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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 (beta) PDGID:

S013

${{\mathit K}_L^0}$

$I(J^P)$ = $1/2(0^{-})$

See related reviews:

$\mathit V_{{\mathit {\mathit u}}{\mathit {\mathit d}}}$, $\mathit V_{{\mathit {\mathit u}}{\mathit {\mathit s}}}$ the Cabibbo Angle, and CKM Unitarity
$\mathit CP$ Violation in ${{\mathit K}_L^0}$ Decays
$\Delta \mathit S$ = $\Delta \mathit Q$ in ${{\mathit K}^{0}}$ Decays

${\mathit m}_{{{\mathit K}_L^0} }–{\mathit m}_{{{\mathit K}_S^0} }$

$(52.93 \pm0.09) \times 10^{8}$ $\hbar{}$ s${}^{-1}$ (S = 1.3) ...

${{\mathit K}_L^0}$ MEAN LIFE

$(5.116 \pm0.021) \times 10^{-8}$ s (S = 1.1)

▸	ENERGY DEPENDENCE OF ${{\mathit K}_L^0}$ DALITZ PLOT

▸	${{\mathit K}_L^0}$ FORM FACTORS

▸	$\mathit CP$-VIOLATION PARAMETERS IN ${{\mathit K}_L^0}$ DECAYS

▸	PARAMETERS for ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit \pi}^{+}}{{\mathit \pi}^{-}}{{\mathit \gamma}}$ DECAY

$\mathit T$ VIOLATION TESTS IN ${{\mathit K}_L^0}$ DECAYS

Im($\xi $) in ${{\mathit K}_{{\mu3}}^{0}}$ DECAY (from transverse ${{\mathit \mu}}$ pol.)

$-0.007 \pm0.026$

▸	$\mathit CPT$-INVARIANCE TESTS IN ${{\mathit K}_L^0}$ DECAYS

▸	$\mathit x$ = A( ${{\overline{\mathit K}}^{0}}$ $\rightarrow$ ${{\mathit \pi}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}}$ )/A( ${{\mathit K}^{0}}$ $\rightarrow$ ${{\mathit \pi}^{-}}{{\mathit \ell}^{+}}{{\mathit \nu}}$ ) = A($\Delta \mathit S=−\Delta \mathit Q)/A(\Delta \mathit S=\Delta \mathit Q$)

${{\mathit K}_L^0}$ DECAY MODES ▸ Expand all decays

▸	Semileptonic modes

▸	Hadronic modes, including Charge conjugation${\times }$Parity Violating ($\mathit CPV$) modes

▸	Semileptonic modes with photons

▸	Hadronic modes with photons or ${{\mathit \ell}}{{\overline{\mathit \ell}}}$ pairs

▸	Other modes with photons or ${{\mathit \ell}}{{\overline{\mathit \ell}}}$ pairs

▸	Charge conjugation ${\times }$ Parity ($\mathit CP$) or Lepton Family number ($\mathit LF$) violating modes, or $\Delta \mathit S$ = 1 weak neutral current ($\mathit S1$) modes

▸	Lorentz invariance violating modes

FOOTNOTES

Constrained Fit information

Except where otherwise noted, content of the 2023 Review of Particle Physics is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy), JPS and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2023. See LBNL disclaimers.

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${{\mathit K}_L^0}$