Particle production and femtoscopy in $\sqrt{s_{\textrm{NN}}} =$ 5.02 TeV $p$-Pb collisions with ATLAS

Mean charged particle multiplicity, per-event charged particle spectra and nuclear modification factors are measured with the ATLAS detector at the LHC in $p$+Pb interactions at sqrt(s_NN)=5.02 TeV. Results are presented as a function of transverse momentum, rapidity, and in different intervals of collision centrality, which is characterized in $p$+Pb collisions by the total transverse energy measured over the pseudorapidity interval $-3.2<\eta<-4.9$ in the direction of the lead beam. Three different calculations of the number of nucleons participating in $p$+Pb collisions have been performed, assuming the Glauber model and its Glauber-Gribov Colour Fluctuation extensions. The results using different models are compared with each other, as well as with other measurements made under the same conditions and also with centrality definition based on different rapidity intervals. In addition, Bose-Einstein correlations between identified charged pions are measured for $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02~\mathrm{TeV}$ with the ATLAS detector with a total integrated luminosity of 28 $\mathrm{nb}^{-1}$. Pions are identified using ionization 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 ($k_{\mathrm{T}}$) and rapidity ($y^{*}_{k}$) as well as collision centrality. Pairs are selected with a rapidity $-2 < y^{*} < 1$ and with an average transverse momentum $0.1 < k_{\mathrm{T}} < 0.8$ 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 substantially larger in more central collisions and are observed to decrease with increasing pair $k_{\mathrm{T}}$. Radii are also evaluated in intervals of $y^{*}$ and a correlation with the local multiplicity $dN/dy^{*}$ is demonstrated. The scaling of the extracted radii with the mean number of participants is also used to compare the different Glauber-Gribov initial-geometry models.