Spin-Dependent Forces in Elastic pp Scattering at 6 GeV/c

Abstract

The data on differential cross sections, polarizations and spin-correlation parameters eNN, eLL, ess and esL of elastic proton-proton scattering at 6GeV/c are analyzed in the eikonal model with spin-dependent eikonals of spin-orbit, spin-spin and tensor couplings in addition to the spin-independent central eikonal. The behavior of the measured values of eLL and ess is shown to require a certain magnitude of spin-spin and tensor forces. These forces have turned out to have two components of short-range (0.8~1.2 fm) and long-range (1.5~ 2 fm). The long-range one is interpreted as due to one-pion exchange, since it reproduces the so-called spike in neutron-proton charge-exchange scattering cross sections. § l. Introduction Recent measurements of spin-correlation parameters of elastic proton-proton scattering at 6 Ge VIc with Argonne ZGS polarized beams and polarized targets have exhibited a remarkable feature that the correlation parameters have unexpec­ tedly large valUes, for example, eLL~- 0.3 at momentum-transfer squared t=- 2.5 (GeVIc) 2 and C88~-0.2 at t~-1.5(GeVIc) 2 .n' 2l The absolute magnitude of these values is comparable to or even a little larger than the polarization value of 0.15~0.20 around t = -1.5 (Ge VI c) 2 of the same process. 3l This behavior of experiments leads us to expect that spin-dependent part of the interaction in PP scattering is stronger than was expected before. Phenomeno­ logically, there has not yet appeared any overall good fit to the data on all these observables over wide t range in the Regge model even with an enormous number of poles!l As an alternative to Regge approach, it would be interesting to see behavior of the spin-dependent interaction in the impact parameter plane. In the low energy region below 1 Ge VIc, dynamics of one-pion and one-boson exchanges have played a major role in the nucleon-nucleon scattering. 5l On the contrary, in the high energy region above about 10 Ge VIc, Regge pole exchange mechanism works well and has been able to explain especially the energy-dependence of the peripheral scattering. 6l But, it is not yet known so well how the dynamics undergoes transi­ tion between the two mechanisms in the energy region of 1~ 10 Ge VI c. For the analysis of this region, eikonal model based on the impact parameter representation for scattering amplitude seems to be applicable for the following reasons ;'l (i) *l Present address: Osaka Prefectural Higashi-Neyagawa High School, Neyagawa, Osaka 572.