What are the factors that determine the different lifetimes of particle decays?

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SUMMARY

The discussion centers on the factors influencing the lifetimes of particle decays, specifically highlighting the differences between strong, electromagnetic (EM), and weak interactions. Strong decays occur in approximately 10^-23 seconds due to the limitations of information crossing a nucleus, while EM decays, such as the pi-zero decay to two photons, take about 10^-16 seconds. Weak decays are the slowest, averaging around 10^-10 seconds, primarily due to the mass of the W and Z bosons, which mediates the weak force. The discussion emphasizes the role of chiral considerations and the chiral anomaly in these decay processes.

PREREQUISITES
  • Understanding of particle physics concepts, including particle interactions
  • Familiarity with decay processes and their associated lifetimes
  • Knowledge of the Standard Model, particularly the roles of W and Z bosons
  • Basic grasp of chiral symmetry and anomalies in particle physics
NEXT STEPS
  • Research the role of chiral anomalies in particle decay processes
  • Study the properties and interactions of W and Z bosons in the Standard Model
  • Explore the mathematical formulation of decay rates, including factors like α_EM and (M_p/M_W)^2
  • Investigate the implications of particle lifetime differences on experimental particle physics
USEFUL FOR

This discussion is beneficial for students and researchers in particle physics, particularly those studying decay processes, the Standard Model, and the interactions of fundamental particles.

Scottbob
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I'm revising for an exam on particle physics and understand the lot, however I'd like clarification on the calculation of lifetimes of particles.

I understand that particles decaying by the strong interaction last roughly 10^-23s because that is the minimum time that information can cross a nucleus of order a fermi (ie at light speed). Also I know that EM decays take about 10^-16 seconds (like in the pi-zero decay to 2 photons), but I'd like to know why? Also why does the weak decay take about 10^-10s? (give or take a few orders of magnitude!)

Thanks.
 
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One could expect EM decays in general to be as faster as strong decays, shouln't one? but the ones you have mentioned are very special ones, they are impossible due to chiral considerations (which I do not remember) and they happen because of the chiral anomaly.
 
Although the weak nuclear force used to be described by Fermi's theory of a contact four-fermion interaction, today we know that it is mediated by the W and Z bosons. Because of their large mass of about 90 GeV/c2, their mean life is limited to about 3 * 10^{-25}seconds
Hope that is helpfull, and sorry about my english.
 
EM decays usually have a factor of \alpha^2_EM (=1/137) in calculating their rate. This makes them about 10^4-10^5 slower than strong decays.
Weak decays have another factor of (M_p/M_W)^2 [~(1/80)^2],
which makes them slowest of all.
 

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