Rubin-LSST

Abstract:

We present a measurement of the top-quark pair-production cross section in pp̄ collisions at √s=1.96TeV using a data sample corresponding to 1.7fb-1 of integrated luminosity collected with the Collider Detector at Fermilab. We reconstruct tt̄ events in the lepton+jets channel, consisting of eν+jets and μν+jets final states. The dominant background is the production of W bosons in association with multiple jets. To suppress this background, we identify electrons from the semileptonic decay of heavy-flavor jets ("soft electron tags"). From a sample of 2196 candidate events, we obtain 120 tagged events with a background expectation of 51±3 events, corresponding to a cross section of σtt̄=7. 8±2.4(stat)±1.6(syst)±0.5(lumi)pb. We assume a top-quark mass of 175GeV/c2. This is the first measurement of the tt̄ cross section with soft electron tags in run II of the Tevatron. © 2010 The American Physical Society.

Abstract:

Management of the large volume of data collected by any large scale scientific experiment requires the collection of coherent metadata quantities, which can be used by reconstruction or analysis programs and/or user interfaces, to pinpoint collections of data needed for specific purposes. In the ATLAS experiment at the LHC, we have collected metadata from systems storing non-event-wise data (Conditions) into a relational database. The Conditions metadata (COMA) database tables not only contain conditions known at the time of event recording, but also allow for the addition of conditions data collected as a result of later analysis of the data (such as improved measurements of beam conditions or assessments of data quality). A new web based interface called "runBrowser" makes these Conditions Metadata available as a Run based selection service. runBrowser, based on PHP and JavaScript, uses jQuery to present selection criteria and report results. It not only facilitates data selection by conditions attributes, but also gives the user information at each stage about the relationship between the conditions chosen and the remaining conditions criteria available. When a set of COMA selections are complete, runBrowser produces a human readable report as well as an XML file in a standardized ATLAS format. This XML can be saved for later use or refinement in a future runBrowser session, shared with physics/detector groups, or used as input to ELSSI (event level Metadata browser) or other ATLAS run or event processing services.

Abstract:

We investigate the effect of dust on spiral galaxies by measuring the inclination-dependence of optical colours for 24,276 well-resolved SDSS galaxies visually classified in Galaxy Zoo. We find clear trends of reddening with inclination which imply a total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4 magnitudes for the ugri passbands. We split the sample into "bulgy" (early-type) and "disky" (late-type) spirals using the SDSS fracdeV (or f_DeV) parameter and show that the average face-on colour of "bulgy" spirals is redder than the average edge-on colour of "disky" spirals. This shows that the observed optical colour of a spiral galaxy is determined almost equally by the spiral type (via the bulge-disk ratio and stellar populations), and reddening due to dust. We find that both luminosity and spiral type affect the total amount of extinction, with "disky" spirals at M_r ~ -21.5 mags having the most reddening. This decrease of reddening for the most luminous spirals has not been observed before and may be related to their lower levels of recent star formation. We compare our results with the latest dust attenuation models of Tuffs et al. We find that the model reproduces the observed trends reasonably well but overpredicts the amount of u-band attenuation in edge-on galaxies. We end by discussing the effects of dust on large galaxy surveys and emphasize that these effects will become important as we push to higher precision measurements of galaxy properties and their clustering.

Abstract:

We report a search for single top quark production with the CDF II detector using 2.1fb-1 of integrated luminosity of pp̄ collisions at √s=1.96TeV. The data selected consist of events characterized by large energy imbalance in the transverse plane and hadronic jets, and no identified electrons and muons, so the sample is enriched in W→τν decays. In order to suppress backgrounds, additional kinematic and topological requirements are imposed through a neural network, and at least one of the jets must be identified as a b quark jet. We measure an excess of signal-like events in agreement with the standard model prediction, but inconsistent with a model without single top quark production by 2.1 standard deviations (σ), with a median expected sensitivity of 1.4σ. Assuming a top quark mass of 175GeV/c2 and ascribing the excess to single top quark production, the cross section is measured to be 4.9-2.2+2.5(stat+syst)pb, consistent with measurements performed in independent data sets and with the standard model prediction. © 2010 The American Physical Society.