53 research outputs found
Resummation of QCD Corrections to the eta_c Decay Rate
We examine the ratio of the decay rate of the eta_c into light hadrons to the
decay rate into photons and find that most of the large next-to-leading-order
(NLO) correction is associated with running of the strong coupling alpha_s. We
resum such contributions by analyzing final-state chains of vacuum-polarization
bubbles. We show that the nonperturbative parts of the bubble chains can be
absorbed into a color-octet matrix element, once one has used contour
deformations of the phase-space integrals to cancel certain contributions. We
argue that these contributions are incompatible with the uncertainty principle.
We also argue that perturbation theory is reliable only if one carries out the
phase-space integrations before the perturbation summation. Our results are in
good agreement with experiment and differ considerably from those that one
obtains by applying the scale-setting method of Brodsky, Lepage, and Mackenzie
to the NLO result.Comment: 41 pages, REVTEX, corrected minor typos in tex
Strangeness in the proton and N*(1535)
The newest progress on the study of the strangeness in the proton and in the
lowest negative parity nucleon excited state is reviewed.
Implications on the internal quark structure of the proton, and
other baryons are discussed. The diquark cluster picture for the 5-quark
components in baryons gives a natural explanation not only to the empirical
indications for a positive strangeness magnetic moment and positive
strangeness radius of the proton but also the longstanding mass-reverse problem
of , and resonances as well as the
unusual decay pattern of the resonance. Evidence for possible
existence of 's SU(3) nonet partners in this picture is
pointed out, and suggestion is made to search for these hyperon excited
states under the well known , and
peaks in various reactions.Comment: 6 pages, 2 figures, Plenary talk at 18th International IUPAP
Conference on Few-Body Problems in Physics August 21-26. 2006 Santos SP
Brazil; to be published in Nuclear Physics
Proton strangeness form factors in (4,1) clustering configurations
We reexamine a recent result within a nonrelativistic constituent quark model
(NRCQM) which maintains that the uuds\bar s component in the proton has its
uuds subsystem in P state, with its \bar s in S state (configuration I). When
the result are corrected, contrary to the previous result, we find that all the
empirical signs of the form factors data can be described by the lowest-lying
uuds\bar s configuration with \bar s in P state that has its uuds subsystem in
state (configuration II). Further, it is also found that the removal of the
center-of-mass (CM) motion of the clusters will enhance the contributions of
the transition current considerably. We also show that a reasonable description
of the existing form factors data can be obtained with a very small probability
P_{s\bar s}=0.025% for the uuds\bar s component. We further see that the
agreement of our prediction with the data for G_A^s at low-q^2 region can be
markedly improved by a small admixture of configuration I. It is also found
that by not removing CM motion, P_{s\bar s} would be overestimated by about a
factor of four in the case when transition dominates over direct currents.
Then, we also study the consequence of a recent estimate reached from analyzing
the existing data on quark distributions that P_{s\bar s} lies between 2.4-2.9%
which would lead to a large size for the five-quark (5q) system, as well as a
small bump in both G^s_E+\eta G^s_M and G^s_E in the region of q^2 =< 0.1
GeV^2.Comment: Prepared for The Fifth Asia-Pacific Conference on Few-Body Problems
in Physics 2011 in Seoul, South Korea, 22-26 August 201
Pinch Technique and the Batalin-Vilkovisky formalism
In this paper we take the first step towards a non-diagrammatic formulation
of the Pinch Technique. In particular we proceed into a systematic
identification of the parts of the one-loop and two-loop Feynman diagrams that
are exchanged during the pinching process in terms of unphysical ghost Green's
functions; the latter appear in the standard Slavnov-Taylor identity satisfied
by the tree-level and one-loop three-gluon vertex. This identification allows
for the consistent generalization of the intrinsic pinch technique to two
loops, through the collective treatment of entire sets of diagrams, instead of
the laborious algebraic manipulation of individual graphs, and sets up the
stage for the generalization of the method to all orders. We show that the task
of comparing the effective Green's functions obtained by the Pinch Technique
with those computed in the background field method Feynman gauge is
significantly facilitated when employing the powerful quantization framework of
Batalin and Vilkovisky. This formalism allows for the derivation of a set of
useful non-linear identities, which express the Background Field Method Green's
functions in terms of the conventional (quantum) ones and auxiliary Green's
functions involving the background source and the gluonic anti-field; these
latter Green's functions are subsequently related by means of a Schwinger-Dyson
type of equation to the ghost Green's functions appearing in the aforementioned
Slavnov-Taylor identity.Comment: 45 pages, uses axodraw; typos corrected, one figure changed, final
version to appear in Phys.Rev.
A Study of the Roper Resonance as a Hybrid State from Decays
The structure of the Roper resonance as a hybrid baryon is investigated
through studying the transitional amplitudes in J/psi-> p\barN*, N*\barN*
decays. We begin with perturbative QCD to describe the dynamical process for
the J/psi-> 3\bar q+3q decay to the lowest order of \alpha_s, and by extending
the modified quark creation model to the J/psi energy region to describe the
J/psi-> 3\bar q+3q +g process. The non-perturbative effects are incorporated by
a simple quark model of baryons to evaluate the angular distribution parameters
and decay widths for the processes J/psi-> pbar N*,N*bar N*. From fitting the
decay width of J/psi->gamma p pbar to the experimental data, we extract the
quark-pair creation strength g_I=15.40 GeV. Our numerical results for
J/psi->pbar N*,N* bar N* decays show that the branching ratios for these decays
are quite different if the Roper resonance is assumed to be a common state
or a pure hybrid state. For testing its mixing properties, we present a scheme
to construct the Roper wave function by mixing |qqqg> state with a normal
|qqq,2s> state. Under this picture, the ratios of the decay widths to that of
the J/psi->p pbar decay are re-evaluated versus the mixing parameter. A test of
the hybrid nature of the Roper resonance in J/psi decays is discussed.Comment: 18 pages,3 figures, To appear in Nuclear Physics
Measurements of decays into Vector- Tensor final states
Decays of the into vector plus tensor meson final states have been
studied with 14 million events collected with the BESII detector.
Branching fractions of \psi(2S) \rt \omega f_{2}(1270), ,
and are
determined. They improve upon previous BESI results and confirm the violation
of the "12%" rule for decays to VT channels with higher precision.Comment: 7 pages, 7 figures and 2 table
Observation of the decay \psip\rar\kstark
Using 14 million events collected with the BESII detector,
branching fractions of \psip\rar\kstarkpm and \kstarknn are determined to
be: \calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5} and
\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}. The
results confirm the violation of the "12%" rule for these two decay channels
with higher precision. A large isospin violation between the charged and
neutral modes is observed.Comment: 5 pages, 3 figure
Measurements of psi(2S) decays to octet baryon-antibaryon pairs
With a sample of 14 million psi(2S) events collected by the BESII detector at
the Beijing Electron Positron Collider (BEPC), the decay channels psi(2S)->p
p-bar, Lambda Lambda-bar, Sigma0 Sigma0-bar, Xi Xi-bar are measured, and their
branching ratios are determined to be (3.36+-0.09+-0.24)*10E-4,
(3.39+-0.20+-0.32)*10E-4, (2.35+-0.36+-0.32)*10E-4, (3.03+-0.40+-0.32)*10E-4,
respectively. In the decay psi(2S)->p p-bar, the angular distribution parameter
alpha is determined to be 0.82+-0.17+-0.04.Comment: 8 pages, 8 figure
Study of five quark system with three kinds of quark-quark hyperfine interaction
The low-lying energy spectra of five quark systems (I=1/2, S=0)
and (I=0, S=-1) are investigated with three kinds of schematic
interactions: the chromomagnetic interaction, the flavor-spin dependent
interaction and the instanton-induced interaction. In all the three models, the
lowest five quark state ( or ) has an orbital angular
momentum L=0 and the spin-parity ; the mass of the lowest
state is heavier than the lowest state
Evidence for the Onset of Color Transparency in Electroproduction off Nuclei
We have measured the nuclear transparency of the incoherent diffractive
process in C and Fe targets relative to H
using a 5 GeV electron beam. The nuclear transparency, the ratio of the
produced 's on a nucleus relative to deuterium, which is sensitive to
interaction, was studied as function of the coherence length (),
a lifetime of the hadronic fluctuation of the virtual photon, and the
four-momentum transfer squared (). While the transparency for both
C and Fe showed no dependence, a significant
dependence was measured, which is consistent with calculations that included
the color transparency effects.Comment: 6 pages and 4 figure
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