Standard model appears to be flawed

[popeyespappy]

A while back the Fermilabs Tevatron data yielded what appeared to be evidence for the Higgs Boson. Thing is that if confirmed it doesn’t fit the standard model.

The original paper: Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in p_p Collisions at ps = 1.96 TeV

Here is what they were looking at.



Apparently the original results are being confirmed. Blog Post

The bump is getting bigger.

[lilphil1989]

I know that in the hadronic top quark decay t -> W+b -> jets, the invariant mass of the b-jet with one light jet peaks at around 150GeV, and given that the CDF simulations don't even describe the W/Z peak particularly well, I'd be quite worried at this stage that they're just not properly accounting for SM backgrounds.
I'd quite like to see what this would look like with single-top backgrounds subtracted using data instead of Monte-Carlo, and what the D0 data looks like following the same CDF analysis procedure.

[popeyespappy]

Technically speaking Phil you lost me at I. However there does seem to be some independent verification going on along the lines of your concerns.

We have presented NLO predictions for cross sections and dijet invariant mass distributions for one lepton, missing ET and two jets at the Tevatron. We have used a variety of cuts, including those used by the CDF collaboration who have recently reported an excess in this distribution around 150 GeV. By calculating the distribution of the invariant mass of the dijets at NLO we have ruled out large NLO K-factors as a possible source of the excess within the context of the SM. At NLO the cross sections have only a moderate dependence on the renormalisation and factorisation scales of QCD, indicating that our results could be used to constrain the overall
normalisation of these backgrounds.

The SM predicts a parton-level edge in the top background around 150 GeV, an edge that is softened into a broader peak by the parton shower. Detector effects, that we have not considered here, will certainly modify this feature further. In order to gain better control over the shape of this background we would advocate the use of the more inclusive cuts for which the top background is much larger and thus more easily constrained. It becomes even more significant for cuts demanding harder jets. For instance a pj T > 40 GeV cut yields a top cross section in the region of the broad peak only a factor of 2.5 lower than the W+ jets contribution. Further information on this background could be gleaned by investigating the dijet mass distribution for the case of b-tagged (or anti-tagged) jets. In particular, the dominant source of two anti-b-tagged jets is from the hadronic decay of the W. The invariant mass of two anti-b-tagged jets should therefore peak sharply around mW, with no significant peak in the 100–150 GeV region.

NLO predictions for a lepton, missing transverse momentum and dijets at the Tevatron

According to the blog post the CDF crew appears to be waiting for confirmation of their observations either from D0 or one of the LHC instruments. Meanwhile the more data they add to their analysis the bigger the bump gets.

[lilphil1989]

Technically speaking Phil you lost me at I. However there does seem to be some independent verification going on along the lines of your concerns.

In proton-proton collisions, you can create a single top quark which decays weakly to a bottom quark plus a W boson. The W can decay to a quark-antiquark pair, and because the energy in the colour fields between the quarks increases as they move apart, you get lots of quark-antiquark pairs created, and it's these that make up the hadronic jets.
The invariant mass of the bottom jet + 1 "weak jet" peaks at around 150GeV.

The problem is that in a particle physics experiment, if you want to say "this is what we expect to see based on the standard model", you have to build a computer simulation of your detector, and if you don't understand your detector as well as you could, then this is a possible source of considerable error.
The problem as I see it is that the CDF simulation doesn't predict the 2 weak boson peak (the red peak in the graph you linked) particularly well, implying that they don't understand their detector quite as well as they need to. But it will be interesting to see what the D0 data looks like!


Also, why would this break the SM if it did turn out be a Higgs signal? Am I missing something obvious here?

[popeyespappy]

Also, why would this break the SM if it did turn out be a Higgs signal? Am I missing something obvious here?

The way I understand it (from the blog post quoted below) a 150 GeV SM Higgs should have a dijet cross section of around 12fb. The CDF bump at 150 GeV is 4pb. If the CDF results are confirmed as a Higgs particle it does not conform to what the standard model predicts it should be.

If this bump really does come from a particle with mass around 150 GeV, then the first thing one might think is that this is the first hint of the Higgs boson. Indeed, we even showed above that the production of the Higgs includes diagrams that would give this particular signal when the Higgs decays into two quarks. However, one very, very interesting part of the analysis is that it does not seem like this bump could come from the standard Higgs boson!

The reason is simple: we understand the standard Higgs well enough to know that if it had a mass of 150 GeV, then we would expect an effect (a bump) that would be about three hundred times smaller. In the parlance of the field, the observed bump corresponds to a particle with a 4 picobarn dijet cross section, while a 150 GeV Higgs is expected to have a 12 femtobarn dijet cross section.

Source

[lilphil1989]

The way I understand it (from the blog post quoted below) a 150 GeV SM Higgs should have a dijet cross section of around 12fb. The CDF bump at 150 GeV is 4pb.

Ahh, ok.

I can't help but think that this will turn out to be poor background modelling, conveniently giving the Tevatron a "please give us more funding!" moment

[Autumnlicious]

I wonder if it is possible that there isn't a single Higgs per say, but a family of Higgs, much like the lepton and boson groups...

[popeyespappy]

I wonder if it is possible that there isn't a single Higgs per say, but a family of Higgs, much like the lepton and boson groups...

Some are saying that if confirmed this could lend weight to Supersymmetry or Technicolor. Supersymmetry has multiple Higgs particles. Technicolor includes none.