  In this paper we study the jet response (particularly azimuthal anisotropy)
as a hard probe of the harmonic fluctuations in the initial condition of
central heavy ion collisions. By implementing the fluctuations via cumulant
expansion for various harmonics quantified by $\epsilon_n$ and using the
geometric model for jet energy loss, we compute the response
$\chi^h_n=v_n/\epsilon_n$. Combining these results with the known hydrodynamic
response of the bulk matter expansion in the literature, we show that the
hard-soft azimuthal correlation arising from their respective responses to the
common geometric fluctuations reveals a robust and narrow near-side peak that
may provide the dominant contribution to the "hard-ridge" observed in
experimental data.
