Abstract: This Letter describes a model-agnostic search for pairs of jets (dijets) produced by resonant and non-resonant phenomena beyond the Standard Model in 3.6 fb(-1) of proton-proton collisions with a centre-of-mass energy of root s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the smoothly falling prediction of the Standard Model. The data are also compared to a Monte Carlo simulation of Standard Model angular distributions derived from the rapidity of the two jets. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% CL, quantum black holes with threshold masses below 8.3 TeV, 8.1 TeV, or 5.1 TeV in three different benchmark scenarios; resonance masses below 5.2 TeV for excited quarks, 2.6 TeV in a W' model, a range of masses starting from mZ' = 1.5 TeVand couplings from g(q) = 0.2 in a Z' model; and contact interactions with a compositeness scale below 12.0 TeV and 17.5 TeV respectively for destructive and constructive interference between the new interaction and QCD processes. These results significantly extend the ATLAS limits obtained from 8 TeV data. Gaussian-shaped contributions to the mass distribution are also excluded if the effective cross-section exceeds values ranging from approximately 50-300 fb for masses below 2 TeV to 2-20 fb for masses above 4 TeV.

Abstract: This paper presents a new method of reconstructing the individual charged and neutral hadrons in tau decays with the ATLAS detector. The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the existing tau reconstruction. The performance of the reconstruction algorithm is optimised and evaluated using simulation and validated using samples of Z -> tau tau and Z(-> μmu)+jets events selected from proton-proton collisions at a centre-of-mass energy root s = 8 TeV, corresponding to an integrated luminosity of 5 fb(-1).

Abstract: Distributions of transverse momentum p(T)(ll) and the related angular variable phi(eta)*. of Drell-Yan lepton pairs are measured in 20.3 fb(-1) of proton-proton collisions at root s = 8 TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in proton-proton collisions at root s = 7 TeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of phi(eta)*. < 1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of phi(eta)*. this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of p(T)(ll) while the fixed-order prediction of Dynnlo falls below the data at high values of p(T)(ll). ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the phi(eta)*. and p(T)(ll) distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.