The Higgs boson Part 3: Exotic Higgs decays
The Standard Model predicts that the Higgs boson is unstable and falls apart (decays) only 10-22 s (0.0000000000000000000001 seconds) after it is created. Theoretically, it can decay to a quark-anti quark pair (except for top, anti-top), a lepton anti-lepton pair or to two bosons (like photons or gluons).
However, there is also the possibility that it could decay to new particles that have not been observed until now, so-called long-lived scalar particles (scalar means they are spinless just like the Higgs boson). Some theories beyond the Standard Model (e.g. http://arxiv.org/abs/1312.4992) predict that these particles would be unique in that only the Higgs boson would decay to them, meaning it would have been impossible to study them until now – these are one example of what we call ‘exotic particles‘.
The diagram above shows a Higgs boson decaying into two exotic particles, which then themselves decay into many more particles – this is how an off-centre vertex could be produced. In fact, looking for off-centre vertices was proposed way back in 2006 as a way of detecting the Higgs boson, before it had been discovered (http://arxiv.org/abs/hep-ph/0605193)!
Since this process is not predicted by the Standard Model, if we see these in our detector then we will finally be able to realise the dream of obtaining direct evidence for a new theory of nature – opening our eyes to an entirely new realm of physics.
If these exotic decays are real, then they have already happened at the LHC and are sitting in the data we have right now, just waiting to be found by a keen pair of eyes. By helping with this project, you can take us one step closer to a deeper understanding of reality – to answering some of the greatest unsolved mysteries in the universe.
(Next time: ATLAS: How do particle detectors work?)
In reading up on the LHC and ATLAS, I came across Matt Strassler’s blog, and a recent blog post on detecting long-lived particles. This seems to be directly related to what we’re doing, in Higgs Hunters!
He mentions the importance of “trigger strategies”, and how lots of interesting physics may go unnoticed because the “triggers” were not designed to capture events which might point to such physics.
Is this, in fact, related to what we’re doing?
And can you please say something about “trigger strategies”?
Matt and I go back quite a number of years (he was at Seattle when I was a grad student), and his ideas were central to these sorts of searches.
I think he plans to blog specifically about our HiggsHunters project next week.
The trigger for the data for this search was easy. We rely on the fact that the Higgs is often (~10% of the time) produced along with a Z boson, which then sometimes (~3.3% of the time) decays to a pair of muons. This gets a large enough sample of Higgs decays to have a chance of spotting something interesting, but admittedly we are throwing out 99.7% of the Higgs produced!
“The Standard Model predicts that the Higgs boson is unstable and falls apart (decays) only 10-22 s (0.0000000000000000000001 seconds) after it is created.”
If the Higgs boson decays very rapidly and the mass of particles does not change, it seems to me that new Higgs bosons must be being created.
Is that correct?
Do we know how they are created?