US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference

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

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

Observation of H→bbˉ\rightarrow b\bar{b} with the ATLAS detector

A presentation of the latest results of the observation of H$\rightarrow b\bar{b}$ with the ATLAS experiment is made. This result has been obtained through the dataset of 2015+2016+2017 as well as a combination with Run1. The combination with other production mode lead to a 5.4 $\sigma$ observed significance, while the combination with other decay modes from the VH production channel lead to a 5.3 $\sigma$ observed significance

DiHiggs searches (HH, XH) at ATLAS and CMS

In the Standard Model, the ground state of the Higgs field is not found at zero but instead corresponds to one of the degenerate solutions minimising the Higgs potential. In turn, this spontaneous electroweak symmetry breaking provides a mechanism for the mass generation of nearly all fundamental particles. The Standard Model makes a definite prediction for the Higgs boson self-coupling and thereby the shape of the Higgs potential. Experimentally, both can be probed through the production of Higgs boson pairs (HH), a rare process that presently receives a lot of attention at the LHC. Additionally, several physics scenarios beyond the Standard Model predict the existence of new particles that can subsequently decay into a pair of Higgs bosons. These include pairs of SM-like Higgs bosons (HH) as well as asymmetric decays into two scalars of different masses (SH). In this talk, the latest HH searches by the ATLAS and CMS experiments are reported, with emphasis on the results obtained with the full LHC Run 2 dataset at 13 TeV. Non-resonant HH search results are interpreted both in terms of sensitivity to the Standard Model and as limits on the Higgs boson self-coupling and the quartic VVHH coupling. Further, HH searches can be exploited to put constraints on the Wilson coefficients of Effective Field Theories. The Higgs boson self-coupling can be also constrained by exploiting higher-order electroweak corrections to single Higgs boson production. A combined measurement of both results yields the overall highest precision, and reduces model dependence by allowing for the simultaneous determination of the single Higgs boson couplings. Results for this combined measurement are also presented. ATLAS searches for resonant HH and SH production are also presented. Finally, extrapolations of recent HH results towards the High Luminosity LHC upgrade are also discussed

Étude de la désintégration du boson de Higgs en deux quarks b et amélioration du trajectographe de l'expérience ATLAS

This thesis is focussing on the search for the Standard Model Higgs boson decaying to a pair of b-quarks (bb) in the vector boson associated production mode (VH) with the data collected with the ATLAS experiment at 13 TeV corresponding to an integrated luminosity of 79.8 fb-1. An excess of events compatible with the SM Higgs boson is detected with an observed (expected) significance of 4.9 (4.3) standard deviations and a signal strength of 1.16 +/- 0.26. The analysis is combined with the results obtained previously and the analysis performed with other decay modes from one hand and other production modes on the other hand. The observation of the production and decay modes can be claimed with an observed (expected) significance of 5.3 (4.8) standard deviations for the first one and 5.4 (5.5) standard deviations for the second. Several improvements are discussed concerning the QCD background rejection and background modelling using multivariate techniques.From 2026 the LHC will enter in a new phase, providing collisions at an unprecedented rate. To understand the potential gains from that period, an extrapolation study is presented. Two scenarios of extrapolation are proposed, and the results are interpreted in terms of cross-section and signal strength. Due to the new conditions, the ATLAS Inner-Tracker will have to be upgraded to benefit from the new technologies developed to be more radiation hard and improve its resolution. Three productions of planar sensors aiming at reducing their thickness and increasing the geometrical acceptance are presented. The electrical properties and detection efficiencies have been measured on beams and are presented in this document.Cette thèse présente la recherche de la désintégration du boson de Higgs en deux quarks b avec production associée d’un boson vecteur (VH) avec les données collectées par l’expérience ATLAS à 13 TeV correspondant à une luminosité intégrée de 79.8 fb-1. Un excès d’évènements compatible avec cette particule est mesuré avec une significance observée (attendue) de 4.9 (4.3) déviations standard et une intensité de signal de 1.16 +/- 0.26. Le résultat est combiné avec les mesures obtenues précédemment et les analyses utilisant d’autres modes de désintégration et de production. Les modes de désintégration bb et production VH sont observés avec une significance observée (attendue) respective de 5.3 (4.8) et 5.4 (5.5) déviations standard. Plusieurs améliorations possibles sont débattues concernant la réjection de bruit QCD et la modélisation des bruits de fond utilisant des techniques multivariées.À partir de 2026 le LHC entrera dans une phase nouvelle, produisant des collisions à un rythme inégalé. Afin de mesurer les potentiels gains, une étude d'extrapolation est présentée. Deux scénarios d'hypothèses sont proposés, et les résultats sont interprétés en termes de section efficace et d'intensité de signal. Du fait de ces conditions de collision, le trajectographe de l'expérience ATLAS va devoir être changé en utilisant les dernières technologies développées améliorant sa résolution spatiale et sa resistance aux radiations. Trois productions de capteurs planaires présentant une épaisseur réduite et une couverture géométrique étendue sont décrites. Les propriétés électriques et les efficacités de détection ont été mesurées sur faisceau et sont présentées dans ce document

Study of the decay properties of the Higgs boson into two b quarks and upgrade of the ATLAS inner tracker

This thesis is focussing on the search for the Standard Model Higgs boson decaying to a pair of b-quarks (bb) in the vector boson associated production mode (VH) with the data collected with the ATLAS experiment at 13 TeV corresponding to an integrated luminosity of 79.8 fb$^{-1}$. An excess of events compatible with the SM Higgs boson is detected with an observed (expected) significance of 4.9 (4.3) standard deviations and a signal strength of 1.16 $\pm$ 0.26. The analysis is combined with the results obtained previously and the analysis performed with other decay modes from one hand and other production modes on the other hand. The observation of the production and decay modes can be claimed with an observed (expected) significance of 5.3 (4.8) standard deviations for the first one and 5.4 (5.5) standard deviations for the second. Several improvements are discussed concerning the QCD background rejection and background modelling using multivariate techniques. From 2026 the LHC will enter in a new phase, providing collisions at an unprecedented rate. To understand the potential gains from that period, an extrapolation study is presented. Two scenarios of extrapolation are proposed, and the results are interpreted in terms of cross-section and signal strength. Due to the new conditions, the ATLAS Inner-Tracker will have to be upgraded to benefit from the new technologies developed to be more radiation hard and improve its resolution. Three productions of planar sensors aiming at reducing their thickness and increasing the geometrical acceptance are presented. The electrical properties and detection efficiencies have been measured on beams and are presented in this document

Higgs self-coupling (mainly non-resonant di-Higgs)

Constraints on the Higgs self-coupling measured by the ATLAS colaboration (mainly non-resonant di-Higgs)

Search for di-Higgs production at the ATLAS experiment

Search for di-Higgs production at the ATLAS experimen

ATLAS and CMS non-resonant HH->bbyy

Comparison and differences between the ATLAS and CMS Run-2 searches for non resonant HH->yyb