Neutron-Neutron Scattering Length Determinations Using nd Breakup in Different Nucleon Detection Geometries*

Significant differences in the value for the $^1S_0$ neutron-neutron ({\it nn}) scattering length($a_{nn}$) have been obtained with neutron-deuteron (nd) breakup measurements made using different detection geometries [1,2]. We report the results of a new determination of $a_{nn}$ made using the nd breakup reaction in recoil proton geometry. The measurements were made at the Triangle Universities Nuclear Laboratory (TUNL) with a neutron beam energy of 19.0 MeV. The momenta of the recoil proton and one of the outgoing neutrons were measured at mean angles of $\theta_p = 45.0^\circ$ and $\theta_n = 52.1^{\circ}$, respectively. Details of the experiment and analysis will be presented, and results will be discussed. \\[4pt] [1] D.E.~Gon$\acute a$lez Trotter {\em et al.}, Phys. Rev. C {\bf 73}, 034001 (2006).\\[0pt] [2] V.~Huhn {\em et al.}, Phys. Rev. Lett. {\bf 85}, 1190 (2000).