Triangular flow in event-by-event ideal hydrodynamics in Au+Au collisions at √SNN = 200A GeV

The first calculation of triangular flow ν3 in Au+Au collisions at √sNN = 200A GeV from an event-by-event (3 + 1) d transport+hydrodynamics hybrid approach is presented. As a response to the initial triangularity Ie{cyrillic, ukrainian}3 of the collision zone, ν3 is computed in a similar way to the standard event-plane analysis for elliptic flow ν2. It is found that the triangular flow exhibits weak centrality dependence and is roughly equal to elliptic flow in most central collisions. We also explore the transverse momentum and rapidity dependence of ν2 and ν3 for charged particles as well as identified particles. We conclude that an event-by-event treatment of the ideal hydrodynamic evolution startingwith realistic initial conditions generates the main features expected for triangular flow. © 2010 The American Physical Society.

Measurement of the tt̅W and tt̅Z Cross Sections using Proton-Proton Collisions at √s = 8 TeV with the ATLAS Detector

A measurement of the production cross sections of top quark pairs in association with a W or Z boson is presented. The measurement uses 20.3 fb−1 of data from proton-proton collisions at √s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. Four different final states are considered: two opposite-sign leptons, two same-sign leptons, three leptons, and four leptons. The t t̅ W and t t̅ Z cross sections are simultaneously extracted using a maximum likelihood fit over all the final states. The t t̅ Z cross section is measured to be 176+58−52 fb, corresponding to a signal significance of 4.2σ. The t t̅ W cross section is measured to be 369+100−91 fb, corresponding to a signal significance of 5.0σ. The results are consistent with next-to-leading-order calculations for the tt̅W and tt̅Z processes.