Abstract:
The formation of the $^7$He heavy isotope has been studied in the ${}^{11}$B$(\pi^-,\text{pt})^7$He,
${}^{11}$B$(\pi^-,\text{dd})^7$He è
${}^{10}$B$(\pi^-,\text{ðd})^7$He reactions of absorption of stopped ƒÎ$\pi^-$-mesons. No indications of the existence of a low-lying level with $E_x\sim1\,$MeV have been obtained in any of the three reactions. The existence of three narrow states with excitation energies $E_x=3.1(1)$, $4.90(15)$, and $6.65(15)$ MeV has been proven. Highly excited states with $E_x=16.9(5)\,$MeV, $\Gamma=1.0(3)$ MeV, $E_x=19.8(3)$ MeV, $\Gamma=1.5(3)$ MeV, and $E_x=24.8(4)\,$MeV, $\Gamma=4.6(7)$ MeV have been identified.