Particle Classification: Why Do We Class Particles in a Specific Way?

[AntonJD]

I recently read that in the way we class particles if we measure the properties of two different particles and class them as particle A and particle B and continue to measure the properties of a third particle which we find to be only slightly removed from those of particle A that instead of considering the possibility that it might be an altered version of particle A we would instead just class it particle C.

If this is true can somebody please explain to me why we would look at it in this way or point me in the direction of an explanation, if not then i would appreciate the correction.

 

[Forestman]

Give us some more details on what you are trying to explain.

 

[jtbell]

I recently read [...]

Where?

Perhaps if we read the article ourselves we can see what you're asking about.

 

[AntonJD]

The reason i posted it with an example as oposed to source material is because i no longer had access to the source material, of course one could argue it never existed but then why would i post the question if i knew i had made it up myself. I guess i shall just have to wait until i come across it again, good thing the internet is such a small place and I'm clever enough to write things down when i see them. Thanks anyway and this thread can be removed now if needs be.

 

[Drakkith]

All i can say is that as far as I know, all particles of the same type are identical. That is why we don't consider particle C as being an altered version of A. That doesn't mean they are similar or related, but that we classify particle C as C instead of classifying it as particle A-2 or something. But really it's kind of like classifying life. Humans are primates, which are mammals, which are animals and ETC. Well, an Up Quark is a Quark which is a Fermion which is a part of matter. Get it?

 

[AntonJD]

All i can say is that as far as I know, all particles of the same type are identical. That is why we don't consider particle C as being an altered version of A. That doesn't mean they are similar or related, but that we classify particle C as C instead of classifying it as particle A-2 or something. But really it's kind of like classifying life. Humans are primates, which are mammals, which are animals and ETC. Well, an Up Quark is a Quark which is a Fermion which is a part of matter. Get it?

I understand this but my question is, why do we class them as completely separate unrelated particles if there is perhaps only a minor difference between the two and should we not consider the fact that a particles properties could differ depending on the environment it is in or some other factor. I understand the example you have used but I'm not sure it ties into what I'm asking, I'm not sure how accurately one can compare elementary particles to Humans and animals etc but in an attempt; If Humans were to be considered Particle A and Primates Particle B then why would a Human with different hair colour not be considered particle A but instead particle C.

 

[Drakkith]

If Humans were to be considered Particle A and Primates Particle B then why would a Human with different hair colour not be considered particle A but instead particle C.

No no, what I mean is that Particle A is Human, and Particle C would be a Gorilla. Then BOTH would be Primates. Like an electron and an electron neutrino are both different particles, but both are considered leptons, which is 1 of 2 classes of fermions, the other being quarks.

 

[AntonJD]

I understand that at anything above elementary level we can define something by the properties of the particles that make it up but i mean at elementary level how can we be so sure that two particles which differ only slightly from each other are infact different particles at all rather than the same particle in some form of altered state. You could define a proton by saying it is made up of two up quarks and a down quark but then if you were to define the quarks you would have to do so by defining their properties as they are not made up of other particles. So what I am saying is, if the properties by which we define two particles are only slightly different at the elemental level then how can we be sure that some or all of these particles are not just one type of particle acting in a certain way, portraying certain properties under the circumstances we measured them in.

 

[Drakkith]

Put simply, no matter how you measure a particle, it always acts the same way. You don't suddenly have the mass or the charge change when you change the way you measure it. It is always the same.

 

[kloptok]

A concrete example could perhaps be quarkonium: instead of saying that the excited states are all different aspects of the same particle (they have the same elementary constituents), they are (I think) seen as different particles with different names.

Another, perhaps better, example is the [tex]\Delta^+[/tex]-particle which has the same quark ingredients (up, up, down quarks) as the proton but a different mass due to a different spin.

So in this case we distinguish between the particles since they have different properties (spin etc.) and therefore behave differently, even though the constituents are the same.

Is that on the lines of what you were looking for, AntonJD?

Personally I agree with Drakkith, it's all dependent on where your perspective is, and what properties you want to use when classifying particles.

I understand this but my question is, why do we class them as completely separate unrelated particles if there is perhaps only a minor difference between the two and should we not consider the fact that a particles properties could differ depending on the environment it is in or some other factor.

Perform the experiment many times and eliminate all "environmetal" effects. If particle B is still different from A there is clearly something distinguishing the two particles. Whether you want to call A and B different "particles" or not is more of a question of how you define a particle. If you want all particles of the same kind to share all properties then you would obviously classify A and B as different particles.

 

[AntonJD]

A concrete example could perhaps be quarkonium: instead of saying that the excited states are all different aspects of the same particle (they have the same elementary constituents), they are (I think) seen as different particles with different names.

Thankyou, this has helped me to gain the perspective i was looking for and has provided some new reading material.

 

[_PJ_]

When you say "slight differences", particles are very specific, they have definite charges, mass, spin etc. So what may be a 'slight difference' is actually a very definite indication.

Of course, when considering theories of symmetry and unification, where particles are the same when at extreme temperatures, only manifesting a different nature when they fall below a certain level, then it's possible that the classification of particles would be dependant on the energy, but since almost all experience is within extremely low energies (comparitively), I don;t think it matters too much for general use.