Identifying the underlying physics of the ridge via 3-particle $\Delta\eta-\Delta\eta$ correlations

We present the first results on 3-particle $\Delta\eta$-$\Delta\eta$ correlations in minimum bias $d$+Au, peripheral and central Au+Au collisions at $\sqrt{{\it s}_{NN}}$ = 200 GeV measured by the STAR experiment. The analysis technique is described in detail. The ridge particles, observed at large $\Delta\eta$ in dihadron correlations in central Au+Au collisions, appear to be uniformly distributed over the measured $\Delta\eta$-$\Delta\eta$ region in 3-particle correlation. The results, together with theoretical models, should help further our understanding of the underlying physics of the ridge.