Di-Hadron Angular Correlation Dependence on Leading Hadron Identity in Relativistic Heavy Ion Collisions

A unique state of matter is created in ultra-relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), the Quark Gluon Plasma (QGP). It displays the properties of a near-perfect liquid of quarks and gluons (partons) interacting collectively via the strong force. Properties of this medium can be explored using high-energy probes created in the form of back-to-back pairs (jets) in hard scatterings. A distinct feature of the QGP is jet quenching, which describes the large energy loss of such probes observed in measurements of hadron distributions in head-on heavy ion collisions. A more differential measurement of jet quenching is achieved using di-hadron correlations, where relative angular distributions are studied with respect to a leading (high energy) "trigger" hadron. Two striking features found in di-hadron correlations are the emergence of a long-range plateau on the near-side (at small relative azimuth), the so-called "ridge", and a broadening and deformation of the away-side, back to back with the trigger. Using 200 GeV central gold-gold and minimum bias deuteron-gold collision data collected by the STAR detector at RHIC, a systematic study of the dependence of di-hadron correlation structures on the identity of the trigger particle is carried out in this work by statistically separating pion from non-pion (i.e. proton and kaon) triggers, offering new insights into the hadronization mechanisms in the QGP. The jet-like yield at small relative angles is found enhanced for leading pions in Au+Au data with respect to the d+Au reference, while leading non-pions (protons and kaons) do not elicit such an enhancement. These findings are discussed within the context of quark recombination. At large angles, the correlated yield is significantly higher for leading non-pions than pions. Parameters extracted from two-dimensional model fits are used to test consistency with the constituent quark scaling assumptions in an azimuthal harmonics model, as well as the applicability of a mini-jet modification model.