Figure. The measured azimuthal anisotropy parameter divided by the number of quark constituents in the hadron as a function of transverse momentum divided by the number of quark constituents for K0s, and Lambda+anti-Lambda for Au-Au collisions at 200 GeV. The error bars are statistical only.

In Au-Au collisions at RHIC one of the first measurements was the observation of collective harmonic flow for charged hadrons and that this flow showed a strong p_t dependence. This observation has since been extended to that the identified particles. The K⁰_s and Lambda+anti-Lambda also show a strong p_t dependence in the measured v₂. However, they also show that the value of v₂ at a given p_t is mass dependent. This mass dependence is predicted hydrodynamical models and the magnitude is in agreement with the STAR measured results up to p_t ~2 GeV/c . Above this transverse momentum the measured v₂ seems to saturate, this is in contradiction with hydrodynamic predictions. For p_t /n > 0.8 GeV/c, where n is the number of constituent quarks in the hadron, it is interesting to note that the measured v₂/n of the K⁰_s and Lambda+anti-Lambda is equal. If hadrons at intermediate p_t are created via coalescence of co-moving quarks from bulk partonic matter it is predicted that the v₂ /n of the measured particles would behave in such a fashion. In such a scenario this measurement reveals that the partons develop an momentum-space azimuthal anisotropy created by the ellipsoidal shape of the initial collision.

Particle-type dependence of azimuthal anisotropy and nuclear modification of particle production in Au+Au collisions at sqrt(s_nn) = 200 GeV
Phys. Rev. Lett. 92 (2004) 052302
e-Print Archives (nucl-ex/0306007): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

Azimuthal anisotropy of K0s and Lambda + Lambdabar production at mid-rapidity from Au+Au collisions at sqrt(s_nn) = 130 GeV
Phys. Rev. Lett. 89 (2002) 132301
e-Print Archives (hep-ex/0205072): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server