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The DØ Group at the University of California, Riverside Experimental High Energy Physics Research Department of Physics and Astronomy University of California Riverside, CA 92521-0413 |
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The DØ Group at the University of California, Riverside Experimental High Energy Physics Research Department of Physics and Astronomy University of California Riverside, CA 92521-0413 |
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Overview Experimental physicists from UC Riverside have been performing high energy physics research at the DØ experiment since 1986. The DØ detector is at the proton-antiproton Tevatron Collider at the Fermi National Accelerator Laboratory near Chicago, Illinois. We use data collected at the experiment to study properties of fundamental particles including the top and quark and W and Z bosons, and to search for the Higgs boson. We played a leading role in the design and construction of the Silicon Microstrip Tracker for the experiment upgrade in 2001. With DØ, we have published 132 papers in several premier international journals from the data collected in Run I (1992–1996), and a further 72 papers so far from the data collected in Run II (2002–2009). Group Members
Steve has been working on DØ since 1986. John joined in 1989 and Ann in 1992. Bob joined in 2002, and is part time on DØ with most of his time on CMS. Avdhesh and Liang joined the group in September 2005, and Mark joined in 2007. Research Areas Top Quark Physics The top quark is the heaviest known elementary particle. It was first observed at Fermilab in 1995. Since then, many measurements have been made of its properties, including the production cross sections in several decay channels, and its mass. Because its mass is close to the electroweak symmetry breaking scale, it is hoped that information from precision measurements will lead to insights into how that symmetry breaking occurs. Steve Wimpenny's area of research is in top pair physics, in particular in the dilepton decay mode, where each top quark decays to a W boson and a b quark, and both W's decay leptonically to an electron or a muon and a neutrino. He is working to measure the production cross section for this process in these decay channels. Ann Heinson is co-leading the search for single top quark production at DØ. Philip Perea graduated in June 2006 with an analysis that searched for t-channel single top quark production using multiple neural networks to separate the expected signals from background. Liang Li is also working on this search, and has designed the triggers used to collect recent data. Mark Padilla is starting work on this search, summer 2007. In December 2006, we announced the first evidence for single top quark production, a most exciting event. This work is now published, and we are improving the analyses and including newer data to increase the significance of the measurement to the level that can be considered "observation." Higgs Physics The Higgs boson has been postulated to explain electroweak symmetry breaking, when the W and Z bosons gain mass while the photon remians massless. There are many beyond-the-Standard-Model predictions for Higgs boson physics that indicate there could be several different types of Higgs bosons instead of just the one from the Standard Model. One of the main goals of the high energy physics field for the next few years is to elucidate the mechanism for electroweak symmetry breaking; observation of one or more Higgs bosons will be the first step in this process. The work on the search for single top quar production directly improves the sensitivity for the Higgs boson searches in the WH production mode, since the final states have the same set of particles, and thus the backgrounds are the same. Electroweak Physics John Ellison has been a leader in DØ's electroweak phsyics program since we first got data in 1992. He co-led the diboson subgroup that published many papers on anomalous trilinear couplings between the bosons, and then went on to be a convener for all the electroweak measurements. His student, Raymond Gelhaus, recently graduated with a measurement of the Z boson differential cross section and forward-backward asymmetry in the dielectron decay mode. Our recent former postdoc, Ia Iashvili, is co-convener of the electroweak physics group. Bottom Quark Physics Postdoctoral researcher Avdhesh Chandra, together with John Ellison, is doing groundbreaking work on the mixing of Bs mesons, including lifetime difference measurements and CP violation studies. Silicon Microstrip Tracker The SMT was first proposed by Ellison in 1989 for DØ in Run I, and went through many design changes since then before finally being completed and installed in 2001 for Run II. This device, with nearly 800,000 readout channels, measures the 3-d coordinates where charged particles pass through its layers. From this information, we reconstruct the particles' tracks, and hence the position of the collision point on the beamline, and the secondary vertices in jets from heavy flavor decays. We use this jet identification in the reconstruction of top quark and Higgs boson decays. Many members of the UCR group worked on the design and construction of this detector for over a decade, and on the associated software to reconstruct the information from it. It has been used for all data-taking for the past five years, and is expected to be in almost continuous operation for a further three years. Almost every measurement made by DØ relies upon the information produced by this detector. Former Group Members
Ia Iashvili co-led the jet energy scale group, the top mass and top properties subgroups, and is co-convener of the electroweak physics group; she is now an assistant professor at the State University of New York, Buffalo, working on DØ and CMS. Suyong Choi co-led the vertex reconstruction group, the Higgs dilepton subgroup, was reconstruction executable manager, and is co-convener of the Higgs physics group; he is now an assistant professor at Sungkyunkwan University in Seoul, Korea, working on DØ. Jim Cochran is an associate professor at Iowa State University, working on BaBar. Brajesh Choudhary is a full professor at Delhi University, India, working on DØ and CMS. Ray Hall is an associate professor at California State University, Fresno, working on DØ. Valentin Kuznetsov, Krish Gounder, and Chris Boswell are staff scientists. |
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