University of California, Riverside

Faculty Profile System

Stephen Wimpenney

Stephen Wimpenney


Department of Physics & Astronomony
Physics 3019
(951) 827-4529

Research Areas

  • Experimental High Energy Physics

Hadron Collider Physics

The D0 detector is one of the two large multi-purpose detectors at the Fermilab Tevatron in Illinois. With a center-of-mass energy of 1.96 TeV, the Tevatron has the highest collision energy of any machine in the world. This provides a unique window to research at the shortest distance scales and allows fundamental tests of the particle theory. The UCR group have been active members of the D0 Collaboration since 1986 and have contributed to the detector hardware, the control system, and various of the data analyses. The present group is led by Professor Wimpenny and consists of three faculty, two postdoctoral researchers, and two graduate students, The UCR group have focussed their research into two areas: top quark studies (Professor Wimpenny, Dr. Heinson) and electroweak physics (Professor Ellison).

Today we know that the top (t) quark is the +2/3 charge partner of the bottom (b) quark and is the most massive fundamental particle known to science. At the start of the D0 experiment in 1992 it had not been observed, despite some 15 years of searching. By the end of the second data-taking run in 1995 it had been discovered jointly by D0 and its sister experiment CDF. The observations, based on the simultaneous production of a t- and and and anti t- quark, were published  in March 1995. The UCR group played a central role in four of the seven analyses which contributed to the discovery. Subsequent research has focused on the refinement of the measurements of the quark mass and production cross section. Some 10 years later we are operating a greatly improved detector and we are analyzing a data sample more that ten times larger than that of the 1995 analyses.

An important piece ot top quark physics which has yet to be confirmed is the production of single top quarks via the electroweak interaction. At UCR, the search for this second type of t-quark phyiscs is led by Dr. Ann Heinson, who has also been co-leader of the D0 single top research team since its inception in 1997. This is a very challanging piece of research and requires the use sophisticated analyses techniques. Sometime during the next two years this analysis is expected to lead to the first experimental observation of this new process.

In 2007/2008 a new accelerator, the Large Hadron Collider (LHC), will come on-line at the CERN laboratory which lies on the boarder of France and Switzerland. This will take over from the Tevatron and the world's highest energy collider. With a center-of-mass energy of 14 TeV, it is almost an order or magnitude higher in energy than the Fermilab machine and it will provide a unique research tool into the late 2000's and early 2010's. UCR is working on one of the two big detectors for the LHC known as the Compact Muon Solenoid (CMS) experiment. This effort is led by Professors Clare and Hanson and will be supplemented by the present D0 research team who will start to transition into CMS over the next year or so.


Ph.D. 1980, Sheffield University, England


Personal Home Page


  1. "Multivariate searches for single top quark production with the D0 detector",
  2. V. Abavzov et. al., D0 Collaboration - hep-ex/0604020, (submitted to Phys. Rev. D.), (2006).
  3. "A Precision Measurement of the Mass of the Top Quark",
  4. V. Abazov et al., D0 Collaboration - Nature 429, 638-642, (2004).
  5. "The Top Quark",
  6. S.J. Wimpenny and B.L. Winer, Ann. Rev. Nucl. Part. Sci. 46, 149-195, (1996)
  7. "Observation of the Top Quark",
  8. S. Abachi et al., D0 Collaboration - Phys. Rev. Lett. 74, 2632-2637, (1995).
  9. "A Measurement of the Spin Asymmetry and Determination of the Structure Function g1 in Deep Inelastic Muon-Proton Scattering",
  10. J. Ashman et al., European Muon Collaboration - Phys. Lett. B 206, 364-370, (1988).
  11. "The Ratio of the Nucleon Structure Functions F2(n) for Iron and Deuterium",
  12. J.J. Aubert et al., European Muon Collaboration - Phys. Lett. B 123, 275-278, (1983).

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