Department of Physics & Astronomy

Stephen Wimpenny

Stephen Wimpenny

Stephen Wimpenny


Physics 3019

Telephone: 951-827-3868
Email: stephen.wimpenny@ucr.edu
Fax: 951-827-3345

Research Interests:

  • Experimental High Energy Physics


Ph.D. 1980, Sheffield University, England

Current Research:

Professor Wimpenny has been a leader in the study of top quark physics for many years. He led one of the experimental groups responsible for the discovery in 1995 by the D0 Collaboration at Fermilab. This was based on the pair production of top and anti-top quarks via the strong interaction. Subsequent work on the production and decay products laid the groundwork for the many precision measurements that followed. In 2009 members of his group added the first observation of the production of single top quarks via the electroweak interaction.

Professor Wimpenny and his colleagues are now taking part in the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC), which is currently taking data. The LHC provides access to a completely new energy regime and has the potential to provide insights into new areas of physics beyond the Standard Model and to probe the mechanism of electroweak symmetry breaking. The first runs at 7 and 8 TeV were completd in 2012. The accelerator and the experiments are currently offline and being prepared upgraded to run at 13 TeV which is expected to start in 2015.

The first goal of the LHC was to search for the Higgs boson, which is believed to be responsible for electroweak symmetry breaking in the Standard Model. This was largely achieved with the announcement of the observation of a new boson with a mass of 125 GeV on 4th July 2012. Subsequent research is focused on the verification that this new particle is the Higgs of the Standard Model and to measure its properties.

The other goals of the LHC are to search for physics beyond the Standard Model. This can be done in two ways; either by direct searches for new particles, or from precision measurements of known particles. Professor Wimpenny’s group has been following both approaches, using the top quark as the tool. As it is the most massive known fundamental particle, it is a natural line of study as it provides both an important background to and a natural decay path for more massive objects.

Selected Publications:

1.) “Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC’, S. Chatrchyan et al., (CMS Collaboration) Phys. Lett. B716, 30, (2012).

2.) “Observation of the Top Quark”, S. Abachi et al., (D0 Collaboration). Rev. Lett. 74, 2632, (1995).

3.) “The Top Quark”, S.J. Wimpenny and B.L. Winer, Ann. Rev. Nucl. Part. Sci. 46, 149 (1996).

4.) “Observation of Single Top Quark Production”, V. Abazov et al., (D0 Collaboration), Phys. Lett. 103, 092001, (2009).

5.) “Measurement of the ttbar production cross section in the dilepton channel in pp collisions at √s = 7 TeV”, S. Chatrchyan et al., (CMS Collaboration), JHEP, 07, 049, (2011).

6.) “Measurement of the top quark mass in ttbar events with lepton + jets final states in pp collisions at √s = 7 TeV”, S. Chatrchyan et al., (CMS Collaboration), JHEP, 12, 105, (2012).

7.) “Measurement of the mass difference between top and anti-top quarks”, S. Chatrchyan et al., (CMS Collaboration), JHEP, 6, 109, (2012).

8.) “Search for resonant ttbar production in lepton+jets events in pp collisions at √s = 7 TeV”, S. Chatrchyan et al., (CMS Collaboration), JHEP, 12, 015, (2012)

9.) “Determination of the top quark mass circa 2013: methods, subtleties, perspectives”, A. Juste, S. Mantry, A. Mitov, A. Penin, P. Skands, E. Varnes, M. Vos, S. J. Wimpenny, (submitted to JHEP), arXiv:1310.0799, (2013).

10.) “First combination of the Tevatron and LHC measurements of the top-quark mass”, (ATLAS, CDF, CMS and D0 Collaborations), arXiv:1403.4427, (2014).

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