of transition form factors based on this
symmetry. Using BK, BZ and Series Expansion parameterizations of the form
factor slope, we extrapolate transition form factors from
to . It is found that, although being consistent with
each other within error bars, the central values of our results for form factors at , , are much smaller than
predictions of the QCD light-cone sum rules, but are in good agreements with
the ones extracted from hadronic B-meson decays within the SCET framework.
Moreover, smaller form factors are also favored by the QCD factorization
approach for hadronic B-meson decays.Comment: 19 pages, no figure, 5 table
Magnetic properties of the non-stoichiometric TbCo2Nix alloys
The magnetic and magnetothermal properties of the non-stoichiometric TbCo2Nix (0 ≤ x ≤0.2) alloys were studied. It was found that the concentration dependence of the Curie temperature and magnetic moment of the 3d-sublattice have a maximum at x = 0.025. The obtained experimental magnetic properties of the TbCo2Nix alloys were discussed under assumption that the Co magnetic moment in the compounds changes with increasing x. The magnetic entropy change was determined using the temperature dependences of the magnetization and Maxwell's thermodynamic relation. The obtained results for TbCo2Nix were compared with those for the ErCo2Mnx alloys. © 2018 The Authors, published by EDP Sciences.The research was carried out within the state assignment of )$62 of 5Xssia (thePe ³0aJnet´ 1o ȺȺȺȺ-Ⱥ - 118020290129 -5) and supported by project of UB RAS (No. 18-10-2-5)
pi/K -> e nu branching ratios to O(e^2 p^4) in Chiral Perturbation Theory
We calculate the ratios R_{e/mu}^{(P)} = Gamma(P -> e nu)/Gamma (P -> mu nu)
(P=pi,K) in Chiral Perturbation Theory to order e^2 p^4. We complement the one-
and two-loop effective theory results with a matching calculation of the local
counterterm, performed within the large- expansion. We find
R_{e/mu}^{(\pi)} = (1.2352 \pm 0.0001)*10^{-4} and R_{e/mu}^{(K)} = (2.477 \pm
0.001)*10^{-5}, with uncertainty induced by the matching procedure and chiral
power counting. Given the sensitivity of upcoming new measurements, our results
provide a clean baseline to detect or constrain effects from weak-scale new
physics in these rare decays. As a by-product, we also update the theoretical
analysis of the individual pi/K -> \ell nu modes.Comment: 40 pages, 4 figures, 3 table
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