Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2004-06-29
Phys.Rev.D70:093006,2004
Physics
High Energy Physics
High Energy Physics - Phenomenology
15 pages, version accepted for publication in the Physical Review D
Scientific paper
10.1103/PhysRevD.70.093006
Determinations of $\vud$ and $\vus$ along with their implications for the unitarity test $\vud^2+\vus^2+\vub^2=1$ are discussed. The leading two loop radiative corrections to neutron $\beta$-decay are evaluated and used to derive a refined relationship $\vud^2 \tau_n (1+3g_A^2)=4908(4)$sec. Employing $\vud =0.9740(5)$ from superallowed nuclear decays and the measured neutron lifetime $\tau_n = 885.7(7)$sec, leads to the precise prediction $g_A=1.2703(8)$ which is compared with current direct experimental values. Various extractions of $\vus$ are described and updated. The long accepted Particle Data Group value of $\vus$ from fitted $K_{e3}$ decay rates suggests a deviation from CKM unitarity but it is contradicted by more recent experimental results which confirm unitarity with good precision. An outlook for possible future advances is given.
Czarnecki Andrzej
Marciano William J.
Sirlin Alberto
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