What is a quark? ?

Question

And a muon, a good definition please...

thanks!

Answer 1

A quark is an elementary particle - that is, a particle which, as far as we know, is a fundamental piece of matter or energy and cannot be broken down into anything simpler.

Quarks are found within protons and neutrons. A proton contains three quarks, and so does a neutron. There are also particles which contain only two quarks, however all such particles are unstable and are therefore found only in cosmic rays (and particle accelerators.)

There are six flavours of quarks, plus each quark has its antiquark with the opposite charge:

up quark, +2/3 charge, mass 3-4 MeV/c^2

down quark, -1/3 charge, mass 6-10 MeV/c^2

strange quark, -1/3 charge, mass 80-130 MeV/c^2

charm quark, +2/3 charge, mass 1.5 GeV/c^2

bottom quark, -1/3 charge, mass 4.2 GeV/c^2

top quark, +2/3 charge, mass 173 GeV/c^2

Quarks cannot exist by themselves. They must always exist in combination with other quarks (usually two or three quarks in total). This also results in their fractional charges being hidden; for example, combining two up quarks and one down quark gives the proton with a +1 charge; combining one up quark and two down quarks gives the neutron, with zero charge. This is why quarks took so long to be discovered.

A muon is a particle similar to the electron, but about 200 times heavier (mass = 106 MeV/c^2). They are also found only in cosmic rays and particle accelerators. They behave very similarly to electrons. A muon decays into an electron, a muon neutrino, and an electron antineutrino. Muons, like quarks, are elementary particles.