Magnetic Polarisability of Octet Baryons via Lattice QCD

TL;DR

This paper uses advanced lattice QCD techniques to calculate the magnetic polarisability of octet baryons from first principles, compares results with a constituent quark model, and finds excellent agreement with experimental data.

Contribution

It introduces new lattice QCD methods for isolating single states and reducing fit sensitivity, and demonstrates the model's effectiveness in matching lattice results.

Findings

Lattice QCD results align well with constituent quark model predictions.

The model captures the observed patterns of magnetic polarisabilities.

Results agree with experimental measurements for proton and neutron polarisabilities.

Abstract

Drawing on recent advances in lattice-QCD background-field techniques, the magnetic polarisability of octet baryons is calculated from the first principles of QCD. The results are presented in the context of new constituent quark-model calculations providing a framework for understanding the lattice results and a direct comparison with simulation results at unphysical quark masses. Using smeared quark sources, low-lying Laplacian eigenmode projection and final-state Landau mode projection, considerable attention is devoted to ensuring single-state isolation in the lattice correlation functions. We also introduce new weighting methods to reduce the sensitivity to correlation-function fits, averaging over many fits based on merit drawn from the full correlated $\chi^2$ of the fits. The techniques are implemented on the $32^3 \times 64$, 2+1-flavour dynamical-fermion lattices provided by the PACS-CS collaboration following the introduction of uniform magnetic fields quantised to the lowest nontrivial values available. After some fine tuning of the constituent quark model parameters, we find the model captures the patterns observed in the lattice QCD results very well, providing important insights into the physics underpinning the magnetic polarisabilities. Finally, comparison with the most recent results from experiment proceeds through an effective field theory formalism which incorporates estimates of finite-volume corrections and small electro-quenching corrections as the results are brought to the physical point. We find excellent agreement with experiment where available, including the proton and neutron polarisabilities.