Measurement of the generalized spin polarizabilities of the neutron in the low-Q2 region

Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques such as chiral effective field theory(1). Here we present measurements of the neutron's generalized spin polarizabilities that quantify the neutron's spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV2. In this regime, chiral effective field theory calculations(2-4) are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron's spin properties.

Automated summary

Understanding the nucleon spin structure in the regime of strong interaction poses challenges to both experiment and theory. Measurements of neutron's spin properties at very low energy-momentum transfer show discrepancies with chiral effective field theory calculations, challenging the current understanding of neutron's spin properties.