Question

Based on CKM matrix, shouldn't bottom lifetime be longer than strange lifetime?

Answer 1

There are probably several theories for why we have three generations of quarks and leptons, but my favorite —- and it’s just a theory* —- is that the initial imbalance of matter and antimatter at the beginning of the universe was a result of CP violation (charge conjugation - parity reversal), which is equivalent to T (time reversal) violation, because the combined processes (CPT) are NEVER violated. In order for CP violation to occur, there must be a complex phase in the quark mixing angles that derive from the CKM (Cabibbo-Kobayashi-Maskawa) matrix which describes the relative strengths of flavor-changing weak force decays (from one generation to a lower generation). It is only with three generations that a complex phase (representing quark mixing) can arise —- with two generations, any phase angle can be transformed away through a redefinition of the quark fields. With CP violation, time reversal invariance is also violated, which could affect the properties of anti-protons, the main constituent of antimatter, since antiprotons traveling forward in time are identical to protons traveling backwards in time. Thus, even though we observe antiprotons as being stable in a lab environment (in a storage ring) and possessing a “long” lifetime, it may be short compared to the current age of the universe, with all antimatter having decayed away in the early universe epoch.

Answer 2

When discussing the CKM matrix, my professor mentioned that the stability of the bottom quark could be attributed to the very high probability amplitude for b→tb→t transformation, which is kinematically forbidden (unless the bottom quark is accelerated to have sufficient mass, which while in a bound state is not exactly possible). This seems logical enough. Simply because the amplitudes of b→cb→c and b→ub→u are small, it takes longer for those decay modes to occur, manifesting in bottom quark stability.