This may be a bit of numerology, but I'd like to be able to make a statement like "There are 17 particles in the standard model" with some logical definition of a particle.

But this statement is surprisingly difficult to make in a logically consistent way. The problem is, there are a lot of ways to count particles:

  • You can say that every polarization and charge constitutes a distinct particle. This ends up being a huge number of "particles"
  • You could classify by multiplets, in which case you'd get get 9 quark fields (ignoring color-charge and anti-particles), whereas I'd want 6.
  • You could say something about distinct masses, but both photons and gluons are massless
  • You could say something about couplings, but this makes right-handed and left handed fields distinct.

So far the best thing I've come up with is that

  • "Particles" are defined as mass eigenstates
  • Particles are counted as identical to anything they can be mapped onto with global symmetry transformations (i.e. color charge rotation or charge conjugation).

But I feel like this still leaves room for someone to claim this doesn't lead to a count of 17. Is there any simple rule that leads to this count without simply naming all the particles?

  • $\begingroup$ I think it's more that there are 17 known particles which constitue the standard model - rather than the standard model predicts/requires exactly 17particles. $\endgroup$ – Martin Beckett Feb 18 '15 at 17:53
  • $\begingroup$ maybe my question is unclear, but I'm not asking why we have the particles that we have, just for a way to actually count 17 particles in the known fields. We know that there are anti-particles for each fermion, but I don't want to say there are 24 fermions. $\endgroup$ – Shep Feb 18 '15 at 17:59
  • $\begingroup$ Why do you think there are specifically $17$? I think the normal count is six quarks in three colors (18), their antiquarks (18), six leptons, six antileptons, eight gluons, photon, W$^\pm$, Z, Higgs for a total of $60$ $\endgroup$ – Ross Millikan Feb 18 '15 at 22:26
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    $\begingroup$ @RossMillikan, I don't think there are specifically 17; the number depends heavily on the definition as you say. What I'm looking for is a concise definition. Sort of like Jeopardy, but only sort of... $\endgroup$ – Shep Feb 18 '15 at 23:29
  • $\begingroup$ google.com/imgres?imgurl=http://www.quantumdiaries.org/… $\endgroup$ – Virgo Nov 19 '18 at 0:20

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