Signatures of color glass condensate: Forward azimuthal angle di-hadron correlations in PHENIX

Abstract

Measurements using the PHENIX forward detectors in high energy deuteron–gold collisions make it possible to study cold nuclear matter effects in nucleon structure at low x. The high gluon densities in Lorentz-contracted gold nuclei make it possible to probe for gluon saturation or Color Glass Condensate effects. Past RHIC experiments have shown a suppression in nuclear modification factors ( R dA , R cp ) for s NN = 200 GeV d + Au collisions in the forward (deuteron) direction. Multiple theories can explain the observed suppression (including saturation), but a conclusive measurement discriminating between the models has yet to be carried out. Two new forward electromagnetic calorimeters (Muon Piston Calorimeters, − 3.7 < η < − 3.1 , 3.1 < η < 3.9 ) allow the PHENIX experiment to further study forward di-hadron correlations, which have been predicted to show dramatic effects due to gluon saturation. In particular, azimuthal correlations of di-hadron pairs at different pseudorapidities will be shown; the forward pseudorapidity correlations are especially interesting because it is expected that they provide a test of gluon saturation down to x ≈ 10 − 3 in the Au nucleus. The analysis presented is based on the high integrated luminosity data sample of d + Au collisions at s NN = 200 GeV taken at RHIC in 2008.