In 1994, Westfall joined the STAR collaboration, which is carrying out experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory on Long Island, New York.

At American Physical Society meeting in Tampa, Florida, in April 2005 he represented the entire RHIC community in announcing the discovery of the strongly coupled quark-gluon plasma (termed "perfect liquid" because of its vanishingly small viscosity).

They obtained NSF funding to develop novel teaching and laboratory techniques, authored multimedia physics CDs for their students at MSU's Lyman Briggs College, and co-authored a textbook on CD-ROM, called cliXX Physik.

In subsequent years, they were instrumental in creating the LearningOnline Network with CAPA (LON-CAPA), which is now used at more than 70 universities and colleges in the United States and around the world.

This project has received funding from the NSF STEM Talent Expansion Program, and its best practices have been incorporated into their textbook University Physics, which was published in 2010 by McGraw-Hill.