The plenary sessions of EPS HEP 2011 start today and we still don’t know who will give the opening address in one hours time. This is a good moment to review what we have seen so far about the Higgs before the Tevatron and LHC get to have their final word on Wednesday.
A few days ago I said you should hold your breath for some exciting Higgs results over the next few days, weeks or months. There was some skepticism over at Reddit but I have certainly been proved right for the first part of my prediction. The last few days have seen some spectacular results. We can now look forward to more developments for the rest of this year, but first let’s look back at what we have.
Here is a zoomed version of the CMS results showing a promising 2.5 sigma excess at 135 to 145 GeV
These plots have led to a lot of excitement from the media about hints of the Higgs at around 140 GeV, but some caution is required. The excesses are not yet very big. If we believe the theory that the Higgs Boson must exist and that it is ruled out at high mass then we should be ready to accept the observed signal. At the very least the chances are that something good is going on in the mass region for a light Higgs.
But wait, the Tevatron has better reach in this region. What does Fermilab say? For the full answer we will have to wait until Wednesday but here is my prediction for their combined plot
This chart, if correct, excludes the Higgs between 135 GeV and 185 GeV at the 90% confidence level. Above 185GeV a standard model Higgs is ruled out by precision measurements. This is consistent with the Fermilab press release that claims they have shown that the Higgs is “most likely” to be between 114 GeV and 135 GeV.
So there is hope that some kind of Higgs particle is lurking in that region, but the signal is not strong. Some modified form of Higgs mechanism with multiplets may be a better fit to the data. If my predicted full combinations are correct a standard Higgs may already be all but ruled out even at low mass. A SUSY multiplet can still work but searches for MSSM signals have excluded the best parts of the SUSY spectrum. There is certainly a big conundrum here. Theorists may be sent back to the drawing board, but it is too early to say. When will we know more?
The official full LHC combination is due to be presented at Lepton-Photon 2011 in Mumbai, four weeks from now. They are not likely to show much more at that conference because it would mean starting the analysis work now with 1.5/fb recorded. A huge effort would be required again but now the holiday season is upon us and it would not be worth it for the relatively small amount of additional data. There is a slightly better chance that a reanalysis will be start in one months time when the next technical stop provides a natural break with at least another 1/fb added to today’s total collision database. We may even have to wait until the end of this year’s physics run when 5/fb will be recorded in each of ATLAS and CMS.
What if the standard model Higgs is ruled out? Can a SUSY Higgs multiplet survive? Will they be forced to search for a non-standard higher mass Higgs, or will a Higgsless symmetry breaking mechanism be required? All I know for certain is that a lot more Higgs buzz is still to come by the end of this year.
For other bloggy opinions see The Reference Frame, A Quantum Diaries Survivor, Resonaances, Not Even Wrong, Life and Physics, ArcadianPseudofunctor, Of Particular Significance, US LHC Blog, Quantum Diaries, TDG Diary