Nucleon Polarisabilities from Compton Scattering on the Deuteron

Abstract

An analytic calculation of the differential cross section for elastic Compton scattering on the deuteron at photon energies \omega in the range of 25-50 MeV is presented to next-to-next-to-leading order, i.e. to an accuracy of \sim 3%. The calculation is model-independent and performed in the low energy nuclear Effective Field Theory without dynamical pions. The iso-scalar, scalar electric and magnetic nucleon polarisabilities \alpha_0 and \beta_0 enter as free parameters with a theoretical uncertainty of about 20%. Using data at $\omega_{Lab}=49 MeV$ we find $\alpha_0=8.4\pm 3.0(exp)\pm 1.7(theor)$, $\beta_0=8.9\pm 3.9(exp)\pm 1.8(theor)$, each in units of $10^{-4} fm^3$. With the experimental constraint for the iso-scalar Baldin sum rule, $\alpha_0=7.2\pm 2.1(exp)\pm 1.6(theor)$, $\beta_0=6.9\mp 2.1(exp)\mp 1.6(theor)$. A more accurate result can be achieved by: (i) better experimental data, and (ii) a higher order theoretical calculation including contributions from a couple of so far undetermined four-nucleon-two-photon operators.