Multiparton Tomography of Hot and Cold Nuclear Matter

Multiple parton interactions in relativistic heavy ion reactions result in transverse momentum diffusion and medium induced non‐Abelian energy loss of the hard probes traversing cold and hot nuclear matter. A systematic study of the interplay of nuclear effects on the pT ⩾ 2 GeV inclusive hadron spectra demonstrates that the competition between nuclear shadowing, multiple scattering and jet quenching leads to distinctly different enhancement/suppression of moderate and high‐pT hadron production in d + Au and Au + Au collisions at RHIC. The associated increase of di‐jet acoplanarity, measured via the broadening of the back‐to‐back di‐hadron correlation function, provides an additional experimental tool to test the difference in the dynamical properties of the media created in such reactions.