A Higgs particle but which one?

ResearchBlogging.org

After Moriond conference last week, and while Moriond QCD and Aspen conferences are running yet, an important conclusion can be drawn and it is the one given in this CERN press release. The particle announced on 4th July last year is for certain a Higgs particle as it has spin 0, positive parity and couples almost like the Standard Model Higgs particle to all others. The agreement with Standard Model is embarrassingly increasing as cumulated data since last year are analyzed. Today, CMS will also update their results for the decay H\rightarrow\gamma\gamma and we will know if the small deviation observed by ATLAS will be confirmed. It is true that they see such a deviation with a larger dataset but, rather to increase, it has slightly diminished and this is not really encouraging.

So far, no other particle has been seen and no new physics beyond the Standard Model is seen at the horizon. There is some people pushing for a conclusive assignment of the nature of this boson to the vanilla Higgs particle postulated in the sixties. But it is really too early yet to draw such a conclusion and I have explained why in a paper of mine appeared today on arxiv (see here). Indeed, a formulation of the Higgs field is possible such that, at the tree level, coincides with the original Higgs field (a Higgs impostor). This is due to the existence of exact solutions of the equations of motion of such a field (see here). The relevant point to tell which one is realized in nature is through the decay rate in WW and ZZ and, with the current data, there is agreement for both yet. H->ZZ decay at CMSBut, being amplitudes exponentially damped, higher excited states of the Higgs boson cannot be easily seen presently and their eventual observation appears as a statistical fluctuation yet. This can be evaluated quantitatively. It is important because the ZZ decay is sensible to higher masses and displays some peaks that reveal themselves as statistical fluctuations. Increasing the number of events could turn these peaks into real observations.

The interesting point here is that we are moving form the discovery moment to the study phase with a lot of room for improving measurements on this Higgs particle. But the analysis for the existence of higher excited states, Higgs’ brothers, is just at its infancy.

Update: This the analogous figure from ATLAS while the figure for H\rightarrow\gamma\gamma from CMS agrees quite well with the Standard Model: 0.8\pm 0.3.

ATLAS ZZ->4l

Marco Frasca (2013). Revisiting the Higgs sector of the Standard Model arXiv arXiv: 1303.3158v1

Marco Frasca (2009). Exact solutions of classical scalar field equations J.Nonlin.Math.Phys.18:291-297,2011 arXiv: 0907.4053v2

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2 Responses to A Higgs particle but which one?

  1. Alexander Dynin says:

    Marco,

    Am I correct that the Higgs mechanism is not yet verified?

    Alexander

    • mfrasca says:

      Dear Alexander,

      No, not yet. But we have a mounting evidence about it. CERN has found a scalar particle (spin 0 and positive parity data hint) that couples to other matter much in the same way is expected from it. On the other side, in order to be sure it is exactly the particle postulated in the sixties, it must be single (no brothers) and the potential of the scalar field must have the form V(\phi)=-\mu^2\phi^2+\lambda\phi^4 to be sure the mechanism is exactly that one. But to fix the form of the potential from data we have to wait LHC upgrade as one has to check Higgs double production, a very small effect indeed. Finally, the rates it decays in other particles must agree with that of the Standard Model. Presently, we have a large margin yet (20-30%) to be perfectly sure.

      Marco.

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