Rubin-LSST

Abstract:

Using a sample of 2.59×107 ψ(2S) decays collected by the CLEO-c detector, we present results of a study of χc0 and χc2 decays into two-meson final states. We present the world's most precise measurements of the χcJ,(J=0,2)→π+π-, π0π0, K+K-, KS0KS0, ηη, and η′η′ branching fractions, and a search for χc decays into ηη′. These results shed light on the mechanism of charmonium decays into pseudoscalar mesons. © 2009 The American Physical Society.

Abstract:

A common consequence of accretion onto black holes is the formation of powerful, relativistic jets that escape the system. In the case of supermassive black holes at the centres of galaxies this has been known for decades, but for stellar-mass black holes residing within galaxies like our own, it has taken recent advances to arrive at this conclusion. Here, a review is given of the evidence that supports the existence of jets from accreting stellar-mass black holes, from observations made at optical and infrared wavelengths. In particular it is found that on occasion, jets can dominate the emission of these systems at these wavelengths. In addition, the interactions between the jets and the surrounding matter produce optical and infrared emission on large scales via thermal and non-thermal processes. The evidence, implications and applications in the context of jet physics are discussed. It is shown that many properties of the jets can be constrained from these studies, including the total kinetic power they contain. The main conclusion is that like the supermassive black holes, the jet kinetic power of accreting stellar-mass black holes is sometimes comparable to their bolometric radiative luminosity. Future studies can test ubiquities in jet properties between objects, and attempt to unify the properties of jets from all observable accreting black holes, i.e. of all masses. © 2010 Nova Science Publishers, Inc.

Abstract:

We report a measurement of the top quark mass, mt, obtained from pp̄ collisions at s=1.96TeV at the Fermilab Tevatron using the CDF II detector. We analyze a sample corresponding to an integrated luminosity of 1.9fb-1. We select events with an electron or muon, large missing transverse energy, and exactly four high-energy jets in the central region of the detector, at least one of which is tagged as coming from a b quark. We calculate a signal likelihood using a matrix element integration method, where the matrix element is modified by using effective propagators to take into account assumptions on event kinematics. Our event likelihood is a function of mt and a parameter JES (jet energy scale) that determines in situ the calibration of the jet energies. We use a neural network discriminant to distinguish signal from background events. We also apply a cut on the peak value of each event likelihood curve to reduce the contribution of background and badly reconstructed events. Using the 318 events that pass all selection criteria, we find mt=172.7±1.8(stat+JES) ±1.2(syst)GeV/c2. © 2009 The American Physical Society.

Abstract:

We present a measurement of the top quark mass in the all hadronic channel (tt̄→bb̄q1q̄2q3q̄4) using 943pb-1 of pp̄ collisions at s=1.96TeV collected at the CDF II detector at Fermilab (CDF). We apply the standard model production and decay matrix element (ME) to tt̄ candidate events. We calculate per-event probability densities according to the ME calculation and construct template models of signal and background. The scale of the jet energy is calibrated using additional templates formed with the invariant mass of pairs of jets. These templates form an overall likelihood function that depends on the top quark mass and on the jet energy scale (JES). We estimate both by maximizing this function. Given 72 observed events, we measure a top quark mass of 171.1±3.7(stat+JES)±2.1(syst)GeV/c2. The combined uncertainty on the top quark mass is 4.3GeV/c2. © 2009 The American Physical Society.

Abstract:

Using images from the Hubble Space Telescope and the Gemini Telescope, we confirmed the disappearance of the progenitors of two type II supernovae (SNe) and evaluated the presence of other stars associated with them. We found that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed at the SN location and determined its intrinsic brightness using image subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is also no longer present, but its B-supergiant binary companion is still observed. The disappearance of the progenitors confirms that these two supernovae were produced by red supergiants.