CDF finalizes its combined Higgs boson results

Best-fit cross section for inclusive Higgs boson production, normalized to the Standard Model expectation, for the combination of all CDF search channels as a function of the Higgs boson mass. The solid line indicates the fitted cross section, and the associated shaded regions show the 68 percent and 95 percent credibility intervals, which include both statistical and systematic uncertainties.

CDF’s physicists have been searching for the Higgs boson since the early days of Run I, publishing their first paper on the search in 1990. If you asked any of them why they did it, they would say it was to learn about what breaks the symmetries of the Standard Model, which is so successful in explaining the data observed at Fermilab and at other particle physics laboratories. Particles cannot have masses if these symmetries hold true, and the Higgs mechanism is the simplest, but not the only, way to resolve this dilemma. On July 4 of last year, two independent experiments at CERN, ATLAS and CMS, announced the observation of a Higgs-like boson. On July 27 Fermilab’s CDF and DZero experiments submitted a combined analysis showing evidence for a Higgs-like particle. The experiments at CERN were primarily finding the decay of the Higgs-like particle into bosons, while the experiments at Fermilab were finding the decay into fermions.

CDF sought the Higgs boson in many production and decay modes over the years. These searches have now been finalized and documented. The combined results of all of these analyses have been put together and are the last pieces of the chain. Each analysis relied upon the excellent performance of the Tevatron collider and the CDF detector. Analysis teams spent years developing new techniques to squeeze more sensitivity from the data, from improving multivariate analyses to improving the efficiencies of lepton, b-tag and jet requirements and the reconstruction resolutions.

CDF’s analyses include searches for Higgs bosons produced in association with the weak bosons W and Z, in association with a pair of top quarks, and produced in the gluon-gluon fusion and vector-boson fusion processes. CDF looks for Higgs-like boson decays to many different channels (pairs of b quarks, W bosons, Z bosons, photons and tau leptons). To make the most sensitive test for the presence of the Higgs-like boson, scientists combine results from each of these searches. The combined cross section rate is compared with the Standard Model prediction, which is shown in the above figure.

CDF also places constraints on each of the decay modes separately and tests exotic models, such as a model in which the Higgs boson does not couple to fermions and another model in which a fourth generation of fermions enhances its production rate. CDF also places constraints on the couplings to fermions and gauge bosons. The finalized CDF paper is very consistent with the paper submitted in July 2012. The collaborations will soon submit a new paper that finalizes the combined CDF and DZero result.

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edited by Andy Beretvas

The CDF collaboration celebrates the Tevatron on Sept. 30, 2011. Photo: Cindy Arnold