Beam-beam effects with stochastic cooling in the 2012 RHIC 100 GeV heavy ion run

Abstract

The 3-D stochastic cooling has been implemented in RHIC for the first time in the 2012 heavy ion run. In the U-U run, the U beam's transverse emittances were cooled from initially about 13.5 mm.mrad down to 2.5 mm.mrad. The beam-beam parameters reached a maximum of-0.005. In the Cu-Au run, due to the unbalanced transverse beam sizes of the Cu and Au beams in the first several hours at the store, the Cu beam lifetime was significantly reduced by the beam-beam interaction. To maintain the Cu beam lifetime and to maximize the integrated luminosity, we intentionally reduced the cooling rate for the Au beam until the Cu beam got cooled. In this article, we review the beambeam effects in the 2012 RHIC heavy ion run and carry out numerical simulations to interpret the observations.