# How neutron can have an antiparticle since it have zero charge?

Antiparticles are defined as fundamental particles having the same mass but opposite charge.

Now, a neutron has a particular mass (say m) , but zero charge ( =0). Its antiparticle should have mass=m but charge = -0 =0. i.e. another neutron.

So, how can a neutron have an antiparticle? Could a particle be its own antiparticle?

• What about e.g. the Wikipedia article about the anti-neutron is unclear to you? – ACuriousMind Jun 3 '16 at 13:54
• Ok i'm going to delete the question. Should i ? (this question was in my mind from schooldays, & did the question without further studying in web. sorry for that. – Always Confused Jun 3 '16 at 14:06
• You should delete the question, in my opinion. If you're interested, Photons are an example of something which is their own anti-particle. – Matt Jun 3 '16 at 15:38
• I could delete the question, but, its too late. Several users already laboured and contributed answers and comments that are valuable, and these knowledge may come in use to the future. Deleting the question would destroy them. so, i think, instead, edit and improve the question would be better option – Always Confused Jun 3 '16 at 18:35

A neutron has baryon number = 1, while the anti-neutron has baryon number = -1. Physics Guy has much the same here with quarks, that works as well. In the language of CPT the charge operator reverses the charge of the quarks, so the two up quarks with charge $-1/3$ is flipped to $1/3$ and the down quark from $2/3$ to $-2/3$.

I gave this question a 1-vote, in part because somebody gave it a -1 vote. I am writing to express some dismay at down voting questions. This may not be a deep question to those well versed in physics, but it is not a dumb or bad question!

• 1. Don't write stuff in answers that has nothing to do with the actual answer. Your views about votes don't belong in answers, we are not a forum. 2. The downvote tooltip says "This question does not show any research effort; it is unclear or not useful". This question doesn't show any research effort at all, since googling "anti-neutron" would have answered it. – ACuriousMind Jun 3 '16 at 14:48
• Thanks for show your respect... the definition of anti-particle i mentioned, is then an incomplete one. ( I'm not at all a physics person at all... i had physics only upto high-school. I'm just in anger with a part of school-physics because i had to just believe the strange statements like "no object can run faster than light" etc, and had to wrote them on exam. however i'm in love with basic-physics) – Always Confused Jun 3 '16 at 14:48
• @ ACuriousMind please let me know whether i should delete the question? (because deleting a question is usually not cconsidered as good). or delete it yourself. – Always Confused Jun 3 '16 at 14:51
• I'm afraid I have to reluctantly agree with ACuriousMind comments (about writing the second paragraph) but I'm in wholehearted agreement with the sentiment of what you wrote. Maybe consider making a post to physics SE meta: some of the downvoting here is IMO clumsy and churlish to put it mildly, especially with posters who are obviously highschool aged. – Selene Routley Jun 4 '16 at 8:00

Every particle has (or can have) an antiparticle. Sometimes, it is even his own antiparticle.

An antiparticle $D'$ is (easily said) defined as a particle $D$ after a CPT-transformation. CPT-Symmetry is believed to be a fundamental concept of physical nature.

A CPT-transformation is a complete changing of observables of a particle.

The C stands for charge changing, the P for parity and the T for time, so you just invert these values and get a new state for the particle which is still described by the same field equations.

A neutron has no charge, but it has other variables which are (of course) invariant under CPT-transformations. Also, the neutron is not an elementary particle, it is made of two up-quarks and one down-quark, an anti-neutron is made of two anti-up-quarks and one anti-down-quark. These quarks have charges which can be CPT-transformed.

• Thanks for informing that some particle could act as its own antiparticle (though not neutron). But then, does that single partiticle anihilate ownself? (because it is in its own touch) – Always Confused Jun 3 '16 at 14:59
• @Always Confused No, it doesnt. For example, look at the photon (which is its own antiparticle). It is just defined that after a CPt-transformation, nothing changes on the photon, so it is his own antiparticle. – Physics Guy Jun 3 '16 at 15:10