A recent CDF result exploits the advantages of the Tevatron’s 900-GeV run. Photo: Reidar Hahn
Shortly before the Tevatron passed the baton of providing the highest-energy particle collisions to the Large Hadron Collider at CERN, physicists on CDF proposed to spend a few days with colliding beams at lower energy to study the energy dependence of certain reactions. The accelerator experts took up the challenge and delivered.
CDF has just published the first physics paper using this low-energy running, measuring the energy dependence of central, exclusive two-pion production. The paper appears in Physical Review D. Features of this energy dependence were unexpected and pose a challenge to theorists.
Proton and antiproton beams at the Tevatron were routinely injected at 150 GeV (150 billion electronvolts) and then accelerated to 980 GeV. With no acceleration, the beams collided with a total energy of 300 GeV. The collision rate was low — only 1/12 of that of the normal Tevatron run — but nevertheless high enough for some studies. The Tevatron also produced collisions at a total energy of 900 GeV. This energy matches the LHC energy at beam injection, before acceleration, so one can directly compare proton-proton interactions at the LHC with proton-antiproton interactions at the Tevatron.
The CDF collaboration thanks the Accelerator Division for their efforts in providing these unique lower-energy collisions, resulting in a physics publication (with more to come) with just a few days of special running.