So What Is It? That’s the question one hears in all the bars and on all the street corners and on every Twitter feed and in the whispering of the wind. Everybody wants to know. That bump seen on the ATLAS and CMS two-photon plots! What… IS… it…?
Well, to be honest, probably it’s just that: a bump on a plot. But just in case it’s not — just in case it really is the sign of a new particle in Large Hadron Collider [LHC] data — let me (start to) address the question.
First: what it isn’t. It can’t just be a second Higgs particle (a heavier version of the one found in 2012) that is just appended to the known particles, with no other particles added in. If you try to put that idea into the equations, you immediately find the new particle’s mass is so large that it (or anything similar) would decay very often to other known particles, and very rarely to photons.
[Like the Higgs particle, it would only interact with photons indirectly, via direct interactions with the other known particles (see figure 3 of this post); but unlike the Higgs particle, it is heavy ...