Quark doesn't constitutes more fundamental particle and proton and neutron consist of quarks. Now come to beta decay.

$n \rightarrow p + e^{-} + \bar{\nu}_e $

How can an electron emit from an neutron whereas electron is a fundamental particle? Is the electron created from gluon?

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  • $\begingroup$ I've edited you decay equation to more accurately reflect the nature of the neutral lepton. $\endgroup$ – dmckee --- ex-moderator kitten Jul 25 '13 at 20:43

This is a weak decay and it is mediated by a weak boson. In this case a $W^-$.


The Feynman diagram for β− decay of a neutron into a proton, electron, and electron antineutrino via an intermediate W− boson.

At vertex level a down-quark is converted into a up-quark by the emission of virtual W-boson which decays to the electron electron-antineutrino pair. Charge is carried by the mediating boson.

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  • $\begingroup$ so you are saying that quark can decay? Isn't it a fundamental one? $\endgroup$ – Raisa Jul 25 '13 at 21:03
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    $\begingroup$ The weak interaction does not (fully) respect flavor. Weak interaction can convert quarks of one flavor to another. $\endgroup$ – dmckee --- ex-moderator kitten Jul 25 '13 at 22:41
  • $\begingroup$ @Raisa : Weak interactions involve left-handed particles. Left Quarks $d$ and $u$ are a SU(2) doublet, that is you have to consider the doublet left $(u,d)$ as a whole, exactly as a vector with $2$ dimensions, and SU(2) operations on this vector are allowed, for instance, a "rotation" could transform $u$ in $d$. Same thing for the doublet electron/ neutrino. $\endgroup$ – Trimok Jul 26 '13 at 13:03
  • $\begingroup$ so quark is decaying and u turning into d, therefore the electron formation comes from the energy releases by up quark? $\endgroup$ – Raisa Jul 26 '13 at 13:14

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