Suppression of $\pi^0$ production at large $p_\perp$ in central $Au +Au$   collisions at $\sqrt{s_{NN}} = 200$ GeV and quark-gluon plasma
  We investigate the suppression of $\pi^0$-spectrum in a wide range of $p_\perp$ up 60 GeV/c which is caused by the energy loss of the gluon and quark jets in quark-gluon plasma. The physical characteristics of initial and mixed phases were found in the effective quasiparticle model by analogy with previous work \cite{5}. The PHENIX data up 10 GeV/c within the limits of precision are described by quasiparticle model with decrease of the thermal gluon mass and effective coupling in the region of phase transitin (at $T\to T_c$ from above). We also take into account the intrinsic transverse momentum $k_\perp$ of partons.   The suppression factor $R_{AA}(p_\perp)$ shows the weak rise with increase of $p_\perp$ above 4 GeV/c, then it reaches smooth maximum at $p_\perp \sim 20$ GeV/c and then decrease at $p_\perp\sim 60$ GeV/c again to value $R_{AA}$ at $p_\perp\simeq$ 4 GeV/c. The factor $R_{AA}$ in this range of $p_\perp$ is changihg weakly if intrinsic momentum $k_\perp$ is taken into account. 
Yu.A. Tarasov and S.L. Fokin