Experimental study of the nature of the 1− and 2− excited state

The nature of the 1− and 2− excited states in 10Be is studied using the 11Be(p, d) transfer reaction in inverse kinematics at 10A MeV at TRIUMF ISAC-II, in particular to assess whether either of them can be considered as an excited halo state. The angular distributions for both states are extracted using deuteron-γ coincidences and analyzed using a transfer model taking into account one-step and two-step processes. A good fit of the angular distributions is obtained considering only the one-step process, whereby an inner p3/2 neutron of 11Be is removed, leaving the halo neutron intact. Higher-order processes however cannot be rejected. The small spectroscopic factors extracted suggest that the structure of both states is not uniquely halo-like, but rather display a more complex configuration mixing cluster and halo structures. Further insights are limited, as this experiment specifically probed the halo-like (but not cluster-like) 11Be(1/2+) ⊗ (ν p3/2 ) −1 configuration in both states.U.S. Department of Energy (DOE): DE-FG03-93ER40789 (Colorado School of Mines), DE-FG02-96ER40978 (Louisiana State), DE-SC0021422 (Michigan State), DE-AC05-00OR22725 (Oak Ridge National Laboratory)The National Nuclear Security Administration a través de los acuerdos de cooperación del DOE de EE. UU.(NNSA) DE-FG52-08NA28552The National Science Foundation PHY-1811815 (Michigan State)Ministerio español de Ciencia e Innovación y fondos FEDER. RTI2018-098117-B-C21 y PGC2018-096994-BC21Agencia Española de Investigación (AEI). PID2019-104714GB-C2