  The energy resolution is crucial for the reactor neutrino experiments which
aims to determine neutrino mass ordering by precise measurement of the reactor
antineutrino energy spectrum. A non-negligible effect in the antineutrino
energy resolution is the spread of the kinetic energy of the recoiled neutron
and the corresponding positron when detecting the antineutrinos via Inverse
Beta-Decay (IBD) reaction. The emission direction of the produced positron in
IBD reaction can be used to estimate the kinetic energy of neutron and thus the
reconstructed antineutrino energy resolution can be improved. To demonstrate
the feasibility, a simple positron direction reconstruction method is
implemented in a toy liquid scintillator detector like the Taishan Antineutrino
Observatory (TAO) with 4500 photoelectron yield per MeV. A 4% to 26%
improvement of energy resolution can be achieved for 5 MeV reactor
antineutrinos at TAO.
