808 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
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
Charmed mesons in nuclear matter
We obtain the properties of charmed mesons in dense matter using a
coupled-channel approach which accounts for Pauli blocking effects and meson
self-energies in a self-consistent manner. We study the behaviour of
dynamically-generated baryonic resonances together with the open-charm meson
spectral functions in this dense nuclear environment. We discuss the
implications of the in-medium properties of open-charm mesons on the
and the predicted X(3700) scalar resonances, and on the
formation of -mesic nuclei.Comment: 5 pages, 5 figures, 1 table, to appear in Proceedings of XIII
International Conference on Hadron Spectroscopy, November 29 - December 4,
2009, Florida State Universit
Systematic Study of Two-Pion Production in NN Collisions -- from Single-Baryon to Di-Baryon Excitations
The two-pion production in nucleon-nucleon collisions has been studied by
exclusive and kinematically complete experiments from threshold up to =
1.36 GeV at CELSIUS-WASA. At near-threshold energies the total and differential
distributions for the and channels are dominated by
Roper excitation and its decay into and channels. At beam
energies 1.1 GeV the excitation governs the two-pion
production process. In the channel evidence is found for the
excitation of a higher-lying I=3/2 resonance, favorably the . The
isovector fusion processes leading to the deuteron and to quasi-stable He,
respectively, %with the production of an isovector pion-pair exhibit no or only
a modest ABC-effect, {\it i.e.} low-mass enhancement in the -invariant
mass spectrum, and can be described by conventional -channel
excitation. On the other hand, the isoscalar fusion process to the deuteron
%with the production of an isoscalar pion-pair exhibits a dramatic ABC-effect
correlated with a narrow resonance-like energy dependence in the total cross
section with a width of only 50 MeV and situated at a mass 90 MeV below the
mass.Comment: Proceedings HADRON0
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
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
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
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
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
Photoproduction of eta-mesons on the deuteron above S11(1535) in the presence of a narrow P11(1670) resonance
Incoherent photoproduction of eta-mesons on the deuteron is considered. The
main attention is paid to the region above the S11(1535) resonance where rather
narrow resonance like structure in the total cross section extracted for gamma
n -> eta n has been reported. The corresponding experimental results are
analyzed from the phenomenological standpoint within the model containing a
baryon P11 with the mass about 1670 MeV and a width less than 30 MeV. This
resonance was suggested in some recent works as a nonstrange member of the
pentaquark antidecuplet with J^P=1/2^+. The calculation is also performed for
the polarized and nonpolarized angular distributions of mesons. In
addition, we present our predictions for the cross sections of the neutral
kaons and double pion photoproduction, where the same narrow P11(1670)
resonance is assumed to contribute through the decay into K^0 Lambda and pi
Delta configuration.Comment: 11 pages, 5 figure
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