3,493 research outputs found
The Strangeness Physics Program at CLAS
An extensive program of strange particle production off the proton is
currently underway with the CEBAF Large Acceptance Spectrometer (CLAS) in Hall
B at Jefferson Laboratory. This talk will emphasize strangeness photo- and
electroproduction in the baryon resonance region between W =1.6 and 2.5 GeV,
where indications of s-channel structure are suggestive of high-mass baryon
resonances coupling to kaons and hyperons in the final state. Precision
measurements of cross sections and polarization observables are being carried
out with both electron and real photon beams, both of which are available with
high polarization at energies up to 6 GeV.Comment: 10 pages, 6 figures, N*2005 Conferenc
Experimental Evidence for the Pentaquark
The present experimental evidence for the existence of light pentaquarks is
reviewed, including both positive and null results. I also discuss the CLAS
experiments at Jefferson Laboratory that are forthcoming in the near future to
address questions regarding existence, mass, width, and other quantum numbers
of these five-quark baryon states.Comment: 6 pages, 5 figures, Electron-Nucleus Scattering VIII conferenc
Experimental L-band SST satellite communications/surveillance terminal study. Volume 4 - Aircraft antenna studies
Antenna requirements for supersonic transport satellite communications syste
Predictions of the emergence of vaccine-resistant hepatitis B in The Gambia using a mathematical model
Vaccine escape variants of hepatitis B virus (HBV) have been identified world-wide. A mathematical model of HBV transmission is used to investigate the potential pattern of emergence of such variants. Attention is focused on The Gambia as a country with high quality epidemiological data, universal infant immunization and in which escape mutants after childhood infections have been observed. We predict that a variant cannot become dominant for at least 20 years from the start of vaccination, even when using a vaccine which affords no cross protection. The dominant factor responsible for this long time scale is the low rate of infectious contacts between infected and susceptible individuals (we estimate the basic reproduction number of hepatitis B in The Gambia to be 1·7). A variant strain that achieves high prevalence will also take many years to control, and it is questionable whether emergence will be identifiable by sero-surveillance until of high prevalence. The sensitivity of the model predictions to epidemiological and demographic factors is explored
Predictions of the emergence of vaccine-resistant hepatitis B in The Gambia using a mathematical model
Vaccine escape variants of hepatitis B virus (HBV) have been identified world-wide. A mathematical model of HBV transmission is used to investigate the potential pattern of emergence of such variants. Attention is focused on The Gambia as a country with high quality epidemiological data, universal infant immunization and in which escape mutants after childhood infections have been observed. We predict that a variant cannot become dominant for at least 20 years from the start of vaccination, even when using a vaccine which affords no cross protection. The dominant factor responsible for this long time scale is the low rate of infectious contacts between infected and susceptible individuals (we estimate the basic reproduction number of hepatitis B in The Gambia to be 1·7). A variant strain that achieves high prevalence will also take many years to control, and it is questionable whether emergence will be identifiable by sero-surveillance until of high prevalence. The sensitivity of the model predictions to epidemiological and demographic factors is explored
SOME EMPIRICAL METHODS OF ESTIMATING ADVERTISING EFFECTS IN DEMAND SYSTEMS: AN APPLICATION TO DRIED FRUITS
Two different methods of incorporating advertising effects into Almost Ideal Demand Systems (AIDS) are presented. Both advertising schemes are designed to allow theoretical restrictions to hold globally rather than at particular sample points. The models are estimated for California figs, prunes, and raisins. Empirical results indicate that generic advertising effects for these three dried fruits are generally weak when compared to price and total expenditure effects. Estimated cross-commodity effects also are relatively small except for the negative effect of raisin advertising on the quantity of prunes demanded.Demand and Price Analysis, Marketing,
GlueX: The Search for Gluonic Excitations at Jefferson Laboratory
One of the unanswered and most fundamental questions in physics regards the
nature of the confinement mechanism of quarks and gluons in quantum
chromodynamics (QCD). Exotic hybrid mesons manifest gluonic degrees of freedom
and their detailed spectroscopy will provide the precision data necessary to
test assumptions in lattice QCD and the specific phenomenology leading to
confinement. Photoproduction is expected to be a particularly effective manner
to produce exotic hybrids, however, existing data using photon beams are
sparse. At Jefferson Laboratory, plans are underway by the GlueX Collaboration
to use the coherent bremsstrahlung technique to produce a linearly polarized
photon beam. A solenoid-based hermetic detector will be used to collect data on
meson production and decays with statistics that will exceed existing
photoproduction data by several orders of magnitude after the first year of
running. In order to reach the ideal photon energy of 9 GeV required for these
studies, the energy of the Jefferson Laboratory electron accelerator, CEBAF,
will be doubled from its current maximum energy of 6 GeV to 12 GeV. The physics
motivating the search and the status of the project are reviewed.Comment: 10 pages, 4 figures, HADRON05 Conferenc
Experimental Status of Exotic Mesons and the GlueX Experiment
One of the unanswered and most fundamental questions in physics regards the
nature of the confinement mechanism of quarks and gluons in QCD. Exotic hybrid
mesons manifest gluonic degrees of freedom and their spectroscopy will provide
the data necessary to test assumptions in lattice QCD and the specific
phenomenology leading to confinement. Within the past two decades a number of
experiments have put forth tantalizing evidence for the existence of exotic
hybrid mesons in the mass range below 2 GeV. This talk represents an overview
of the available data and what has been learned. In looking toward the future,
the GlueX experiment at Jefferson Laboratory represents a new initiative that
will perform detailed spectroscopy of the light-quark meson spectrum. This
experiment and its capabilities will be reviewed.Comment: 10 pages, 8 figures, 2nd Meeting of the APS Topical Group on Hadron
Physics GHP06, Nashville, TN (10/22-10/24/06
Beam-recoil polarization transfer in the nucleon resonance region in the exclusive e→p→e′K+Λ→ and e→p→e′K+Σ→0 reactions at the CLAS spectrometer
Beam-recoil transferred polarizations for the exclusive e→p→e′K+Λ→,Σ→0 reactions have been measured using the Continuous Electron Beam Accelerator Facility\u27s large acceptance spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. New measurements have been completed at beam energies of 4.261 and 5.754 GeV that span a range of momentum transfer Q2 from 0.7 to 5.4 GeV2, invariant energy W from 1.6 to 2.6 GeV, and the full center-of-mass angular range of the K+ meson. These new data add to the existing CLAS K+Λ measurements at 2.567 GeV, and provide the first-ever data for the K+Σ0 channel in electroproduction. Comparisons of the data with several theoretical models are used to study the sensitivity to s-channel resonance contributions and the underlying reaction mechanism. Interpretations within two semiclassical partonic models are made to probe the underlying reaction mechanism and the ss¯ quark-pair creation dynamics
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