Welcome to D0 Higgs

Fermilab | Preprints

Higgs Physics Group at DØ has been merged with Top group

Conveners: Andreas Jung (Fermilab), Slava Sharyy (CEA-Saclay), Boris Tuchming (CEA-Saclay) 

Click here to go to top group web page

The Higgs boson

Higgs bosons appear in theories with broken local gauge symmetries. In the Standard Model, the Higgs mechanism is the last piece of the puzzle that remained for a long time to be discovered or ruled out until it was discovered in 2012 at CERN. 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.

Tevatron Limits

Quest for the Higgs

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. Indirect evidence from fits to the electroweak observables points to the preferred mass of the Higgs at 89+29-24 GeV at 68% C.L. (updated March 2012). However, the sensitivity of the fit can only constrain the Higgs mass to be below 152 GeV at the 95% C.L. confidence level (without LEP 2 direct search limit).

In 2000, after the final LEP shutdown, direct searches from LEP 2 experiments placed the lower limit on the Higgs mass at MH>114.4 GeV (See hep--ex/0306033 ) Then, Tevatron Run II started in 2001. The CDF and DØ experiments have been searching for the Higgs bosons in the Tevatron collider data for a decade. They provided the first post-LEP era direct constraints on the Higgs particle by excluding the possibility of a Higgs boson mass around 165 GeV in Summer 2008 (see arXiv:0808.0534 and arXiv:0808.0534). In Summer 2012, They found an evidence of the Higgs production associated with a vector boson and decaying to a pair of bottom quarks (see arXiv:1207.6436). This evidence was complementary to the Higgs boson observation at the CERN LHC in bosonic modes. (see arXiv:1207.7235 and arXiv:1207.7214).

Tevatron couplings  

The final D0 results on the Higgs, which are based on the full Tevatron Run II (2001-2011) dataset, are now published in Phys. Rev. D 88, 052011 (2013), also in arXiv:1303.0823. They have been combined with the CDF analyses to provide the final Tevatron results on the Higgs, published in Phys. Rev. D 88, 052014 (2013), also in arXiv:1303.6346. Both figures on the left are extract from the later Article.

The top left figure illustrates the final Tevatron limits on Higgs bosons production in the range 90 ≤ MH ≤ 200 GeV. It is based on the full dataset of Tevatron Run II (2001-2011). The results exclude a Higgs mass in the ranges 90 ≤ MH ≤ 109 GeV and 149 ≤ MH ≤ 182 GeV. The bottom left figures displays the cross-section measurements in the various Higgs search channels. Altogether these channels provide an evidence at the 3 standard deviation level for the production of a Higgs boson of 125 GeV at Tevatron. The overall measured production rate is 1.44+/-0.58 times the Standard Model expected value, which is in perfect agreement with the Standard Model.


Many Other Higgses

    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.

The different topics handled by the group


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.

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.