Rubin-LSST

Abstract:

Measurements of the production of jets of particles in association with a Z boson in pp collisions at √s=7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb-1 collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p T > 30 GeV and rapidity |y| < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton showers. [Figure not available: see fulltext.] © 2013 CERN for the benefit of the ATLAS collaboration.

Abstract:

A measurement is presented of the ratio of the inclusive 3-jet cross section to the inclusive 2-jet cross section as a function of the average transverse momentum, 〈pT1,2〉, of the two leading jets in the event. The data sample was collected during 2011 at a proton-proton centre-of-mass energy of 7 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 5.0 fb-1. The strong coupling constant at the scale of the Z boson mass is determined to be αS(MZ)=0.1148±0.0014 (exp.)±0.0018 (PDF)±0.0050(theory), by comparing the ratio in the range 0.42 < 〈pT1,2〉 < 1.39 TeV to the predictions of perturbative QCD at next-to-leading order. This is the first determination of αS(M Z) from measurements at momentum scales beyond 0.6 TeV. The predicted ratio depends only indirectly on the evolution of the parton distribution functions of the proton such that this measurement also serves as a test of the evolution of the strong coupling constant. No deviation from the expected behaviour is observed. © 2013 CERN for the benefit of the CMS collaboration.

Abstract:

A measurement is presented of the t̄t production cross section σt̄t in proton-proton collisions at a centre-of-mass energy of 7 TeV, in the all-jet final state that contains at least six jets, two of which are tagged as originating from b quarks. The data correspond to an integrated luminosity of 3.54 fb-1, collected with the CMS detector at the LHC. The cross section is determined through an unbinned maximum likelihood fit of background and t̄t signal to the reconstructed mass spectrum of t̄t candidates in the data, in which events are subjected to a kinematic fit assuming a t̄t → W+bW-̄b → 6 jets hypothesis. The measurement yields σt̄t = 139±10(stat.)±26(syst.)±3(lum.)pb, a result consistent with those obtained in other t̄t decay channels, as well as with predictions of the standard model. © 2013 CERN for the benefit of the CMS collaboration.

Abstract:

A measurement of the λb0 lifetime using the decay λb0-1, was recorded with the CMS experiment at the Large Hadron Collider using triggers that selected dimuon events in the J/ψ mass region. The λb0 lifetime is measured to be 1.503 ± 0.052 (stat.) ± 0.031 (syst.) ps. [Figure not available: see fulltext.] © 2013 Cern for the benefit of the CMS collaboration.

Abstract:

Context.We report on a detailed study of the Fe K emission/absorption complex in the nearby, bright Seyfert 1 galaxy Mrk 509. The study is part of an extensive XMM-Newton monitoring consisting of 10 pointings (∼60 ks each) about once every 4 days, and includes a reanalysis of previous XMM-Newton and Chandra observations. Aims.We aim at understanding the origin and location of the Fe K emission and absorption regions. Methods.We combine the results of time-resolved spectral analysis on both short and long time-scales including model-independent rms spectra. Results.Mrk 509 shows a clear (EW = 58±4 eV) neutral Fe Ka emission line that can be decomposed into a narrow (s = 0.027 keV) component (found in the Chandra HETG data) plus a resolved (s = 0.22 keV) component.We find the first successful measurement of a linear correlation between the intensity of the resolved line component and the 3-10 keV flux variations on time scales of years down to a few days. The Fe Ka reverberates the hard X-ray continuum without any measurable lag, suggesting that the region producing the resolved Fe Ka component is located within a few light days to a week (r ≲ 103 rg) from the black hole (BH). The lack of a redshifted wing in the line poses a lower limit of =40 rg for its distance from the BH. The Fe Ka could thus be emitted from the inner regions of the BLR, i.e. within the ∼80 light days indicated by the Hß line measurements. In addition to these two neutral Fe Ka components, we confirm the detection of weak (EW ∼ 8-20 eV) ionised Fe K emission. This ionised line can be modelled with either a blend of two narrow Fe xxv and Fe xxvi emission lines (possibly produced by scattering from distant material) or with a single relativistic line produced, in an ionised disc, down to a few rg from the BH. In the latter interpretation, the presence of an ionised standard a-disc, down to a few rg, is consistent with the source high Eddington ratio. Finally, we observe a weakening/disappearing of the mediumand high-velocity high-ionisation Fe K wind features found in previous XMM-Newton observations. Conclusions. This campaign has made the first reverberation measurement of the resolved component of the Fe Ka line possible, from which we can infer a location for the bulk of its emission at a distance of r ∼ 40-1000 rg from the BH. © 2012 ESO.