746 research outputs found
The Experimental Status of Glueballs
Glueballs and other resonances with large gluonic components are predicted as
bound states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is
estimated to have a mass in the range from 1 to 2 GeV/c**2; a pseudoscalar and
tensor glueball are expected at higher masses. Many different experiments
exploiting a large variety of production mechanisms have presented results in
recent years on light mesons with J(PC) = 0(++), 0(-+), and 2(++) quantum
numbers. This review looks at the experimental status of glueballs. Good
evidence exists for a scalar glueball which is mixed with nearby mesons, but a
full understanding is still missing. Evidence for tensor and pseudoscalar
glueballs are weak at best. Theoretical expectations of phenomenological models
and QCD on the lattice are briefly discussed.Comment: 62 pages, 26 figure
CLAS+FROST: new generation of photoproduction experiments at Jefferson Lab
A large part of the experimental program in Hall B of the Jefferson Lab is
dedicated to baryon spectroscopy. Photoproduction experiments are essential
part of this program. CEBAF Large Acceptance Spectrometer (CLAS) and
availability of circularly and linearly polarized tagged photon beams provide
unique conditions for this type of experiments. Recent addition of the Frozen
Spin Target (FROST) gives a remarkable opportunity to measure double and triple
polarization observables for different pseudo-scalar meson photoproduction
processes. For the first time, a complete or nearly complete experiment becomes
possible and will allow model independent extraction of the reaction amplitude.
An overview of the experiment and its current status is presented.Comment: 6 pages, 7 figures. Invited paper NSTAR 2009 conferenc
decays to from new data on
Data on the reaction with ,
taken with unpolarized or polarized beams in combination with an unpolarized or
polarized proton-target, were analyzed within the Bonn-Gatchina (BnGa) partial
wave analysis. Differential cross sections, several spin density matrix
elements, the beam asymmetry , the normalized helicity difference ,
and the correlation between linear photon and longitudinal target
polarization were included in a large data base on pion and photo-induced
reactions. The data on photoproduction are used to determine twelve
branching ratios; most of these are determined for the first
time.Comment: 6 pages, 4 figures, 2 table
Photoproduction of Baryons Decaying into N pi and N eta
A combined analysis of photoproduction data on \gamma p to \pi N, eta N was
performed including the data on K Lambda and K Sigma. The data are interpreted
in an isobar model with s--channel baryon resonances and pi, rho,(omega), K,
and K^* exchange in the t--channel. Three baryon resonances have a substantial
coupling to eta N, the well known N(1535)S_{11}, N(1720)P_{13}, and
N(2070)D_{15}. The inclusion of data with open strangeness reveals the presence
of further new resonances, N(1840)P_{11}, N(1875)D_{13} and N(2170)D_{13}.Comment: 13 pages, 14 figure
Measurement of the Beam Asymmetry Sigma and the Target Asymmetry T in the Photoproduction of Omega Mesons off the Proton Using CLAS at Jefferson Laboratory
The photoproduction of omega mesons off the proton has been studied in the reaction γp -\u3e pω using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry T has been measured in photoproduction from the decay ω -\u3e π+π-π0, using a transversely polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant nonzero values are observed for these asymmetries, reaching about 30-40% in the third-resonance region. New measurements for the photon-beam asymmetry Σ are also presented, which agree well with previous CLAS results and extend the world database up to 2.1 GeV. These data and additional ω photoproduction observables from CLAS were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from s-channel resonance production were found in addition to t-channel exchange processes
Baryon resonances and polarization transfer in hyperon photoproduction
A partial wave analysis is presented of data on photoproduction of hyperons
including single and double polarization observables. The large spin transfer
probability reported by the CLAS collaboration can be successfully described
with an isobar partial wave analysis.Comment: 12 pages, 9 figure
Selected topics on Hadrons in Nuclei
In this talk we report on selected topics on hadrons in nuclei. The first
topic is the renormalization of the width of the in a nuclear
medium. This is followed by a short update of the situation of the in
the medium. The investigation of the properties of in the nuclear
medium from the study of the reaction is also addressed, as
well as properties of X,Y,Z charmed and hidden charm resonances in a nuclear
medium. Finally we address the novel issue of multimeson states.Comment: Talk at the International Nuclear Physics Conference, Vancouver, July
201
Partial decay widths of baryons in the spin-momentum operator expansion method
The cross sections for photo- and pion-induced production of baryon
resonances and their partial decay widths to the two--body and multi--body
final states are calculated in the framework of the operator expansion method.
The approach is fully relativistic invariant, and it allows us to perform
combined analyses of different reactions imposing directly the analyticity and
unitarity constraints. All formulae are given explicitly in the form used by
the Crystal Barrel collaboration in the partial wave analysis.Comment: 15 pages, 6 figure
Note on the definitions of branching ratios of overlapping resonances
Branching ratios for the decay of hadrons with large width or near thresholds
depend on their definition. We test different definitions and show that rather
different branching ratios can be obtained. For wide resonances and for
sequential decays with wide intermediate resonances, integration over the
spectral functions is mandatory. The tests are performed exploiting the latest
solution of the Bonn-Gatchina multi-channel analysis and published values for
residues of light scalar mesons. For a resonance overlapping with a threshold,
in case its pole lies in a non-adjacent sheet, we show how the total width,
needed for the branching ratios, does not correspond to the imaginary part of
the pole position. We use the Madrid-Krakow dispersive parameterizations to
illustrate this situation with the .Comment: Report, 9 pages (extended to light scalar mesons
Primakoff effect in eta-photoproduction off protons
We analyse data on forward eta-meson photoproduction off a proton target and
extract the eta to gamma gamma decay width utilizing the Primakoff effect. The
hadronic amplitude that enters into our analysis is strongly constrained
because it is fixed from a global fit to available gamma p to p eta data for
differential cross sections and polarizations. We compare our results with
present information on the two-photon eta-decay from the literature. We provide
predictions for future PrimEx experiments at Jefferson Laboratory in order to
motivate further studies.Comment: 5 pages, 6 figures, gamma-gamma*-eta form factor included, version to
appear in Eur. Phys. J. A
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