2,394 research outputs found
Nature of the f_0(600) from its N_c dependence at two loops in unitarized Chiral Perturbation Theory
By using unitarized two-loop Chiral Perturbation Theory partial waves to
describe pion-pion scattering we find that the dominant component of the
lightest scalar meson does not follow the q-qbar dependence on the number of
colors that, in contrast, is obeyed by the lightest vectors. The method
suggests that a subdominant q-qbar component of the f_0(600) possibly
originates around 1 GeV.Comment: 4 pages, 1 Figure. To appear in Phys. Rev. Let
How Resonances can synchronise with Thresholds
The mechanism by which a threshold may capture a resonance is examined. It
involves a threshold cusp interfering constructively with either or both (i) a
resonance produced via confinement, (ii) attractive t- and u-channel exchanges.
The fo(980), X(3872) and Z(4430) are studied in detail. The fo(980) provides a
valuable model of the locking mechanism. The X(3872) is too narrow to be fitted
by a cusp, and requires either a resonance or virtual state. The Z(4430) can be
fitted as a resonance but also can be fitted successfully by a cusp with no
nearby resonant pole.Comment: 19 pages, 6 figures. Replaces 0709.125
A Uniform Description of the States Recently Observed at B-factories
The newly found states Y(4260), Y(4361), Y(4664) and Z(4430) stir broad
interest in the study of spectroscopy in a typical charmonium scale. The
Y(4260) which was observed earlier has been interpreted as hybrid, molecular
state, and baryonium, etc. In this note we show for the first time that these
new structures, which are hard to be interpreted as charmonium states, can be
systematically embedded into an extended baryonium picture. According to this
assignment, the so far known characters of these states are understandable.
And, in the same framework, we make some predictions for experimenters to
measure in the future.Comment: 6 pages in Latex. to appear in J.Phys.
The Goldberger-Treiman Discrepancy
The Golberger- Treiman discrepancy is related to the asymptotic behaviour of
the pionic form factor of the nucleon obtained from baryonic QCD sum rules. The
result is .015<=Delta_{GT}<=.022Comment: References updated and minor correction
Three channel model of meson-meson scattering and scalar meson spectroscopy
New solutions on the scalar -- isoscalar phase shifts are analysed
together with previous results using a separable potential model of
three coupled channels (, and an effective
system). Model parameters are fitted to two sets of solutions obtained in a
recent analysis of the CERN-Cracow-Munich measurements of the reaction on a polarized target. A relatively
narrow (90 -- 180 MeV) scalar resonance is found, in contrast
to a much broader ( MeV) state emerging from the analysis
of previous unpolarized target data.Comment: 10 Latex pages + 6 postscript figure
The preliminary lattice QCD calculation of meson decay width
We present a direct lattice QCD calculation of the meson decay width
with the s-wave scattering phase shift for the isospin pion-kaon () system. We employ a special finite size formula, which is the extension of
the Rummukainen-Gottlieb formula for the system in the moving frame, to
calculate the scattering phase, which indicates a resonance around
meson mass. Through the effective range formula, we extract the effective
coupling constant GeV and
decay width MeV. Our simulations are done with the MILC
gauge configurations with flavors of the "Asqtad" improved staggered
dynamical sea quarks on a lattice at and lattice spacing fm.Comment: To make it concise. arXiv admin note: text overlap with
arXiv:1110.1422, but much of v1 text overlap with articles by same and other
authors remove
Analysis of NN Amplitudes up to 2.5 GeV: An Optical Model and Geometric Interpretation
We analyse the SM97 partial wave amplitudes for nucleon--nucleon (NN)
scattering to 2.5 GeV, in which resonance and meson production effects are
evident for energies above pion production threshold. Our analyses are based
upon boson exchange or quantum inversion potentials with which the
sub-threshold data are fit perfectly. Above 300 MeV they are extrapolations, to
which complex short ranged Gaussian potentials are added in the spirit of the
optical models of nuclear physics and of diffraction models of high energy
physics. The data to 2.5 GeV are all well fit. The energy dependences of these
Gaussians are very smooth save for precise effects caused by the known
and N resonances. With this approach, we confirm that the geometrical
implications of the profile function found from diffraction scattering are
pertinent in the regime 300 MeV to 2.5 GeV and that the overwhelming part of
meson production comes from the QCD sector of the nucleons when they have a
separation of their centres of 1 to 1.2 fm. This analysis shows that the
elastic NN scattering data above 300 MeV can be understood with a local
potential operator as well as has the data below 300 MeV.Comment: 49 pages, including 23 figures, LaTeX2e/RevTeX/ps fil
Precision Pion-Proton Elastic Differential Cross Sections at Energies Spanning the Delta Resonance
A precision measurement of absolute pi+p and pi-p elastic differential cross
sections at incident pion laboratory kinetic energies from T_pi= 141.15 to
267.3 MeV is described. Data were obtained detecting the scattered pion and
recoil proton in coincidence at 12 laboratory pion angles from 55 to 155
degrees for pi+p, and six angles from 60 to 155 degrees for pi-p. Single arm
measurements were also obtained for pi+p energies up to 218.1 MeV, with the
scattered pi+ detected at six angles from 20 to 70 degrees. A flat-walled,
super-cooled liquid hydrogen target as well as solid CH2 targets were used. The
data are characterized by small uncertainties, ~1-2% statistical and ~1-1.5%
normalization. The reliability of the cross section results was ensured by
carrying out the measurements under a variety of experimental conditions to
identify and quantify the sources of instrumental uncertainty. Our lowest and
highest energy data are consistent with overlapping results from TRIUMF and
LAMPF. In general, the Virginia Polytechnic Institute SM95 partial wave
analysis solution describes our data well, but the older Karlsruhe-Helsinki PWA
solution KH80 does not.Comment: 39 pages, 22 figures (some with quality reduced to satisfy ArXiv
requirements. Contact M.M. Pavan for originals). Submitted to Physical Review
Meson-Baryon Form Factors in Chiral Colour Dielectric Model
The renormalised form factors for pseudoscalar meson-baryon coupling are
computed in chiral colour dielectric model. This has been done by rearranging
the Lippmann-Schwinger series for the meson baryon scattering matrix so that it
can be expressed as a baryon pole term with renormalized form factors and
baryon masses and the rest of the terms which arise from the crossed diagrams.
Thus we are able to obtain an integral equation for the renormalized
meson-baryon form factors in terms of the bare form factors as well as an
expression for the meson self energy. This integral equation is solved and
renormalized meson baryon form factors and renormalized baryon masses are
computed. The parameters of the model are adjusted to obtain a best fit to the
physical baryon masses. The calculations show that the renormalized form
factors are energy-dependent and differ from the bare form factors primarily at
momentum transfers smaller than 1 GeV. At nucleon mass, the change in the form
factors is about 10% at zero momentum transfer. The computed form factors are
soft with the equivalent monopole cut-off mass of about 500 MeV. The
renormalized coupling constants are obtained by comparing the chiral colour
dielectric model interaction Hamiltonian with the standard form of
meson-nucleon interaction Hamiltonian. The ratio of and
coupling constants is found to be about 2.15. This value is very close to the
experimental value.Comment: 16 pages, 7 postscript figure
Spin observables of the reactions NN -> DeltaN and pd -> Delta (pp)(1S0) in collinear kinematics
A general formalism for double and triple spin-correlations of the reaction
NN -> DeltaN is developed for the case of collinear kinematics. A complete
polarization experiment allowing to reconstruct all of the four amplitudes
describing this process is suggested. Furthermore, the spin observables of the
inelastic charge-exchange reaction pd -> Delta^0(pp)(1S0) are analyzed in
collinear kinematics within the single pN scattering mechanism involving the
subprocess pn -> Delta^0p. The full set of spin observables related to the
polarization of one or two initial particles and one final particle is obtained
in terms of three invariant amplitudes of the reaction pd -> Delta (pp)(1S0)
and the transition form factor d->(pp)(1S0). A complete polarization experiment
for the reaction pd -> Delta^0(pp)(1S0) is suggested which allows one to
determine three independent combinations of the four amplitudes of the
elementary subprocess NN -> DeltaN.Comment: 12 pages, 1 figur
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