- #1

- 43

- 4

Here (page 6) https://people.phys.ethz.ch/~pheno/PPP/PPP2.pdf it is claimed

The key factor for investigating the proton substructure is the wavelength of the probing

photon, which is related to the transferred momentum by

$$\lambda\sim \frac{1}{\sqrt{Q^2}}$$

Where ##Q^2## is not actually "momentum" but its the square of the four momentum transferred by the photon.

I can't understand why this is used, since the square root of square of four momentum is

$$\sqrt{p\cdot p}=\sqrt{|\textbf{p}|^2-E^2/c^2}$$

While De Broglie relation usually involves the three momentum ##\textbf{p}##

$$\lambda\sim \frac{1}{|\textbf{p}|}$$

So is in this case ##\sqrt{Q^2}## approximately the three momentum? Or is the De Broglie relation in the relativistic case to be written using ##\sqrt{Q^2}## instead of three momentum?