2022/04/21 by David Ruth, R. Zielinski, Ruth, D. +190
Physics and Astronomy · #Atomic and Subatomic Physics Research #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex) #Physics of Superconductivity and Magnetism #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2204.10224
openalex publication_date 2022/04/21 · openalex created_date 2022/04/26 · openalex updated_date 2026/07/28
The strong interaction is not well understood at low energy, or for interactions with low momentum transfer Q2, but one of the clearest insights we have comes from Chiral Perturbation Theory (χPT). This effective treatment gives testable predictions for the nucleonic generalized polarizabilities -- fundamental quantities describing the nucleon's response to an external field. We have measured the proton's generalized spin polarizabilities in the region where χPT is expected to be valid. Our results include the first ever data for the transverse-longitudinal spin polarizability δLT, and also extend the coverage of the polarizability d2 to very low Q2 for the first time. These results were extracted from moments of the structure function g2, a quantity which characterizes the internal spin structure of the proton. Our experiment ran at Jefferson Lab using a polarized electron beam and a polarized solid ammonia (NH3) target. The δLT polarizability has remained a challenging quantity for χPT to reproduce, despite its reduced sensitivity to higher resonance contributions; recent competing calculations still disagree with each other and also diverge from the measured neutron data at very low Q2. Our proton results provide discriminating power between existing calculations, and will help provide a better understanding of this strong QCD regime.