Study of the Number of Quark Scaling of $v_2$ at High Transverse Momentum

The number of quark (NCQ) scaling in the anisotropy parameter $v_2$, for almost all measured hadrons at transverse momentum region up to $p_T$ about 5GeV/c, has been observed in high-energy nuclear collisions at RHIC. The scaling results imply the formation of the de-confined matter with partonic collectivity in the collisions. In this talk, we report systematic studies of $v_2$ at midrapidity for $\pi$, p, $K_s^0$ and $\Lambda$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector. The FTPC detectors, which sit at large rapidity, were used for the determination of the event plane. Comparing to previous results, a high statistics data set is used in the analysis. We find that in the high transverse momentum region, $p_T \ge$ 6GeV/c ($(m_T-m)/n_q>1.5$ GeV/$c$), the NCQ in $v_2$ is breaking down. A comparison to models suggests this is mainly caused by an increase in particles coming from hard process at high $p_T$.