Centrality dependence of pion freeze-out radii in Pb-Pb collisions at $\sqrt{\mathbf{s_{NN}}}$=2.76 TeV

Abstract : We report on the measurement of freeze-out radii for pairs of identical-charge pions measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV as a function of collision centrality and the average transverse momentum of the pair $k_{\rm T}$. Three-dimensional sizes of the system (femtoscopic radii), as well as direction-averaged one-dimensional radii are extracted. The radii decrease with $k_{\rm T}$, 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 $\left< \mathrm{d}N_{\rm ch}/\mathrm{d}\eta \right>^{1/3}$. This behaviour is compared to world data on femtoscopic radii in heavy-ion collisions. While the dependence is qualitatively similar to results at smaller $\sqrt{s_{\rm NN}}$, a decrease in the $R_{\rm out}/R_{\rm side}$ ratio is seen, which is in qualitative agreement with specific predictions from hydrodynamic models. The results provide further evidence for the production of a collective, strongly coupled system in heavy-ion collisions at the LHC.
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http://hal.in2p3.fr/in2p3-01180410
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Submitted on : Monday, July 27, 2015 - 7:28:50 AM
Last modification on : Thursday, July 25, 2019 - 1:14:02 PM

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J. Adam, Laurent Aphecetche, B. Audurier, A. Baldisseri, Guillaume Batigne, et al.. Centrality dependence of pion freeze-out radii in Pb-Pb collisions at $\sqrt{\mathbf{s_{NN}}}$=2.76 TeV. Physical Review C, American Physical Society, 2016, 93, pp.024905 ⟨10.1103/PhysRevC.93.024905⟩. ⟨in2p3-01180410⟩

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