Probing Nuclear Matter With Jets and $\gamma$-Hadron Correlations: Results from PHENIX

Abstract

Fully reconstructed jets and direct photon-tagged jet fragments significantly reduce energy-loss bias, the bias toward mostly measuring particles from partons which suffer little energy loss. In d+Au collisions, one accesses the physics at large $x$, which yields important constraints for nuclear parton distribution functions. In both d+Au and A+A collisions, coherent multiple-scattering models of energy loss can be tested. In this contribution, we present the current results from the PHENIX experiment on fully reconstructed jets and direct $\gamma$-hadron correlations. Baseline measurements of jets in p+p collisions as well as their yield and correlation modifications in d+Au and Cu+Cu will be given. From $\gamma$-hadron correlations, we present the fragmentation function in p+p and Au+Au collisions and its modification in Au+Au to $z_T$ lower than what has previously been studied. Implications of this data on our understanding of both cold and hot, dense nuclear matter created at RHIC are discussed.