Rubin-LSST

Abstract:

This Letter reports a measurement of the WW production cross section in √s=7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb-1 collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is σ(pp→WW)=54.4±4.0(stat.)±3.9(syst.)±2.0(lumi.) pb, consistent with the Standard Model prediction of σ(pp→WW)=44.4±2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event. © 2012 CERN.

Abstract:

This Letter reports a measurement of the WW production cross section in √s=7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb^-1 collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is σ(pp→WW)=54.4±4.0(stat.)±3.9(syst.)±2.0(lumi.) pb, consistent with the Standard Model prediction of σ(pp→WW)=44.4±2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event. © 2012 CERN.

Abstract:

A measurement is reported of the production cross section of top-quark pairs (tt̄) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. Candidate events have a signature consistent with containing two isolated leptons, large missing transverse momentum, and at least two jets. Using a data sample corresponding to an integrated luminosity of 0.70 fb-1, a tt̄ production cross section σtt̄ = 176 ± 5(stat.)-1111+(syst.) ± 8(lum.) pb is measured for an assumed top-quark mass of mt = 172.5 GeV. This measurement is in good agreement with Standard Model predictions. © CERN.

Abstract:

We present the results from a Chandra pilot study of 12 massive galaxy mergers selected from Galaxy Zoo. The sample includes major mergers down to a host galaxy mass of 10$^{11}$ $M_\odot$ that already have optical AGN signatures in at least one of the progenitors. We find that the coincidences of optically selected active nuclei with mildly obscured ($N_H \lesssim 1.1 \times 10^{22}$ cm$^{-2}$) X-ray nuclei are relatively common (8/12), but the detections are too faint ($< 40$ counts per nucleus; $f_{2-10 keV} \lesssim 1.2 \times 10^{-13}$ erg s$^{-1}$ cm$^{-2}$) to reliably separate starburst and nuclear activity as the origin of the X-ray emission. Only one merger is found to have confirmed binary X-ray nuclei, though the X-ray emission from its southern nucleus could be due solely to star formation. Thus, the occurrences of binary AGN in these mergers are rare (0-8%), unless most merger-induced active nuclei are very heavily obscured or Compton thick.

Abstract:

Dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 150 μb -1 is analyzed. Jets are reconstructed using combined information from tracking and calorimetry, using the anti-k T algorithm with R=0.3. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the same collision energy is found, while more central collisions show a strong imbalance of leading and subleading jet transverse momenta attributed to the jet-quenching effect. The dijets in central collisions are found to be more unbalanced than the reference, for leading jet transverse momenta up to the highest values studied. © 2012 CERN.