Search results for "Detectors de radiació"
showing 10 items of 120 documents
Measurements of the tau polarisation in Z0 decays
1995
A sample of Z0→τ+τ- events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the τ polarisation in the exclusive decay channels {Mathematical expression}, {Mathematical expression}, πν, ρν and a1ν. The τ polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the τ polarisation as a function of production angle yields the values for the mean τ polarisation 〈P〉τ=-0.148±0.022 and for the Z0 polarisation PZ=-0.136±0.027. These results are used to determin…
MEASUREMENT OF THE GAMMA(B-B-OVER-BAR)/GAMMA(HAD) BRANCHING RATIO OF THE Z BY DOUBLE HEMISPHERE TAGGING
1995
Two measurements of {Mathematical expression} are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, {Mathematical expression} is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018 {Mathematical expression}. © 1995 Springer-Verlag.
A Study of radiactive muon-pair events at Z° energies and limits on an additional Z' gauge boson
1995
An analysis is reported on the channele + e −→μ+μ−(nγ), n=1,2..., using data taken with the DELPHI detector at LEP from 1990 to 1992. Differential cross sections of the radiative photons as a function of photon energy and of the angle between the photon and the muon are presented. No significant deviations from expectations are observed. The data are also used to extract the muon-pair cross section and asymmetry below the Z0 peak by using those events with relatively hard initial state radiative photon(s). The measured cross section and asymmetry show no significant deviation from the Standard Model expectations. These results together with the DELPHI cross section and asymmetry measurement…
Operation and first results of the NEXT-DEMO prototype using a silicon photomultiplier tracking array
2013
NEXT-DEMO is a high-pressure xenon gas TPC which acts as a technological test-bed and demonstrator for the NEXT-100 neutrinoless double beta decay experiment. In its current configuration the apparatus fully implements the NEXT-100 design concept. This is an asymmetric TPC, with an energy plane made of photomultipliers and a tracking plane made of silicon photomultipliers (SiPM) coated with TPB. The detector in this new configuration has been used to reconstruct the characteristic signature of electrons in dense gas, demonstrating the ability to identify the MIP and "blob" regions. Moreover, the SiPM tracking plane allows for the definition of a large fiducial region in which an excellent e…
A study of the material in the ATLAS inner detector using secondary hadronic interactions
2011
The ATLAS inner detector is used to reconstruct secondary vertices due to hadronic interactions of primary collision products, so probing the location and amount of material in the inner region of ATLAS. Data collected in 7 TeV pp collisions at the LHC, with a minimum bias trigger, are used for comparisons with simulated events. The reconstructed secondary vertices have spatial resolutions ranging from ~ 200μm to 1 mm. The overall material description in the simulation is validated to within an experimental uncertainty of about 7%. This will lead to a better understanding of the reconstruction of various objects such as tracks, leptons, jets, and missing transverse momentum.
The ATLAS Inner Detector commissioning and calibration
2010
The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and insitu calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energ…
Readiness of the ATLAS liquid argon calorimeter for LHC collisions
2010
The ATLAS liquid argon calorimeter has been operating continuously since August 2006. At this time, only part of the calorimeter was readout, but since the beginning of 2008, all calorimeter cells have been connected to the ATLAS readout system in preparation for LHC collisions. This paper gives an overview of the liquid argon calorimeter performance measured in situ with random triggers, calibration data, cosmic muons, and LHC beam splash events. Results on the detector operation, timing perfor-mance, electronics noise, and gain stability are presented. High energy deposits from radiative cosmic muons and beam splash events allow to check the intrinsic constant term of the energy resolutio…
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at √s = 7 TeV with the ATLAS detector
2011
The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton–proton collisions at a centre-of-mass energy of √s =7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb[superscript −1]. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the ra…
Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in $pp$ collisions at $\sqrt{s}=7$…
2012
In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at s√=7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb[superscript −1] collected with the ATLAS detector in 2011. The pT spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production…
Search for heavy neutrinos and right-handed W bosons in events with two leptons and jets in pp collisions at √s=7 TeV with the ATLAS detector
2012
This letter reports on a search for hypothetical heavy neutrinos, N, and right-handed gauge bosons, WR, in events with high transverse momentum objects which include two reconstructed leptons and at least one hadronic jet. The results were obtained from data corresponding to an integrated luminosity of 2.1 fb−1 collected in proton–proton collisions at √s=7 TeV with the ATLAS detector at the CERN Large Hadron Collider. No excess above the Standard Model background expectation is observed. Excluded mass regions for Majorana and Dirac neutrinos are presented using two approaches for interactions that violate lepton and lepton-flavor numbers. One approach uses an effective operator framework, t…