Decay study of ^11Be with an Optical TPC detector

The decay of one-neutron halo nucleus ^11Be was investigated using the Warsaw Optical Time Projection Chamber (OTPC) detector to measure -delayed charged particles. The results of two experiments are reported. In the first one, carried out in LNS Catania, the absolute branching ratio for -delayed emission was measured by counting incoming ^11Be ions stopped in the detector and the observed decays with the emission of particle. The result of 3. 27 (46) \% is in good agreement with the literature value. In the second experiment, performed at the HIE-ISOLDE facility at CERN, bunches containing several hundreds of ^11Be ions were implanted into the OTPC detector followed by the detection of decays with the emission of charged particles. The energy spectrum of -delayed particles was determined in the full energy range. It was analysed in the R-matrix framework and was found to be consistent with the literature. The best description of the spectrum was obtained assuming that the two 3/2^+ and one 1/2^+ states in ^11B are involved in the transition. The search for -delayed emission of protons was undertaken. Only the upper limit for the branching ratio for this process of (2. 2 0. 6 ₒₓ₀ₓ 0. 6 ₒₘₒ) 10^-6 could be determined. This value is in conflict with the result published in Ayyad et al. Phys. Rev. Lett. 123, 082501 (2019) but does agree with the limit reported in Riisager et al. , Eur. Phys. J. A (2020) 56: 100