Evelyn Thomson

Evelyn Thomson
Standing Faculty



Research Areas: Experimental Particle Physics, Collider Physics



American Physical Society (APS) Fellow (2022)
Ira H. Abrams Memorial Award for Distinguished Teaching (2017)

Evelyn Thomson has performed experiments at e+e− and hadron colliders at the leading particle physics laboratories around the world. Her research interests include precision measurements of the W boson mass at ALEPH, precision measurements of top quark properties and searches for the Higgs boson at CDF, and searches for physics beyond the standard model at ATLAS.

In 1995, she started her research as a graduate student at the University of Glasgow with the ALEPH experiment at the CERN Large Electron Positron (LEP) collider, near Geneva, Switzerland. She studied W+W- pair production and performed measurements of theW boson mass in the WW->lvqq channel. The W boson is one of the particles that carries the weak nuclear force, essential for the nuclear fusion reactions that power stars, and was discovered in 1983 at CERN. The W boson acquires mass in the standard model of particle physics via a Higgs boson. Interpretation of improved measurements of the W boson mass in the context of the standard model of particle physics led to a better constraint on the mass of the much-hunted and exceeding elusive Higgs boson, giving a useful clue for where and how to search for it. The Higgs boson was finally discovered by proton collider experiments at CERN much later in 2012!

In 1999, as a postdoctoral fellow with the Ohio State University, she joined the CDFcollaboration at the FermilabTevatron proton anti-proton collider, near Chicago. She successfully commissioned the extremely fast track (XFT) processor. The XFT made extensive use of parallel processing and pipelining in Programmable Logic Devices to reconstruct charged-particle tracks in time for the first-level trigger in every proton anti-proton collision - a first at a hadron collider. At the heart of the CDF trigger system, which tackled the challenge of choosing the few hundred most interesting events to save for analysis from the one million seven hundred thousand head-on collisions between bunches of protons and bunches of anti-protons each second, the XFT was essential for the Top, Exotic, Electroweak and B physics programs at CDF. The top quark is by far the most massive of the sixteen known fundamental particles, and has approximately the same mass as a gold nucleus (which contains about 197 nucleons). Intrigued by the possibility that the unexplained large mass of the top quark could be due to effects from physics beyond the standard model, she developed and supported a versatile analysis package used by most physics analyses in the CDF Top Quark Physics Group. She measured the pair production rate of top quarks at CDF in the ttbar-> lvqqbb channel with an advanced multivariate technique, featured here in the Fermilab result of the week. She has continued to support the combination of several CDF and D0 results.

In 2004, she moved to the University of Pennsylvania as a tenure-track assistant professor, promoted to associate professor with tenure in 2010. In recognition of her research on CDF, she was named an Outstanding Junior Investigator by the U.S. Department of Energy in 2005 and an Alfred P. Sloan Research Fellow in 2006. From April 2004 to April 2006, she was co-leader of the CDF Top Quark Physics Group, which consisted of over 100 active researchers, including over fifty graduate students from universities in the U.S. and abroad. She worked with postdoctoral researcher Dr. Aafke Kraan to analyze the angular distribution of the decay products of the top quark. Dr. Kraan won a Marie Curie Fellowship in 2006 from the European Union. In relation to the search for the standard model Higgs boson at CDF in the WH->lvbb channel, she worked with postdoctoral researcher Dr. Chris Neu on the first measurement of W + b-jet production. Dr. Neu advanced in 2009 to a tenure-track assistant professorship at the University of Virginia. With graduate student Justin Keung, she worked on improved b-jet identification and a search for WZ->lvbb production. Dr. Keung advanced to a postdoctoral fellowship at the University of Toronto in 2010.

In 2007, she joined the ATLAS experiment at the CERN Large Hadron Collider (LHC). With postdoctoral researchers Dr. James Degenhardt and Dr. Sasa Fratina and graduate students Dominick Olivito, Elizabeth Hines, and Brett Jackson, we have contributed to the commissioning and successful operation of the ATLAS detector's transition radiation tracker.  ATLAS started collecting proton-proton collisions in 2009, and Jim was ATLAS data-taking shift leader at the time of the first collisions.  The Higgs boson discovery, the primary goal of the rest of the Penn ATLAS group, was announced in July 2012. Our physics interests from Run 1 included direct searches for physics beyond the standard model, including new massive vector bosons (W' and Z') decaying to leptons, an anomalous rate of production of lepton pairs (e+e+, e-e-, mu+mu+, mu-mu-, e+mu+, e-mu-) with the same sign of electric charge (same-sign dileptons) in exotic models (doubly charged Higgs), and supersymmetry (direct gaugino production), and finally searches for a supersymmetric partner to the top quark in R-Parity violating supersymmetry models.  These searches formed the Ph.D. work of graduate students Brett Jackson, Elizabeth Hines, and Dominick Olivito.

For Run 2 (2015-2018) with postdoc Jeff Dandoy and graduate students Leigh Schaefer, Ian Dyckes and Lucas Flores, our physics interests expanded the search for R-Parity violating supersymmetry at the higher center-of-mass energy of 13 TeV, where more massive stops could be produced than ever before, and to searches for electroweak gauginos, where the large dataset gives sensitivity to these rare processes. We contributed to the successful operation of the TRT, with Ian Dyckes as a DAQ expert, Leigh Schaefer as TRT software convener, studies of the TRT occupancy by Leigh Schaefer to characterize the pile-up on an event-by-event basis, studies of electron identification by Lucas Flores, and studies of jets calibration by Jeff Dandoy. Jeff Dandoy served as co-convener of the SUSY Electroweak group on ATLAS from 2018-2020. With double the Run 2 data expected in Run 3 (2022-2025), my group is looking forward to designing new seaches for more signatures of R-Parity violating supersymmetry. I am serving as co-convener of the SUSY RPV Long-Lived Particle group on ATLAS from April 2022-2024. Graduate students James Heinlein and Lauren Osojnak are extending the stop search, with decay to a charged lepton and b quark, using the full Run 2 data, with plans to adapt the search with new postdoc Michael Hank to a chargino decay to a charged lepton and boosted Higgs decaying to b quarks. We continue to contribute to the operation of the TRT in Run 3, with Lauren Osojnak serving as a DAQ expert.

To prepare for the high luminosity LHC starting in 2029, the entire charged particle tracking detector will need to be replaced during 2026-2028. My group, with postdocs Jeff Dandoy and Michael Hank, graduate students James Heinlein and Bobby McGovern, is working closely with Penn's electronics and instrumentation group on the testing of the front-end readout electronics for the silicon strip detector. Jeff Dandoy, Bobby McGovern, and several members of the Penn group recently gave talks and posters at TWEPP 2022 on the successful results of these tests. I am also the US L3 manager for readout electronics for the silicon strip detector upgrade. 


Ph.D. Experimental Particle Physics, University of Glasgow, 1999,
“Measurements of the W boson mass from semileptonic WW events with the ALEPH detector.”
B.Sc.(Hons) First Class, Physics, University of Glasgow, 1995.

Courses Taught

Physics 522: Introduction to Elementary Particle Physics

Physics 230: Principles of Physics on Special Relativity, Thermodynamics, Vibrations and Waves

Physics 150/140: Principles of Physics on Classical Mechanics

Physics 151/141: Principles of Physics on Electricity & Magnetism


Selected Publications
PhD theses:
  • James Heinlein, A search for B-L-R-Parity violating scalar top decays with the ATLAS experiment (2023). Dissertation
  • Lucas Flores, Identifying Electrons And Searching For Electroweak R-Parity Violating Supersymmetry At ATLAS (2021). Dissertation
  • Ian Dyckes, Search for trilepton resonances from R-parity violating chargino decays in the B-L MSSM (2021). Dissertation
  • Leigh Schaefer, A Search For Wino Pair Production With B-L R-Parity Violating Chargino Decay To A Trilepton Resonance With The ATLAS Experiment (2019). Dissertation
  • Brett Jackson, A Search for B-L R-parity-violating scalar top decays in sqrt(s)= 8 TeV pp collisions with the ATLAS experiment, (2015). Dissertation
  • Elizabeth Hines, Search for weakly-produced supersymmetry in the same -sign di-lepton final state at sqrt(s)=8 TeV with the ATLAS detector, (2015). Dissertation
  • Dominick Olivito, Search for anomalous production of prompt like-sign lepton pairs at sqrt(s)=$ 7 TeV with the ATLAS detector, (2012). Dissertation
  • Justin Keung, Search for the production of the Standard Model Z boson in association with W+- boson in proton anti-proton collisions at 1.96 TeV center of mass energy, (2010). Dissertation
CV (file)