Towards resolving the ${}_{\Lambda }^3$H lifetime puzzle

Abstract

Recent ${}_{\Lambda }^3$H lifetime measurements in relativistic heavy ion collision experiments have yielded values shorter by (30$\pm$8)% than the free $\Lambda$ lifetime ${\tau }_{\Lambda }$, thereby questioning the naive expectation that $\tau ({}_{\Lambda }^3\mathrm{H})\approx {\tau }_{\Lambda }$ for a weakly bound $\Lambda$ hyperon. Here we apply the closure approximation introduced by Dalitz and coworkers to evaluate the ${}_{\Lambda }^3$H lifetime, using ${}_{\Lambda }^3$H wavefunctions generated by solving three-body Faddeev equations. Our result, disregarding pion final-state interaction (FSI), is $\tau ({}_{\Lambda }^3\mathrm{H})$=(0.90$\pm$0.01)${\tau }_{\Lambda }$. In contrast to previous works, pion FSI is found attractive, reducing further $\tau ({}_{\Lambda }^3\mathrm{H})$ to $\tau ({}_{\Lambda }^3\mathrm{H})$=(0.81$\pm$0.02)${\tau }_{\Lambda }$. We also evaluate for the first time $\tau ({}_{\Lambda }^3\mathrm{n})$, finding it considerably longer than ${\tau }_{\Lambda }$, contrary to the shorter lifetime values suggested by the GSI HypHI experiment for this controversial hypernucleus.

Comments: v2--14 pages, 1 figure, 2 tables, replaced title of v1 and recalculated a shorter ${}_{\Lambda }^3$H lifetime than reported in v1; v3--updated references, matching published version