Preliminary results of the Standard Model Higgs Boson search at LEP in 2000

A search for the Standard Model Higgs boson is performed using the data collected by the four LEP experiments at center-of-mass energies between 202 GeV and 209 GeV. An average luminosity of 140 $pb^{-1}$ per experiment has been analyzed. A 2.6 $\sigma$ excess is observed in the LEP-wide combination for a Higgs boson mass hypothesis of around 114 GeV. All results are preliminary.Comment: 4 pages, 2 figures include

The central track trigger of the DO experiment

©2004 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.The general purpose DO collider detector, located at Fermi National Accelerator Laboratory, is operated in the high luminosity (L = 2 X 10(32) cm(-2) s(-1)) and high-collision-rate environment (396 ns between beam crossings) of the upgraded Tevatron proton anti-proton accelerator. DO uses a three-tiered trigger system to select events for offline storage and analysis. This paper describes the architecture and performance of the DO central track trigger (CTT) system based on the new central fiber tracker, central preshower and forward preshower detectors, with emphasis on the interface to and integration with the second tier L2 Trigger system

Measurements of four-fermion cross -sections at LEP

The production of four fermions in e+e− collisions at LEP allows the verification of the Standard Model of the Electroweak Interactions in the Charged and Neutral Current Sectors. Among the four-fermion final states, the highest purity and the clearest four-fermion events are characterized by the presence of leptons in the final state. The identification of such final states in the full data sample collected by the L3 experiment at LEP in the years from 1997 through 2000 is described. The total amount of data analyzed in this thesis corresponds to the total integrated luminosity 675.5 pb−1. This thesis presents the results of the selection of the Z boson pair production together with the measurement of the cross-section for leptonic four-fermion final states, and the first measurement of cross-sections in the four-lepton and two-lepton and missing energy channels of the [special characters omitted] production with the L3 detector. The cross-section average over the whole data sample was found to be: [special characters omitted]This thesis also presents the results of the selection of the single W production and the cross-section measurements of the semileptonic decays of the W boson. All measurements are consistent with the Standard Model expectations

A note on adaptivity in factorized approximate inverse preconditioning

The problem of solving large-scale systems of linear algebraic equations arises in a wide range of applications. In many cases the preconditioned iterative method is a method of choice. This paper deals with the approximate inverse preconditioning AINV/SAINV based on the incomplete generalized Gram-Schmidt process. This type of the approximate inverse preconditioning has been repeatedly used for matrix diagonalization in computation of electronic structures but approximating inverses is of an interest in parallel computations in general. Our approach uses adaptive dropping of the matrix entries with the control based on the computed intermediate quantities. Strategy has been introduced as a way to solve difficult application problems and it is motivated by recent theoretical results on the loss of orthogonality in the generalized Gram-Schmidt process. Nevertheless, there are more aspects of the approach that need to be better understood. The diagonal pivoting based on a rough estimation of condition numbers of leading principal submatrices can sometimes provide inefficient preconditioners. This short study proposes another type of pivoting, namely the pivoting that exploits incremental condition estimation based on monitoring both direct and inverse factors of the approximate factorization. Such pivoting remains rather cheap and it can provide in many cases more reliable preconditioner. Numerical examples from real-world problems, small enough to enable a full analysis, are used to illustrate the potential gains of the new approach