[Boxing Day Update: Indication over at NEW are that this rumour is not being backed up by other ATLAS sources. Chances are it will melt away and we will never know its origins. Update: of course it could also be that the analysis has not been communicated to the whole team yet.]
A rumour has surfaced in the comments at Not Even Wrong that ATLAS have a 5 sigma signal (local significance?) in like-sign dimuons at 105 GeV. This plot shows the relevant events from an earlier analysis with 2011 data where a small excess can already be seen.
First thoughts are of a doubly charged Higgs boson as predicted in Higgs triplet models with the potential to also explain the digamma over-excess in the Higgs decays. However, the signal is much weaker than expected for a doubly charged Higgs because CMS and ATLAS have already set lower limits around 300 – 400 GeV for H++. In a comment here yesterday on the digamma excess Frank Close pointed out that if a doubly charged Higgs is responsible for the digamma excess it should also affect the Bs to dimuon decay (see e.g. Resonaances) which is disappointingly inline with the Standard Model.
Of course the rumour could be incorrect or based on an analysis too preliminary to hold water, but if it pans out it will certainly pose an intriguing puzzle. A particle that decays to two like-signed muons must have lepton number two as well as charge two, unless the decay breaks lepton number conservation or there are missing neutrinos. It could be a spin two particle rather than a scalar. Working out what best fits other observations is not an exercise that can be done in the head, but it will be interesting to see what other first thoughts come out. It is also possible that this could be related to signals in multi-lepton channels that have been seen in the past (see e.g. Motl at TRF). Until we get an official report at perhaps Moriond 2013 this should not be taken too seriously. Some rumours evaporate during internal review and never see the light of day.