2,995 research outputs found
Exclusive decay of heavy quarkonium into photon and two pions
We study the exclusive decay of heavy quarkonium into one photon and
two pions in the kinematic region, where the two-pion system has a invariant
mass which is much smaller than the mass of heavy quarkonium. Neglecting
effects suppressed by the inverse of the heavy quark mass, the decay amplitude
can be factorized, in which the nonperturbative effect related to heavy
quarkonium is represented by a non-relativistic QCD matrix element, and that
related to the two pions is represented by a distribution amplitude of two
gluons in the isoscalar pion pair. By taking the asymptotic form for the
distribution amplitude and by using chiral perturbative theory we are able to
obtain numerical predictions for the decay. Numerical results show that the
decay of \jpsi can be observed at BEPC and at CESR. Experiment observation of
this process in this kinematic region at BEPC and CESR can provide information
about how gluons are converted into the two pions and may supply a unique
approach to study s-wave scattering.Comment: 9 pages, Latex file, 5 EPS figures, 1) Just before summarizing our
work, a paragraph is added to clarify the contribution of D-wave pion pair.
2) one reference is added, 3) exponential factor in Eq.(2) is delete
Factorization Approach for Inclusive Production of Doubly Heavy Baryon
We study inclusive production of doubly heavy baryon at a collider
and at hadron colliders through fragmentation. We study the production by
factorizing nonpertubative- and perturbative effects. In our approach the
production can be thought as a two-step process: A pair of heavy quarks can be
produced perturbatively and then the pair is transformed into the baryon. The
transformation is nonperturbative. Since a heavy quark moves with a small
velocity in the baryon in its rest frame, we can use NRQCD to describe the
transformation and perform a systematic expansion in the small velocity. At the
leading order we find that the baryon can be formed from two states of the
heavy-quark pair, one state is with the pair in state and in color
, another is with the pair in state and in color . Two matrix elements are defined for the transformation from the two
states, their perturbative coefficients in the contribution to the
cross-section at a collider and to the function of heavy quark
fragmentation are calculated. Our approach is different than previous
approaches where only the pair in state and in color is
taken into account. Numerical results for colliders at the two
-factories and for hadronic colliders LHC and Tevatron are given.Comment: Add results for large p_t, minor change
Scale Dependence of Twist-3 Quark-Gluon Operators for Single Spin Asymmetries
We derive the scale dependence of twist-3 quark-gluon operators, or ETQS
matrix elements, at one-loop. These operators are used to factorize transverse
single spin asymmetries, which are studied intensively both in experiment and
theory. The scale dependence of two special cases are particularly interesting.
One is of soft-gluon-pole matrix elements, another is of soft-quark-pole matrix
elements. From our results the evolutions in the two cases can be obtained. A
comparison with existing results of soft-gluon-pole matrix elements is made.Comment: typo in Eq.(10) corrected, references adde
Inclusive Photoproduction of Polarized Quarkonium
We analyse inclusive photoproduction of polarized quarkonium in the
framework of QCD. To separate nonperturbative and perturbative parts in the
density matrix of the produced quarkonium we use a method , which is equivalent
to the diagramatic expansion widely used in analysing deeply inelastic
scatterings. A systematic expansion in a small velocity , with which a heavy
quark moves inside the quarkonium in its rest frame, is performed for the
nonperturbative parts, and they are expressed as matrix elements in
nonrelativistic QCD. At the leading order of there are four matrix elements
representing nonperturbative physics. The perturbative parts are calculated at
the leading order of coupling constants. Some numerical results, especially,
numerical results for HERA are given.Comment: 19 pages+7 Figures as one compressed and encoded postcript fil
Gluon Fragmentation into Quarkonium
The functions of the gluon fragmentation into quarkonium are
calculated to order . With the recent progress in analysing
quarkonium systems in QCD we show explicitly how the socalled divergence in the
limit of the zero-binding energy, which is related to -wave quarkonia, is
treated correctly in the case of fragmentation functions. The obtained
fragmentation functions satisfy explicitly at the order of the
Altarelli-Parisi equation and when they behave as as
expected. Some comments on the previous results are made.Comment: Type-errors in the text and equations are eliminated. Several
sentences are added in Sect.4. The file is compressed and uuencoded (E-Mail
contact [email protected]
Calculating Fragmentation Functions from Definitions
Fragmentation functions for hadrons composed of heavy quarks are calculated
directly from the definitions given by Collins and Soper and are compared with
those calculated in another way. A new fragmentaion function for a P-wave meson
is also obtained and the singularity arising at the leading order is discussed.Comment: Preptint UM-P-94/01, 12 pages, 2 pages with Figures can be sent on
request. Using Plain Te
CP Test in the W Pair Production via Photon Fusion at NLC
We study the possibility to test CP invariance in the production via
photon fusion at NLC. The predictions of the CP violation effects are made
within two Higgs doublet extensions of the minimal standard model, where CP
violation is introduced by a neutral Higgs exchange in s channel in our case.
The width effect in the Higgs propagator on the CP violation effects is studied
in detail. The CP violation effects can be measured in some parameter region of
the extensions.Comment: 11 pages, Tex, UM-P-93/16, OZ-93/6 One figure not include
On Transverse-Momentum Dependent Light-Cone Wave Functions of Light Mesons
Transverse-momentum dependent (TMD) light-cone wave functions of a light
meson are important ingredients in the TMD QCD factorization of exclusive
processes. This factorization allows one conveniently resum Sudakov logarithms
appearing in collinear factorization. The TMD light-cone wave functions are not
simply related to the standard light-cone wave functions in collinear
factorization by integrating them over the transverse momentum. We explore
relations between TMD light-cone wave functions and those in the collinear
factorization. Two factorized relations can be found. One is helpful for
constructing models for TMD light-cone wave functions, and the other can be
used for resummation. These relations will be useful to establish a link
between two types of factorization.Comment: add more discussions and reference
Perturbative Prediction for Parton Fragmentation into Heavy Hadron
By expanding functions of parton fragmentation into a heavy hadron in the
inverse of the heavy quark mass we attempt to factorize them into
perturbative- and nonperturbative parts. In our approach the nonperturbative
parts can be defined as matrix elements in heavy quark effective theory, the
shape of the functions is predicted by perturbative QCD. In this work we
neglect effect at order of and calculate the perturbative parts at
one-loop level for heavy quark- and gluon fragmentation. We compare our results
from leading log approximation with experimental results from
colliders and find a deviation below or at 10% level. Adding effect of higher
order in it can be expected to reduce the deviation. The size of
matrix elements appearing at the order we consider for several types of heavy
hadrons is determined.Comment: 21 pages + 3 pages figures, plain te
Revisiting spin alignment of heavy mesons in its inclusive production
In the heavy quark limit inclusive production rate of a heavy meson can be
factorized, in which the nonperturbative effect related to the heavy meson can
be characterized by matrix elements defined in the heavy quark effective
theory. Using this factorization, predictions for the full spin density matrix
of a spin-1 and spin-2 meson can be obtained and they are characterized only by
one coefficient representing the nonperturbative effect. Predictions for spin-1
heavy meson are compared with experiment performed at colliders in the
energy range from GeV to GeV, a complete agreement
is found for - and -meson. For meson, our prediction suffers
a large correction, as indicated by experimental data. There exists another
approach by taking heavy mesons as bound systems, in which the total angular
momentum of the light degrees of freedom is 1/2 and 3/2 for spin-1 and spin-2
meson respectively, then the diagonal parts of spin density matrices can be
obtained. However, there are distinct differences in the predictions from the
two approaches and they are discussed in detail.Comment: 14 pages with one figur
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