Observation of a Near-Threshold Proton Resonance in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">B</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>11</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math>
E. López-Saavedra, S. Almaraz-Calderon, Benjamin Asher, L. T. Baby, N. Gerken, K. Hanselman, K. W. Kemper, A. N. Kuchera, Ashton Morelock, Jesus Perello, E. Temanson, Alexander Volya, I. Wiedenhöver
Abstract
A near-threshold proton resonance in $^{11}\mathrm{B}$ at ${E}_{\mathrm{ex}}=11.44\ifmmode\pm\else\textpm\fi{}0.04\text{ }\text{ }\mathrm{MeV}$ is observed via the reaction $^{10}\mathrm{Be}(d,n)^{11}\mathrm{Be}\ensuremath{\rightarrow}^{10}\mathrm{Be}+p$ in inverse kinematics, measured with a beam of the radioactive isotope $^{10}\mathrm{Be}$. The resonance energy at ${E}_{\mathrm{res}}=211(40)\text{ }\text{ }\mathrm{keV}$ is consistent with a proton signal observed by Ayyad et al. in the $\ensuremath{\beta}$-delayed proton decay of $^{11}\mathrm{Be}$. By comparison to a distorted wave Born approximation calculation, a 0.27(6) spectroscopic factor is extracted and a tentative ($\ensuremath{\ell}=0$) character is assigned for this resonance. The significant cross section in the proton-transfer $(d,n)$ reaction, as well as the observation of its proton-decay signal, point to the threshold-resonance character of this state. The position of this state, its structure, and strong coupling to the $s$-wave continuum represent an ideal case to study quantum near-threshold many-body dynamics of unstable states. The presence of this state is an important step toward understanding the excessively large beta-delayed proton-decay branch of $^{11}\mathrm{Be}$.