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I recently visited my child's elementary school to speak to a science classroom about rocks and minerals. While trying to explain what a crystal is, I got sloppy and mis-spoke that an atom was the smallest possible piece of matter (rather than an element!) I was quickly stopped and corrected by a 9-year-old that told me in fact atoms can be split into leptons and baryons. I told her she was right, and explained that if an atom of an element is divided it becomes a different element (overlooking isotopes!).

My knowledge of particle physics is limited and later I began wonder what I might be leaving out, that should not be left out, when talking of the types of 'ordinary matter' in nature. What happens in high-energy physics experiments aside. I know that there are other elementary particles besides leptons and baryons, photons are obviously everywhere.

But if we restrict the discussion to radioactive decay, fusion in stars, cosmic rays, is everything a lepton, baryon, or a photon?

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  • $\begingroup$ elements aren't the smallest piece of matter $\endgroup$ – user37390 Mar 8 '14 at 0:43
  • $\begingroup$ "I got sloppy and mis-spoke that an atom was the smallest possible piece of matter (rather than an element!)" What's the difference? $\endgroup$ – Brandon Enright Mar 8 '14 at 0:57
  • $\begingroup$ The International Union of Crystallography defines a crystal as any body that returns a sharp diffraction pattern (x-ray, electron, neutron, etc). Periodic crystals are thus joined by quasicrystals, modulated crystals, composite crystals, and polytypes. "8^>) $\endgroup$ – Uncle Al Mar 8 '14 at 1:36
  • $\begingroup$ @Brandon Enright - An element is defined by it's atomic number. A nuclear reaction that changes the atomic number transmutes the reactant atoms into atoms of other elements plus (possibly)other products. Anna's answer explains, as I understand it, that at high energy the products would include 'elementary particles' - which is also properly referred to as 'matter'- although at this scale the duality of matter/energy and particles/waves become significant. $\endgroup$ – Mark Rovetta Mar 17 '14 at 15:58
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Your

What happens in high-energy physics experiments aside

partially contradicts your final question

But if we restrict the discussion to radioactive decay, fusion in stars, cosmic rays, is everything a lepton, baryon, or a photon?

Radioctive decay has as end products photons, leptons and baryons.

Fusion and cosmic rays are the realm of elementary particle physics, the energies involved much higher than the ones in natural radiaoctivity.

The reality of what "everything is made up of" depends on the energy with which you look at "everything". The answer is that everything is made up by the elementary particles, following the rules of the standard model, nuclear models, atomic models as the energies involved in "looking" at everything diminish. It is a compositeness built up consecutively. You might be interested in this answer to a similar question.

These are the elementary particles out of which all matter is formed. Every day matter involve mainly the first column and the last column . The two middle ones have been found in cosmic rays to start with and in accelerator experiments that led to the discovery of the standard model. They are particles that cannot come out from nuclear decays or fissions, i.e. "naturally" but need excess energy to materialize.

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But if we restrict the discussion to radioactive decay, fusion in stars, cosmic rays, is everything a lepton, baryon, or a photon?

No. Baryons are not elementary particle, but are composed of 3 quarks bound by gluons. There is a class of particles called mesons, which consist of a quark and antiquark. The pion is an example of a meson. Pions are found in comic rays.

Also, beta decay involves W- bosons. W-, W+ and Z bosons are carriers of the weak force.

There is also the Higgs boson, which is responsible for the mass of other particles.

There may also be gravitons, which mediate gravity, but this is unconfirmed.

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  • $\begingroup$ Aren't Pions the product of cosmic rays? That is, mesons are unstable so they can't travel significant distances. Instead they're created in our upper atmosphere by cosmic rays made of something more stable. Of course, there surely are a ton of mesons in stellar cores too. $\endgroup$ – Brandon Enright Mar 8 '14 at 0:59
  • $\begingroup$ yes, pions are secondary cosmic rays, products of primary cosmic rays encountering the atmosphere $\endgroup$ – DavePhD Mar 8 '14 at 1:16

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