T. Hryn’ova

Muon reconstruction performance of the ATLAS detector in proton-proton collision data at √s=13 TeV

This article documents the performance of the ATLAS muon identification and reconstruction using the LHC dataset recorded at √ s = 13 TeV in 2015. Using a large sample of J/ψ → μμ and Z → μμ decays from 3.2 fb−1 of pp collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to 99 % over most of the covered phase space (|η| < 2.5 and 5 < pT < 100 GeV). The isolation efficiency varies between 93 and 100 % depending on the selection applied and on the momentum of the muon. Both efficiencies are well reproduced in simulation. In the central region of the detector, the momentum resolution is measured to be 1.7 % (2.3 %) for muons from J/ψ → μμ (Z → μμ) decays, and the momentum scale is known with an uncertainty of 0.05 %. In the region |η| > 2.2, the pT resolution for muons from Z → μμ decays is 2.9 % while the precision of the momentum scale for low-pT muons from J/ψ → μμ decays is about 0.2 %.

Measurement of the total cross section from elastic scattering in pp collisions at √s=8 TeV with the ATLAS detector

A measurement of the total pp cross section at the LHC at View the MathML sources=8 TeV is presented. An integrated luminosity of 500 μb−1500 μb−1 was accumulated in a special run with high-β⋆β⋆ beam optics to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the −t range from 0.014 GeV20.014 GeV2 to 0.1 GeV20.1 GeV2 to extrapolate t→0t→0, the total cross section, σtot(pp→X)σtot(pp→X), is measured via the optical theorem to be View the MathML sourceσtot(pp→X)=96.07±0.18(stat.)±0.85(exp.)±0.31(extr.)mb, where the first error is statistical, the second accounts for all experimental systematic uncertainties and the last is related to uncertainties in the extrapolation t→0t→0. In addition, the slope of the exponential function describing the elastic cross section at small t is determined to be View the MathML sourceB=19.74±0.05(stat.)±0.23(syst.)GeV−2.

Search for high-mass new phenomena in the dilepton final state using proton–proton collisions at s=13TeV with the ATLAS detector

A search is conducted for both resonant and non-resonant hig h-mass new phenomena in dielectron and dimuon final states. The search uses 3.2 fb −1 o proton–proton collision data, collected at √ s= 13 TeV by the ATLAS experiment at the LHC in 2015. The dilepton invariant mass is used as the discriminating variable. No significa t deviation from the Standard Model prediction is observed; therefore limits are set on th e signal model parameters of interest at 95% credibility level. Upper limits are set on the c ross-section times branching ratio for resonances decaying to dileptons, and the limits are con verted into lower limits on the resonance mass, ranging between 2.74 TeV and 3.36 TeV, depen ing on the model. Lower limits on thellqq contact interaction scale are set between 16.7 TeV and 25.2 T eV, also depending on the model. c

Measurement of the

A bstractA measurement of the ZZ production cross section in the ℓ−ℓ+ℓ′ −ℓ′ + and ℓ−ℓ+νν¯

production cross section in

{\ell}^{-}{\ell}^{+}\nu \overline{\nu}

collisions at

channels (ℓ = e, μ) in proton-proton collisions at s=8

= 8 TeV using the

\sqrt{s}=8