Extended Data Fig. 7: Estimation of the systematic uncertainty.
(a) Calculated χ2 values as a function of the offset added to the theoretical distribution used to describe the energy of the two-neutron system in the \({}^{6}{\rm{H}}{\rm{e}}({\rm{p}},{\rm{p}}{}^{4}{\rm{H}}{\rm{e}})\) reaction. The systematic uncertainty for the energy is taken as the offset values at \({\chi }_{{\rm{\min }}}^{2}\pm 1,\) shown by the dashed lines. (b) The corresponding distributions of the data (black symbols), the original (solid red) and the shifted (dashed red) theoretical curves. Distributions are presented for the low-energy region, where the difference between the theory curves is visible. (c) Same as (a) but as a function of the energy resolution (using an offset of zero). The systematic uncertainty for the width is taken as the resolution values at \({\chi }_{{\rm{\min }}}^{2}\pm 1,\) shown by the dashed lines. (d) The corresponding distributions of the data (black symbols), the original (solid red) and the \({\chi }_{{\rm{\min }}}^{2}\pm 1\) resolution smeared (dashed red) theoretical curves. For comparison, the original distribution is also shown, where only the acceptance of the set-up has been taken into account but not the resolution, i.e., a resolution of zero MeV has been assumed. The distribution is scaled by a factor of 1/2 to match the scale of the figure
