Femtoscopy with identified charged pions in proton-lead collisions at $\sqrt{s}_{NN} = 5.02$ TeV with ATLAS

Bose-Einstein correlations between identified charged pions are measured for $p+\textrm{Pb}$ collisions at $\sqrt{s_{\textrm{NN}}} = 5.02~\textrm{TeV}$ with the ATLAS detector with a total integrated luminosity of $28~\textrm{nb}^{-1}$. Pions are identified using ionisation energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of average transverse pair momentum ($k_\textrm{T}$) and collision centrality. Pairs are selected with a pseudorapidity between -1.5 and 1.5 and with an average transverse momentum $0.1 < k_\textrm{T} < 0.8$ GeV. The effect on the two-particle correlation function from jet fragmentation is studied, and a new method for constraining its contributions to the measured correlations is described. The measured source sizes are observed to decrease with increasing pair $k_\textrm{T}$ and increase significantly in more central collisions. Linear scaling of the volume with average multiplicity is observed. The scaling of the extracted radii with the mean number of participants are also used to compare a selection of initial-geometry models