Underlying event background in two-pion correlations in p + p Collisions at $\sqrt{s}$ = 0.9 TeV and 7 TeV

When analyzing two-particle correlations for identical pions in p + p collisions at - s = 0.9 and 7 TeV, significant background correlation structures are observed. The structures are also observed for pairs of non-identical pions and are reproduced by Monte-Carlo simulations. We analyze these structures quantitatively and propose methods to account for their impact on the system sizes extracted from the fits to the identical pion correlation functions.