Spin dependence of high energy proton scattering - art. no. 114010.

Motivated by the need for an absolute polarimeter to determine the beam pol arization for the forthcoming BNL RHIC spin program, we study the spin depe ndence of the proton-proton elastic scattering amplitudes at high energy an d small momentum transfer. In particular, we examine experimental evidence for the existence of an asymptotic part of the helicity-flip amplitude phi( 5) which is not negligible relative to the largely imaginary average nonfli p amplitude phi(+) = 1/2(phi(1) + phi(3)) We discuss theoretical estimates of r(5) = m phi(5)/root-t Im phi(+) based upon several approaches: exuapola tion of low and medium energy Regge phenomenological results to high energi es, models based on a hybrid of perturbative QCD and nonrelativistic quark models, and models based on eikonalization techniques. We also apply the ri gorous, model-independent methods of analyticity and unitarity. We find the preponderence of evidence at currently available energy indicates that r(5 ) is small, probably less than 10%. The best available experimental limit c omes from Fermilab E704: combined with rather weak theoretical assumptions those data indicate that \r(5)\ < 15%. These bounds are important because r igorous methods allow much larger values. Furthermore, in contradiction to a widely held prejudice that r(5) decreases with energy, general principles allow it to grow as fast as Ins asymptotically, and some of the models we consider show an even faster growth in the RHIC range. One needs a more pre cise measurement of r(5) or to bound it to be smaller than 5% in order to u se the classical Coulomb-nuclear interference technique for RHIC polarimetr y. Our results show how important the measurements of spin dependence at RH IC will be to our understanding of proton structure and scattering dynamics . As part of this study, we demonstrate the surprising result that proton-p roton elastic scattering is self-analyzing, in the sense that all the helic ity amplitudes can, in principle, be determined experimentally at small mom entum transfer without a knowledge of the magnitude of the beam and target polarization. [S0556-2821(99)09109-2].