Three differences: opposite lepton number, opposite helicity, and opposite production context. Specifically:
- A neutrino carries lepton number +1, is produced together with a positron in β⁺ decay, and is left-handed (spin opposite to its direction of motion).
- An antineutrino carries lepton number −1, is produced together with an electron in β⁻ decay, and is right-handed.
Whether they are actually two distinct particles or the same particle in two different helicity states is still an open question — that’s the Majorana vs Dirac question.
Lepton number
The cleanest way to distinguish a neutrino from an antineutrino is by conservation of lepton number. Every charged lepton (electron, muon, tau) carries lepton number +1, and their antiparticles (positron, antimuon, antitau) carry −1. Neutrinos and antineutrinos extend this:
- $\nu_e$, $\nu_\mu$, $\nu_\tau$: lepton number +1.
- $\bar\nu_e$, $\bar\nu_\mu$, $\bar\nu_\tau$: lepton number −1.
Lepton number is conserved in all known reactions (at the tree level). So in beta-minus decay:
$$n \to p + e^- + \bar\nu_e$$
A neutron decays to a proton + electron + electron-antineutrino. The electron carries +1 lepton number, so the antineutrino must carry −1 to keep the total at 0 (the same as the original neutron).
In beta-plus decay (in some nuclei):
$$p \to n + e^+ + \nu_e$$
A proton decays to a neutron + positron + electron-neutrino. The positron carries −1, so the neutrino carries +1.
Helicity
Wu’s 1957 parity-violation experiment showed that neutrinos and antineutrinos come out of beta decays with a strongly preferred handedness:
- Neutrinos are left-handed: their spin angular momentum points opposite to their direction of motion.
- Antineutrinos are right-handed: spin points along their direction of motion.
This is a consequence of the V−A structure of the weak interaction. The weak force “sees” only left-handed particles and right-handed antiparticles. The other helicity components don’t participate at all in standard weak processes.
For massless particles, helicity is Lorentz-invariant. For massive particles (which neutrinos are, just barely), it’s not — a fast-moving observer could in principle catch up with a neutrino and see its helicity flip. But for any practical experiment, neutrinos are produced and detected exclusively in their left-handed state and antineutrinos in their right-handed state.
Production context
Different physical processes produce neutrinos or antineutrinos:
| Process | Produces |
|---|---|
| β⁻ decay ($n \to p + e^- + \bar\nu_e$) | $\bar\nu_e$ |
| β⁺ decay ($p \to n + e^+ + \nu_e$) | $\nu_e$ |
| Electron capture ($p + e^- \to n + \nu_e$) | $\nu_e$ |
| Reactor fission (neutron-rich fragments β⁻ decay) | $\bar\nu_e$ |
| Solar fusion (pp chain) | $\nu_e$ |
| Atmospheric (cosmic-ray air showers) | mix of $\nu_\mu$ and $\bar\nu_\mu$ |
| Accelerator beams | tunable: ν or $\bar\nu$ via horn polarity |
A nuclear reactor is the canonical antineutrino source: about $6 \times 10^{20}$ $\bar\nu_e$ per second per gigawatt of thermal power. The Cowan-Reines 1956 detection used a reactor for exactly this reason — antineutrinos detected via inverse beta decay.
The Sun is a pure neutrino source (no antineutrinos), because fusion involves β⁺ decays and electron captures.
How experiments tell them apart
The simplest way: look at the charged lepton produced.
A muon neutrino interacting via charged current produces a μ⁻:
$$\nu_\mu + n \to \mu^- + p$$
A muon antineutrino produces a μ⁺:
$$\bar\nu_\mu + p \to \mu^+ + n$$
In a magnetic field, μ⁻ and μ⁺ curve in opposite directions, so the sign is directly readable. This is how accelerator experiments like T2K, NOvA, and DUNE measure neutrino vs antineutrino oscillation rates separately.
For reactor antineutrinos at low energy, the signature is inverse beta decay:
$$\bar\nu_e + p \to n + e^+$$
The positron annihilates promptly with an electron, producing two 511-keV gammas. The neutron thermalizes over a few microseconds and is captured by a gadolinium nucleus (in Gd-loaded detectors) or hydrogen, releasing more gammas. The prompt-delayed coincidence is the unmistakable antineutrino signature.
Are they really different particles?
This is the Majorana-vs-Dirac question.
- If neutrinos are Dirac fermions, then the neutrino and antineutrino are genuinely different particles (like an electron and positron).
- If neutrinos are Majorana fermions, then they are their own antiparticles — and the “neutrino” and “antineutrino” we observe are really two helicity states of a single particle.
The Majorana hypothesis is being tested by neutrinoless double-beta decay experiments. If this process is ever observed, neutrinos must be Majorana. Current limits (KamLAND-Zen, LEGEND-200) are tightening but the question remains open as of 2026.
The short answer
A neutrino has lepton number +1, is left-handed, and is produced together with a positron in β⁺ decay. An antineutrino has lepton number −1, is right-handed, and is produced together with an electron in β⁻ decay. Experimentally they’re easy to tell apart by the sign of the charged lepton in the interaction. Theoretically it remains open whether they’re really distinct particles or two faces of one Majorana fermion.
For the deeper theoretical question, see Majorana or Dirac?. For why this matters cosmologically, see Leptogenesis: how a heavy neutrino might explain why anything exists.
Frequently asked
What's the difference between a neutrino and an antineutrino?
Three differences. (1) Lepton number: neutrinos carry +1, antineutrinos −1. (2) Helicity: ordinary neutrinos are left-handed (spin opposite their motion); antineutrinos are right-handed. (3) Production: neutrinos appear in beta-plus decay (proton → neutron + positron + neutrino); antineutrinos appear in beta-minus decay (neutron → proton + electron + antineutrino).
Are neutrinos and antineutrinos really different particles?
Not necessarily. If neutrinos are Majorana fermions (their own antiparticles), then a neutrino and an antineutrino are really the same particle observed in two different helicity states. If they are Dirac fermions, they are genuinely distinct. The question is being tested by neutrinoless double-beta decay experiments.
Can a neutrino become an antineutrino?
Not via known oscillation. Standard neutrino oscillation changes flavor (electron ↔ muon ↔ tau) but not lepton number. A neutrino-to-antineutrino transition would violate lepton number by 2 and is only possible if neutrinos are Majorana fermions. Direct observation has never been claimed.
How do we tell a neutrino from an antineutrino experimentally?
By the charged lepton they produce in a detector. A muon neutrino interacting via charged current produces a μ⁻; a muon antineutrino produces a μ⁺. The sign of the resulting muon (visible from its curvature in a magnetic field) tells you which species you saw. Reactor experiments observe antineutrinos by their inverse-beta-decay signature: prompt positron annihilation followed by delayed neutron capture.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2025, August 8). What's the difference between a neutrino and an antineutrino?. Neutrino Times. https://neutrino-times.com/articles/neutrino-vs-antineutrino-difference/
Chicago
Neutrino Times Editorial Team. "What's the difference between a neutrino and an antineutrino?." Neutrino Times, August 8, 2025. https://neutrino-times.com/articles/neutrino-vs-antineutrino-difference/.
MLA
Neutrino Times Editorial Team. "What's the difference between a neutrino and an antineutrino?." Neutrino Times, 8 Aug. 2025, https://neutrino-times.com/articles/neutrino-vs-antineutrino-difference/.
BibTeX
@misc{neutrino-times-neutrino-vs-antineutrino-difference,
author = {Neutrino Times Editorial Team},
title = {What's the difference between a neutrino and an antineutrino?},
howpublished = {Neutrino Times},
year = {2025},
month = {aug},
url = {https://neutrino-times.com/articles/neutrino-vs-antineutrino-difference/},
note = {Accessed: 2025-08-08}
} RIS
TY - GEN TI - What's the difference between a neutrino and an antineutrino? AU - Neutrino Times Editorial Team PY - 2025 DA - 2025-08-08 PB - Neutrino Times UR - https://neutrino-times.com/articles/neutrino-vs-antineutrino-difference/ ER -