---
title: "An incident photon with momentum \\(\\vec{p}_0\\) traveling in the \\(+x\\)-direction collides with a stationary electron. After the collision, the scattered photon moves with momentum \\(\\vec{p}_\\gamma\\) at an angle \\(\\theta\\) above the \\(+x\\)-axis, and the electron recoils with momentum \\(\\vec{p}_e\\) at an angle \\(\\phi\\) below the \\(+x\\)-axis. Which of the following vector diagrams correctly represents the relationship between the momentum vectors for this system?"
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url: "https://nerd-notes.com/ubq/123607/"
date_modified: "2026-09-28T12:00:32+00:00"
---

# An incident photon with momentum \(\vec{p}_0\) traveling in the \(+x\)-direction collides with a stationary electron. After the collision, the scattered photon moves with momentum \(\vec{p}_\gamma\) at an angle \(\theta\) above the \(+x\)-axis, and the electron recoils with momentum \(\vec{p}_e\) at an angle \(\phi\) below the \(+x\)-axis. Which of the following vector diagrams correctly represents the relationship between the momentum vectors for this system?

An incident photon with momentum \(\vec{p}_0\) traveling in the \(+x\)-direction collides with a stationary electron. After the collision, the scattered photon moves with momentum \(\vec{p}_\gamma\) at an angle \(\theta\) above the \(+x\)-axis, and the electron recoils with momentum \(\vec{p}_e\) at an angle \(\phi\) below the \(+x\)-axis. Which of the following vector diagrams correctly represents the relationship between the momentum vectors for this system?

![A schematic diagram of a Compton collision. On the left, a wavy arrow labeled \vec{p}_0 points horizontally to the right along a dashed horizontal reference line labeled +x. The arrow points toward a solid circular dot representing an electron labeled e^-. To the right of the dot, the dashed horizontal reference line continues. A wavy arrow labeled \vec{p}_\gamma extends upward and to the right from the dot at an angle \theta relative to the horizontal line. A straight arrow labeled \vec{p}_e extends downward and to the right from the dot at an angle \phi relative to the horizontal line. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790596831-UacAsI.jpg)

- **A.** Diagram A
- **B.** Diagram B
- **C.** Diagram C
- **D.** Diagram D

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123607/*