Two-pion femtoscopy in $p+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$ with ATLAS

Measurement of the ridge and Bose-Einstein correlations in pp and pPb collisions with the ATLAS detector at the LHC $$ $$ ATLAS measurements 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 (|η|<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 ($k_\mathrm{T}$) 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.