For a discussion of ${{\mathit B}_{{s}}^{0}}-{{\overline{\mathit B}}_{{s}}^{0}}$ mixing see the note on “${{\mathit B}^{0}}-{{\overline{\mathit B}}^{0}}$ Mixing” in the ${{\mathit B}^{0}}$ Particle Listings above.
${{\mathit \chi}_{{s}}}$ is a measure of the time-integrated ${{\mathit B}_{{s}}^{0}}-{{\overline{\mathit B}}_{{s}}^{0}}$ mixing probability that produced ${{\mathit B}_{{s}}^{0}}({{\overline{\mathit B}}_{{s}}^{0}}$) decays as a ${{\overline{\mathit B}}_{{s}}^{0}}({{\mathit B}_{{s}}^{0}}$). Mixing violates $\Delta \mathit B{}\not=$2 rule.
${{\mathit \chi}_{{s}}}$ = ${\mathit x{}^{2}_{\mathit s}\over 2(1+\mathit x{}^{2}_{\mathit s})}$

$\mathit x_{\mathit s}$ = ${\Delta {\mathit m}_{{{\mathit B}_{{s}}^{0}}}\over \Gamma _{{{\mathit B}_{{s}}^{0}}}}$ = (${\mathit m}_{\mathrm {{{\mathit B}}{}^{0}_{ {{\mathit s}} {{\mathit H}} }}}$ $-$ ${\mathit m}_{\mathrm {{{\mathit B}}{}^{0}_{ {{\mathit s}} {{\mathit L}} }}}){\mathit \tau}_{{{\mathit B}_{{s}}^{0}}}$ ,
where $\mathit H$, $\mathit L$ stand for heavy and light states of two ${{\mathit B}_{{s}}^{0}}$ $\mathit CP$ eigenstates and ${\mathit \tau}_{{{\mathit B}_{{s}}^{0}}}$ = ${1\over 0.5 (\Gamma _{{{\mathit B}}{}^{0}_{ {{\mathit s}} {{\mathit H}} }}+\Gamma _{{{\mathit B}}{}^{0}_{ {{\mathit s}} {{\mathit L}} }})}$.