
#1
Jan1113, 03:51 AM

P: 109

Say we have a particle, what are the most fundamental properties that distinguishes it from another kind of a particle. What is written in it's identity card?
Spin, electric charge, rest mass, mean lifetime.. what else? 



#2
Jan1513, 04:44 AM

P: 222

Any intrinsic quantum number, like baryon number, strangeness, charm, beauty. But also which kind of interaction the particle can have, like electromagnetic, weak, strong.




#3
Jan1513, 03:44 PM

Mentor
P: 10,767

=> mass and all quantum numbers. Where mass follows from its interaction with the Higgs field, so you can replace "mass" by the corresponding interaction strength. Just the Higgs boson itself has its own mass (plus contributions from its selfinteraction). 



#4
Jan2413, 07:09 AM

P: 109

What are the fundamental properties of matter?
Is there a particle that have exactly same mass, spin and charge value? I guess not. So if we represent (distinguish) each particle with that numbers, can't we gather all other properties in terms of mass, spin and charge? Can we say that some properties are more fundamental?




#5
Jan2413, 11:05 AM

Mentor
P: 10,767

If you want to create a function like hypercharge(mass,spin,electriccharge)=whatever: While this would be possible, it does not give you anything new. There is not a nice relation between those parameters.
With the exception of massless particles, mass is unique to all particle/antiparticle pair in the usual meaning: A particle with a mass of 511keV is an electron or its antiparticle. But in quantum field theory, you have more: You have left and righthanded electrons. You have six different upquarks, one left/right pair for each color. You have 8 gluons, and there is not even a unique way to define them (you have some freedom). Do you count those as different particles? ;) 



#6
Jan2413, 11:34 AM

P: 109





#7
Jan2413, 11:48 AM

Mentor
P: 10,767

The first one couples to the weak interaction, the second one does not. See Chirality for details.




#8
Jan2413, 12:09 PM

P: 109





#9
Jan2413, 12:27 PM

Mentor
P: 10,767





#10
Jan2413, 12:39 PM

P: 109





#11
Jan2413, 03:14 PM

Sci Advisor
Thanks
P: 3,846





#12
Jan2413, 08:31 PM

P: 308





#13
Jan2513, 05:44 AM

Sci Advisor
Thanks
P: 3,846

Chirality is just a projection operator. It does not commute with the Hamiltonian, and consequently its eigenvalues do not represent a property of a free fermion. It does not distinguish two 'kinds' of fermions. Its role in weak interactions is only to make the interaction V  A. It is not really a particle property, but if it were, it would be more correctly a property of the W boson than the fermions.
It makes no sense to describe lefthanded fermions and righthanded fermions as separate particles. That would make it sound like I could accumulate a box full of righthanded muons, for example, that fail to participate in the weak interaction and so would never decay. Yes, if electrons were massless, righthandedness and lefthandedness would be conserved, and then we could talk about two kinds of particles. But they are not massless. (Neither are neutrinos.) And highenergy particles look to be 'almost' massless, but again they are not. It is just that for a highenergy particle, chirality projects unequal proportions of the wavefunction. 



#14
Jan2513, 10:58 AM

Mentor
P: 10,767

Please do not remove the context:



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