554 research outputs found
Puzzles in physics
I discuss some puzzles observed in exclusive meson decays, concentrating
on the large difference between the direct CP asymmetries in the and modes, the large
branching ratio, and the large deviation of the mixing-induced CP asymmetries
in the penguins from those in the trees.Comment: 6 pages, 1 figure, talk presented at the 9th Workshop on High Energy
Physics Phenomenology, Bhubaneswar, Orissa, India, Jan. 3-14, 2006; reference
adde
Quarkonium momentum distributions in photoproduction and B decay
According to our present understanding many production processes
proceed through a coloured state followed by the emission of soft
particles in the quarkonium rest frame. The kinematic effect of soft particle
emission is usually a higher-order effect in the non-relativistic expansion,
but becomes important near the kinematic endpoint of quarkonium energy
(momentum) distributions. In an intermediate region a systematic resummation of
the non-relativistic expansion leads to the introduction of so-called `shape
functions'. In this paper we provide an implementation of the kinematic effect
of soft gluon emission which is consistent with the non-relativistic shape
function formalism in the region where it is applicable and which models the
extreme endpoint region. We then apply the model to photoproduction of
and production in meson decay. A satisfactory description of
decay data is obtained. For inelastic charmonium photoproduction we conclude
that a sensible comparison of theory with data requires a transverse momentum
cut larger than the currently used 1 GeV.Comment: latex, 45 pages; (v2) some typos corrected, version to appear in PR
QCD analysis of inclusive B decay into charmonium
We compute the decay rates and -energy distributions of mesons into
the final state , where can be any one of the -wave or -wave
charmonia, at next-to-leading order in the strong coupling. We find that a
significant fraction of the observed , and must be
produced through pairs in a colour octet state and should therefore
be accompanied by more than one light hadron. At the same time we obtain
stringent constraints on some of the long-distance parameters for colour octet
production.Comment: 40 pages, RevTeX, 4 figure
Flavor SU(3) symmetry and QCD factorization in and decays
Using flavor SU(3) symmetry, we perform a model-independent analysis of
charmless decays. All the relevant
topological diagrams, including the presumably subleading diagrams, such as the
QCD- and EW-penguin exchange diagrams and flavor-singlet weak annihilation
ones, are introduced. Indeed, the QCD-penguin exchange diagram turns out to be
important in understanding the data for penguin-dominated decay modes. In this
work we make efforts to bridge the (model-independent but less quantitative)
topological diagram or flavor SU(3) approach and the (quantitative but somewhat
model-dependent) QCD factorization (QCDF) approach in these decays, by
explicitly showing how to translate each flavor SU(3) amplitude into the
corresponding terms in the QCDF framework. After estimating each flavor SU(3)
amplitude numerically using QCDF, we discuss various physical consequences,
including SU(3) breaking effects and some useful SU(3) relations among decay
amplitudes of and .Comment: 47 pages, 3 figures, 28 table
Chi_1 and Polarisation Asymmetries for Quarkonia at High Orders in Non-relativistic QCD
We study doubly polarised asymmetries of c-cbar and b-bbar mesons in hadro-
and photo-production at low transverse momentum in non-relativistic QCD to high
orders in the relative velocity of the pair, v. We give the complete set of
expressions required for the asymmetries up to order v^9. The asymmetries in
the production of eta_{c,b} states are a stable measure of the polarised gluon
densities. The asymmetries for chi_{c,b}, J/psi, psi', and the various Upsilon
states are stringent tests of the NRQCD scaling relations.Comment: 21 pages LaTeX including 2 figure
Quarkonia and the Pole Mass
The pole mass of a heavy quark is ambiguous by an amount of order
. We show that the heavy-quark potential, , is similarly
ambiguous, but that the total static energy, , is unambiguous
when expressed in terms of a short-distance mass. This implies that the
extraction of a short-distance mass from the quarkonium spectrum is free of an
ambiguity of order , in contrast with the pole mass.Comment: 6 pages, LateX. Minor revisions for publicatio
Color Octet Contribution to J/psi Photoproduction Asymmetries
We investigate photoproduction asymmetries in the framework of the
NRQCD factorization approach. It is shown that the color octet contribution
leads to large uncertainties in the predicted asymmetries which rules out the
possibility to precisely measure the gluon polarization in the nucleon through
this final state. For small values of the color octet parameters being
compatible with photoproduction data it appears possible that a
measurement of asymmetries could provide a new test for the NRQCD
factorization approach, on one hand, or a measurement of the polarized gluon
distribution from low inelasticity events , on the otherComment: 12 pages, LaTeX, with 6 figs. Final version published in Phys.Rev.
Nuclear Effects in Charmonium Production in QCD
It is shown that the nuclear shadowing of charmonium due to the modification
of the nuclear parton distribution is similar in the factorization approach
based on non relativistic QCD and in the color evaporation model. In the first
model, a separate study of the color octet and color singlet contributions to
the yields of the various charmonium states as well as the contributions of
these states to the total production is performed. It is found a clear
dependence of these contributions which can reproduce experimental data
for moderate .Comment: 11 pages, 5 Postscript figure
Soft-Collinear Factorization in Effective Field Theory
The factorization of soft and ultrasoft gluons from collinear particles is
shown at the level of operators in an effective field theory. Exclusive
hadronic factorization and inclusive partonic factorization follow as special
cases. The leading order Lagrangian is derived using power counting and gauge
invariance in the effective theory. Several species of gluons are required, and
softer gluons appear as background fields to gluons with harder momenta. Two
examples are given: the factorization of soft gluons in B->D pi, and the
soft-collinear convolution for the B->Xs gamma spectrum.Comment: 32 pages, 11 figs, journal versio
Heavy Flavours at Colliders
I review some topics in the production and decays of heavy flavours that are
relevant for collider physics. In particular, I discuss the present status and
some recent progress related to masses, parton densities and fragmentation
functions of heavy quarks, as well as threshold resummation, polarized onium
production at high transverse momentum, and a factorization theorem for decays.Comment: 12 pages. Plenary talk given at UK Phenomenology Workshop on Collider
Physics, Durham, England, 19-24 Sep 1999 Comments and references adde
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