# Extension of finite-volume three-body formalism to scattering of particles with spin

The extension to include spin in the three-particle formalism was carried out in the context of the three-neutron system in a paper by ExoHad members Zack Draper (UW graduate student) and Steve Sharpe (UW, co-PI) in collaboration with Max Hansen (Edinburgh) and Fernando Romero-Lopez (MIT). The inclusion of spin is more complicated for three-particle systems than for two-particles, because of the need to consider several reference frames: the overall center-of-mass frame (CMF), and the three choices of pair CMFs. This leads to the presence of Wigner rotations in the formalism, and thus nontrivial spin-dependence. The inclusion of spin also complicates the form of the three-particle K-matrix that enters in the formalism. Although the explicit results are for three identical spin-1/2 particles, the methods are straightforward to generalize to other systems, including higher spins and nonidentical particles.

Papers: JHEP **07** (2023), 226