2 research outputs found
The Hubble Constant from (CLASS) Gravitational Lenses
One of the main objectives of the Cosmic Lens All-Sky Survey (CLASS)
collaboration has been to find gravitational lens (GL) systems at radio
wavelengths that are suitable for the determination of time delays between
image pairs. The survey is now near completion and at least 18 GL systems have
been found. Here, I will discuss our efforts to measure time delays from
several of these systems with the ultimate aim of constraining the Hubble
Constant (H0). Thus far three CLASS GL systems (i.e. B0218+357, B1600+434 and
B1608+656) have yielded measurements of time delays, from which values of
H0=60-70 km/s/Mpc have been estimated. Although most GL systems give similar
values of H0, statistical and systematic uncertainties are still considerable.
To reduce these uncertainties, I will shortly mention two monitoring programs
that we are undertaking to (re)measure time delays in 15 CLASS GL systems and
address several important issues for the near future.Comment: 4 pages, no figures; based on a talk given at the "The OzLenz
Workshop" in Melbourne (Au), 2000 dec. 4-6; to appear in PAS
Beam-Target Helicity Asymmetry E in K 0 Λ and K 0 Σ 0 Photoproduction on the Neutron
We report the first measurements of the E beam-target helicity asymmetry for the →γ→n→K0Λ and K0Σ0 channels in the energy range 1.70 ≤ W ≤ 2.34 GeV. The CLAS system at Jefferson Lab uses a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride with low background contamination for the measurements. The multivariate analysis method boosted decision trees is used to isolate the reactions of interest. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the isospin I=0 and I=1 photocoupling transition amplitudes in pseudoscalar meson photoproduction