Our group is currently studying the properties of top quarks. The top is the most massive of the elementary particles and may hold the key to understanding the nature of the Higgs-like boson. Top quarks for our studies are created in high energy collisions of protons and anti-protons at the Fermilab Tevatron and recorded with the Collider Detector at Fermilab (CDF). The CDF and D0 experiments have both observed an unexpectedly large forward-backward asymmetry in the direction of the top quark as it emerges from the collision. In a new analysis, CDF has established the functional dependence of the asymmetry on the top production angle and the invariant mass of the top pair system. Our goal now is to determine if this behavior is an amplified version of a small asymmetry expected in QCD, or something unexpected with the top quark. We are developing new techniques to study the asymmetry with leptons, angular distributions, and the top pair system momentum. We are also searching for analogous effects in bottom quark production. The top asymmetry is difficult to measure at LHC, but techniques under development there should yield an interesting comparison in the near future.
We are also continuing a search for a supersymmetric counterpart of the Higgs boson.
If supersymmetry exists, the Higgs-like boson observed at the LHC must be part of a larger family of related bosonic particles. We search for one member of this family with a distinctive signature of three high momentum bottom quark jets. A SUSY Higgs search in the first half of the CDF data showed a tantalizing but statistically inclusive excess, and we are following up with the full data set. This is another difficult measurement at LHC, and we again look forward to improved techniques there and an eventual comparison.
Search for Higgs Bosons Produced in Association with Bottom Quarks, T. Aaltonen et al.,
The CDF Collaboration, Phys. Rev. D 85, 032005 (2012).
The CDF Collaboration, Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production, T. Aaltonen et al., Phys. Rev. D 83:112003, (2011).
Measurement of Top Pair Spin Correlation in Proton-Anti-Proton Collisions Using the CDF II Detector at the Tevatron, T. Aaltonen et al., The CDF Collaboration, Phys. Rev. D 83,
Search for the Production of Narrow Top-Bottom Resonances in Proton-Anti-Proton Collisions at Sqrt(s) = 1.96 TeV, T. Aaltonen et al., The CDF Collaboration, Phys. Rev. Lett.,
103, 041801 (2009).
Forward-Backward Asymmetry in Top Quark Production In Proton-Anti-Proton Collisions at Sqrt(s) = 1.96 TeV, T. Aaltonen et al., The CDF Collaboration, Phys. Rev. Lett., 101,
Limits on the Production of Narrow Top-AntiTop Resonances in Proton-Anti-Proton Collisions at Sqrt(s) = 1.96 TeV, T. Aaltonen et al., The CDF Collaboration, Phy. Rev. D 051102 (2008).
Measurement of the Top Quark Pair Production Cross Section in Proton-Anti-Proton Collisions at Sqrt(s) = 1.96 TeV Using Lepton + Jets Events with Secondary Vertex b-Tagging”, D. Acosta et al., The CDF Collaboration, Phys. Rev D 71, 052003 (2005).