Absolute differential cross-sections for elastic π±p scattering at 30 ≤ Tπ ≤ 140 MeV

Differential cross sections for elastic π±p scattering have been measured at TRIUMF for 10 incident pion energies in three separate experiments at 66.8 ≤ Tπ ≤ 138.8 MeV, Tπ = 66.8 MeV (π+p only), and 30 ≤ Tπ ≤ 66.8 MeV, using three independent techniques. Typical statistical accuracies are 1-3% and normalization uncertainties are 1.2-3.0%. Extensive experimental checks were employed to minimize systematic errors. All measurements used solid targets. Thin scintillators and time-of-flight (TOF) techniques were used to count and identify particles incident on the targets and to detect the scattered pions. Recoil protons were detected in coincidence with the scattered pions in two of the three experiments. At incident pion energies of 100 MeV and above, all π±p results from these three measurements are in good agreement with previous measurements, as are the π-p results at all energies. However, while the π±p results of these three experiments are consistent within experimental error at the overlapping energy of 66.8 MeV, they are 10-25% lower than predicted by recent phase shift analyses and the previous data on which they are based, forcing the conclusion that these previous measurements are in error by several times their stated experimental uncertainties. The scattering lengths determined from the present cross sections are three standard deviations higher than those deduced from pionic atom studies, and support previous π±p scattering measurements in that they are incompatible with the currently accepted value of the πN σ term as calculated from the QCD Lagrangian in the chiral limit