Zero-energy neutron–triton and proton–Helium-3 scattering with EFT(π̸)

Abstract

Model-independent constraints for the neutron–triton and proton–Helium-3 scattering lengths are calculated with a leading-order interaction derived from an effective field theory without explicit pions. Using the singlet neutron–proton scattering length, the deuteron-, and triton binding energy as input, the predictions as(t–n)=9.2±2.6 fm, at(t–n)=7.6±1.6 fm, asC(He3–p)=3.6±0.32 fm, and atC(He3–p)=3.1±0.23 fm are obtained.The calculations employ the resonating group method and include the Coulomb interaction when appropriate. The theoretical uncertainty is assessed via a variation of the regulator parameter of the short-distance interaction from 400 MeV to 1.6 GeV. The phase-shift and scattering-length results for the proton–Helium-3 system are consistent with a recent phase shift analysis and with model calculations. For neutron–triton, the results for the scattering lengths in both singlet and triplet channels are significantly smaller than suggested by R-matrix and partial-wave-analysis extractions from data.For a better understanding of this discrepancy, the sensitivity of the low-energy four-body scattering system to variations in the neutron–neutron and proton–proton two-nucleon scattering lengths is calculated. Induced by strong charge-symmetry-breaking contact interactions, this dependence is found insignificant. In contrast, a strong correlation between the neutron–triton scattering length and the triton binding energy analogous to the Phillips line is found.