# Do anti-particles have opposite parity?

1. Aug 10, 2011

### johne1618

Hi,

I understand that anti-particles have the opposite charge to particles.

Do anti-particles have the opposite parity to particles as well?

John

2. Aug 10, 2011

### xts

Anti-particles have not only charge, but all their conservation numbers, among them charge and parity, opposite to their "normal" particles.

3. Aug 10, 2011

### johne1618

Thanks!

4. Aug 10, 2011

### johne1618

Actually, is that right?

I looked on hyperphysics and it said only the "internal" quantum numbers are reversed under charge conjugation not the spatial coordinates.

John

5. Aug 10, 2011

### xts

Sure! You're right. I gave too quick answer...
Parity of compound particle (e.g. hadrons) is composed (multiplicatively) of internal parities of quarks and the parity of their relative geometry. The last do not differ from particle to anti-particle.
So both mesons and their anti-mesons have same parity ($-1^{spin+1}$). Baryons, as composed of 3 quarks, have parity +1, while their counterparts have -1.

6. Aug 10, 2011

### Bill_K

Still too quick. There are plenty of mesons that obey this rule, and plenty more that do not. The spin-parity of a meson includes contributions from both the intrinsic properties of the quarks and the orbital wavefunction as well. Take a look at a list of the charmonium and bottomonium states.

7. Aug 10, 2011

### clem

The parity of meson considered as q-qbar bound states is (-1)^L+1.
The spin of the meson equals L if the q-qbar are in a spin zero state, but can be different if the q-qbar are in a spin 1 state. Gauge bosons have negative intrinsic parity.
The parity of a boson antiparticle is the same as the particle.

8. Aug 10, 2011

### clem

Fermions have only relative parity. For instance, the intrinsic relative parity of the proton and antiproton is negative.

9. Feb 5, 2012

### Soph_the_Oaf

So, when in texts it refers to applying charge conjuction (C) as replacing a particle with its antiparticle... this isn't strictly true? As particles whose antiparticle has opposite parity, would need you to apply CP to the particle to get the antiparticle?

10. Feb 5, 2012

### clem

An antimeson has the same parity as the corresponding meson.
A fermion.s only has relative parity with another fermion or its antifermion.
The relative parity of the proton and antiproton is negative.
The relative parity of the nucleon and the and the Delta is positive.
Relative parity of a nucleon and the Lambda cannot be defined because parity is not conserved in Lambda decay.