Higgs Bosons and 750 GeV Resonance: Top Force Calculation?

[mitchell porter]

I was thinking about the possible 750 GeV resonance, and the joke idea that it could be a bound state of six Higgs bosons, and I suddenly realized that Higgs bosons might feel a "top force" (from top loops) because the top yukawa is so big. Has anyone calculated this?

 

[ChrisVer]

why 6 Higgs?

 

[mfb]

We know what the result of all contributions to the Higgs mass is, because we measured it: 125 GeV. It is not sometimes 125 GeV and sometimes some other value.

@Chris: That is just a joke (I hope).

 

[mitchell porter]

why 6 Higgs?

6 x 125 = 750

We know what the result of all contributions to the Higgs mass is, because we measured it

I'm not talking about corrections to the Higgs mass, but actual resonances. Like an octahedral skyrmion. :-)

 

[ChrisVer]

6 x 125 = 750

As a general rule (doesn't only have to do with the Higgs question), I don't believe you can predict a resonance's mass in such a way...

 

[mfb]

The SM does not have additional resonances.
Various new models have new particles, but those are different from the Higgs.

There is a more than 20% chance that an excess so poorly constrained like the 750-760 GeV one is consistent with an integer multiple of the Higgs mass just by random chance. And I am not aware of models that would give such a relation.

 

[mitchell porter]

The SM does not have additional resonances.

Is that a theorem? Are e.g. Higgs-force toponia completely ruled out?

 

[mfb]

It is the definition of the Standard Model.

 

[ChrisVer]

It is the definition of the Standard Model.

I think he has in mind 6 Higgs boson bound state, interacting with top quark loops...
just for a ref, there were produced approximately 15 Higgs bosons per minute at LHC.

 

[mfb]

Such a thing would not make sense. Even if you could get them in a bound state, either the Higgs bosons would decay or the bound state would break, but either way you would not get two photons out of the whole state. There is also no way to produce 6 Higgs bosons at the same time with any reasonable rate.
There is no model predicting anything like that, and speculating further without anything backing the speculations woud be both pointless and against the forum rules.

 

[mitchell porter]

I have discovered a series of papers discussing whether a bound state of 6 tops and 6 anti-tops could exist - see references cited in sections 4 and 5 of arXiv:1601.03231. There are two schools of thought, Nielsen et al who think it can exist and be light, and Kuchiev et al who think it would not be a bound state at all. Now Nielsen et al have proposed that it might be the 750 GeV resonance.

 

[mfb]

I don't see any references to this, probably for a good reason...
They use old measured Higgs masses (larger uncertainties are easier to fit to?), they treat the diphoton excess like a discovery, and so on. The justification why such a bound state should exist is missing, which is strange as it would be a crucial point of the whole discussion.

 

[mitchell porter]

Froggatt and Nielsen have now posted guesstimates for the branching ratios and cross sections of their 6 $t\bar{t}$ resonance... Their idea is simply that this is the maximum number of tops and anti-tops that can exist in the same state, so if such Higgs/gluon toponia exist at all, this one will be the most strongly bound.

 

[mfb]

I can't comment on the theoretical side, from the experimental side current searches cannot exclude it. Rough estimates would be 3.5 fb for diphotons, 1.3 pb for t+tbar, 50 fb for di-Higgs and ZZ, 100 fb for WW, and everything a factor 10 lower for 8 TeV. Gluon-gluon experimentally: forget it.

Top:
ATLAS searched for t+tbar resonances, and the limit for production*branching ratio at 8 TeV at 750 GeV is ~1 pb depending on details of the model (spin, width), see slide 19. Not sufficient to exclude those predictions, but it shows the 2016 dataset should be sensitive to it. Didn't look further for a CMS analysis, they won't be better by a factor 5-10.

Higgs:
~40 fb for 8 TeV from both ATLAS and CMS, found here. Same picture here.

WW/ZZ:
Upper limits of ~50 fb from CMS in 8 TeV in ZZ, worse in WW (figure 9), with a Graviton model but it shouldn't be too different for other particles.

13 TeV diphotons roughly match the size of the excess seen by the experiments, but that is not surprising as the prediction came after the excess. The large cross section ratio of 10 does not leave any tension with 8 TeV data.