Scaling Behavior of the Azimuthal and Centrality Dependencies of Jet Production in Heavy-ion Collisions

Abstract

For heavy-ion collisions at RHIC a scaling behavior is found in the dependencies on azimuthal angle $\phi$ and impact parameter $b$ for pion production at high $p_T$ essentially independent of the hadronization process. The scaling variable is in terms of a dynamical path length $\xi$ that takes into account detailed properties of geometry, medium density and probability of hard scattering. It is shown in the recombination model how the nuclear modification factor depends on the average $\bar\xi(\phi,b)$. The data for $\pi^0$ production at $p_T=$ 4-5 and 7-8 GeV/c at RHIC are shown to exhibit the same scaling behavior as found in the model calculation. Extension to back-to-back dijet production has been carried out, showing the existence of $\bar\xi$ scaling also in the away-side yield per trigger. At LHC the hard-parton density can be high enough to realize the likelihood of recombination of shower partons arising from neighboring jets. It is shown that such 2-jet recombination can cause strong violation of $\bar\xi$ scaling. Furthermore, the large value of $R_{AA}$ that exceeds 1 can become a striking signature of such a hadronization process at high energy.