Electron-Muon Correlations in Proton+Proton and Deuteron+Gold Collisions at PHENIX

This dissertation presents the first measurement of electron-muon azimuthal correlations at the PHENIX experiment at RHIC in 200 GeV proton-proton and deuteron-gold collisions. Electron-muon pairs result from the semileptonic decay of D mesons, which come from correlated charm pairs. The pairs are measured at forward rapidity, with η < 0.5 for the electron and 1.4 < η < 2.1 for the muon. Electron-muon pairs exhibit a characteristic peak at Δφ = π in the azimuthal distribution due to momentum conservation in the c\bar{c} decay, and this enables clear identification. The shape of the azimuthal pair distribution in p+p collisions helps us determine which hard scattering processes contribute to charm production, and it allows us to test NLO QCD predictions. The p+p result also serves as a baseline measurement for understanding heavy ion collisions. Pairs were also measured in d+Au collisions at forward rapidity in the deuteron-going direction, which is a kinematic region at which we expect suppression effects to be evident. The pair yield in d+Au was found to be suppressed relative to that in p+p. Also the peak in Δφ almost disappears in d+Au, indicating either a change in charm production mechanisms or interactions with the nuclear matter.