The lepton neutrino's are represented by the small white squares. Their rest energy is still subject for research and debate. Their positions along the energy axis depicts their upper limit values according to current estimations.
Decay paths of quarks
The arrows between the small squares representing the quarks are depicting the decay paths. There are bold, dotted and thin arrows. The bold arrows are representing the most likely decay path and the thin arrows the least likely.
During the decay of a quark to another kind of quark, a quark transformation, a lepton and a neutrino are emitted. But since the weak force governs this decay process, W± and Z0 bosons are involved to mediate this weak interaction.
Some remarks about the weak nuclear force
The mediation process differs from the mediation process regarding strong nuclear and electro-magnetic force. In the latter massless gluons and photons are exchanged to mediate the forces. In the case of the weak interaction a W± or a Z0 boson is actually emitted by the decaying quark. Within 10-25 seconds this boson decays into a lepton and a neutrino. This boson appears to be very heavy which is consistent with the very short range of the weak interaction (about 10-17 m), but it was a mystery how such a boson could acquire so much mass.
(see the paragraph above about the Higgs boson to learn more)
Lifetime of quarks
The lifetimes of the t, b, c, and s quarks are extremely short, between 10-25 and 10-8 seconds. The lifetime of the d quark is 900 seconds.
The u quark is the most stable one. Its lifetime has not been determined.
Lifetime of a proton
The quark configuration of a proton is "uud". The d quark with its 900 seconds of lifetime is kept stable within and because of this configuration. The lifetime of a proton has not been determined but is assumed to be finite by some scientists. According to theoretical calulations the upper limit for its lifetime is 6 x 1039 years.
Rest energy (proton) = rest energy (the three constituent quarks) + binding energy from gluons
The rest energy of a proton is 938 MeV.
The combined rest energy of the two "up" quarks and one "down" quark, the proton is consisting of, amounts to 9.40 MeV, which is 10 times less than the rest energy of the proton. This illustrates the fact that the gluons, which are responsible for binding the three quarks, represents 90% of the proton's rest energy.
The rest energy of a neutron is 939.37 MeV. Also in this case the binding energy is responsible for 90% of the total rest energy.