  We carry out the first theoretical investigation on yields and the hardest
parton splitting of large-radius jets reclustered from small radius ($R=0.2$)
anti-$k_t$ jets in Pb+Pb collisions, and confront them with the recent ATLAS
measurements.The Linear Boltzmann Transport (LBT) model is employed for jet
propagation and jet-induced medium excitation in the hot-dense medium. We
demonstrate that, with their complex structures, the medium suppression of the
reclustered large radius jets at $R=1$ is larger than that of inclusive $R=0.4$
jets defined conventionally. The large radius jet constituents are reclustered
with the $k_t$ algorithm to obtain the splitting scale $\sqrt{d_{12}}$, which
characterizes the transverse momentum scale for the hardest splitting in the
jet. The large-radius jet production as a function of the splitting scale
$\sqrt{d_{12}}$ of the hardest parton splitting is overall suppressed in Pb+Pb
relative to p+p collisions due to the reduction of jets yields. A detailed
analyses show that the alterations of jet substructures in Pb+Pb also make
significant contribution to the splitting scale $\sqrt{d_{12}}$ dependence of
the nuclear modification factor $R_{AA}$. Numerical results for the medium
modifications of the jet splitting angle $\Delta R_{12}$ and the splitting
fraction $z$ are also presented.
