Measurement of the tt-channel single top-quark and top-antiquark differential cross-sections in pppp collisions at s=8 TeV\sqrt{s} = 8~\textrm{TeV} with the ATLAS detector

In this document, differential cross-section measurements of $t$-channel single top-quark production are presented. 20.2fb$^{-1}$ of data collected by the ATLAS experiment in proton-proton collisions in the LHC at a centre-of-mass energy of 8TeV are used. Differential cross-sections as a function of the transverse momentum and rapidity of both the top quark and the top antiquark have been measured at both parton and particle level. The transverse momentum and rapidity differential cross-sections of the scattered light-quark jet have been measured at particle level. All measurements are compared to different Monte Carlo predictions as well as to available fixed-order QCD calculations.Comment: TOP2016 conferenc

Measurements of differential t-channel single top-quark production cross-sections in proton–proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector

Proton-proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector in 2012, corresponding to an integrated luminosity of 20.2 fb-1, are used to measure absolute and normalised differential cross-sections of single top quarks produced in the t-channel. They are measured as a function of the transverse momentum and the absolute value of the rapidity of the top quarks and the top antiquarks at both parton level and particle level. The transverse momentum and rapidity differential cross-sections of the scattered light-quark jets are extracted at particle level. Selected events contain one charged lepton, missing transverse momentum, and two jets, one of which is identified as originating from a b-quark. An artificial neural network is used to separate thet-channel signal from its background. A cut on the neural network discriminator is applied to achieve a good signal-to-background ratio. The differential cross-sections are extracted using an iterative Bayesian unfolding. The measured cross-sections are compared to different Monte Carlo predictions as well as to available fixed-order QCD calculations. All results agree with the Standard Model predictions

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