STRANGE MESONS
($\mathit S$ = $\pm1$, $\mathit C$ = $\mathit B$ = 0)
${{\mathit K}^{+}}$ = ${\mathit {\mathit u}}$ ${\mathit {\overline{\mathit s}}}$, ${{\mathit K}^{0}}$ = ${\mathit {\mathit d}}$ ${\mathit {\overline{\mathit s}}}$, ${{\overline{\mathit K}}^{0}}$ = ${\mathit {\overline{\mathit d}}}$ ${\mathit {\mathit s}}$, ${{\mathit K}^{-}}$ = ${\mathit {\overline{\mathit u}}}$ ${\mathit {\mathit s}}$, similarly for ${{\mathit K}^{*}}$'s
INSPIRE   JSON PDGID:
S010

${{\mathit K}^{\pm}}$

$I(J^P)$ = $1/2(0^{-})$ 
${{\mathit K}^{\pm}}$ MASS   $493.677 \pm0.015$ MeV (S = 2.8)
 
${\mathit m}_{{{\mathit K}^{+}}}–{\mathit m}_{{{\mathit K}^{-}}}$   $-0.03 \pm0.09$ MeV 
 
${{\mathit K}^{\pm}}$ MEAN LIFE   $(1.2380 \pm0.0020) \times 10^{-8}$ s (S = 1.8)
 
$({\mathit \tau}_{{{\mathit K}^{+}}}–{\mathit \tau}_{{{\mathit K}^{-}}})/{\mathit \tau}_{\mathrm {average}}$   $(1.0 \pm0.9) \times 10^{-3}$  (S = 1.2)
 
${{\mathit K}^{\pm}}$ CHARGE RADIUS   $0.560 \pm0.031$ fm 
 
${{\mathit K}^{+}}$ LONGITUDINAL POLARIZATION OF EMITTED ${{\mathit \mu}^{+}}$   $<-0.990$   CL=90.0%
 
FORWARD-BACKWARD ASYMMETRY IN ${{\mathit K}^{\pm}}$ DECAYS
A$_{FB}({{\mathit K}}{}^{\pm{}}_{{{\mathit \pi}} {{\mathit \mu}} {{\mathit \mu}} }$) = ${\Gamma\mathrm {(cos({{\mathit \theta}}_{{{\mathit K}} {{\mathit \mu}}})>0)}−\Gamma\mathrm {(cos({{\mathit \theta}}_{{{\mathit K}} {{\mathit \mu}}})<0)}\over \Gamma\mathrm {(cos({{\mathit \theta}}_{{{\mathit K}} {{\mathit \mu}}})>0)}+\Gamma\mathrm {(cos({{\mathit \theta}}_{{{\mathit K}} {{\mathit \mu}}})<0)}}$   $<0.009$   CL=90.0%
 
${{\mathit K}^{-}}$ modes are charge conjugates of the modes below.
FOOTNOTES
Constrained Fit information