Physics at Virginia

"Search for the Standard Model Higgs Boson at CDF Run II"

Brandon Parks , Ohio State University
[Host: Chris Neu]
One of the greatest theoretical triumphs in the history of physics has been the unification of the electromagnetic and weak forces. This theory successfully predicted the masses of the W and Z bosons which were later measured at CERN, and involves a mechanism that provides all particles with mass. This mechanism also predicts the existence of another observable particle, known as the Higgs boson. Experiments at the LEP collider have placed a lower bound on its mass of 114 Gev/c2, but direct measurement of the Higgs has thus far eluded all efforts. Currently, the CDF and D0 experiments at Fermilab are pushing to probe the mass regions not excluded by LEP with a number of analyses optimized for masses extending from 100 to 200 GeV/c2. Near the LEP boundary where the Higgs is expected to decay primarily to a pair of bottom quarks, the most promising channels involve Higgs produced in association with a W or Z boson. In particular, the ZH modes have very interesting properties which can be taken advantage of at the analysis level. The mode in which the Z decays to electrons or muons is extremely "clean", as leptons from vector boson decay are typically well measured and all final state particles are directly reconstructed. Conversely, the mode in which the Z decays to neutrinos is extremely challenging, as the presence of the Z can only be inferred from momentum imbalance provided by recoil with the Higgs. Utilizing new analysis techniques developed to isolate a Higgs signal amongst its seemingly overwhelming backgrounds, no significant excess of signal has currently been observed. However, limits have been set on the production cross section of a Higgs boson. Currently, limits of 16 times the standard model expectation has been set in the ZH->llbb mode, and 8 times the standard model expectation in the ZH->vvbb mode for a Higgs mass of 115 GeV/c2. Combining these results with all low mass analyses at CDF and D0, the Tevatron has placed a limit of 3.7 times the standard model expectation directly above LEP's lower mass limit.
High Energy Physics Seminar
Wednesday, September 3, 2008
3:30 PM
Physics Building, Room 204
Note special room.

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