Emission angle and particle mass dependence of HBT radii in Au+Au collisions at √(s_NN)=200 GeV

Hydrodynamic features of quark–gluon plasma (QGP) are being studied via various observables in high-energy heavy-ion collisions. Measurement of space–time structure via two-particle interferometry is one of those and is known as Hanbury Brown and Twiss (HBT) method. This gives geometrical and temporal information as well as dynamical information such as collective expansion during the freeze-out stage. The azimuthal-angle dependence of the HBT radii for various particle species (ππ and KK) and for various event plane orders (2nd and 3rd) are measured in √(s_NN)=200 GeV Au+Au collisions at RHIC-PHENIX experiment. The extracted parameters for KK pairs are slightly different from those for ππ pairs for a given m_T, which may indicate earlier freeze-out and longer emission duration for K than for π. The azimuthal dependences relative to the 2nd and 3rd order event planes are observed to be consistent with a strong and rapid expansion, which has also been known as sudden freeze-out with a short duration time. Large v₂ events are selected by the 2nd order flow vector magnitude Q₂ in order to test the Event Shape Engineering (ESE) via final eccentricity ϵ_final measurement. The results confirm a significant correlation between elliptic flow v₂ and final eccentricity ϵ_final, which is supposed to originate from the initial geometrical eccentricity ϵ_initial