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. IntroductionRecent 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 unexpectedly 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' 2 l 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. 3 l This behavior of experiments leads us to expect that spin-dependent part of the interaction in PP scattering is stronger than was expected before. Phenomenologically, 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. 5 l 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. 6 l But, it is not yet known so well how the dynamics undergoes transition 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)

THE EFFECTS OF THE SMALL-t PROPERTIES OF HADRONIC SCATTERING AMPLITUDE ON THE DETERMINATION OF ITS REAL PART

“…It was found from the analysis of the π ± p → π ± p and pp → pp reactions at p L = 20 ÷ 30 GeV /c that the slope of the "residual" spin-flip amplitude is about twice as large as the slope of the spin-non flip amplitude. This conclusion was confirmed by the phenomenological analysis carried out in [8] for spin correlation parameters of the elastic proton-proton scattering at p L = 6 GeV /c.…”

“…The difficulty is that we do not know the energy dependence of these amplitudes and individual contributions of the asymptotic non-dying spin-flip amplitudes. As was noted in [8], the spin-dependent part of the interaction in pp scattering is more important than expected and a good fit to the data in the Regge model requires an enormous number of poles.…”

Is there a hadron spin-flip contribution to the Coulomb-hadron interference at small momentum transfer and high energies?

“…The difficulty is that we do not know the energy dependence of these amplitudes and individual contributions of the asymptotic non-dying spin-flip amplitudes. As was noted in [15], the spin-dependent part of the interaction in pp scattering is stronger than was expected and a good fit to the data in the Regge model requires an enormous number of poles.…”

“…As a low energy amplitude let us take the one obtained in [15] where the full analysis of experimental data was carried out and the full set of the helicity spin amplitudes and their eikonals of the proton-proton scattering at p L = 6 GeV/c was extracted. Let us take the eikonal of the spin-non-flip amplitudes in the form similar to the form and size obtained in [15] at p L = 6 GeV /c :…”

Spin-Dependent Forces and Scattering Amplitudes for Elastic pp Scattering at 6 GeV/c

“…The expansion is performed up to second order in XLs and Xss and up to first order in XQ and Xr, as the second order terms in XQ and Xr affect the observables at most by ""'0.5% as examined in I. See I for the explicit expressions for the five independent scattering amplitudes for PP-"PP represented in terms of these five eikonals 4. ) § 3.…”