Methods to Select Soft Diffraction Dissociation at the LHC

Diffractive events at hadron colliders are typically characterised by a region of the detector without particles, known as a rapidity gap. In order to observe diffractive events in this way, we consider the pseudorapidity acceptance in the forward region of the ATLAS and CMS detectors at the Large Hadron Collider (LHC) and discuss the methods to select soft diffractive dissociation for pp collisions at sqrt(s) = 7 TeV. We showed that in the limited detector rapidity acceptance, it is possible to select diffractive dissociated events by requiring a rapidity gap in the event, however, it is not possible to distinguish single diffractive dissociated events from double diffractive dissociated events with a low diffractive mass.

LO vs NLO comparisons for Z + jets: MC as a tool for background determination for NP searches at LHC

The leptonic decays of the heavy gauge bosons W and/or Z provide a clear experimental signature at hadron colliders. The production of accompanying jets is an excellent signal to probe QCD, while also being the main background to many searches for new physics. Describing the complex final state of W or Z + jets is a theoretical challenge with most existing calculations combining matrix elements for high energy jet production with a parton shower for lower energy jet production. We focus on two models: SHERPA, which uses Leading Order matrix elements for boson and jet production; and POWHEG with HERWIG++, which uses a Next-To-Leading Order Matrix element for Z production. In order to isolate the impact of the matrix elements for jet production, it is first essential to constrain the differences in the rest of the calculation in each case: specifically, the Multiple Parton Interaction models, and the tuning of the parton shower interfaced to the matrix elements. We test all three aspects of these models against data from the Tevatron, and perform a study of some basic kinematic variables at the LHC energy.

W production and properties at CDF

I present measurements of the W boson charge asymmetry and the W boson width G_W using 350 pb-1 of CDF Run II data. The charge asymmetry is the first direct measurement, which uses a new technique to reconstruct the W rapidity by constraining its mass; the result will further constrain Parton Distribution Functions in future fits. The width measurement relies on a fit to the W transverse mass distribution. We measure G_W = 2032 +/- 71 MeV which is in good agreement with the Standard Model prediction.