3,990 research outputs found
Online Determination of the LHC Luminous Region with the ATLAS High-Level Trigger
No full textDuring stable-beams operations of the LHC, the ATLAS High Level Trigger (HLT) offers the fastest and most precise online measurement available of the position, size and orientation of the luminous region at the interaction point. Taking advantage of the high rate of triggered events, a dedicated algorithm is executed on the HLT processor farm of several hundred nodes that uses tracks registered in the silicon detectors to reconstruct event vertices. The distribution of these vertices is aggregated across the farm and its shape is extracted through fits every 60 seconds. A correction is applied online to adjust for the intrinsic vertex resolution by examining the displacement of split vertices. The location, widths and tilts of the luminosity distribution are fed back to the LHC operators in real time. The transverse luminous centroid mirrors variations in the IP orbit, while its position along the beam axis is sensitive to the relative RF phase of the two beams. The time evolution of the luminous width tracks the emittance growth over the course of a fill. The HLT measurements can be correlated with data from machine instrumentation such as beam-position monitors, wire scanners and synchrotron-light monitors. Beginning in 2011, the HLT beam spot measurement also started reconstructing the parameters of each individual filled bunch. This gives rise to a study of single-bunch distributions and opens a window to understanding dynamical features such as electron-cloud effects. We will briefly describe how the measurement is performed and discuss the results and observations of the luminous region parameters and their time evolution during the high luminosity running in 2011
Measurement of the Michel parameters in leptonic decays using the OPAL detector at LEP
No full textA measurement of the Michel parameters in tau decays is presented which involves a novel method to fit the energy spectra and energy- energy correlations of the charged decay leptons from tau -pair events produced in e/sup +/e/sup -/ collisions close to square root s =m/sub Z0/. The parameters rho /sub l/, xi /sub l/, ( xi delta )/sub l/ (with l=e, mu ) and nu /sub mu / have been extracted from a global likelihood fit of Monte Carlo generated events to the data set recorded with the OPAL detector in the years 1990-1995. If e- mu universality is assumed and inferring the tau polarization from neutral current data, the measured Michel parameters are rho 0.781+or-0.028+or-0.018, xi =0.98+or-0.22+or-0.10, xi delta =0.65+or-0.14+or-0.07 and eta =0.027+or-0.055+or-0.005, where the value of eta has been constrained using the published OPAL measurements of the leptonic branching ratios and the tau lifetime. Limits on the masses of new intermediate bosons and on non-standard couplings are obtained. It is explained how such limits can be derived from an investigation of the Michel parameter space. (16 refs)
Measurement of the Michel parameters in leptonic decays with the OPAL detector at LEP
No full textAn upper limit for the tau -neutrino mass has been determined from the decay tau to 5 pi /sup +or-/ nu /sub tau / using data collected with the OPAL detector from 1991 to 1995 in e/sup +/e/sup -/ collisions at square root (s) approximately=M/sub Z0/. A limit of 43.2 MeV at 95Ø.000554330L is obtained using a two-dimensional method in the 5 pi invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement using tau /sup +/ tau /sup -/ to 3h/sup +or-/v/sub tau /+3h/sup -or+/ nu tau decays, a new combined limit of m/sub nu tau / <27.6 MeV (95 CL) is obtained
Determination of an Upper Limit for the Mass of the
No full textAn upper limit for the ø mass is determined through the kinematic reconstruction of the decay ø ! 5ß \Sigma ø in the OPAL detector at LEP. The limit is obtained using a new method based on the comparison of the two--dimensional distribution of energy and invariant mass of the five--pion system with expectations from different neutrino mass hypotheses. From a sample of five events surviving the selection criteria we obtain an upper limit of 74 MeV at 95% confidence level. It is the first measurement at LEP energies, where the larger average multiplicity of e + e \Gamma ! qq events makes the suppression of this background more robust compared to lower energies. (Submitted to Zeitschrift fur Physik C) The OPAL Collaboration R. Akers 16 , G. Alexander 23 , J. Allison 16 , K.J. Anderson 9 , S. Arcelli 2 , S. Asai 24 , A. Astbury 28 , D.Axen 29 , G. Azuelos 18;a , A.H. Ball 17 , E. Barberio 26 , R.J. Barlow 16 , R. Bartoldus 3 , J.R. Batley 5 , G. Beaud..
ATLAS Detector Overview
No full textAn overview of the ATLAS detector, performance and data taking in 2011
The OPAL Collaboration
No full textFrom 1 105 045 hadronic Z 0 decays observed with the OPAL detector at the LEP e + e \Gamma collider, 21 732 four-jet events are selected. A simultaneous fit of three selected angular variables from these events by the second order QCD matrix element calculation yields CA=C F = 2:11 \Sigma 0:16(stat:) \Sigma 0:28(syst:) T F =C F = 0:40 \Sigma 0:11(stat:) \Sigma 0:14(syst:) for the ratios of colour factors, in agreement with SU(3) expectations of CA=C F = 9=4 and T F =C F = 3=8. (Submitted to Physics Letters B) The OPAL Collaboration R. Akers 16 , G. Alexander 23 , J. Allison 16 , K.J. Anderson 9 , S. Arcelli 2 , S. Asai 24 , A. Astbury 28 , D. Axen 29 , G. Azuelos 18;a , A.H. Ball 17 , E. Barberio 26 , R.J. Barlow 16 , R. Bartoldus 3 , J.R. Batley 5 , G. Beaudoin 18 , A. Beck 23 , G.A. Beck 13 , J. Becker 10 , C. Beeston 16 , T. Behnke 27 , K.W. Bell 20 , G. Bella 23 , P. Bentkowski 18 , S. Bentvelsen 8 , P. Berlich 10 , S. Be..
Bestimmung der K0s-Produktion aus Zerfaellen mit dem OPAL Detektor: Vergroesserung des Akzeptanzbereiches durch Anwendung der Endpunkt-Methode
No full textThe BaBar detector: Upgrades, operation and performance
No full textContains fulltext :
121729.pdf (Author’s version preprint ) (Open Access
Search for R-parity-violating supersymmetry in events with four or more leptons in root s=7 TeV pp collisions with the ATLAS detector
No full textATLAS Contributors: Paul Douglas Jackson and Nitesh Soni of School of Chemistry and Physics, University of Adelaide, Adelaide, Australia. Extent: 36p.A search for new phenomena in final states with four or more leptons (electrons or muons) is presented. The analysis is based on 4.7 fb⁻¹ of √s=7TeV proton-proton collisions delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in two signal regions: one that requires moderate values of missing transverse momentum and another that requires large effective mass. The results are interpreted in a simplified model of R-parity-violating supersymmetry in which a 95% CL exclusion region is set for charged wino masses up to 540 GeV. In an R-parity-violating MSUGRA/CMSSM model, values of m₁₍₂ up to 820 GeV are excluded for 10 < tan β < 40.The ATLAS collaboratio
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