Measurement of the ridge and Bose-Einstein correlations in pp and pPb collisions with the ATLAS detector at the LHC

ATLAS measurement of azimuthal correlations between particle pairs at large pseudorapidity separation in pp and pPb collisions are presented. The data were collected using a combination of the minimum-bias and high track-multiplicity triggers. A detailed study of the dependence of two-particle correlations on the charged particle multiplicity, transverse momentum of the pair constituents and the pseudorapidity separation between particles forming a pair is shown. Measurements of multi-particle cumulants in the azimuthal angles of produced particles in wide pseudorapidity ($|\eta|<2.5$) and multiplicity ranges, with the aim to extract a single particle anisotropy coefficient, $v_1$-$v_5$, are also presented. These measurements can help to understand the origin of the long-range correlations seen in high-multiplicity pp and p+Pb collisions. In addition, one and three-dimensional HBT radii in p+Pb collisions are presented as a function of event centrality. An estimation of dE/dx in the pixel detector is used to identify charged pions. These particles are selected from $|\eta| < 2.5$ and the measurement is performed in several pair-average momentum ($k_T$) bins from 0.1 GeV to 1.0 GeV. The measured source sizes are observed to increase with collision centrality. The contribution to the correlation function from hard processes is studied and a novel method for tuning the amplitude of this background in the data is introduced.