Thursday, August 02, 2012

Is it really Higgs?

New Scientist informs that ATLAS has published its improved analysis of the newly discovered spinless particle. The overall conclusion from graphs in the article is that the production rates for weak gauge boson pairs are somewhat too high whereas the rate for decays to tau pairs and for associated production of W and Z and of Higgs decaying to bpair are too low (see Figure 10 of the article).

Statistical fluctuations could be in question but the spokesperson Fabiola Gianotti says that "It could well be that it's not the standard model Higgs boson" and later continues "When the uncertainties become even smaller, when we have even more data and more studies, we'll be able to understand better the properties of this particle, if it's a Higgs boson or a more exotic object". So we still do not know if it is Higgs, Higgs like particle, or something else.

The reported decay rates of the new particle to electro-weak gauge bosons give important guidelines in the attempts to guess the production mechanism and the effective action responsible for the decays. The surplus of gamma pairs is an important hint and suggests an additional decay channel to gamma pairs. The recent data from ATLAS (figure 10) support the Higgs like behavior for the decays to Z and W pairs. The decay rates to tau pairs and to b pairs in associated production together with W are lower than predict.

The characteristic Higgs like behavior is implied by the vacuum expectation value in the gauged kinetic term for the pion field whereas for gamma pairs this term gives only decays via W loop. This suggests that the pion field generates vacuum expectation as indeed happens in the general model for the production of lepto-pions. The additional decay channel would by PCAC hypothesis correspond to the coupling of the pion to electromagnetic instanton density giving also rise to the vacuum expectation. Hence one would obtain Higgs like behavior with anomalous gamma pair production.

  1. The models for the electro-pion and tau-pion production via the formation of a coherent state of pions is a natural first guess for the production mechanism. The strong non-orthogonal electric and magnetic fields of colliding quarks give rise to non-vanishing instanton density E•B and by PCAC hypothesis pion field develops a vacuum expectation value proportional to E•B. Note that nonvanishing of E•B means that the dimension d of the CP2 projection of preferred extremal is higher than d=2: this holds always true for the proposed ansatz for the preferred extremals of Kähler action.

  2. To get perspective, consider first the the decays of Higgs to electroweak gauge boson pairs. The gauged kinetic term in the action of Higgs is responsible for the primary decays to W and Z bosons and contains terms quadratic in Higgs and gauge bosons. As Higgs develops a vacuum expectation, this term gives in the lowest order a term, which is linear in both Higgs field and Higgs vacuum expectation, and quadratic in gauge fields W and Z.

    The gauged kinetic term gives rise to decays to virtual W and Z pairs decaying in turn to lepton and quark pairs. The ratio of rates to Z pairs and rate to W pairs reported by ATLAS is consistent with Higgs interpretation and poses a strong constraint on modeling. Decays to gamma pairs take place via W loop and the rate contains additional α2 factor tending to reduce the decay rate. The loop integral gives an additional numerical factor expressible in terms of the mass ratios but the naive expecation is that the decay rate to gamma pairs is slower than to W and Z pairs.

  3. In the case of pion-like states the kinetic term for pion gives exactly similar structure with vacuum expectation of E•B replacing that of Higgs. Hence the basic predictions for the decay rates to weak boson pairs are essentially identical as for Higgs apart from the anomalously high rate to gamma pairs. In particular, the rate ratios R(π→ ZZ)/R(π→ WW) and R(π→ γγ)/R(π→ WW) are predicted to be the same as for Higgs option.

    PCAC however predicts an additional decay channel to gamma pairs due to the coupling pion to the quantum part of E•B. This terms gives additional contribution to the decay rate proportional to α2 rather than α3. By a suitable choice of the parameter fπ it might well be possible to explain the observed anomalously high rate of gamma pairs.

The pseudoscalar nature of pionlike state, the existence of charged pionlike states, the weak dependence on fermion mass of the decay rates to fermion pairs are the relatively easily testable killer predictions.

For a TGD based discussion of the general theoretical background for Higgs and possible TGD inspired interpretation of the new particle as pionlike state of scaled variant of hadron physics see Is it really Higgs?.

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