Higgs bosons appear in theories with broken local gauge symmetries. In the Standard Model, the Higgs mechanism is the last piece of the puzzle remaining to be discovered or ruled out. Unification of the weak force and the electromagnetic force is achieved via the Higgs coupling to the electroweak gauge bosons. This interaction imparts a large "effective" mass to the weak vector bosons and reduces the range of the weak interaction, hence making the weak force "weak". This effective mass depends on the coupling between the particle and the massive Higgs boson.
There is
abundant evidence that the Higgs particle in the Standard Model is
light. Consistency of the standard model places some loose bounds on
the range of the Higgs mass possible from theory. Direct searches
from LEP 2 experiments places the lower limit on the Higgs mass at
MH>114 GeV. Indirect evidence from fits to the
electroweak observables points to the preferred mass of the Higgs at
89+35-26 GeV
at 68% C.L. However, the sensitivity of the fit can only constrain
the Higgs mass to be below 158 GeV at the 95% C.L. confidence
level (without LEP 2 direct search limit), or 185 GeV (including
this limit). The figure to the left illustrates the current limits on
Higgs bosons production in the range 100 &le MH &le 200 GeV.
The results exclude a Higgs mass in the ranges
100 &le MH &le 109 GeV and 158 &le MH &le 175 GeV
In general, Higgs particles arrise in any model with a broken local gauge symmetry. In models extending the Standard Model, there can be more than one Higgs particle and it is possible that in these models none of them behaves like the Higgs in the Standard Model.
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SM Higgs searchesAt the Tevatron, the dominant production channel for MH<130 GeV are associated production (W/Z + Higgs), wherein leptonic decays of W/Z and H decays to two b-jets provide handles against the more copious SM backgrounds. For higher mass we are can use the high rates of gg→H production with at H→WW and H→ZZ decays. |
Exotic Higgs searchesDoubly charged Higgs bosons (H++,H--) are predicted by some beyond the SM models with Higgs triplets, we can look for these in like-signed lepton final states. In some models with reduced coupling to fermions, Higgs decays to two photons (H→γγ) can be enhanced. |
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W/Z+jets measurements These are important physics and instrumental backgrounds to Higgs searches at the Tevatron. Even with NLO calculations, these are predicted with large theoretical uncertainties. We are going to measure W/Z+ jets, with and without b-tagging. |
Search for MSSM Higgs There are 2 Higgs doublets in the mimimal supersymmetric standard model (MSSM), which couple to particles of different weak isospin. This woudl give rise to 5 Higgs bosons (H+,H-, H0, h, A) The Higgs coupling to down-type quarks and leptons (such as τ) can be significantly enhanced in large tan β parameter space of the model, thus enhancing the sensitivity for this type of search. |
