# Why protons are stable but Neutrons not?

just read something about standard model and find it very interesting, proton is made of there subatomic particle U,U,D and neutron have U,D,D . electromagnetic force between U,U,D wants to rip apart it but strong force make it stable .

when compare it with proton in neutron electromagnetic force is less and strong force also there between U,D,D . but why neutron is not stable and a single free neutron will decay in less than 15 min ?

it must be vice versa !

so why proton is stable but neutron is not?

Masses: $$m_n-m_p\approx 1.5$$ MeV, so the neutron β-decays to a proton, by emission of an electron (0.5 MeV) and a practically massless antineutrino. But the proton has nothing to decay to, at least in established, non-speculative physics. (So no GUT theorizing here.)
Why? You already appreciated that EM works against this. But $$m_d -m_u\approx 2.5$$ MeV. Why? nobody knows that.
They get it right on the nose: $$m_n-m_p = 1.51(16)(23)~ MeV, \\ \Delta_{QCD}= 2.52(17)(24) ~ MeV, \\ \Delta_{QED}= –1.00(07)(14) ~MeV .$$