Rubin-LSST

Abstract:

We report an observation of the decay Bs0→Ds-π+ in pp̄ collisions at s=1.96TeV using 115pb-1 of data collected by the CDF II detector at the Fermilab Tevatron. We observe 83±11(stat) Bs0→Ds-π+ candidates, representing a large increase in statistics over previous measurements and the first observation of this decay at a pp̄ collider. We present the first measurement of the relative branching fraction B(Bs0→Ds-π+)/B(B0→D-π+)=1.32±0.18(stat)±0.38(syst) . We also measure B(B+→D̄0π+)/B(B0→D-π+)=1.97±0. 10(stat)±0.21(syst), which is consistent with previous measurements. © 2006 The American Physical Society.

Abstract:

We present a measurement of the tt̄ production cross section in pp̄ collisions at s=1.96TeV which uses events with an inclusive signature of significant missing transverse energy and jets. This is the first measurement which makes no explicit lepton identification requirements, so that sensitivity to W→τν decays is maintained. Heavy flavor jets from top quark decay are identified with a secondary vertex tagging algorithm. From 311pb-1 of data collected by the Collider Detector at Fermilab, we measure a production cross section of 5.8±1.2(stat)-0.7+0.9(syst)pb for a top quark mass of 178GeV/c2, in agreement with previous determinations and standard model predictions. © 2006 The American Physical Society.

Abstract:

The Faulkes Telescope Project is the educational arm of the Las Cumbres Observatory Global Telescope Network (LCOGT). It currently has two 2-metre robotic telescopes, located at Haleakala on Maui (FT North) and Siding Spring in Australia (FT South). It is planned to increase this to six 2-metre telescopes in the future, complemented by a network of 30-40 smaller (0.4 - 1 metre) telescopes providing 24 hour coverage of both northern and southern hemispheres. We are undertaking a monitoring project of 10 low-mass X-ray binaries (LMXBs) using FT North to study the optical continuum behaviour of X-ray transients in quiescence. The introduction of FT South in September 2006 allows us to extend this monitoring to include 17 southern hemisphere LMXBs. With new instrumentation, we also intend to expand this monitoring to include both infrared wavelengths and spectroscopy.

Abstract:

We report the observation of Bs ⁰- B̄s ⁰ oscillations from a time-dependent measurement of the Bs ⁰-B̄s ⁰ oscillation frequency Δms. Using a data sample of 1 fb^-1 of pp collisions at √ = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron, we find signals of 5600 fully reconstructed hadronic B s decays, 3100 partially reconstructed hadronic Bs decays, and 61500 partially reconstructed semileptonic Bs decays. We measure the probability as a function of proper decay time that the Bs decays with the same, or opposite, flavor as the flavor at production, and we find a signal for Bs ⁰-B̄s ⁰ oscillations. The probability that random fluctuations could produce a comparable signal is 8 × 10^-8, which exceeds 5σ significance. We measure Δms = 17.77 ± 0.10(stat) ± 0.07(syst) ps^-1 and extract |Vtd/Vts| = 0.2060 ± 0.0007(Δms)-0.0060 ^+0.0081 (Δmd + theor). © 2006 The American Physical Society.

Abstract:

We present two-degree field spectroscopic observations of a sample of 96 A-type stars selected from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Our aim is to identify blue horizontal branch (BHB) stars in order to measure the kinematic properties of the tidal tails of the Sagittarius dwarf spheroidal galaxy. We confine our attention to the 44 classifiable stars with spectra of signal-to-noise ratio > 15 Å-1. Classification produces a sample of 29 BHB stars at distances of 5-47 kpc from the Sun. We split our sample into three bins based on their distance. We find 10 of the 12 stars at 14-25 kpc appear to have coherent, smoothly varying radial velocities which are plausibly associated with old debris in the Sagittarius tidal stream. Further observations along the orbit and at greater distances are required to trace the full extent of this structure on the sky. Three of our BHB stars in the direction of the globular cluster Palomar (Pal) 5 appear to be in an overdensity but are in the foreground of Pal 5. More observations are required around this overdensity to establish any relation to Pal 5 and/or the Sgr stream. We emphasize observations of BHB stars have unlimited potential for providing accurate velocity and distance information in old distant halo streams and globular clusters alike. The next-generation multi-object spectrographs provide an excellent opportunity to accurately trace the full extent of such structures. © 2006 RAS.