PION-NUCLEON PARTIAL-WAVE ANALYSIS WITH FIXED-T DISPERSION-RELATION CONSTRAINTS

We have performed a set of partial-wave analyses of the pion-nucleon elastic scattering data to 2 GeV employing rigorous constraints from simultaneous forward and fixed-t dispersion relations. Constraints were generated from the forward C+/- amplitudes and the invariant amplitudes A and B at fixed t in the range 0 to -0.3 GeV2. Solutions were generated for a range of pion-nucleon coupling constants (g2/4pi). and isoscalar scattering lengths (a(+)). A chi-squared map for these (g2/4pi, a(+)) solutions exhibits a clear minimum near g2/4pi = 13.75 (f 2/4pi = 0.07.6) for both the fits to the data and the dispersion relations. While favoring a particular 92/4pi, this work shows that it is possible to obtain good, stable fits for nearby values, but at the cost of increased chi squared. Consequently, this approach provides a criterion for defining the preferred value and uncertainty of g2/4pi from pion-nucleon scattering data. On this basis, we conclude that g2/4pi = 13.75 +/- 0.15 (f2/4pi 0.076 +/- 0.001).