Precise measurements of the total cross sections of positive and negative
π
mesons on hydrogen have revealed the presence of structure or enhancements in these cross sections at various momenta up to 3 GeV/
c
. The present paper discusses measurements of this type and in particular, a recent experiment to search for structure in the region 3 to 7 GeV/
c
, where previous experiments have shown that, if structure were present, it was likely to reveal itself as an amplitude in the total cross section of 1 mb or less. The recent measurements indicate four regions of structure, two in each of the isotopic spin states 3/2 and 1/2. The possible relation of these regions of structure to the formation of pion-nucleon resonances is discussed.
Bootstrap and the Parameters of Pion-Nucleon Resonances
