Timeline for Why is the (free) neutron lifetime so long?
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7 events
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| Jul 8, 2012 at 2:52 | comment | added | Terry Bollinger | Cool, I look forward to your answer! I've been sloppy on this point for a long time, and hadn't even stopped to think about my inconsistency until you and @Forever_a_Newcomer pointed it out. This really is a more interesting question than I had realized at first glance. | |
| Jul 8, 2012 at 2:49 | comment | added | dmckee --- ex-moderator kitten | "dmckee, ball's in your court if you want to give it a shot..." @TerryBollinger I actually started to right after the question was posted only to realize that I'm unable to offer a full picture right now. I need to take some of my copious spare time and refresh myself on this matter. | |
| Jul 8, 2012 at 2:46 | comment | added | Terry Bollinger | Well, @dmckee is correct: That was a very incomplete explanation I attempted, and only some approach that addresses the product phase spaces can explain the huge range of weak force decay times. dmckee, ball's in your court if you want to give it a shot... | |
| Jul 8, 2012 at 0:54 | comment | added | Forever_a_Newcomer | I not completely satisfied with the answer. It seems to me that dr-bdo-adams and @terry-bollinger are explaining this based on the off-shellness of the W. But still the diference is too big, the neutron lifetime is $10^9$ times bigger than that of the Muon, but the "liberated energy" is only $10^2$ smaller. Is this going like $\left(\frac{E_L}{M_W}\right)^4$? ($E_L$ is the liberated energy). Can someone give me pointers of why we have such a high power in the dependence? | |
| Jul 7, 2012 at 16:14 | comment | added | dmckee --- ex-moderator kitten | This is actually very incomplete, because other weak decays can proceed very much faster. Muon decay is a weak process and has a halflife of $10^{-6}$ seconds. The charged pion decay is a weak process with a halflife of $10^{-8}$ seconds and so on. Then there are weak decay processes which are much slower as in many long-lived beta active isotopes. The phase space available to the products plays a big part in the full answer. | |
| Jul 7, 2012 at 14:48 | comment | added | Terry Bollinger | Dr BDO already nailed it, so just to give another angle on it: The neutron decays very slowly because it has one option available for decaying into the slightly lower mass proton. That option is weak decay, which requires that one of the neutrons inner parts, a down quark (charge -1/3) emit a very massive force particle called a $W^-$. The $W^-$ then promptly decays into a ordinary electron and an anti-neutrino. Quantum time-energy uncertainty allows $W^-$ particles to form, but only very rarely due to their super-high masses. | |
| Jul 7, 2012 at 9:25 | history | answered | Dr BDO Adams | CC BY-SA 3.0 |