Of indirect methods used to determine the 1 s 0 neutron-neutron scattering length

Calculations with realistic potential models show that a 1% change in the 1S0 nucleonnucleon (NN) potential strength changes the scattering length by 30%. It is this high sensitivity that makes the 1S0 NN scattering lengths important in quantifying the amount to which charge symmetry is broken in the strong nuclear force. Of the three 1S0 NN scattering lengths, the value of the neutron-neutron scattering length ann is the most uncertain. A number of reactions that produce two neutrons with low relative energy have been used to determine ann. However, the two reactions that give ann with the least theoretical uncertainty are pion-deuteron capture (π− + d → n + n + γ) and neutrondeuteron breakup (n + d → n + n + p). Curiously, the values obtained using these two reactions are significantly different. In this talk the experimental techniques and theory used to determine ann for each of these popular reactions will be reviewed. In addition, the results of the two most recent nd breakup experiments will be reported.