Di-Jet Imbalance Measurements in Central Au + Au Collisions at sNN=200 GeV from STAR

The STAR collaboration reports the first measurements of the transverse momentum asymmetry AJ of di-jet pairs in central gold-gold collisions and minimum bias proton-proton collisions at sNN=200 GeV at RHIC. We focus on anti-kT di-jets with a leading jet pT>20 GeV/c and a subleading jet pT>10 GeV/c, with a constituent cut of 2 GeV/c, which reduces the effect of the underlying heavy-ion background. We examine the evolution of AJ while reclustering these same di-jets with a lower constituent cut of 200 MeV/c. For the low pT constituent cut with a resolution parameter of R=0.4, the balance between the di-jets is restored to the level of p+p collisions which indicates the lost energy observed for di-jets with a constituent cut of pTCut>2 GeV/c is recovered. Further variations of R and the constituent pT-cutoff indicate that the lost energy is redistributed in the form of soft particles, accompanied by a broadening of the jet structure.