Jet studies in STAR via di-jet (2+1) correlations in d+Au and Au+Au

We report a correlation work for Au+Au and d+Au collisions at $\sqrt{s}=$ 200GeV from STAR experiment at RHIC. This correlation is defined as a three-particle technique called ``2+1'', by using a di-jet trigger of two back-to-back high-pT particles including both charged hadrons and high-energy photons. This analysis explores the relative distributions of soft hadrons with the two triggers. The trigger $p_T$ ranges are varied to control the relative strength of jet modification. In contrast to those di-hadron correlations with a single high- pT trigger, the associated hadron distributions in our ``2+1'' analysis reveal no modification in either $\Delta\phi$ or $\Delta\eta$ from d+Au to central Au+Au collisions. The present results indicate that di-jet triggered correlations select those jets that undergo no interactions or energy-loss with the medium created in collisions. The associated yields and trigger rates for such di-jets are studied as a function of $N_{part}$ to provide additional insights into medium properties.