Centrality dependence of pion freeze-out radii in Pb-Pb collisions at root s(NN)=2.76 TeV

J. Adam, D. Adamova, M.M. Aggarwal, G. Aglieri Rinella, Maria Agnello, N. Agrawal, Z. Ahammed, S. U. Ahn, I. Aimo, S. Aiola, A. Akindinov, Alessandro D , Ian Bearden, Hans Bøggild, Christian Holm Christensen, Kristjan Herlache Gulbrandsen, Jens Jørgen Gaardhøje, Hans Hjersing Dalsgaard, Børge Svane Nielsen, Alexander Colliander HansenAnte Bilandzic, Marek Chojnacki, Valentina Zaccolo, You Zhou, Christian Alexander Bourjau

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Abstract

We report on the measurement of freeze-out radii for pairs of identical-charge pions measured in Pb-Pb collisions at sNN=2.76 TeV as a function of collision centrality and the average transverse momentum of the pair kT. Three-dimensional sizes of the system (femtoscopic radii), as well as direction-averaged one-dimensional radii are extracted. The radii decrease with kT, following a power-law behavior. This is qualitatively consistent with expectations from a collectively expanding system, produced in hydrodynamic calculations. The radii also scale linearly with (dNch/dη)1/3. This behavior is compared to world data on femtoscopic radii in heavy-ion collisions. While the dependence is qualitatively similar to results at smaller sNN, a decrease in the ratio Rout/Rside is seen, which is in qualitative agreement with a specific prediction from hydrodynamic models: a change from inside-out to outside-in freeze-out configuration. The results provide further evidence for the production of a collective, strongly coupled system in heavy-ion collisions at the CERN Large Hadron Collider.

OriginalsprogEngelsk
Artikelnummer024905
TidsskriftPhysical Review C
Vol/bind93
Udgave nummer2
ISSN2469-9985
DOI
StatusUdgivet - 4 feb. 2016

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