2,837 research outputs found

    A Fast Tracking Algorithm for the ATLAS Level 2 Trigger

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    A set of conceptually simple and robust algorithms for fast pattern recognition and track reconstruction using 3D space points developed for the ATLAS Level 2 (LVL2) Trigger at the LHC is presented. Results on execution time and physics performance demonstrating the effectiveness of this approach in a demanding, online trigger environment are presented. Both this strategy and a complimentary lookup table based strategy provided results appearing in the recent ATLAS High-Level Trigger, Data Acquisition and Controls Technical Design Report and were successfully implemented online during data taking for the recent ATLAS combined test beam

    Trigger Selection Software for Beauty Physics in ATLAS

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    The unprecedented rate of beauty production at the LHC will yield high statistics for measurements such as CP violation and Bs oscillation and will provide the opportunity to search for and study very rare decays, such as Bâ ï­ï­ .The trigger is a vital component for this work and must select events containing the channels of interest from a huge background in order to reduce the 40 MHz bunch crossing rate down to 100-200 Hz for recording, of which only a part will be assigned to B-physics. Requiring a single or di-muon trigger provides the first stage of the B-trigger selection. Track reconstruction is then performed in the Inner Detector, either using the full detector, at initial luminosity, or within Regions of Interest identified by the first level trigger at higher luminosities. Based on invariant mass, combinations of tracks are selected as likely decay products of the channel of interest and secondary vertex fits are performed. Events are selected based on properties such as fit quality and invariant mass. We present fast vertex reconstruction algorithms suitable for use in the second level trigger and event filter (level three). We discuss the selection software and the flexible trigger strategies that will enable ATLAS to pursue a B-physics programme from the first running at a luminosity of about 1031 cm-2s-1 through to the design luminosity running at 1034 cm-2s-1

    Triggering events with GPUs at ATLAS

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    The growing complexity of events produced in LHC collisions demands increasing computing power both for the online selection and for the offline reconstruction of events. In recent years there have been significant advances in the performance of Graphics Processing Units (GPUs) both in terms of increased compute power and reduced power consumption that make GPUs extremely attractive for use in a complex particle physics experiments such as ATLAS. A small scale prototype of the full ATLAS High Level Trigger has been implemented that exploits reconstruction algorithms optimized for this new massively parallel paradigm. We discuss the integration procedure followed for this prototype and present the performance achieved and the prospects for the future.Peer Reviewe

    An evaluation of GPUs for use in an upgraded ATLAS High Level Trigger

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    ATLAS is a general purpose particle physics experiment located on the LHC collider at CERN. The ATLAS Trigger system consists of two levels, the first level (L1) implemented in hardware and the High Level Trigger (HLT) implemented in software running on a computing cluster of commodity CPUs. The HLT reduces the trigger rate from the 100 kHz L1 accept rate to 1 kHz for recording, requiring an average per-event processing time of ~300 ms for this task. The HLT selection is based on reconstructing tracks in the Inner Detector and Muon Spectrometer and clusters of energy deposited in the calorimeters (electromagnetic and hadronic). Performing this reconstruction within the available HLT computing cluster resources presents a significant challenge. Future HLT upgrades will result in higher detector occupancies and, consequently, will harden the reconstruction constraints. General purpose Graphics Processor Units (GPGPU) are being evaluated for possible future inclusion in an upgraded HLT computing cluster. We report on a demonstrator that has been developed consisting of GPGPU implementations of the calorimeters clustering and Inner Detector and Muon tracking algorithms integrated within the HLT software framework. We give a brief overview of the algorithm implementation and present preliminary measurements comparing the performance of the GPGPU algorithms with the current CPU versions.Peer Reviewe

    Open and Hidden Charm Production in 920 GeV Proton-Nucleus Collisions

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    The HERA-B collaboration has studied the production of charmonium and open charm states in collisions of 920 GeV protons with wire targets of different materials. The acceptance of the HERA-B spectrometer covers negative values of xF up to xF=-0.3 and a broad range in transverse momentum from 0.0 to 4.8 GeV/c. The studies presented in this paper include J/psi differential distributions and the suppression of J/psi production in nuclear media. Furthermore, production cross sections and cross section ratios for open charm mesons are discussed.Comment: 5 pages, 9 figures, to be published in the proceedings of the 6th International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04), Chicago, IL, June 27 - July 3, 200

    Search for the Flavor-Changing Neutral Current Decay D0μ+μD^0 \to \mu^+\mu^- with the HERA-B Detector

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    We report on a search for the flavor-changing neutral current decay D0μ+μD^0 \to \mu^+\mu^- using 50×10650 \times 10^6 events recorded with a dimuon trigger in interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find no evidence for such decays and set a 90% confidence level upper limit on the branching fraction Br(D0μ+μ)<2.0×106Br(D^0 \to \mu^+\mu^-) <2.0 \times 10^{-6}.Comment: 17 pages, 4 figures (of which 1 double), paper to be submitted to Physics Letters

    Inclusive V0V^0 Production Cross Sections from 920 GeV Fixed Target Proton-Nucleus Collisions

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    Inclusive differential cross sections dσpA/dxFd\sigma_{pA}/dx_F and dσpA/dpt2d\sigma_{pA}/dp_t^2 for the production of \kzeros, \lambdazero, and \antilambda particles are measured at HERA in proton-induced reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to s=41.6\sqrt {s} = 41.6 GeV in the proton-nucleon system. The ratios of differential cross sections \rklpa and \rllpa are measured to be 6.2±0.56.2\pm 0.5 and 0.66±0.070.66\pm 0.07, respectively, for \xf 0.06\approx-0.06. No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions dσpA/dpt2d\sigma_{pA}/dp_t^2 also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections σpA\sigma_{pA} on the atomic mass AA of the target material is discussed, and the deduced cross sections per nucleon σpN\sigma_{pN} are compared with results obtained at other energies.Comment: 17 pages, 7 figures, 5 table

    Measurement of the J/Psi Production Cross Section in 920 GeV/c Fixed-Target Proton-Nucleus Interactions

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    The mid-rapidity (dsigma_(pN)/dy at y=0) and total sigma_(pN) production cross sections of J/Psi mesons are measured in proton-nucleus interactions. Data collected by the HERA-B experiment in interactions of 920 GeV/c protons with carbon, titanium and tungsten targets are used for this analysis. The J/Psi mesons are reconstructed by their decay into lepton pairs. The total production cross section obtained is sigma_(pN)(J/Psi) = 663 +- 74 +- 46 nb/nucleon. In addition, our result is compared with previous measurements

    Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector