Top Pair Production Cross-Section Measurement in the All-Hadronic Channel at CDF and Dzero

Measurements of the ttbar production cross-section at \sqrt{s} = 1.96TeV in proton-antiproton collisions were performed by the CDF and Dzero collaborations using ttbar final states where both W's decay hadronically. Each experiment uses luminosity of about 160pb^-1 of data collected during Run II of the Fermilab Tevatron collider. Beside kinematical observables both experiments take advantage of identifying b-jets based on lifetime tagging. While CDF counts the number of b-tags over background after a cut based analysis, Dzero counts the excess of events after a neural network based kinematical selection and requiring a b-tagged jet. CDF obtains $\sigma_{ttbar}=7.8+-2.5{stat}^{+4.7}_{-2.3}{syst}; Dzero$\sigma_{ttbar}=7.7^{+3.4}_{-3.3}{stat}^{+4.7}_{-3.8}{syst}+-0.5{lumi}.Comment: 4 pages, 2 figures, Proceedings to DPF2004, Riverside, C

Distributed Computing Concepts in D0

The D0 experiment faces many challenges enabling access to large datasets for physicists on four continents. The new concepts for distributed large scale computing implemented in D0 aim for an optimal use of the available computing resources while minimising the person-power needed for operation. The real live test of these concepts is of special interest for the LHC Computing GRID, LCG, which follows a similar strategy.Comment: 3 pages, 3 figures, LaTeX, epj style (included), Proceedings of the International Europhysics Conference on High Energy Physics EPS 2003 (July 17-23, 2003), Aachen, German

Single and Double Top Quark Production at the Tevatron

The CDF and D0 experiments have measured single and double top quark production in ppbar collisions at the Tevatron at a centre-of-mass energy of 1.96TeV. The applied methods are used to constrain properties of the top quark and to search for new physics. Several methods of signal to background separation and of the estimation of the background contributions are discussed. Experimental results using an integraged luminosity up to 5.3fb^-1 are presented.Comment: 8 pages with figures, Proceedings of Les Rencontres de Physique de la Vall\'ee d'Aoste (La Thuile 2010), v2 with updated reference

Hadronic event structure, power corrections and the strong coupling at LEP

Infrared and collinear events shapes are suited to directly probe properties of hard QCD. They are traditionally used to measure the strong coupling and to test the gauge structure of QCD. Perturbative predictions exist in several variations all of which depend on the renormalisation scheme leading to large theoretical uncertainties in the determination of $alpha_s$. To overcome this dominating error more and more schemes for setting the renormalisation scale are investigated. The application of RGI perturbation theory shows an incredible small spread of $\alpha_s$ indicating a reduced uncertainty and allows a measurement of the $\beta$-function directly from mean values.Comment: 5 pages, uses moriond.sty (included). Contribution to "XXXVIIth Rencontres de Moriond, QCD and hadronic interactions", Les Arcs, France, March 2002. See http://www.delphi.uni-wuppertal.de/qcd/Talks.html#Moriond200

Non-perturbative QCD Effects and the Top Mass at the Tevatron

The modelling of non-perturbative effects is an important part of modern collider physics simulations. In hadron collisions there is some indication that the modelling of the interactions of the beam remnants, the underlying event, may require non-trivial colour reconnection effects to be present. We recently introduced a universally applicable toy model of such reconnections, based on hadronising strings. This model, which has one free parameter, has been implemented in the Pythia event generator. We then considered several parameter sets (`tunes'), constrained by fits to Tevatron minimum-bias data, and determined the sensitivity of a simplified top mass analysis to these effects, in exclusive semi-leptonic top events at the Tevatron. A first attempt at isolating the genuine non-perturbative effects gave an estimate of order +-0.5GeV from non-perturbative uncertainties. The results presented here are an update to the original study and include recent bug fixes of Pythia that influenced the tunings investigated.Comment: 8 pages, 5 figures, Submitted to the Proceedings of Top2008, 18-24 May 2008, La Biodola, Isola d'Elba, Ital