Abstract: ATLAS measurements of two-particle correlations are presented for root s = 5.02 and 13 TeV pp collisions and for root(NN)-N-s = 5.02 TeV p + Pb collisions at the LHC. The correlation functions are measured as a function of relative azimuthal angle Delta phi, and pseudorapidity separation Delta eta, using charged particles detected within the pseudorapidity interval |eta| < 2.5. Azimuthal modulation in the long-range component of the correlation function, with | Delta eta| > 2, is studied using a template fitting procedure to remove a “back-to-back” contribution to the correlation function that primarily arises from hard-scattering processes. In addition to the elliptic, cos(2 Delta phi), modulation observed in a previous measurement, the pp correlation functions exhibit significant cos(3 Delta phi) and cos(4 Lambda phi) modulation. The Fourier coefficients v(n),(n) associated with the cos (n Lambda phi) modulation of the correlation functions for n = 2-4 are measured as a function of charged-particle multiplicity and charged-particle transverse momentum. The Fourier coefficients are observed to be compatible with cos(n phi) modulation of per-event singleparticle azimuthal angle distributions. The single-particle Fourier coefficients vn are measured as a function of charged-particle multiplicity, and charged-particle transverse momentum for n = 2-4. The integrated luminosities used in this analysis are, 64 nb(-1) for the root s = 13 TeV pp data, 170 nb(-1) for the root s = 5.02 TeV pp data, and 28 nb(-1) for the root(NN)-N-s = 5.02 TeV p + Pb data.

Abstract: Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and psi(2S), in the decay mode J/psi pi (+) pi (-), measured using 11.4 fb(-1) of pp collisions at root s = 8 Tev by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/psi(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and psi(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and psi(2S) production gives separating short- and long-lived contributions, assuming that the short-lived component is due to B (c) decays, gives R (B) = (3.57 +/- 0.33(stat) +/- 0.11(sys)) x 10(-2), with the fraction of non-prompt X(3872) produced via B (c) decays for p (T)(X(3872)) > 10 GeV being (25 +/- 13(stat) +/- 2(sys) +/- 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and psi(2S) decays are also measured and compared to theoretical predictions.

Abstract: Measurements of top quark spin observables in tt events are presented based on 20.2 fb(-1) of root s = 8TeV proton-proton collisions recorded with the ATLAS detector at the LHC. The analysis is performed in the dilepton final state, characterised by the presence of two isolated leptons ( electrons or muons). There are 15 observables, each sensitive to a different coefficient of the spin density matrix of tt production, which are measured independently. Ten of these observables are measured for the first time. All of them are corrected for detector resolution and acceptance effects back to the parton and stable-particle levels. The measured values of the observables at parton level are compared to Standard Model predictions at next-to-leading order in QCD. The corrected distributions at stable-particle level are presented and the means of the distributions are compared to Monte Carlo predictions. No significant deviation from the Standard Model is observed for any observable.