We had evidence in ATLAS of the Higgs boson decaying to two leptons and a photon. Quite a rare phenomenon, observed for the first time and known as “Dalitz decay”. The most famous Dalitz decay is the one of the neutral pion:
very important also for intepreting rare kaon-decays measurements. Three-body decays are also crucial for CP measurements, as the three angles between final products allow to probe the invariance of the decay if matter and antimatter are exchanged.
The process measured by ATLAS is
With respect to the neutral pion case, muons pairs are considered besides the electrons and positrons. You can find evidence of the observation in the following plot of the invariant mass of the system:
The peak at 125 GeV is more than 3 sigmas above the background hypothesis.