139,266 research outputs found
Improving topological cluster reconstruction using calorimeter cell timing in ATLAS
No full textClusters of topologically connected calorimeter cells around cells with large absolute signal-to-noise ratio (topo-clusters) are the basis for calorimeter signal reconstruction in the ATLAS experiment. Topological cell clustering has proven performant in LHC Runs 1 and 2. It is, however, susceptible to out-of-time pile-up of signals from soft collisions outside the 25 ns proton-bunch-crossing window associated with the event’s hard collision. To reduce this effect, a calorimeter-cell timing criterion was added to the signal-to-noise ratio requirement in the clustering algorithm. Multiple versions of this criterion were tested by reconstructing hadronic signals in simulated events and Run 2 ATLAS data. The preferred version is found to reduce the out-of-time pile-up jet multiplicity by for jet GeV and by for jet GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, -leptons), reducing the overall event size on disk by about in early Run 3 pile-up conditions. Offline reconstruction for Run 3 includes the timing requirement
ATLAS Overview Week group photo in Thessaloniki
No full textA group photo was taken during the ATLAS Overview Week, which was held in Thessaloniki, Greece, in June 2024
Study of decays at = 8 TeV with the ATLAS detector
No full textThis paper presents a study of decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton–proton data sample corresponding to an integrated luminosity of 20.2 fb collected at a centre-of-mass energy = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of decays are also reported
Measurement of the W-boson mass and width with the ATLAS detector using proton–proton collisions at s = 7 TeV
No full textAbstract Proton–proton collision data recorded by the ATLAS detector in 2011, at a centre-of-mass energy of 7 TeV, have been used for an improved determination of the W-boson mass and a first measurement of the W-boson width at the LHC. Recent fits to the proton parton distribution functions are incorporated in the measurement procedure and an improved statistical method is used to increase the measurement precision. The measurement of the W-boson mass yields a value of m W = 80 , 366.5 ± 9.8 ( stat. ) ± 12.5 ( syst. ) MeV = 80 , 366.5 ± 15.9 MeV, and the width is measured as Γ W = 2202 ± 32 ( stat. ) ± 34 ( syst. ) MeV = 2202 ± 47 MeV. The first uncertainty components are statistical and the second correspond to the experimental and physics-modelling systematic uncertainties. Both results are consistent with the expectation from fits to electroweak precision data. The present measurement of m W is compatible with and supersedes the previous measurement performed using the same data
Underlying-event studies with strange hadrons in pp collisions at s = 13 TeV with the ATLAS detector
No full textAbstract Properties of the underlying-event in pp interactions are investigated primarily via the strange hadrons K S 0 , Λ and Λ ¯ , as reconstructed using the ATLAS detector at the LHC in minimum-bias pp collision data at s = 13 TeV. The hadrons are reconstructed via the identification of the displaced two-particle vertices corresponding to the decay modes , Λ → π - p and Λ ¯ → π + p ¯ . These are used in the construction of underlying-event observables in azimuthal regions computed relative to the leading charged-particle jet in the event. None of the hadronisation and underlying-event physics models considered can describe the data over the full kinematic range considered. Events with a leading charged-particle jet in the range of 10 < p T ≤ 40 GeV are studied using the number of prompt charged particles in the transverse region. The ratio N ( Λ + Λ ¯ ) / N ( K S 0 ) as a function of the number of such charged particles varies only slightly over this range. This disagrees with the expectations of some of the considered Monte Carlo models
An overview of the ATLAS High Level Trigger Dataflow and Supervision.
No full textThe ATLAS high-level trigger (HLT) system provides software-based event selection after the initial LVL1 hardware trigger. It is composed of two stages, the LVL2 trigger and the event filter (EF). The LVL2 trigger performs event selection with optimized algorithms using selected data guided by Region of Interest pointers provided by the LVL1 trigger. Those events selected by LVL2 are built into complete events, which are passed to the EF for a further stage of event selection and classification using off-line algorithms. Events surviving the EF selection are passed for off-line storage. The two stages of HLT are implemented on processor farms. The concept of distributing the selection process between LVL2 and EF is a key element in the architecture, which allows it to be flexible to changes (luminosity, detector knowledge, background conditions, etc.) Although there are some differences in the requirements between these subsystems there are many commonalities. An overview of the dataflow (event selection) and supervision (control, configuration, monitoring) activities in the HLT is given, highlighting where commonalities between the two subsystems can be exploited and indicating where requirements dictate that implementations differ. An HLT prototype system has been built at CERN. Functional testing is being carried out in order to validate the HLT architecture
Part of the Hong Kong team in a group meeting at CERN
No full textPart of the Hong Kong team in a group meeting at CERN Image supporting ATLAS Blog - 19 May 201
ATLAS Week Group Photo, Copenhagen 2010
No full textGroup photo of ATLAS collaboration members attending the ATLAS Overview week in June 2010. This image was taken in the main gala hall of the University of Copenhagen
ATLAS Overview Week group photo in Lisbon
No full textA group photo was taken during the ATLAS Overview Week, which was held in Lisbon, Portugal, in October 2022
ATLAS Event Display: Anomaly Detection
No full textA display of an event with the reconstructed invariant mass of mjμ=4.72 TeV (Run Number: 310634, Event Number 295535084). It is recorded by ATLAS on 14th October 2016 with LHC stable beams at a pp collision energy of 13 TeV. This event belongs to the group of eight events with mjμ>4.7 TeV contributing to the largest deviation from the background hypothesis in the 10 pb AR. The top-left panel presents a transverse (x-y plane) view of the event. The gray cones represent jets and the red lines represent muons. The green arrow indicates a missing transverse energy (EmissT) of 256 GeV. The red line closest to MET represents a muon with pμT=430 GeV. The jet shown on the left side of the display (pjT=1376GeV, η=−1.79) forms the mass of mjμ=4.72 TeV. Other jets with pT>20 GeV and muons with pμT>60 GeV are also displayed. The top-right panel shows the distribution of energy deposited in the calorimeters in the η-ϕ plane, where muons are marked in red and jets in yellow. The bottom panel displays the event in the longitudinal (z -y plane) perspective
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