Two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

The first measurement of two-pion Bose--Einstein correlations in central Pb-Pb collisions at  $\sqrt{s_{\rm NN}}$ = 2.76 TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.

Figures

Figure 1

Projections of the three-dimensional $\pi^-$$\pi^+$ correlation function (points)and of the respective fits (lines) for seven $k_T$ intervals When projecting on one axis the other two components were required to be within (-0.03,0.03) GeV/$c$ The $k_T$ range is indicated on the right-hand side axis in GeV/$c$.
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Figure 2

Pion HBT radii for the 5% most central Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76~$TeV, as function of $\langle$$k_T$$\rangle$ (red filled dots). The shaded bands represent the systematic errors. For comparison, parameters for Au--Au collisions at $\sqrt{s}$ =200 GeV are shown as blue open circles (The combined, statistical and systematic, errors on these measurements are below 4%.)The lines show model predictions (see text).
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Figure 3

Pion HBT radii at $k_T$ = 0.3 GeV/$c$ for the 5% most central Pb-Pb at $\sqrt{s_{\rm NN}}=2.76~$TeV(red filled dot) and the radii obtained for central gold and lead collisions at lower energies at the AGS [35], SPS [36,37,38] and RHIC [39,40,41,42,30,43]. Model predictions are shown as lines.
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Figure 4

Product of the three pion HBT radii at $k_T$ = 0.3 GeV/$c$ The ALICE result (red filled dot) is compared to those obtained for central gold and lead collisions at lower energies at the AGS [35], SPS [36,37,38] and RHIC [39,40,41,42,30,43].
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Figure 5

The decoupling time extracted from $R_{\rm long}$($k_T$). The ALICE result (red filled dot) is compared to those obtained for central gold and lead collisions at lower energies at the AGS [35], SPS [36,37,38] and RHIC [39,40,41,42,30,43].
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