892 research outputs found

    PropriĂ©tĂ©s du Boson de Higgs se dĂ©sintĂ©grant en 4 leptons au LHC dans l’expĂ©rience ATLAS : masse, limite sur la contribution Ă  haute masse et sur la largeur

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    The theme of the analyses presented in this Thesis is the measurement of the Higgs boson properties in the H→ZZ→4l decay channel with the ATLAS experiment at the LHC. A detailed overview on the electron calibration process is first presented. In this regard, the track-cluster combination algorithm is found to improve the energy resolution of low ET electrons by exploiting both track and cluster information into a maximum likelihood fit. The improvement in resolution is approximately 18-20% for J/Κ dielectron decays, and of the order of 3% for Z→ee events. In addition, the E-p combination algorithm has also been applied to the H→ZZ→4l channel with electrons in the final state resulting in a non-negligible gain on the invariant mass distribution (4-5%). Secondly, the Higgs mass and its total width are evaluated in the H→ZZ→4l channel. The Higgs mass is measured in the 4l decay channel with particular interest on the beneficial effects brought by the improved electron calibration and the track-cluster combination. The mass on the full 2011 and 2012 datasets is worked out with a 2-dimensional fit on the invariant mass of the 4 lepton final state, m4l, and on a boosted decision tree (BDT)-based output conceived against the main ZZ irreducible background and constructed on variables that are sensitive to the Higgs boson spin-parity state. Regarding the Higgs width, results are based on a relatively recent approach aimed at indirectly constraining the Higgs boson width by exploiting the m4l high-mass region where the Higgs boson acts as a propagator. The Higgs production cross section in the on-shell m4l region, where the Higgs boson is a resonance, depends on the total Higgs width, whereas this is not the case for the high mass m4l (off-shell). Limits on the Higgs width can be therefore set when merging the off-shell results with the on-shell ones. A limit of ∌ 6.7 times ΓSMH is obtained in the four lepton channel. Secondly, by combining with the on-shell measurement and using all the decay channels in the analysis, i.e. ZZ→4l, ZZ→2l2Îœ and WW→lÎœlÎœ, the results lead to an observed (expected) 95% C.L. upper limit on the Higgs boson total width of 22.7 (33.0) MeV (4.2 MeV is the Standard Model predicted Higgs width at mH=125 GeV).The last section of the thesis is devoted to the evaluation of the Higgs width at √s=14 TeV in the high luminosity scenario (High Luminosity LHC), 300 fb⁻Âč and 3000 fb⁻Âč, by employing the same techniques exploited in the previous Run 1 analysis at √s=8 TeV.Le thĂšme des analyses prĂ©sentĂ©es dans ce document est la mesure des propriĂ©tĂ©s du boson de Higgs se dĂ©sintĂ©grant dans le mode H→ZZ→4l dans l'expĂ©rience ATLAS au CERN. Le document commence par un rĂ©sumĂ© dĂ©taillĂ© concernant la procĂ©dure d'Ă©talonnage des Ă©lectrons: l'algorithme de combinaison trace-cluster amĂ©liore la rĂ©solution en Ă©nergie (surtout pour les Ă©lectrons ayant une faible Ă©nergie transverse) en exploitant les informations du cluster et de la trace dans un ajustement par maximum de vraisemblance. L'amĂ©lioration en rĂ©solution est approximativement de 18-20% pour les dĂ©sintĂ©grations du J/Κ en di-Ă©lectrons, et 3% pour Z→ee. Par la suite, la combinaison E-p est appliquĂ©e au canal H→ZZ→4l avec Ă©lectrons dans l'Ă©tat final permettant d’obtenir un gain modĂ©rĂ© sur la distribution de la masse invariante (4-5%). En deuxiĂšme lieu, la masse du boson de Higgs et sa largeur sont estimĂ©es, en particulier afin de comprendre les effets apportĂ©s par l'utilisation de l'algorithme de combinaison trace-cluster. La masse a Ă©tĂ© calculĂ©e en se servant d'un ajustement Ă  deux dimensions appliquĂ© sur la masse invariante m4l et un score de discrimination du signal contre le bruit de fond ZZ*. Cette discrimination est obtenue en exploitant les corrĂ©lations angulaires dont les distributions sont sensibles au spin et Ă  la paritĂ© du boson de Higgs. L’étude sur la largeur du boson est ensuite dĂ©taillĂ©e : les rĂ©sultats sont basĂ©s sur une approche qui vise Ă  contraindre cette largeur en analysant la rĂ©gion de haute masse m4l oĂč le boson de Higgs se comporte comme un propagateur. La section efficace au pic de la rĂ©sonance (« on-shell ») dĂ©pend de la largeur totale du boson de Higgs, ce qui n’est pas le cas pour la production dans la rĂ©gion de haute masse (« off-shell »). Par consĂ©quent, des limites indirectes sur la largeur peuvent ĂȘtre dĂ©terminĂ©es en combinant les rĂ©gions « on-shell » et « off-shell ». Une limite Ă  6.7 fois la largeur Higgs ΓSMH est obtenue via le canal 4l. En combinant la mesure « on-shell » avec tous les canaux de dĂ©sintĂ©gration Ă©tudiĂ©s (notamment ZZ→4l, ZZ→2l2Îœ and WW→lÎœlÎœ), les rĂ©sultats aboutissent Ă  une limite observĂ©e (attendue) sur la largeur totale de 22.7 (33.0) MeV. La derniĂšre partie de ce travail de thĂšse est consacrĂ©e Ă  l'analyse sur la largeur du boson de Higgs en quatre leptons Ă  haute (High-Luminosity LHC) luminositĂ© intĂ©grĂ©e (respectivement 300 fb⁻Âč et 3000 fb⁻Âč) : il s’agit d’une Ă©tude extrapolant Ă  √s =14 TeV les techniques utilisĂ©es pour l’analyse Ă  8 TeV (Run 1)

    InGaAs/InP SPAD with Monolithically Integrated Zinc-Diffused Resistor

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    Afterpulsing and optical crosstalk are significant performance limitations for applications employing near-infrared single-photon avalanche diodes (SPADs). In this paper, we describe an InGaAs/InP SPAD with monolithically integrated resistor that is fully compatible with the planar fabrication process and provides a significant reduction of the avalanche charge and, thus, of afterpulsing and optical crosstalk. In order to have a fast SPAD reset (<50 ns), we fabricated quenching resistors ranging from 10 to 200 k\Ω, smaller than what is available in the literature. The resistor, fabricated with the zinc diffusions already used for avoiding premature edge-breakdown, promptly reduces the avalanche current to a low value ∌ 100~ ÎŒ A in less than 1 ns, while an active circuit completes the quenching and enforces a well-defined hold-off. The proposed mixed-quenching approach guarantees an avalanche charge reduction of more than 20 times compared with similar plain SPADs, enough to reduce the hold-off time down to 1 ÎŒ s. Finally, a compact single-photon counting module based on this detector and featuring 70-ps photon-timing jitter is presented

    InGaAs/InP single-photon detector with low noise, low timing jitter and high count rate

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    We present a new InGaAs/InP Single-Photon Avalanche Diode (SPAD) with high detection efficiency and low noise, which has been employed in a sinusoidal-gated setup to achieve very low afterpulsing probability and high count rate. The new InGaAs/InP SPAD has lower noise compared to previous generations thanks to the improvement of Zinc diffusion conditions and the optimization of the vertical structure. A detector with 25 ÎŒm active-area diameter, operated in gated-mode with ON time of tens of nanoseconds, has a dark count rate of few kilo-counts per second at 225 K and 5 V of excess bias, 30% photon detection efficiency at 1550 nm and a timing jitter of less than 90 ps (FWHM) at 7 V of excess bias. In order to reduce significantly the afterpulsing probability, these detectors were operated with a sinusoidal gate at 1.3 GHz. The extremely short gate ON time (less than 200 ps) reduces the charge flowing through the junction, thus reducing the number of trapped carriers and, eventually, lowering the afterpulsing probability. The resulting detection system achieves a maximum count rate higher than 650 Mcount/s with an afterpulsing probability of about 1.5%, a photon detection efficiency greater than 30% at 1550 nm and a temporal resolution of less than 90 ps (FWHM)

    Predictores de respuesta favorable a la colocaciĂłn de derivaciĂłn ventriculoperitoneal en pacientes con hidrocefalia normotensiva idiopĂĄtica

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    Introduction: The indication of a ventriculoperitoneal shunt (VPS) is discussed in patients with idiopathic normal pressure hydrocephalus (iNPH), due to the heterogeneity of the response to treatment and the risks involved in neurosurgery. Objective: To search for clinical factors and complementary studies in order to determine predictors of a favorable response to the VPS placement in patients with iNPH. Methodology: A retrospective study of patients with probable iNPH (according to international guidelines) treated with VPS assisted in a neurological clinic from January 2014 to January 2017 was conducted. A univariate statisticalanalysis of the variables considered as possible prognostic factors was performed. Results: 58 patients were included. Women presented 3.68 times more chances of improvement after the VPS (p=0.019). Good response to the gait test was associated with better response to the VPS (p=0.024). Conclusions: Female sex and good response to the gait test could be considered as predictors of a favorable response to the VPS placement in patients with iNPH. A prospective study is necessary to achieve a homogeneous diagnostic evaluation and a more extensive longitudinal follow-up to evaluate the clinical evolution in this group of patients.IntroducciĂłn: La indicaciĂłn de la derivaciĂłn ventriculoperitoneal (DVP) se discute en pacientes con hidrocefalia normotensiva idiopĂĄtica (HNTi), debido a la heterogeneidad de la respuesta al tratamiento y los riesgos que conlleva la neurocirugĂ­a. Objetivo: BĂșsqueda de factores clĂ­nicos y estudios complementarios, para determinar predictores de respuesta favorable a la colocaciĂłn de DVP en pacientes con HNTi. MetodologĂ­a: Estudio retrospectivo de pacientes con probable HNTi (segĂșn guĂ­as internacionales) tratados con DVP asistidos en una clnica neurolĂłgica desde enero de 2014 hasta enero de 2017. Se realizĂł un anĂĄlisis estadĂ­stico univariado de las variables consideradas como posibles factores pronĂłsticos. Resultados: seincluyeron 58 pacientes. Las mujeres presentaron 3,68 veces mĂĄs posibilidades de mejora tras la DVP (p=0,019). La buena respuesta a la prueba de la marcha se asociĂł con una mejor respuesta a la DVP (p=0,024). Conclusiones: el sexo femenino y la buena respuesta a la prueba de la marcha podrĂ­an&nbsp; considerarse predictores de una respuesta favorable a la colocaciĂłn de la DVP en pacientes con HNTi. Es necesario un estudio prospectivo para lograr una evaluaciĂłn diagnĂłstica homogĂ©nea y un seguimiento longitudinal mĂĄs extenso para evaluar la evoluciĂłn clĂ­nica en este grupo de pacientes

    Report from Working Group 3: Beyond the standard model physics at the HL-LHC and HE-LHC

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    This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as 33 ab−1^{-1} of data taken at a centre-of-mass energy of 14 TeV, and of a possible future upgrade, the High Energy (HE) LHC, defined as 1515 ab−1^{-1} of data at a centre-of-mass energy of 27 TeV. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by 20−50%20-50\% on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will, generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics

    Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

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    A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

    Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at s √ =8  TeV with the ATLAS detector