STRANGE MESONS($\boldsymbol S$ = $\pm1$, $\boldsymbol C$ = $\boldsymbol B$ = 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 search

# ${{\boldsymbol K}^{\pm}}$ $I(J^P)$ = $1/2(0^{-})$

 See related reviews: Charged Kaon Mass Rare Kaon Decays Dalitz Plot Parameters for ${{\mathit K}}$ $\rightarrow$ 3 ${{\mathit \pi}}$ Decays ${{\mathit K}}{}^{\pm}_{{{\mathit \ell}}3}$ and ${{\mathit K}}{}^{0}_{{{\mathit \ell}}3}$ Form Factors
 ${{\mathit K}^{\pm}}$ MASS $493.677 \pm0.016$ 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)
 $({\mathit \tau}_{{{\mathit K}^{+}}}–{\mathit \tau}_{{{\mathit K}^{-}}})/{\mathit \tau}_{\mathrm {average}}$ $0.0010 \pm0.0009$  (S = 1.2)
$\boldsymbol CPT$ VIOLATION TESTS IN ${{\boldsymbol K}^{\pm}}$ DECAYS
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \mu}^{\pm}}{{\mathit \nu}_{{\mu}}}$ ) RATE DIFFERENCE/SUM $-0.0027 \pm0.0021$
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}$ ) RATE DIFFERENCE/SUM $0.004 \pm0.006$
$\boldsymbol CP$ VIOLATION TESTS IN ${{\boldsymbol K}^{\pm}}$ DECAYS
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ ) RATE DIFFERENCE/SUM $-0.022 \pm0.016$
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ ) RATE DIFFERENCE/SUM $0.010 \pm0.023$
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \gamma}}$ ) RATE DIFFERENCE/SUM $0.0000 \pm0.0012$
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ ) RATE DIFFERENCE/SUM $(4 \pm6) \times 10^{-4}$
 $\Delta$( ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ ) RATE DIFFERENCE/SUM $-0.0002 \pm0.0028$
$\boldsymbol T$ VIOLATION TESTS IN ${{\boldsymbol K}^{+}}$ AND ${{\boldsymbol K}^{-}}$ DECAYS
 $\mathit P_{T}$ in ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}$ $-0.0017 \pm0.0025$
 $\mathit P_{T}$ in ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}{{\mathit \gamma}}$ $-0.006 \pm0.019$
 Im($\xi$) in ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \mu}^{+}}{{\mathit \nu}_{{\mu}}}$ DECAY (from transverse ${{\mathit \mu}}$ pol.) $-0.006 \pm0.008$
ENERGY DEPENDENCE OF ${{\boldsymbol K}^{\pm}}$ DALITZ PLOT
 LINEAR COEFFICIENT $\mathit g$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $-0.21134 \pm0.00017$
 QUADRATIC COEFFICIENT $\mathit h$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $0.0185 \pm0.0004$
 QUADRATIC COEFFICIENT $\mathit k$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $-0.00463 \pm0.00014$
 ($\mathit g_{+}$ $–$ $\mathit g_{-}$) $/$ ($\mathit g_{+}$ + $\mathit g_{-}$) FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ $(-1.5 \pm2.2) \times 10^{-4}$
 LINEAR COEFFICIENT $\mathit g$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $0.626 \pm0.007$
 QUADRATIC COEFFICIENT $\mathit h$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $0.052 \pm0.008$
 QUADRATIC COEFFICIENT $\mathit k$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $0.0054 \pm0.0035$  (S = 2.5)
 ($\mathit g_{+}$ $–$ $\mathit g_{-}$) $/$ ($\mathit g_{+}$ + $\mathit g_{-}$) FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $(1.8 \pm1.8) \times 10^{-4}$
ALTERNATIVE PARAMETRIZATIONS OF ${{\boldsymbol K}^{\pm}}$ $\rightarrow$ ${{\boldsymbol \pi}^{\pm}}{{\boldsymbol \pi}^{0}}{{\boldsymbol \pi}^{0}}$ DALITZ PLOT
 LINEAR COEFFICIENT ${\mathit g}_{0}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $0.6525 \pm0.0034$
 QUADRATIC COEFFICIENT $\mathit h{}^{'}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $-0.0433 \pm0.0027$
 QUADRATIC COEFFICIENT ${{\mathit k}_{{0}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $0.0095 \pm0.0005$
 LINEAR COEFFICIENT ${{\mathit g}_{{BB}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $0.6219 \pm0.0034$
 QUADRATIC COEFFICIENT ${{\mathit h}_{{BB}}^{\,'}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{\pm}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ $-0.0520 \pm0.0028$
${{\boldsymbol K}_{{{{\boldsymbol \ell}}3}}^{\pm}}$ FORM FACTORS
 $\lambda _{+}$ (LINEAR ENERGY DEPENDENCE OF $\mathit f_{+}$ IN ${{\mathit K}_{{e3}}^{\pm}}$ DECAY) $0.0297 \pm0.0005$
 $\lambda _{+}$ (LINEAR ENERGY DEPENDENCE OF $\mathit f_{+}$ IN ${{\mathit K}_{{\mu3}}^{\pm}}$ DECAY) $0.0296 \pm0.0017$
 $\lambda _{0}$ (LINEAR ENERGY DEPENDENCE OF $\mathit f_{0}$ IN ${{\mathit K}_{{\mu3}}^{\pm}}$ DECAY) $0.0196 \pm0.0013$
 $\lambda$'$_{+}$ (LINEAR ${{\mathit K}_{{e3}}^{\pm}}$ FORM FACTOR FROM QUADRATIC FIT) $0.0249 \pm0.0017$
 $\lambda$'$_{+}$(QUADRATIC ${{\mathit K}_{{e3}}^{\pm}}$ FORM FACTOR) $0.0019 \pm0.0009$
 $\vert \mathit f_{\mathit S}/\mathit f_{+}\vert$ FOR ${{\mathit K}_{{e3}}^{\pm}}$ DECAY $-0.003 {}^{+0.008}_{-0.007}$
 $\vert \mathit f_{\mathit T}/\mathit f_{+}\vert$ FOR ${{\mathit K}_{{e3}}^{\pm}}$ DECAY $-0.012 \pm0.023$
 $\mathit f_{\mathit S}/\mathit f_{+}$ FOR ${{\mathit K}_{{\mu3}}^{\pm}}$ DECAY $0.002 \pm0.006$
 $\mathit f_{\mathit T}/\mathit f_{+}$ FOR ${{\mathit K}_{{\mu3}}^{\pm}}$ DECAY $-0.001 \pm0.007$
${{\boldsymbol K}_{{{{\boldsymbol \ell}}4}}^{\pm}}$ FORM FACTORS
 ${{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $5.712 \pm0.032$
 ${{\mathit f}_{{s}}^{\,'}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $0.152 \pm0.009$
 ${{\mathit f}_{{s}}^{''}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $-0.073 \pm0.009$
 ${{\mathit f}_{{e}}^{\,'}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $0.068 \pm0.009$
 ${{\mathit f}_{{p}}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $-0.048 \pm0.005$
 ${{\mathit g}_{{p}}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $0.868 \pm0.014$
 ${{\mathit g}_{{p}}^{\,'}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $0.089 \pm0.021$
 ${{\mathit h}_{{p}}}/{{\mathit f}_{{s}}}$ FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit e}^{\pm}}{{\mathit \nu}}$ DECAY $-0.398 \pm0.017$
 DECAY FORM FACTOR FOR ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \pi}^{0}}{{\mathit \pi}^{0}}{{\mathit e}^{\pm}}{{\mathit \nu}}$
${{\boldsymbol K}^{\pm}}$ $\rightarrow$ ${{\boldsymbol \ell}^{\pm}}{{\boldsymbol \nu}}{{\boldsymbol \gamma}}$ FORM FACTORS
 $\mathit F_{\mathit A}$ $+$ $\mathit F_{\mathit V}$, SUM OF AXIAL-VECTOR AND VECTOR FORM FACTOR FOR ${{\mathit K}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{e}}}{{\mathit \gamma}}$ $0.133 \pm0.008$  (S = 1.3)
 $\mathit F_{\mathit A}$ $+$ $\mathit F_{\mathit V}$, SUM OF AXIAL-VECTOR AND VECTOR FORM FACTOR FOR ${{\mathit K}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \nu}_{{\mu}}}{{\mathit \gamma}}$ $0.165 \pm0.013$
 $\mathit F_{\mathit A}$ $−$ $\mathit F_{\mathit V}$, DIFFERENCE OF AXIAL-VECTOR AND VECTOR FORM FACTOR FOR ${{\mathit K}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{e}}}{{\mathit \gamma}}$ $<0.49$   CL=90.0%
 $\mathit F_{\mathit A}$ $−$ $\mathit F_{\mathit V}$, DIFFERENCE OF AXIAL-VECTOR AND VECTOR FORM FACTOR FOR ${{\mathit K}}$ $\rightarrow$ ${{\mathit \mu}}{{\mathit \nu}_{{\mu}}}{{\mathit \gamma}}$ $-0.21 \pm0.06$
 ${{\mathit K}^{\pm}}$ CHARGE RADIUS $0.560 \pm0.031$ fm
 ${{\mathit K}^{+}}$ LONGITUDINAL POLARIZATION OF EMITTED ${{\mathit \mu}^{+}}$ $<-0.990$   CL=90.0%
FORWARD-BACKWARD ASYMMETRY IN ${{\boldsymbol K}^{\pm}}$ DECAYS
 A$_{FB}({{\mathit K}}{}^{\pm{}}_{{{\mathit \pi}} {{\mathit \mu}} {{\mathit \mu}} }$) = ${\Gamma\mathrm {(cos({{\mathit \theta}}_{ {{\mathit K}} {{\mathit \mu}} })>0)}−\Gamma\mathrm {(cos({{\mathit \theta}}_{ {{\mathit K}} {{\mathit \mu}} })<0)}\over \Gamma\mathrm {(cos({{\mathit \theta}}_{ {{\mathit K}} {{\mathit \mu}} })>0)}+\Gamma\mathrm {(cos({{\mathit \theta}}_{ {{\mathit K}} {{\mathit \mu}} })<0)}}$ $<0.023$   CL=90.0%
${{\mathit K}^{-}}$ modes are charge conjugates of the modes below.
 constrained fit information