The second moment of Maass form symmetric square L-functions at the central point

Recently R.Khan and M.Young proved a mean Lindelöf estimate on the second moment of central values of Maass form symmetric-square $L$-function on the interval $T<|t_j|<T+T^{1/5+\epsilon}$, where $t_j$ is a spectral parameter of the Maass form. We provide another proof of this result.