Pion, kaon, and proton femtoscopy in Pb-Pb collisions at $\sqrt{s_{\mathit{NN}}}=2.76$ TeV modeled in (3+1)D hydrodynamics

Femtoscopy is providing information on system size and its dynamics in heavy-ion collisions. At ultrarelativistic energies, such as those obtained at the Large Hadron Collider (LHC), significant production of pions, kaons, and protons enables femtoscopic measurements for these particles. In particular, the dependence of system size on pair momentum and particle type is interpreted as evidence for strong collective flow. Such phenomena are naturally modeled by hydrodynamics. We present calculations within the (3+1)D hydrodynamic model coupled to statistical hadronization code therminator 2, corresponding to Pb-Pb collisions at $\sqrt{s_{\mathit{NN}}}=2.76$ TeV. We obtain femtoscopic radii for pions, kaons, and protons, as a function of pair transverse momentum and collision centrality. We find that an approximate universal scaling of radii with pair transverse mass and final-state event multiplicity is observed and discuss the consequences for the interpretation of experimental measurements.

Figure 1

Femtoscopic radii in LCMS calculated for pions, as a function of pair transverse momentum and centrality. Dashed lines show power-law fits to selected centralities. For completeness, calculations for $b=2.3$ fm are compared to ALICE data [13] at the corresponding centrality. The two data sets are slightly shifted in $x$ direction for visibility.

Figure 2

Femtoscopic radii in LCMS for pions as a function of cube root of the charged particle multiplicity for several $k_{\mathrm{T}}$ ranges. Lines represent linear fits to selected $k_{\mathrm{T}}$ ranges.

Figure 3

Femtoscopic radii in LCMS calculated for kaons, as a function of pair transverse momentum and centrality.

Figure 4

Femtoscopic radii in LCMS calculated for protons, as a function of pair transverse momentum and centrality.

Figure 5

Femtoscopic radii in LCMS for pions, kaons, and protons, for selected centralities. Lines represent power-law fits to the combined pion, kaon, and proton data points at a given centrality and direction (see text for details).

Figure 6

Comparison of the $R_{\mathrm{inv}}$ obtained directly from the fit to the one-dimensional correlation function in PRF and a result $R_{\mathrm{eff}}$ of the approximate procedure to estimate $R_{\mathrm{inv}}$ from values of $R_{\mathrm{out}},R_{\mathrm{side}}$, and $R_{\mathrm{long}}$ measured in LCMS (see text for details).

Figure 7

(a) One-dimensional femtoscopic radius $R_{\mathrm{inv}}$ for pions, kaons, and protons calculated in the PRF for selected centralities. (b) $R_{\mathrm{inv}}$ for pions, kaons, and protons scaled with the kinematic factor, for selected centralities (see text for details). Lines represent power-law fits. (c) Averaged one-dimensional radius in LCMS $R_{\mathrm{LCMS}}$ for pions, kaons, and protons for selected centralities. Lines represent power-law fits.