Pion-nucleon scattering up to 10 Gev/c

Backward pion-nucleon scattering

“…We also indicate the averaged values given by the Particle Data Group [52] and the most recent systematic analysis by Klempt and Richard [53]. The analysis by Hendry [28,48] is based on an impact parameter approach that differs significantly from our result for the K 1,13 (2700). results.…”

“…The data indicate considerable structures for center-ofmass energies up to ≃ 3 GeV or even higher. There were intense discussions [27,46,47,48] whether these structures originate from the excitation of high mass baryons. Indeed, these data on pion scattering at 180 0 seem to be up to now the only direct evidence of the existence of excited baryons with masses above 2.4 GeV.…”

Transition from resonances to surface waves in pi^+-p elastic scattering

“…Another piece of current dogma, taking much support from the baryon spectrum, is the widely-held belief in linear Regge trajectories as a function of mass-squared ". But, after a more careful phenomenological analysis, based, in particular, on the work of Hendry [2], they conclude: "The conventional picture of linear Regge trajectories with universal slope is not well-established." Regarding the π + -p collision, Hendry writes [3]: "The first few resonances are consistent with a straight-line trajectory; however, as we increase the spins, the resonances appear to deviate from this trajectory.…”

“…In the conventional Regge-type phenomenology, the relationship between the total spin J and the squared-mass is given (with standard notation) by: J = α 0 + α ′ m 2 , the slope of the trajectory being α ′ ∼ 1/(GeV) 2 .…”

“…. A widely-held belief takes for granted that this sequence can be connected by a moving pole in the complex angular momentum (CAM) plane, which gives rise to a linear trajectory of the form J = α 0 + α ′ m 2 , α ′ ∼ 1/(GeV) 2 , which is the standard expression of the Regge pole trajectory. But the phenomenology shows that only the first few resonances lie on a trajectory of this type.…”