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 ${\displaystyle A+B\rightarrow A+\sum C_{i}}$, that is experiments in which particle A scatters off particle B, possibly producing particles ${\displaystyle C_{i}}$ 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 ${\displaystyle A+\gamma \rightarrow A'}$. The Breit frame is defined as the frame in which ${\displaystyle {\vec {p}}_{A}+{\vec {p}}_{A'}=0}$. There are different occasions when Breit frame can be useful, e.g., in measuring the electromagnetic form factor of a hadron, ${\displaystyle A}$ is the scattered hadron; while for deep inelastic scattering process, the elastically scattered parton should be considered as ${\displaystyle A}$. 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.