CONSIDERATIONS ON ODR BEAM-SIZE MONITORING FOR GAMMA = 1000 BEAMS*

Abstract We discuss the feasibility of monitoring the beam size of γ=1000 beams with 3000 times more charge in a video frame time and with a more sensitive 12-to 16-bit camera than were used in the previous electron beam studies at 7 GeV at the Advanced Photon Source. Such a beam would be generated at Fermilab in a new facility in the coming years. Numerical integrations of our base model show beam size sensitivity for ± 20% level changes at 200-and 400-µm base beam sizes. We also evaluated impact parameters of 5 σ y and 12 σ y for both 800-nm and 10-µm observation wavelengths. The latter examples are related to a proposal to apply the technique to an ~ 0.98 TeV proton beam, and this study shows there are trades on photon intensity and beam size sensitivity to be considered at such gammas. In addition, we report on first results at γ=1800 on a superconducting rf linac

An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t_E ~ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462, in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry shows a parallactic signature of the effect of the Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 +/- 1.3 M_Sun and a distance of 1.58 +/- 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic-disk stars at similar distances by an amount corresponding to a transverse space velocity of ~45 km/s, suggesting that the BH received a modest natal 'kick' from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial-velocity measurements of Galactic X-ray binaries, and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first ever for an isolated stellar-mass BH using any technique