Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks at √s = 8 TeV with the ATLAS detector.

A search for dark matter produced in association with a Higgs boson decaying to two bottom quarks has been carried out using data from 20.3 fb−1 of pp collisions at a center-of-mass energy of 8 TeV collected by the ATLAS detector at the LHC. Events with large missing transverse energy are selected. The decay of the Higgs boson is reconstructed at low momentum with two resolved b-tagged small radius jets, and at high momentum with one large radius jet containing two b-tagged subjets. Exclusion limits are presented for the mass scales of various effective field theory operators and for the mass of the Z' mediator and tan(beta) of a Z'-2HDM simplified model that describe the interaction between dark matter particles and the Higgs boson

Identification of bb-jets in boosted and dense jet event topologies

This talk presents the calibration of various ATLAS $b$-tagging algorithms using reconstructed $t \bar{t}$ candidate events in the final state of one charged lepton, missing transverse momentum, and at least four jets, in the ATLAS $\sqrt{s}=8~\mathrm{TeV}$ $pp$ collision data sample. Expanding on previous $b$-tagging calibration studies, the $b$-tagging efficiencies are measured not only as a function of the transverse momentum or the pseudorapidity of the jets, but also as a function of quantities that are sensitive to close-by jet activity. The results measured in data are in good agreement with the predictions from simulation

Searching for Dark Matter with Boosted Higgs Decays in Proton-Proton Collisions at sqrt(s) = 13 TeV with the ATLAS Detector

Thesis (Ph.D.)--University of Washington, 2018If Dark Matter particles interact with Standard Model particles, it could be possible to pair produce Dark Matter particles in association with a detectable Standard Model particle at a collider such as the LHC. If this associated particle is a Higgs boson, the process is called ``mono-Higgs,'' since the resulting signature is a single Higgs boson balanced by missing energy from the undetected Dark Matter particles. Various Dark Matter models predict that this process could result in very boosted Higgs bosons that, if they decay to a pair of b-quarks, are reconstructed as jets using boosted Higgs tagging techniques. This thesis presents the results of a mono-Higgs search using 79.8 fb^-1 of proton-proton collision data collected at a center-of-mass energy of 13 TeV by the ATLAS detector. The observed data are found to be consistent with the expected Standard Model backgrounds. The results are interpreted and exclusion limits are set using a Z' two-Higgs-doublet model where the pseudo-scalar Higgs particle, A, couples to Dark Matter. In order to increase the sensitivity reach of the search, new boosted Higgs tagging techniques are explored and a variable radius track jet Higgs tagging technique is employed

Upgrade of the YARR DAQ system for the ATLAS Phase-II pixel detector readout chip

Yet Another Rapid Readout (YARR) is a DAQ system based on a software driven architecture using PCIe FPGA boards. It was designed for the readout of current generation ATLAS Pixel detector readout chips, which have a readout bandwidth of 160 Mb/s. YARR has been upgraded to accommodate the higher 5 Gb/s bandwidth of the next generation readout chip in development by the RD53 collaboration for the Phase-II upgrade of the ATLAS and CMS detectors. The performance results of the migration to a new PCIe FPGA board, the PLDA XpressK7, will be presented

Measurement of the W±ZW^{\pm}Z boson pair-production cross section in pppp collisions at s=13\sqrt{s}=13 TeV with the ATLAS Detector

The production of $W^{\pm}Z$ events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb$^{-1}$. The $W^{\pm}Z$ candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is $\sigma_{W^\pm Z \rightarrow \ell^{'} \nu \ell \ell}^{\textrm{fid.}} = 63.2 \pm 3.2$ (stat.) $\pm 2.6$ (sys.) $\pm 1.5$ (lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is $53.4^{+3.6}_{-2.8}$ fb. The extrapolation of the measurement from the fiducial to the total phase space yields $\sigma_{W^{\pm}Z}^{\textrm{tot.}} = 50.6 \pm 2.6$ (stat.) $\pm 2.0$ (sys.) $\pm 0.9$ (th.) $\pm 1.2$ (lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of $48.2^{+1.1}_{-1.0}$ pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent $W^+Z$ and $W^-Z$ cross sections and their ratio