Testing <i>ab initio</i> nuclear structure in neutron-rich nuclei: Lifetime measurements of second <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:msup></mml:math> state in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">C</mml:mi><mml:mprescripts/><mml:none/><mml:mn>16</mml:mn></mml:mmultiscripts></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">O</mml:mi><mml:mprescripts/><mml:none/><mml:mn>20</mml:mn></mml:mmultiscripts></mml:math>
M. Ciemała, S. Ziliani, F. C. L. Crespi, S. Leoni, B. Fornal, A. Maj, P. Bednarczyk, G. Benzoni, A. Bracco, C. Boiano, S. Bottoni, S. Brambilla, M. Bast, M. Beckers, T. Braunroth, F. Camera, N. Cieplicka-Oryńczak, E. Clément, S. Coelli, O. Dorvaux, S. Ertürk, G. de France, C. Fransen, A. Goldkuhle, J. Grȩbosz, M.N. Harakeh, Ł. W. Iskra, B. Jacquot, А. В. Карпов, M. Kicińska-Habior, Y. Kim, M. Kmiecik, A. Lemasson, S. M. Lenzi, M. Lewitowicz, H. Li, I. Matéa, K. Mazurek, C. Michelagnoli, M. Matejska-Minda, B. Million, C. Müller-Gatermann, V. Nanal, P. Napiorkowski, D. R. Napoli, R. Palit, M. Rejmund, C. Schmitt, M. Stănoiu, I. Stefan, E. Vardaci, B. Wasilewska, O. Wieland, M. Ziębliński, M. Zielińska, A. Ataç, D. Barrientos, B. Birkenbach, A. J. Boston, B. Cederwall, L. Charles, J. Collado, D. M. Cullen, P. Désesquelles, C. Domingo‐Pardo, J. Dudouet, J. Eberth, V. González, J. Goupil, L. J. Harkness-Brennan, H. Hess, D. S. Judson, A. Jungclaus, W. Korten, M. Labiche, A. Lefèvre, R. Menegazzo, D. Mengoni, J. Nyberg, R. M. Pérez-Vidal, Zs. Podolyák, A. Pullia, F. Recchia, P. Reiter, F. Saillant, M.-D. Salsac, E. Sanchís, O. Stézowski, Ch. Theisen, J. J. Valiente‐Dobón, J. D. Holt, J. Menéndez, A. Schwenk, J. Simonis
Abstract
To test the predictive power of ab initio nuclear structure theory, the lifetime of the second ${2}^{+}$ state in neutron-rich $^{20}\mathrm{O},\phantom{\rule{0.28em}{0ex}}\ensuremath{\tau}({2}_{2}^{+})={150}_{\ensuremath{-}30}^{+80}\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$, and an estimate for the lifetime of the second ${2}^{+}$ state in $^{16}\mathrm{C}$ have been obtained for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds of femtoseconds range by analyzing the Doppler-shifted $\ensuremath{\gamma}$-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction $^{18}\mathrm{O}\phantom{\rule{0.28em}{0ex}}(7.0\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{u})+^{181}\mathrm{Ta}$. The requested sensitivity could only be reached owing to the excellent performances of the Advanced $\ensuremath{\gamma}$-Tracking Array AGATA, coupled to the PARIS scintillator array and to the $\mathrm{VAMOS}++$ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two- and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for $^{20}\mathrm{O}$ and with the no-core shell model for $^{16}\mathrm{C}$. The present measurement shows the power of electromagnetic observables, determined with high-precision $\ensuremath{\gamma}$ spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetime measurements in unexplored regions of the nuclear chart, including $r$-process nuclei, when intense beams, produced by Isotope Separation On-Line (ISOL) techniques, become available.