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