Particle physics basics: the rest mass of a positron (anti-electron) is equal to the rest mass of which particle?

Introduction / Context:
The positron is the antiparticle of the electron. Recognizing matter–antimatter pairs and their properties—mass, charge, and spin—is fundamental in nuclear and particle physics and underpins phenomena like beta-plus decay and pair production.

Given Data / Assumptions:

• Positron (e+) is the electron’s antiparticle.
• We compare rest masses of basic particles: electron, proton, neutron, alpha particle, muon.
• Non-relativistic rest mass equality is considered.

Concept / Approach:
By definition, a particle and its antiparticle have equal rest mass and spin, and opposite electric charge and certain quantum numbers. Therefore, the positron’s rest mass equals the electron’s (≈ 9.11×10^-31 kg, or 0.511 MeV/c^2). Protons and neutrons are about 1836 and 1839 times heavier than an electron; alpha particles (He-4 nuclei) are heavier still. The muon is a heavier lepton (~105.7 MeV/c^2), not equal to the electron mass.

Step-by-Step Solution:

Verification / Alternative check:
Conversions between mass and energy (E = m*c^2) yield the same rest energy for e− and e+ (0.511 MeV). Beta-plus decay emits a positron with the same mass as an electron.

Why Other Options Are Wrong:

• Proton/neutron/alpha: many orders of magnitude heavier.
• Muon: a lepton but substantially heavier than an electron.

Common Pitfalls:
Assuming “similar” leptons (like muons) share mass with electrons; confusing rest mass with charge magnitude.

Final Answer:
Electron