Rubin-LSST

Abstract:

We present results from the first successful millimetre (combined 33 and 35GHz) observations of the neutron star X-ray binary Circinus X-1, using the Australia Telescope Compact Array. The source was clearly detected in all three observing epochs. We see strong evidence for a periastron flare beginning at MJD 55519.9 ± 0.04 with estimated peak flux densities of up to 50mJy and which proceeds to decline over the following 4d. We directly resolve jet structures on sub-arcsecond scales. Flux density variability and distance from the core of nearby components suggest recent shock re-energization, though we are unable to directly connect this with the observed flare. We suggest that, if the emission is powered by an unseen outflow, then a phase delay exists between flare onset and subsequent brightening of nearby components, with flows reaching mildly relativistic velocities. Given resolved structure positions, in comparison to past observations of Cir X-1, we find evidence that jet direction may vary with distance from the core, or the source's precession parameters have changed. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

The performance of τ-lepton reconstruction and identification algorithms is studied using a data sample of proton-proton collisions at s = 7 TeV, corresponding to an integrated luminosity of 36 pb-1 collected with the CMS detector at the LHC. The τ leptons that decay into one or three charged hadrons, zero or more short-lived neutral hadrons, and a neutrino are identified using final-state particles reconstructed in the CMS tracker and electromagnetic calorimeter. The reconstruction efficiency of the algorithms is measured using τ leptons produced in Z-boson decays. The τ-lepton misidentification rates for jets and electrons are determined. © 2012 CERN for the benefit of the CMS collaboration, published under license by IOP Publishing Ltd and SISSA.

Abstract:

We present results from the first radio observations of a complete orbit (~17d) of the neutron star X-ray binary CircinusX-1 using the Australia Telescope Compact Array Broadband Backend, taken while the system was in an historically faint state. We have captured the rapid rise and decline of a periastron passage flare, with flux densities for 9d prior to the event stable at ~1mJy at 5.5GHz and ~0.5mJy at 9GHz. The highest flux densities of 43.0 ± 0.5mJy at 5.5GHz and 29.9 ± 0.6mJy at 9GHz were measured during the flare's decline (MJD 55206.69) which continues towards pre-flare flux densities over the following 6d. Imaging of pre-flare data reveals steady structure including two stable components within 15arcsec of the core which we believe may be persistent emission regions within the system's outflows, one of which is likely associated with the system's counter jet. Unlike past observations carried out in the system's brighter epochs, we observe no significant structural variations within ≈3arcsec of the core's position. Model subtraction and difference mapping provide evidence for variations slightly further from the core: up to 5arcsec away. If related to the observed core flare, then these variations suggest very high outflow velocities with Γ > 35, though this can be reduced significantly if we invoke phase delays of at least one orbital period. Interestingly, the strongest structural variations appear to the north-west of the core, opposite to the strongest arcsec-scale emission historically. We discuss the implications of this behaviour, including the possibility of precession or a kinked approaching jet. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

A study of dijet production in proton-proton collisions was performed at √s = 7TeV for jets with pT>35 GeV and {pipe}y{pipe}<4. 7 using data collected with the CMS detector at the LHC in 2010. Events with at least one pair of jets are denoted as "inclusive". Events with exactly one pair of jets are called "exclusive". The ratio of the cross section of all pairwise combinations of jets to the exclusive dijet cross section as a function of the rapidity difference between jets {pipe}Δy{pipe} is measured for the first time up to {pipe}Δy{pipe}=9. 2. The ratio of the cross section for the pair consisting of the most forward and the most backward jet from the inclusive sample to the exclusive dijet cross section is also presented. The predictions of the Monte Carlo event generators pythia6 and pythia8 agree with the measurements. In both ratios the herwig++ generator exhibits a more pronounced rise versus {pipe}Δy{pipe} than observed in the data. The BFKL-motivated generators cascade and hej+ariadne predict for these ratios a significantly stronger rise than observed. © 2012 CERN for the benefit of the CMS collaboration.

Abstract:

A search for the rare decays B0s → μ+μ- and B0 → μ+ μ- is performed in pp collisions at ps = 7TeV, with a data sample corresponding to an integrated luminosity of 5 fb-1 collected by the CMS experiment at the LHC. In both decays, the number of events observed after all selection requirements is consistent with the expectation from background plus standard model signal predictions. The resulting upper limits on the branching fractions are B(B0s → μ+ μ-) < 7:7 × 10-9 and B(B0 → μ+μ-) < 1:8 × 10-9 at 95% confidence level.