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 ⁠ $\textstyle A+B\rightarrow A+\sum C_{i}$ ⁠, 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.

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