Hanbury Brown--Twiss Interferometry and Collectivity in Small Systems

Abstract

Hanbury Brown--Twiss interferometry (HBT) provides crucial insights into both the space-time structure and the momentum-space evolution of ultrarelativistic nuclear collisions at freeze-out. In particular, the dependence of the HBT radii on the transverse pair momentum $K_T$ and the system charged multiplicity $d{N}_{\mathrm{ch}}/d\eta$ may reflect the mechanisms driving collective behavior in small systems. This paper argues that certain features observed in the multiplicity dependence of the HBT radii can be naturally understood if small systems evolve hydrodynamically at high-multiplicity. This study thus establishes a baseline for the multiplicity dependence of HBT in hydrodynamics which may prove useful in discriminating between competing models of collectivity in nuclear collisions.

33 pages, 6 figures, 1 table

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• Theoretical and Experimental Constraints for the Equation of State of Dense and Hot Matter
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• Anisotropic fluid dynamical simulations of heavy-ion collisions
• Femtoscopic correlations of identical charged pions and kaons in pp collisions at $\sqrt{s}=13$ TeV with event-shape selection
• Kaonic Hanbury-Brown-Twiss radii at 200 GeV and 5.02 TeV