Freeze-out radii extracted from three-pion cumulants in pp, p-Pb and Pb-Pb collisions at the LHC

Abelev, B. and Adam, J. and Adamová, D. and Aggarwal, M. M. and Agnello, M. and Agostinelli, A. and Agrawal, N. and Ahammed, Z. and Ahmad, N. and Ahmed, I. and Ahn, S. U. and Ahn, S. A. and Aimo, I. and Aiola, S. and Ajaz, M. and Akindinov, A. and Alam, S. N. and Aleksandrov, D. and Alessandro, B. and Alexandre, D. and Alici, A. and Alkin, A. and Alme, J. and Alt, T. and Altinpinar, S. and Altsybeev, I. and Alves, Garcia Prado C. and Andrei, C. and Andronic, A. and Anguelov, V. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Kiss, Gábor and Lévai, Péter and Molnár, Levente and Oláh, László and Pochybova, Sona (2014) Freeze-out radii extracted from three-pion cumulants in pp, p-Pb and Pb-Pb collisions at the LHC. PHYSICS LETTERS B, 739. pp. 139-151. ISSN 0370-2693

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Abstract

In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose-Einstein correlations of identical bosons at low relative momen- tum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially al- tered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the sys- tem at freeze-out extracted from three-pion cumulant correlations in pp, p–Pb and Pb–Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p–Pb collisions are found to be 5–15% larger than those in pp, while those in Pb–Pb are 35–55% larger than those in p–Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p–Pb as compared to pp collisions at similar multiplicity.

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