Particles and Antiparticles


by Shyan
Tags: antiparticles, particles
Shyan
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#1
Feb22-13, 02:16 PM
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I've been trying to understand the exact differences of a particle and its corresponding antiparticle.I know maybe the best way is via checking that the two particles annihilate each other when came to contact or not.But I'm talking about their properties now.
In some places,it is written that only the electric charge has opposite sign.
In some other places,its written that,in addition to electric charge,quantum numbers also have opposite sign.
I have two questions
1-Can we include other charges too?
2-Quantum numbers don't seem so intrinsic to a particle.So its just confusing for me that they are used to tell the difference between a particle and its antiparticle.How would you explain it?
Thanks
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jedishrfu
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#2
Feb22-13, 02:48 PM
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all properties are the same except for charge"

http://en.wikipedia.org/wiki/Anti-particles

the writeup talks about neutral particles as well.
bossman27
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#3
Feb22-13, 02:55 PM
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Quote Quote by jedishrfu View Post
all properties are the same except for charge"

http://en.wikipedia.org/wiki/Anti-particles
I assume you're referring to:

"the same mass m
the same spin state J
opposite electric charges q and -q."

This is accurate, but I think some of the OP's confusion comes from the fact that "quantum number" is not one property but refers to a group of properties that are conserved in a quantum system. See the chart at the bottom of this page for a more complete table: http://scienceworld.wolfram.com/phys...iparticle.html

mathman
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#4
Feb22-13, 03:20 PM
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Particles and Antiparticles


Uncharged particles may have antiparticles - neutrons or neutrinos.
bossman27
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#5
Feb22-13, 03:32 PM
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Quote Quote by mathman View Post
Uncharged particles may have antiparticles - neutrons or neutrinos.
Yes, but +0 is the same as -0.
mfb
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#6
Feb22-13, 06:43 PM
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Quote Quote by bossman27 View Post
Yes, but +0 is the same as -0.
I think that is mathman's point: Those antiparticles are different from the particles, even if they have the same charge of 0.

The weak hypercharge and the color charge have the opposite sign, too. And all those quantum numbers related to quark types (isospin, strangeness etc.) have a different sign as well.
Shyan
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#7
Feb22-13, 10:49 PM
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I can't accept quantities like strangeness or lepton number or such things as properties of a particle.I mean,they are,but they're just conventional things.You may tell "hey,they're conserved" But in fact they're just approximately conserved and not conserved at all in weak interactions.So I may as well define "shyaness"() as [itex] \frac{1}{2}(n_u+n_s) [/itex].Therefore,From the list that bossman27 suggested(thanks bossman27),I just choose electric charge,z-component of isospin and parity.
And I should tell I agree with mfb since if you search about color charge,you'll probably encounter words like anticolor,antired,antigreen and antiblue.Also gluons are said to have a color and an anticolor simultaneously.I just wonder why hypercharge and color charge are not mentioned anywhere.
Thanks all guys
mfb
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#8
Feb23-13, 06:28 AM
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Well, strangeness is conserved in the strong interaction, and the weak interaction is weak. Shyaness is conserved in the strong interaction as well, but it can be derived from strangeness and "upness" (which is usually expressed via isospin).
Shyan
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#9
Feb23-13, 08:16 AM
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Can't I define shyaness as sth that is not conserved?
I think such a thing can be found.
If it can be,how will you explain that the conserved thing is a parameter of nature and the non-conserved one,is not?I mean,what's their difference?
Is it just that its realized one combination is conserved and so they say its good or there are other reasons too?
mfb
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#10
Feb23-13, 08:22 AM
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?
The conservation of some numbers in some interactions is an experimental result. Our theories are developed to reflect those observations.
Shyan
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#11
Feb23-13, 08:46 AM
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Oh...Of course you're right
I think I said that in a state of confusion!
Thanks


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