Temperature uniformity of the bulk medium produced in relativistic heavy-ion collisions

The success of hydrodynamic models of elliptic flow in relativistic heavy ion collisions is often touted as evidence for rapid thermal equilibration. However, large momentum scale two-particle correlations indicate that a significant fraction of the final-state hadrons retain jet-like correlation structure associated with early stage, non-equilibrated low-$Q^2$ partons [1]. In addition, correlations on transverse momentum $(p_{t1} \times p_{t2})$ suggest that low-$Q^2$ parton momentum is partially dissipated causing fluctuations in the effective temperature (thermal and/or collective motion) of the bulk medium[2]. We first show that both global and local temperature fluctuation models describe the available $(p_{t1} \times p_{t2})$ correlation data equally well. Results of an analytical model are then presented which tests the sensitivity of $(p_{t1} \times p_{t2})$ correlations to the first few lower-order cumulants of the two-point temperature distribution for the event ensemble. Unique signatures in the predicted $(p_{t1} \times p_{t2})$ correlations are observed for each cumulant term studied. The prospects for direct measurement of the absolute temperature distribution in the bulk medium produced in relativistic heavy-ion collisions using $(p_{t1} \times p_{t2})$ and other correlation measures are discussed. [1] J. Adams et al., Phys. Rev. C {\bf 73}, 064907 (2006); J. Phys.G. {\bf 32}, L37 (2006). [2]J. Adams et al., nucl-ex/0408012.