Breit frame

In particle physics, the Breit frame (also known as infinite-momentum frame or IMF) is a frame of reference used to describe scattering experiments of the form formula_1, that is experiments in which particle A scatters off particle B, possibly producing particles formula_2 in the process. The frame is defined so that the particle A has its momentum reversed in the scattering process.
Another way of understanding the Breit frame is to look at the elastic scattering formula_3. The Breit frame is defined as the frame in which formula_4. There are different occasions when Breit frame can be useful, e.g., in measuring the electromagnetic form factor of a hadron, formula_5 is the scattered hadron; while for deep inelastic scattering process, the elastically scattered parton should be considered as formula_5. It is only in the latter case the Breit frame gets related to infinite-momentum frame.
It is named after the American physicist Gregory Breit.