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arXiv · 1107.1684

First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He

M. Brodeur·T. Brunner·C. Champagne·S. Ettenauer·M. J. Smith·A. Lapierre·R. Ringle·V. L. Ryjkov·S. Bacca·P. Delheij·G. W. F. Drake·D. Lunney·A. Schwenk·J. Dilling
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Abstract

The first direct mass-measurement of $^{6}$He has been performed with the TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the mass of $^{8}$He was determined with improved precision over our previous measurement. The obtained masses are $m$($^{6}$He) = 6.018 885 883(57) u and $m$($^{8}$He) = 8.033 934 44(11) u. The $^{6}$He value shows a deviation from the literature of 4$σ$. With these new mass values and the previously measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and 1.959(16) fm for $^{6}$He and $^{8}$He respectively. We present a detailed comparison to nuclear theory for $^6$He, including new hyperspherical harmonics results. A correlation plot of the point-proton radius with the two-neutron separation energy demonstrates clearly the importance of three-nucleon forces.

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M. Brodeur, T. Brunner, C. Champagne, S. Ettenauer, M. J. Smith, A. Lapierre, R. Ringle, V. L. Ryjkov, S. Bacca, P. Delheij, G. W. F. Drake, D. Lunney, A. Schwenk, J. Dilling. 2011-12-24. First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He. https://doi.org/10.1103/physrevlett.108.052504

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