REACTION PI-P-]ETA IN THE 15 TO 40 GEV-C MOMENTUM RANGE

A high-statistics measurement of the reaction π-p→ηn; η→2γ has been performed at the 70 GeV Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small |t|, as exponentials with the same slopes to within a few percent. For |t| ≳ 1 (GeV/c)2 there is a break in the differential cross section. In addition, the A2 effective trajectory deviates markedly for |t| ≳ 1 GeV/c)2 from the linear behaviour valid for smaller |t|. © 1979.