Helicity in Proton-Proton Elastic Scattering and the Spin Structure of the Pomeron

TL;DR

This paper evaluates different models of the spin structure of the pomeron in proton-proton elastic scattering, finding the tensor model aligns with experimental data while others are inconsistent.

Contribution

It introduces and compares scalar, vector, and tensor models for the nonperturbative pomeron's spin structure, validating the tensor model against experimental results.

Findings

Scalar pomeron model is excluded by data.

Vector pomeron model is inconsistent with quantum field theory.

Tensor pomeron model agrees with STAR experimental data.

Abstract

We discuss different models for the spin structure of the nonperturbative pomeron: scalar, vector, and rank-2 symmetric tensor. The ratio of single-helicity-flip to helicity-conserving amplitudes in polarised high-energy proton-proton elastic scattering, known as the complex r_5 parameter, is calculated for these models. We compare our results to experimental data from the STAR experiment. We show that the spin-0 (scalar) pomeron model is clearly excluded by the data, while the vector pomeron is inconsistent with the rules of quantum field theory. The tensor pomeron is found to be perfectly consistent with the STAR data.