Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">H</mml:mi><mml:mprescripts/><mml:mi mathvariant="normal">Λ</mml:mi><mml:mn>3</mml:mn></mml:mmultiscripts></mml:math> lifetime in Au+Au collisions at the BNL Relativistic Heavy Ion Collider

An improved measurement of the $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}$ lifetime is presented. In this paper, the mesonic decay modes $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}\ensuremath{\rightarrow}^{3}\mathrm{He}$ + ${\ensuremath{\pi}}^{\ensuremath{-}}$ and $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}\ensuremath{\rightarrow}d+p+{\ensuremath{\pi}}^{\ensuremath{-}}$ are used to reconstruct the $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}$ from Au+Au collision data collected by the STAR collaboration at Relativistic Heavy Ion Collider (RHIC). A minimum ${\ensuremath{\chi}}^{2}$ estimation is used to determine the lifetime of $\ensuremath{\tau}=\phantom{\rule{4pt}{0ex}}{142}_{\ensuremath{-}21}^{+24}\phantom{\rule{0.16em}{0ex}}(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}29\phantom{\rule{0.16em}{0ex}}(\mathrm{syst}.)$ ps. This lifetime is about 50% shorter than the lifetime $\ensuremath{\tau}=263\ifmmode\pm\else\textpm\fi{}2$ ps of a free $\mathrm{\ensuremath{\Lambda}}$, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy ${\mathrm{B}.\mathrm{R}.}_{(^{3}\mathrm{He}+{\ensuremath{\pi}}^{\ensuremath{-}})}/({\mathrm{B}.\mathrm{R}.}_{(^{3}\mathrm{He}+{\ensuremath{\pi}}^{\ensuremath{-}})}+{\mathrm{B}.\mathrm{R}.}_{(d+p+{\ensuremath{\pi}}^{\ensuremath{-}})})=\phantom{\rule{4pt}{0ex}}0.32\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.08\phantom{\rule{0.16em}{0ex}}(\mathrm{syst}.)$. Our ratio result favors the assignment $J(_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H})=\frac{1}{2}$ over $J(_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H})=\frac{3}{2}$. These measurements will help to constrain models of hyperon-baryon interactions.