806 research outputs found
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
Post-Cartel Tacit Collusion: Determinants, Consequences, and Prevention
We experimentally investigate the determinants of post-cartel tacit collusion (PCTC), the effects of PCTC on market outcomes, and potential policy measures aimed at its prevention. PCTC occurs robustly with or without fines or leniency and is determined both by collusive price hysteresis and learning about cartel partners’ characteristics and strategies. As a result, it is also strongly related to the preceding cartel success. PCTC generates a downward bias in the estimated cartel overcharges. This threatens the effectiveness of deterrence induced by private damage litigation and fines imposed on colluding firms based on the overcharge. This bias further increases with preceding cartel stability such that especially more stable sets of colluding firms may be deterred less when PCTC is present. Rematching colluding subjects with strangers within a session prevents PCTC. This indicates that barring colluding managers from their posts could help impede PCTC in the field
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
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
On the cross section ratio sigma_n/sigma_p in eta photoproduction
The recently discovered enhancement of eta photoproduction on the quasi-free
neutron at energies around sqrt(s)~1.67 GeV is addressed within a SU(3) coupled
channel model. The quasi-free cross sections on proton and neutron, sigma_n and
sigma_p, can be quantitatively explained. In this study, the main source for
the peak in sigma_n/sigma_p is a coupled channel effect in S-wave that explains
the dip-bump structure in gamma n --> eta n. In particular, the photon coupling
to the intermediate meson-baryon states is important. The stability of the
result is extensively tested and consistency with several pion- and
photon-induced reactions is ensured.Comment: Version accepted by Phys. Lett.
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
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
Radiative open charm decay of the Y(3940), Z(3930), X(4160) resonances
We determine the radiative decay amplitudes for decay into and , or and of some of the charmonium like
states classified as X,Y,Z resonances, plus some other hidden charm states
which are dynamically generated from the interaction of vector mesons with
charm. The mass distributions as a function of the or
invariant mass show a peculiar behavior as a consequence of
the nature of these states. The experimental search of these
magnitudes can shed light on the nature of these states.Comment: 18 pages, 9 figure
Exploration of hyperfine interaction between constituent quarks via eta productions
In this work, the different exchange freedom, one gluon, one pion or
Goldstone boson, in constituent quark model is investigated, which is
responsible to the hyperfine interaction between constituent quarks, via the
combined analysis of the eta production processes,
and . With the Goldstone-boson exchange, as well as
the one-gluon or one-pion exchange, both the spectrum and observables, such as,
the differential cross section and polarized beam asymmetry, are fitted to the
suggested values of Particle Data Group and the experimental data. The first
two types of exchange freedoms give acceptable description of the spectrum and
observables while the one pion exchange can not describe the observables and
spectrum simultaneously, so can be excluded. The experimental data for the two
processes considered here strongly support the mixing angles for two lowest S11
sates and D13 states as about -30 and 6 degree respectively.Comment: 7 pages, 4 figures, 4 table
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