Cross sections of the →π reaction between 310 and 425 MeV

The legacy of the experimental hadron physics programme at COSY

“…As discussed in sect. 4.3.2, the ANKE data at 353 MeV [120] seem to be consistent with the PROMICE-WASA results at 360 MeV [117].…”

“…The measured total cross sections for excess energies between about 6 and 9 MeV seem to be about 50% higher than those found at IUCF [116] and CELSIUS [117] and the COSY-TOF authors speculated that this might be associated with the beam-pipe problem in these two experiments. This could have significant implications for the value of the s-wave π 0 production amplitudes but a greater energy range would be needed to confirm this.…”

“…frame are parameterized in the form dσ/dΩ ∼ 1 + b cos 2 θ π , the COSY-TOF data yield b = −1.00 ± 0.02 for E pp < 3 MeV and b = −0.17 ± 0.01 for the whole data sample. The corresponding numbers obtained in the PROMICE-WASA (CELSIUS) experiment at 400 MeV [117] are b = −0.58 ± 0.03 and b = +0.19 ± 0.01, respectively. There are therefore unresolved systematic differences that are much larger than the statistical uncertainties.…”

“…This becomes more problematic at low energies where, as threshold is approached, more and more events fall into the beam pipe trap. Since there is a strong proton-proton final state interaction, it has been argued [115] that results of the near-threshold missingmass measurements carried out at IUCF [116] and the PROMICE-WASA facility at CELSIUS [117] have significant model dependence caused, in part, by uncertainties in the Monte Carlo estimation of the acceptance.…”

“…There were pioneering measurements of the pp → {pp} s π 0 differential cross section carried out at the CELSIUS storage ring at a series of beam energies from close to threshold up to 425 MeV [117]. Here the {pp} s denotes a protonproton pair with low excitation energy E pp such that the Pauli principle forces them to be in the 1 S 0 state.…”