12 research outputs found

    Belle II Pixel Detector Commissioning and Operational Experience

    Get PDF

    Status of the BELLE II Pixel Detector

    Get PDF
    The Belle II experiment at the super KEK B-factory (SuperKEKB) in Tsukuba, Japan, has been collecting e+ee^+e^− collision data since March 2019. Operating at a record-breaking luminosity of up to 4.7×1034cm2s14.7×10^{34} cm^{−2}s^{−1}, data corresponding to 424fb1424 fb^{−1} has since been recorded. The Belle II VerteX Detector (VXD) is central to the Belle II detector and its physics program and plays a crucial role in reconstructing precise primary and decay vertices. It consists of the outer 4-layer Silicon Vertex Detector (SVD) using double sided silicon strips and the inner two-layer PiXel Detector (PXD) based on the Depleted P-channel Field Effect Transistor (DePFET) technology. The PXD DePFET structure combines signal generation and amplification within pixels with a minimum pitch of (50×55)μm2(50×55) μm^2. A high gain and a high signal-to-noise ratio allow thinning the pixels to 75μm75 μm while retaining a high pixel hit efficiency of about 9999%. As a consequence, also the material budget of the full detector is kept low at 0.21≈0.21%XX0\frac{X}{X_0} per layer in the acceptance region. This also includes contributions from the control, Analog-to-Digital Converter (ADC), and data processing Application Specific Integrated Circuits (ASICs) as well as from cooling and support structures. This article will present the experience gained from four years of operating PXD; the first full scale detector employing the DePFET technology in High Energy Physics. Overall, the PXD has met the expectations. Operating in the intense SuperKEKB environment poses many challenges that will also be discussed. The current PXD system remains incomplete with only 20 out of 40 modules having been installed. A full replacement has been constructed and is currently in its final testing stage before it will be installed into Belle II during the ongoing long shutdown that will last throughout 2023

    Development of a Concept for the Muon Trigger of the ATLAS Detector at the HL-LHC

    No full text
    Highly selective first level triggers are essential to exploit the full physics potential of the ATLAS experiment at the High Luminosity-Large Hadron Collider, where the instantaneous luminosity will exceed the LHC Run 1 instantaneous luminosity by almost an order of magnitude. The ATLAS experiment plans to increase the rate of the first trigger level to 1 MHz at 6 µs latency. The momentum resolution of the existing first level muon trigger is limited by the moderate position resolution of the trigger chambers. Including the data of the precision Monitored Drift Tube (MDT) chambers in the first level muon trigger decision will increase the selectivity of the first level muon trigger substantially. Run 1 LHC data with a centre-of-mass energy of s=8TeV\sqrt{s} = 8\, \textrm{TeV} and a bunch spacing of 25 ns was used to study the achievable selectivity of a muon trigger making use of the MDT data. It could be shown that it is not necessary to fully reconstruct the muon trajectory. The position and direction information of the straight track segments reconstructed in the MDT chambers is sufficient to measure the momentum with a precision that allows for a rate reduction compared to the expected Phase-I trigger rate of over 70 % for the whole ATLAS muon spectrometer. Fast algorithms employed in the trigger electronics are required for the reconstruction of the track segments within the trigger latency. For the end-cap (1.05<η<2.41.05 < |\eta| < 2.4) the ATLAS collaboration considered a 1-dimensional Hough transform algorithm, which is seeded by the trigger chamber data. The algorithm is not applicable in the barrel region (0<η<1.050 < |\eta| < 1.05) because of the lower spatial resolution of the trigger chambers in the barrel region than in the end-cap region. Extending the algorithm to a Binned 2D-Hough Transform, which improves the track segment reconstruction quality sufficiently for all regions apart from the outer barrel MDT chambers. In this thesis, a new track segment finding algorithm, that makes use of tangents to drift radii, was developed and shown to be applicable to the entire muon spectrometer (η<2.4 |\eta| < 2.4)

    Search for Dark Matter in association with a hadronically decaying Z' vector boson with the ATLAS detector in pp collisions at 13 TeV

    No full text
    A search for dark matter pair production in association with a Z' boson in pp collisions, at 13 TeV, using 36.1 fb−1 of LHC pp collision data recorded with the ATLAS detector is presented. Events are characterised by large missing transverse momentum and a hadronically decaying vector boson reconstructed as either a pair of small-radius jets, or as a single large-radius jet with substructure. Results are interpreted in terms of simplified models which describe the interaction of dark matter and standard model particles

    ATLAS Highlights on DM Searches in Exotic Models

    No full text
    Dark matter could be produced at the LHC if it interacts weakly with the Standard Model. The search for dark matter can be performed directly, by looking for a signature of large missing transverse momentum coming from the dark matter candidates escaping the detector, measured against an accompanying visible object (jet, photon, vector boson). It can also be performed indirectly, by looking for the intermediate mediators which would couple the dark matter particles to the Standard Model. The mediator could indeed decay to jets or leptons, leading to a resonant signature which can be probed. A broad and systematic search program covering these various possibilities with the ATLAS detector is in place: the talk will review the latest results of these searches, excluding the searches involving a Higgs boson which will be covered in a dedicated talk

    Search for dark matter produced in association with a hadronically decaying Z’ vector boson with the ATLAS detector at the LHC

    No full text
    A search for dark matter pair production in association with a ZZ' boson is performed using 36.1\,fb1^{-1} of LHC pppp collision data at s=13\sqrt{s} = 13\,TeV recorded with the ATLAS detector.Events are characterised by large missing transverse momentum and a hadronically decaying vector boson reconstructed as either a pair of small-radius jets, or as a single large-radius jet with a two-body decay substructure.Results are interpreted in terms of simplified models which describe the interaction of dark matter and Standard Model particles

    Umami: flavour tagging algorithm development for Run-3

    No full text
    The identification of b-jets is a powerful tool central to many ATLAS physics analyses.Therefore, a variety of different algorithms (b-taggers) is developed and maintained.Among those, a feed-forward deep neural network algorithm (DL1) which is based mainly on jet features and an algorithm exploiting Deep Sets (DIPS) using solely track information are highlighted in this contribution.The Umami framework provides a harmonized ecosystem for producing training samples and training both DL1 and DIPS algorithms in the same framework.It improves training times due to special data loading techniques and is flexible for future developments.Additionally, within this framework, a new tagger is developed: the UMAMI tagger. It combines the architectures of DL1 and DIPS and thereby simplifies the training procedure while maintaining the intermediate DIPS output. Due to its ability to better exploit correlations between the DL1 and DIPS sub-networks, compared to the two taggers independently, a major performance gain is expected.In this contribution, the advantages of the Umami framework and first performance studies of the UMAMI tagger are discussed

    Data quality monitors of vertex detectors at the start of the Belle II experiment

    No full text
    The Belle II experiment features a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric e+e− collider at KEK in Tsukuba, Japan. The accelerator completed its first phase of commissioning in 2016, and the Belle II detector saw its first electron-positron collisions in April 2018. Belle II features a newly designed silicon vertex detector based on double-sided strip layers and DEPFET pixel layers. A subset of the vertex detector was operated in 2018 to determine background conditions (Phase 2 operation). The collaboration completed full detector installation in January 2019, and the experiment started full data taking. This paper will report on the final arrangement of the silicon vertex detector part of Belle II with a focus on online monitoring of detector conditions and data quality, on the design and use of diagnostic and reference plots, and on integration with the software framework of Belle II. Data quality monitoring plots will be discussed with a focus on simulation and acquired cosmic and collision data

    Alignment for the first precision measurements at Belle II

    No full text
    International audienceOn March 25th 2019, the Belle II detector recorded the first collisions delivered by the SuperKEKB accelerator. This marked the beginning of the physics run with vertex detector.The vertex detector was aligned initially with cosmic ray tracks without magnetic field simultaneously with the drift chamber. The alignment method is based on Millepede II and the General Broken Lines track model and includes also the muon system or primary vertex position alignment. To control weak modes, we employ sensitive validation tools and various track samples can be used as alignment input, from straight cosmic tracks to mass-constrained decays.With increasing luminosity and experience, the alignment is approaching the target performance, crucial for the first physics analyses in the era of Super-BFactories. We will present the software framework for the detector calibration and alignment, the results from the first physics run and the prospects in view of the experience with the first data

    Alignment for the first precision measurements at Belle II

    Get PDF
    On March 25th 2019, the Belle II detector recorded the first collisions delivered by the SuperKEKB accelerator. This marked the beginning of the physics run with vertex detector. The vertex detector was aligned initially with cosmic ray tracks without magnetic field simultaneously with the drift chamber. The alignment method is based on Millepede II and the General Broken Lines track model and includes also the muon system or primary vertex position alignment. To control weak modes, we employ sensitive validation tools and various track samples can be used as alignment input, from straight cosmic tracks to mass-constrained decays. With increasing luminosity and experience, the alignment is approaching the target performance, crucial for the first physics analyses in the era of Super-BFactories. We will present the software framework for the detector calibration and alignment, the results from the first physics run and the prospects in view of the experience with the first data
    corecore