Lifetimes of Light Hyperfragments

We have studied the lifetimes of light hyperfragments, making use of two stacks of nuclear-emulsion pellicles exposed to K^--meson beams at the Bevatron and the Brookhaven A. G. S. In these two stacks we obtained 18 mesonic decays in flight from a total of 258 mesonic decays of hyperfragments. The values we found for the lifetimes are the following: For _ΛHe⁴, _ΛHe⁵, and _ΛHe4,5 events combined (8 in flight, 117 at rest), we obtained the value τ(_ΛHe4,5)=(2.2_-0.6+1.5)×10^-10 sec. By suitably apportioning the _ΛHe4,5 events between _ΛHe⁴ and _ΛHe⁵ we obtain the values τ(_ΛHe⁵)=(1.8_-0.6+1.5)×10^^-10 sec and τ(_ΛHe⁴)≥1.0×10^-10 sec. For _ΛH³, using only two-body decays (3 in flight, 4 at rest), we obtain τ(_ΛH³)=(0.8_-0.3+1.9)×10^-10 sec. Using both two-body and three-body decays (5 in flight, 18 at rest), we obtain τ(_ΛH³)=(3.4_-1.4+8.2)×10^-10 sec. This value may be an overestimate owing to _ΛH⁴ contamination in the three-body _ΛH³ events. This point is discussed in the text. For _ΛH⁴ we obtain τ(_ΛH⁴)=(2.4_-1.0+6.0)×10^-10 sec using only three-body decays (4 in flight, 14 at rest), and τ(_ΛH⁴)=(3.6_-1.3+4.9)×10^-10 sec using all _ΛH⁴ decays (5 in flight, 40 at rest). This last value may suffer from a bias against finding two-body _ΛH⁴ decays in flight which simulate small-angle scatterings under low magnifying power, although all scatterings were examined closely. The above results are compared with theoretical estimates of hyperfragment lifetimes.