  A search is presented for a new, light boson with a mass of about 1 GeV and
decaying promptly to jets of collimated electrons and/or muons (lepton-jets).
The analysis is performed with 20.3 fb$^{-1}$ of data collected by the ATLAS
detector at the Large Hadron Collider in proton--proton collisions at a
centre-of-mass energy of 8 TeV. Events are required to contain at least two
lepton-jets. This study finds no statistically significant deviation from
predictions of the Standard Model and places 95\% confidence-level upper limits
on the contribution of new phenomena beyond the SM, incuding SUSY-portal and
Higgs-portal models, on the number of events with lepton-jets.
