Higgs search leaves no stone unturned

Every search channel counts when looking for the Higgs boson in the remaining allowed mass region.

The Higgs boson, the elusive final fundamental particle predicted by the Standard Model, is running out of hiding places. Until the search is over and the Higgs boson is either observed or excluded, efforts remain focused on improving the sensitivity of our search in the remaining allowed mass range.

Currently, two or more experiments exclude Higgs boson masses below 115 GeV and above 129 GeV. Near a Higgs mass of 125 GeV the sensitivity of the combined search at the Tevatron transitions from being dominated by Higgs boson decays into bottom quarks to decays into W bosons. In this transition region, searches in complementary channels are particularly important to the combined search sensitivity.

A recent DZero analysis captures a large number of complementary channels at once by focusing on final states with a tau lepton and an electron or muon. Heavy cousins of the electron, tau leptons are nearly twice as massive as a proton and can decay into neutrinos plus either electrons, muons or hadrons (particles made of quarks). Many processes can lead to a pair of tau leptons, including direct Higgs boson decays and Higgs bosons being produced with or decaying into W or Z bosons that subsequently decay into tau leptons. The analyzers looked for events where one tau lepton decayed into a neutrino and hadrons and the electron or muon came from a tau lepton, W boson, or Z boson decay. Three different categories of hadronic tau decays were considered, and each category was individually optimized.

By combining a large number of Higgs boson production and decay channels, this analysis represents a significant improvement in the Higgs boson search using tau leptons at DZero. The observed exclusion limit is a factor of 15.7 times the Standard Model production rate at a Higgs boson mass of 125 GeV. The signal sensitivity in this analysis is relatively stable across the Higgs boson decay transition region near 125 GeV, where every contribution is important to the final combination.

—Mike Cooke

These physicists made major contributions to this analysis.

Before the path of a charged particle through the DZero detector can be reconstructed, the position of every element of the tracking detector must be determined accurately. The tracking algorithms group recently completed a series of high precision alignment studies that will benefit all legacy analyses.