Measurements of the midrapidity transverse energy distribution, dET /dη, are presented for p+p, d+Au, and Au+Au collisions at √ s N N = 200 GeV and additionally for Au+Au collisions at √ s N N = 62.4 and 130 GeV. The dET /dη distributions are first compared with the number of nucleon participants Npart, number of binary collisions N coll , and number of constituent-quark participants Nqp calculated from a Glauber model based on the nuclear geometry. For Au+Au, dET /dη /Npart increases with Npart, while dET /dη /Nqp is approximately constant for all three energies. This indicates that the two component ansatz, dET /dη ∝ (1 − x)Npart/2 + xN coll , which has been used to represent ET distributions, is simply a proxy for Nqp, and that the N coll term does not represent a hard-scattering component in ET distributions. The dET /dη distributions of Au+Au and d+Au are then calculated from the measured p+p ET distribution using two models that both reproduce the Au+Au data. However, while the number-of-constituent-quark-participant model agrees well with the d+Au data, the additive-quark model does not.

The PHENIX experiment has measured midrapidity ([FORMULA: SEE TEXT]) transverse momentum spectra ([FORMULA: SEE TEXT]) of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT]. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in p+p collisions. A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.

Azimuthal correlations of jet-induced high-p(T) charged hadron pairs are studied at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The distribution of jet-associated partner hadrons (1.0