It is no secret that neutrinos change flavor or oscillate as they travel from one place to another, and that the amount they change depends on how much time they have to change. This time is directly related to the distance the neutrino traveled and the energy of the neutrino itself. Measuring the distance is easy. The hard part is measuring the neutrino energy.
Over the last decade, measurements by the CDF and DZero collaborations of how top quarks flee the scene of the crime, the so-called “forward-backward asymmetry,” caused quite a stir as they clashed with then state-of-the-art theoretical predictions for the Tevatron. The disagreement tantalized physicists with visions of new, unexpected particles influencing the behavior of the top quark. Now, with the final, combined word from the experiments, Fermilab has placed a capstone on its study of the forward-backward asymmetry, and the measurements and theory now agree.
You may be familiar with particles of light, called photons. Physicists give the name “prompt photons” to those that are produced by two particles smashing together — hard collisions — as contrasted with those resulting from the decay of other particles. The Tevatron produced prompt photons by the hard collisions between protons and antiprotons.