477 research outputs found
Photoproduction of the doubly-strange Xi Hyperons
We report on the first measurement of exclusive Xi- and Xi0 photoproduction.
The Xi- states are produced in the reaction gamma p --> K+ K+ Xi-, and the Xi0
states in gamma p --> K+ K+ pi- Xi0. Identification is made by the unique mass
measured as the missing mass of the K+ K+ (or K+ K+ pi-) system using the CLAS
detector at the Thomas Jefferson National Accelerator Facility. A systematic
study of the excited Xi spectrum improves our understanding of the N* and
Delta* states, since the Xi* states are related to them by SU(3) flavor
symmetry. At the highest energies available at Jefferson Lab, we begin to find
evidence for known excited Xi- states in the photoproduction process, and
possibly new states at 1770 and 1860 MeV, although we do not have enough
statistics to draw a strong conclusion. A search for the Xi5--(1862) pentaquark
state seen by NA49 is made using the process gamma p -> K+ K+ pi+ X, but the
result is inconclusive for lack of statistics.Comment: 7 pages, 9 figures; invited talk given at the 8th International
Conference on Hypernuclear and Strange Particle Physics, Jefferson Lab,
Newport News, VA, 14-18 October 200
Parity Doubling in the Meson Spectrum
A simple argument for the restoration of parity symmetry high in the hadron
spectrum is presented. The restoration scale is estimated to be 2.5 GeV. This
in turn implies that typical quark model phenomenology such as scalar
confinement or the decay model are only useful for low lying states.
Minimal requirements for constructing more general phenomenologies are
discussed. An additional mass degeneracy between and states
is shown to occur and an isovector state is predicted at roughly 1700
MeV, in contradiction with the naive quark model. Similarly, isovector and
isoscalar states are predicted at 2000 MeV. Finally, these results
imply that Regge trajectories must become nonlinear at high spin.Comment: 5 pages, revtex, no figures, no tables. Version to appear in PL
PMU31 early cost-effectiveness analysis of continuous monitoring of lung-aeration with electrical impedance tomography in preterm neonates with respiratory distress syndrome
Objectives
Respiratory distress syndrome (RDS) is relatively common in preterm neonates due to lung immaturity. Clinical management by respiratory support is associated with high complications rates. Guidance on appropriate lung-aeration is limited using conventional thorax X-ray monitoring. Electrical impedance tomography (EIT) allows radiation-free, continuous lung-aeration monitoring to guide effective respiratory support. EIT produces dynamic images of air volume changes whereas X-ray shows 2-D structure. Clinicians expect EIT implementation to reduce the number of patients requiring mechanical ventilation, overall complication rates and hospitalisation length. We conducted an early cost-effectiveness analysis of EIT-monitoring in preterm neonates with RDS versus standard care in the Netherlands.
Methods
A decision-analytic model was constructed comparing costs and effects of conventional X-ray versus EIT-monitoring for preterm neonates with RDS from the healthcare perspective with a time horizon of two years. Input parameters were based on literature and cost databases. The effects of EIT-monitoring were based on consensus by 6 clinical experts for two scenarios, (1) a conservative scenario assuming only a decrease of patients on mechanical ventilation under EIT-monitoring, and (2) an optimistic scenario including scenario (1) and assuming an additional 10% relative complication rate decrease in comparison to standard care. Main outcomes were total average costs per patient, number of patients with bronchopulmonary dysplasia (BPD), and mortality. One-way sensitivity analyses were conducted.
Results
EIT-monitoring was estimated to be cost-saving in both scenarios, mainly due to a shorter average hospital length of stay. Total incremental costs per patient for EIT-monitored care versus standard care were -€929 and -€10,706 for scenario (1) and (2), respectively. The number of patients with BPD and deaths were reduced. Results were robust to changes in input parameters.
Conclusions
EIT lung-aeration monitoring in preterm neonates is expected to result in cost-savings and lower mortality and BPD rates, in comparison to standard care, in a Dutch hospital setting.
Copyright © 2019 Published by Elsevier Inc
Ratios of Elastic Scattering of Pions from 3H and 3He
We have measured the elastic-scattering ratios of normalized yields for
charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we
completed the angular distribution begun with our earlier measurements, adding
six data points in the angular range of 119 deg to 169 deg in the pi-nucleus
center of mass. We also measured an excitation function with data points at
142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle
for each energy between 160 deg and 170 deg in the pi-nucleus center of mass.
This excitation function corresponds to the energies of our forward-hemisphere
studies. The data, taken as a whole, show an apparent role reversal of the two
charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data >
100 deg we observe a strong dependence on the four-momentum transfer squared
(-t) for all of the ratios regardless of pion energy or scattering angle, and
we find that the superratio R data match very well with calculations based on
the forward-hemisphere data that predicts the value of the difference between
the even-nucleon radii of 3H and 3He. Comparisons are also made with recent
calculations incorporating different wave functions and double scattering
models.Comment: RevTex 8pages, 12 figure file
UCLA Intermediate Energy Nuclear and Particle Physics Research: Final Report
This project covers the following research: (a) Investigations into the structure of the proton and neutron. This is done by investigating the different resonance states of nucleons with beams of tagged, polarized photons, linearly as well as circularly, incident on polarized hydrogen/deuterium targets and measuring the production of {pi}{sup #25;0}, 2{pi}{sup #25;}0, 3{pi}{sup #25;0}, {eta}#17;, {eta}', {omega}, etc. The principal detector is the Crystal Ball multiphoton spectrometer which has an acceptance of nearly 4#25;. It has been moved to the MAMI accelerator facility of the University of Mainz, Germany. We investigate the conversion of electromagnetic energy into mesonic matter and conversely. (b) We investigate the consequences of applying the "standard" symmetries of isospin, GâÂÂparity, charge conjugation, C, P, T, and chirality using rare and forbidden decays of light mesons such as the {eta}#17;,{eta}' and {omega}. We also investigate the consequences of these symmetries being slightly broken symmetries. We do this by studying selected meson decays using the Crystal Ball detector. (c) We determine the mass, or more precisely the mass difference of the three light quarks (which are inputs to Quantum Chromodynamics) by measuring the decay rate of specially selected {eta}#17; and {eta}' decay modes, again we use the Crystal Ball. (d)We have started a new program to search for the 33 missing cascade baryons using the CLAS detector at the Thomas Jefferson Laboratory. Cascade resonances are very special: they have double strangeness and are quite narrow. This implies that they can be discovered by the missing mass technique in photoproduction reactions such as in {gamma}p{yields}{Xi}{sup #4;âÂÂ}K{sup +}K{sup +}. The cascade program is of particular importance for the upgrade to 12 GeV of the CLAS detector and for design of the Hall D at JLab. (e) Finally, we are getting more involved in a new program to measure the hadronic matter form factor of complex nuclei, in particular the "neutron skin" of {sup 208}Pb, which is of great interest to astroparticle physics for determining the properties of neutron stars. Processes of study are coherent and nonâÂÂcoherent #25;0 photoproduction. The Crystal Ball is uniquely suited for these studies because of the large acceptance, good direction and energy resolution and it is an inclusive detector for the #25;{pi}{sup 0} final state and exclusive for background such as 2#25;{pi}{sup 0}
Magnetic Moments of the Baryon Decuplet in a Relativistic Quark Model
The magnetic moments of the baryon decuplet are calculated in a relativistic
constituent quark model using the light-front formalism. Of particular interest
are the magnetic moments of the and for which new
recent experimental measurements are available. Our calculation for the
magnetic moment ratio is in excellent agreement with
the experimental ratio, while our ratio is
slightly higher than the experimental ratio.Comment: 10 pages ReVTeX, SLAC-PUB-621
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