333 research outputs found

    Avancées technologiques dans le domaine des pixels planaires pour l'expérience ATLAS Phase 2

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    The Large Hadron Collider (LHC) will go through the accelerator complex upgrade during the LS3 long shutdown in 2023-2025 to move to the High Luminosity phase (HL-LHC). As a result, an instantaneous luminosity will increase sevenfold to 7.5×10³⁎ cm⁻ÂČs⁻Âč, corresponding to approximately 200 inelastic collisions per bunch-crossing, whereas the LHC runs resulted in up to 50 collisions per bunch-crossing. During the operation of the HL-LHC, in order to achieve high-precision in studies of Standard Model processes and searches for new physics, about 4000 fb⁻Âč of integrated luminosity be collected, which is of an order of magnitude larger than over the entire LHC period. The present ATLAS Inner Detector (ID) will not be able to efficiently cope with the increased event rate and radiation dose. Due to this fact the complete replacement of the ID is foreseen with fully silicon Inner Tracker (ITk) to provide high tracking performance in harsher environment delivered by the HL-LHC. This thesis is focused on the study of new n+-in-p planar silicon sensors, as a promising option to instrument the ITk pixel layers, considering their radiation hardness and cost-effectiveness. Sensors of different thicknesses ranging from 50 ”m to 150 ”m of active and slim edge designs have been tested at a high energy particle beam to investigate hit efficiency performance analyzed on the pixel active area and on the edge area before and after irradiation. The test beam results and their comparison for the different designs of the pixel sensors compatible with FE-I4 readout chip are discussed. Also, the first results on test beam characterization of the pixel modules employing a newly developed prototype of readout chip for the ITk, RD53A chip, implemented in 65 nm CMOS technology, were obtained. The sensors with the decreased to 25×100 ”mÂČ and 50×50 ”mÂČ pixel pitch to maintain the lower level of occupancy at high particle multiplicity were measured. Additionally, the tests of ring oscillators, contained in RD53A chip, which may be used as a monitor of the received radiation dose, were carried out depending on temperature, supplied voltage and irradiation level up to 500 MRad. Finally, the test bench setup for silicon pixel detectors characterization using an infra-red laser has been the subject of an original development in this thesis. The setup was developed in the clean room at Laboratoire de l'accĂ©lĂ©rateur linĂ©aire (LAL) and it is capable of rapidly measuring the functional characteristics, providing a flexible charge injection with well-defined hit position to characterize the silicon pixel matrixes. The software to control the setup was created using LabVIEW programming environment. The results of the measurements with the FE-I4 module implemented with openings allowing the laser beam passage on a sensor backside are presented in this thesis.Le complexe d'accĂ©lĂ©rateurs du grand collisionneur de hadrons (le Large Hadron Collider - LHC) sera mis Ă  jour lors du long arrĂȘt de la pĂ©riode LS3 en 2023-2025 pour passer Ă  la phase de haute luminositĂ© (HL-LHC). La luminositĂ© instantanĂ©e sera multipliĂ©e par 5 pour atteindre 7.5×10³⁎ cm⁻ÂČs⁻Âč, ce qui correspond Ă  environ 200 collisions inĂ©lastiques par croisement de paquets comparĂ© aux 50 par croisement au LHC. Pendant le fonctionnement du HL-LHC, afin d'atteindre une haute prĂ©cision dans les Ă©tudes des processus physiques du modĂšle standard et les recherches de nouvelle physique, le collisionneur Ă  protons devra fournir une luminositĂ© intĂ©grĂ©e de l’ordre 400 fb⁻Âč par an pendant une dizaine d’annĂ©es soit 4000 fb⁻Âč escomptĂ©es. Ceci reprĂ©sente un ordre de grandeur supĂ©rieur Ă  l'ensemble de la pĂ©riode du LHC. Le dĂ©tecteur interne (Inner Detector) ATLAS actuel ne sera pas en mesure de faire face efficacement Ă  l'augmentation du taux d'Ă©vĂ©nements et de la dose de rayonnement. Afin d’obtenir des performances au minimum Ă©gales ou supĂ©rieures Ă  celles de la phase LHC, et tenant compte d’un environnement plus hostile en termes de radiations et d’empilements d’évĂšnements, il a Ă©tĂ© dĂ©cidĂ© d’opĂ©rer le remplacement complet du trajectomĂštre interne ou Inner Tracker (ITk); Ă  cette fin, une technologie tout silicium a Ă©tĂ© choisie. Cette thĂšse est axĂ©e sur l'Ă©tude de nouveaux capteurs pixels planaires fins Ă  bords trĂšs minces, basĂ©s sur le concept d’utilisation de matrices de diodes Ă  implants dopĂ©s n sur un substrat dopĂ© p. Ce choix est motivĂ© par les critĂšres de meilleure performance intrinsĂšque, de radio-tolĂ©rance Ă©levĂ©e ainsi qu’un coĂ»t de production optimisĂ© pour de grandes surfaces. Dans ce travail, des capteurs de diffĂ©rentes Ă©paisseurs allant de 50 ÎŒm Ă  150 ÎŒm dotĂ©s de bords actifs et minces ont fait l’objet d’études approfondies notamment lors de leur fonctionnement Ă  haut flux de particules chargĂ©es. De nombreuses analyses minutieuses ont Ă©tĂ© menĂ©es pour dĂ©terminer leur rĂ©solution en position Ă  l’aide d’un tĂ©lescope de faisceau de haute Ă©nergie. Les rĂ©gions d’impacts sur la zone active des pixels ainsi que sur la rĂ©gion des contours ont Ă©tĂ© scrutĂ©es avant et aprĂšs leur irradiation. En effet, de nombreux rĂ©sultats obtenus en faisceau de protons et Ă©lectrons seront montrĂ©s, notamment une Ă©tude comparative des diffĂ©rents concepts de matrices de capteurs de pixels planaires lus avec la puce de lecture « FE-I4 » en technologie CMOS 130 nm. PrĂ©parant la phase future du LHC, nous montrerons les premiers rĂ©sultats obtenus avec la nouvelle gĂ©nĂ©ration de pixels granulaires. Ces matrices ont Ă©tĂ© couplĂ©es Ă  la nouvelle puce de lecture frontale rĂ©cemment dĂ©veloppĂ©e au CERN, utilisant la technologie CMOS 65 nm. Ces capteurs dotĂ©s d’ une plus fine granularitĂ© de 50×50 ÎŒmÂČ , ont un pas optimisĂ© lequel est nĂ©cessaire pour maintenir un taux d'occupation aussi bas que possible dans un contexte de multiplicitĂ©s de particules chargĂ©es trĂšs Ă©levĂ©es. Dans ce travail, une contribution personnelle Ă  l’électronique de lecture sera dĂ©taillĂ©e, en particulier les Ă©tudes ont Ă©tĂ© menĂ©es sur la puce nommĂ©e «Ring-Oscillator» ou moniteur de radiations, dĂ©veloppĂ©e au laboratoire. On dĂ©crira son comportement dynamique en fonction de la tempĂ©rature, de la tension nominale et en conditions hautement radiatives (500 MRad). La mise au point d’un nouvel outil de caractĂ©risation de dĂ©tecteurs pixels a fait l’objet d’un dĂ©veloppement important. GrĂące Ă  un ensemble basĂ© sur une excitation laser de 1060 nm, il sera possible de disposer d’un systĂšme prĂ©cis et autonome capable de mesurer rapidement les caractĂ©ristiques fonctionnelles des matrices de pixels avec une excellente rĂ©solution spatiale. Les caractĂ©ristiques de cet outil feront l’objet d’une prĂ©sentation exhaustive

    Development of a compact test board for silicon sensors IV/CV characterization

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    To build silicon trackers of modern and future high-luminosity collider experiments, thousands of silicon strip modules have to be produced and tested. The modules in new trackers must reliably work usually during 5-10 years or more under harsh irradiation conditions, as it will be impossible to replace a failing module once installed inside the detector. It means that reliable and rigorous testing of strip modules and its components is mandatory. To sustain the production throughput we should be able to test several modules in parallel. For this reason a fast, reliable, scalable and cost effective production QC test bench has to be designed and implemented. For the CV and IV measurements of sensors and modules we are developing a low-cost (less than 500 ) integrated electronic board which will be scaled up to ten channels to measure DUTs in parallel. In the current work the design of the IV/CV board and the calibration procedure to increase the accuracy of the current and capacitance measurements, for which a special calibration dipole board based on tight tolerance capacitors and resistors has been designed, as well as future development plans are described.SCOPUS: cp.jinfo:eu-repo/semantics/publishe

    Performance of n-on-p planar pixel sensors with active edges at high-luminosity environment

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    International audienceFuture high-energy physics experiments require highly segmented silicon sensors of increased geometrical efficiency with the ability to withstand extremely high radiation damage. The performance of planar n-on-p sensors with active edges is simulated at high radiation fluences up to 1 × 1016^{16} neq_{eq}/cm2^{2}, using a three-level trap model for p-type silicon material. Taking advantage of the secondary ion mass spectrometry (SIMS) technique, an accurate representation of the structure was obtained in terms of doping profile. The breakdown voltage, leakage current, hole density and electric field distributions as well as the charge collection efficiency (CCE) are studied as a function of radiation fluence

    Evidence for four-top quark production in proton-proton collisions at s=13TeV

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    The production of four top quarks (ttÂŻttÂŻ) is studied with LHC proton-proton collision data samples collected by the CMS experiment at a center-of-mass energy of 13 TeV, and corresponding to integrated luminosities of up to 138fb−1. Events that have no leptons (all-hadronic), one lepton, or two opposite-sign leptons (where lepton refers only to prompt electrons or prompt muons) are considered. This is the first ttÂŻttÂŻ measurement that includes the all-hadronic final state. The observed significance of the ttÂŻttÂŻ signal in these final states of 3.9 standard deviations (1.5 expected) provides evidence for ttÂŻttÂŻ production, with a measured cross section of 36−11+12fb. Combined with earlier CMS results in other final states, the signal significance is 4.0 standard deviations (3.2 expected). The combination returns an observed cross section of 17±4(stat)±3(syst)fb, which is consistent with the standard model prediction.0info:eu-repo/semantics/publishe

    Probing Heavy Majorana Neutrinos and the Weinberg Operator through Vector Boson Fusion Processes in Proton-Proton Collisions at √s = 13 TeV

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    The first search exploiting the vector boson fusion process to probe heavy Majorana neutrinos and the Weinberg operator at the LHC is presented. The search is performed in the same-sign dimuon final state using a proton-proton collision dataset recorded at s = 13 TeV ,collected with the CMS detector and corresponding to a total integrated luminosity of 138 fb − 1 .The results are found to agree with the predictions of the standard model. For heavy Majorana neutrinos, constraints on the squared mixing element between the muon and the heavy neutrino are derived in the heavy neutrino mass range 50 GeV-25 TeV; for masses above 650 GeV these are the most stringent constraints from searches at the LHC to date. A first test of the Weinberg operator at colliders provides an observed upper limit at 95% confidence level on the effective ÎŒ ÎŒ Majorana neutrino mass of 10.8 GeV.0CMS Collaborationinfo:eu-repo/semantics/publishe

    Beam test performance of a prototype module with Short Strip ASICs for the CMS HL-LHC tracker upgrade

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    The Short Strip ASIC (SSA) is one of the four front-end chips designed for the upgrade of the CMS Outer Tracker for the High Luminosity LHC. Together with the Macro-Pixel ASIC (MPA) it will instrument modules containing a strip and a macro-pixel sensor stacked on top of each other. The SSA provides both full readout of the strip hit information when triggered, and, together with the MPA, correlated clusters called stubs from the two sensors for use by the CMS Level-1 (L1) trigger system. Results from the first prototype module consisting of a sensor and two SSA chips are presented. The prototype module has been characterized at the Fermilab Test Beam Facility using a 120 GeV proton beam.0info:eu-repo/semantics/publishe

    Observation of Same-Sign WW Production from Double Parton Scattering in Proton-Proton Collisions at √s = 13 TeV

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    The first observation of the production of Formula Presented bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of Formula Presented recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign Formula Presented bosons decaying leptonically is Formula Presented, whereas the measured fiducial cross section is Formula Presented. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis.0CMS Collaborationinfo:eu-repo/semantics/publishe

    Selection of the silicon sensor thickness for the Phase-2 upgrade of the CMS Outer Tracker

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    During the operation of the CMS experiment at the High-Luminosity LHC the silicon sensors of the Phase-2 Outer Tracker will be exposed to radiation levels that could potentially deteriorate their performance. Previous studies had determined that planar float zone silicon with n-doped strips on a p-doped substrate was preferred over p-doped strips on an n-doped substrate. The last step in evaluating the optimal design for the mass production of about 200 m2 of silicon sensors was to compare sensors of baseline thickness (about 300 ÎŒm) to thinned sensors (about 240 ÎŒm), which promised several benefits at high radiation levels because of the higher electric fields at the same bias voltage. This study provides a direct comparison of these two thicknesses in terms of sensor characteristics as well as charge collection and hit efficiency for fluences up to 1.5 × 1015 neq/cm2. The measurement results demonstrate that sensors with about 300 ÎŒm thickness will ensure excellent tracking performance even at the highest considered fluence levels expected for the Phase-2 Outer Tracker.0info:eu-repo/semantics/publishe

    Comparative evaluation of analogue front-end designs for the CMS Inner Tracker at the High Luminosity LHC

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    The CMS Inner Tracker, made of silicon pixel modules, will be entirely replaced prior to the start of the High Luminosity LHC period. One of the crucial components of the new Inner Tracker system is the readout chip, being developed by the RD53 Collaboration, and in particular its analogue front-end, which receives the signal from the sensor and digitizes it. Three different analogue front-ends (Synchronous, Linear, and Differential) were designed and implemented in the RD53A demonstrator chip. A dedicated evaluation program was carried out to select the most suitable design to build a radiation tolerant pixel detector able to sustain high particle rates with high efficiency and a small fraction of spurious pixel hits. The test results showed that all three analogue front-ends presented strong points, but also limitations. The Differential front-end demonstrated very low noise, but the threshold tuning became problematic after irradiation. Moreover, a saturation in the preamplifier feedback loop affected the return of the signal to baseline and thus increased the dead time. The Synchronous front-end showed very good timing performance, but also higher noise. For the Linear front-end all of the parameters were within specification, although this design had the largest time walk. This limitation was addressed and mitigated in an improved design. The analysis of the advantages and disadvantages of the three front-ends in the context of the CMS Inner Tracker operation requirements led to the selection of the improved design Linear front-end for integration in the final CMS readout chip.0info:eu-repo/semantics/publishe

    Measurement of the double-differential inclusive jet cross section in proton-proton collisions at s\sqrt{s} = 5.02 TeV

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    International audienceThe inclusive jet cross section is measured as a function of jet transverse momentum pTp_\mathrm{T} and rapidity yy. The measurement is performed using proton-proton collision data at s\sqrt{s} = 5.02 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 27.4 pb−1^{-1}. The jets are reconstructed with the anti-kTk_\mathrm{T} algorithm using a distance parameter of RR = 0.4, within the rapidity interval ∣y∣\lvert y\rvert<\lt 2, and across the kinematic range 0.06 <\ltpTp_\mathrm{T}<\lt 1 TeV. The jet cross section is unfolded from detector to particle level using the determined jet response and resolution. The results are compared to predictions of perturbative quantum chromodynamics, calculated at both next-to-leading order and next-to-next-to-leading order. The predictions are corrected for nonperturbative effects, and presented for a variety of parton distribution functions and choices of the renormalization/factorization scales and the strong coupling αS\alpha_\mathrm{S}
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