[Non-experts; sorry, but this paper was written for experts, and probably has a minimum of two words of jargon per sentence. I promise you a summary soon.]
Why is looking for unusual and unexpected decays of the Higgs particle so important? [I’ve written about the possibility of these “exotic” decays before on this website (see here, here, here, here, here, here, here and here).] Because Higgs particles are sensitive creatures, easily altered, possibly in subtle ways, by interactions with new types of particles that we wouldn’t yet know about from the LHC or our other experiments. (This sensitivity of the Higgs was noted as far back to the early 1980s, though its generality was perhaps only emphasized in the last decade.) The Higgs particle is very interesting not only on its own, for what it might reveal about the Higgs field (on which our very existence depends), but also as a potential opportunity for the discovery of currently unknown, lightweight particles, to which it might decay. Such particles might be the keys to unlocking secrets of nature, such as what dark matter is, or maybe even (extreme speculation alert) the naturalness puzzle — very roughly, the puzzle of why the mass of the Higgs particle can be so small compared to the masses of the smallest possible black holes.
The goal of our paper, which is extensive in its coverage (though still not comprehensive — this is a very big subject) is to help our experimental colleagues at ATLAS and CMS, the general purpose experiments at the LHC, decide what to search for in their current (2011-2012) and future (2015-) data, and perhaps assist in their decisions on triggering strategies for the data collecting run that will begin in 2015. (Sorry, LHCb folks, we haven’t yet looked at decays where you’d have an advantage.) And we hope it will guide theorists too, by highlighting important unanswered questions about how to look for certain types of exotic decays. Of course the paper has to go through peer review before it is published, but we hope it will be useful to our colleagues immediately. Time is short; 2015 is not very far away.
Although our paper contains some review of the literature, a number of its results are entirely new. I’ll tell you more about them after I’ve recovered, and probably after most people are back from break in January. (Maybe for now, as a teaser, I’ll just say that one of the strongest limits we obtained, as an estimate based on reinterpreting published ATLAS and CMS data, is that no more than a few × 10-4 of Higgs particles decay to a pair of neutral spin-one particles with mass in the 20 – 62 GeV/c2 range… and the experimentalists themselves, by re-analyzing their data, could surely do better than we did!) But for the moment, I’d simply like to encourage my fellow experts, both from the theory side and the experimental side, to take a look… comments are welcome.
Finally, I’d like to congratulate and thank my young colleagues, all of whom are pre-tenure and several of whom are still not professors yet, on their excellent work… it has been a pleasure to collaborate with them. They led the way, not me. They are (in alphabetical order): David Curtin, Rouven Essig, Stefania Gori, Prerit Jaiswal, Andrey Katz, Tao Liu, Zhen Liu, David McKeen, Jessie Shelton, Ze’ev Surujon, Brock Tweedie, and Yi-Ming Zhong. They hail from around the world, but they’ve worked together like family… a great example of how our international effort to understand nature’s deep mysteries brings unity of purpose from a diversity of origins.