Evidence for pion absorption on four nucleons

Experimental spectra from the coincident detection of three nucleons after the pion absorption in $\rm {}^{4}He$ are displayed. The presence of a mechanism with four nucleons participating in the absorption process is made obvious. The total cross-sections for this absorption mode are: $ \sigma_{\rm abs}^{\rm 4NA}= (1.0 \pm 0.2)\, {\rm mb}\; {\rm at}\; T_{\pi}=120\;{\rm MeV} $ and $ \sigma_{\rm abs}^{\rm 4NA}= (2.18 \pm 0.65)\, {\rm mb}\; {\rm at}\; T_{\pi}=210\;{\rm MeV}\,.