ATLAS

Abstract:

This paper describes a measurement of the top quark mass, Mtop, with the dynamical likelihood method (DLM) using the CDF II detector at the Fermilab Tevatron. The Tevatron produces top/antitop (tt̄) pairs in pp̄ collisions at a center-of-mass energy of 1.96 TeV. The data sample used in this analysis was accumulated from March 2002 through August 2004, which corresponds to an integrated luminosity of 318pb-1. We use the tt̄ candidates in the "lepton+jets" decay channel, requiring at least one jet identified as a b quark by finding a displaced secondary vertex. The DLM defines a likelihood for each event based on the differential cross section as a function of Mtop per unit phase space volume of the final partons, multiplied by the transfer functions from jet to parton energies. The method takes into account all possible jet combinations in an event, and the likelihood is multiplied event by event to derive the top quark mass by the maximum likelihood method. Using 63 tt̄ candidates observed in the data, with 9.2 events expected from background, we measure the top quark mass to be 173.2+2.6-2.4(stat.)±3. 2(syst.)GeV/c2, or 173.2+4.1-4.0GeV/c2. © 2006 The American Physical Society.

Abstract:

We report on a search for the pair production of second generation scalar leptoquarks ( LQ2) in p over(p, ̄) collisions at the center-of-mass energy sqrt(s) = 1.96   TeV, using data corresponding to an integrated luminosity of 294 ± 19   pb-1 recorded with the DØ detector. No evidence for a leptoquark signal in the LQ2 over(LQ, -)2 → μ q μ q channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of mLQ2 > 247   GeV / c2 for β = B ( LQ2 → μ q ) = 1 and mLQ2 > 182   GeV / c2 for β = 1 / 2. Combining these limits with previous DØ results, the lower limits on the mass of a second generation scalar leptoquark are mLQ2 > 251   GeV / c2 and mLQ2 > 204   GeV / c2 for β = 1 and β = 1 / 2, respectively. © 2006 Elsevier B.V. All rights reserved.

Abstract:

The sources of the observed ultra-high energy cosmic rays must also generate ultra-high energy neutrinos. Deep inelastic scattering of these neutrinos with nucleons on Earth probe center-of-mass energies $\sqrt{s} \sim 100$ TeV, well beyond those attainable at terrestrial colliders. By comparing the rates for two classes of observable events, any departure from the benchmark (unscreened perturbative QCD) neutrino-nucleon cross-section can be constrained. Using the projected sensitivity of the Pierre Auger Observatory to quasi-horizontal showers and Earth-skimming tau neutrinos, we show that a `Super-Auger' detector can thus provide an unique probe of strong interaction dynamics.