Quasifree Compton Scattering from the Deuteron and Nucleon Polarizabilities

Abstract

Cross sections for quasifree Compton scattering from the deuteron were measured for incident energies of E(gamma) = 236-260 MeV at the laboratory angle straight theta(gamma(')) = -135 degrees. The recoil nucleons were detected in a liquid-scintillator array situated at straight theta(N) = 20 degrees. The measured differential cross sections were used, with the calculations of Levchuk et al., to determine the polarizabilities of the bound nucleons. For the bound proton, the extracted values were consistent with the accepted value for the free proton. Combining our results for the bound neutron with those from Rose et al., we obtain 1-sigma constraints of alpha;(n) = 7.6-14.0 and beta;(n) = 1.2-7.6.

Electric polarizability of hadrons

“…Experimentally, α n is found through Compton scattering off of a deuteron and the polarizability of a proton must be included in the model. In this data, there are four experimental results, [4,5,6,7]; but [7] incorporates [4]. L'vov [8] corrected the earlier values by adding 0.6 × 10 −4 fm 3 to their results.…”

Dispersion effects in nucleon polarizabilities

“…As the deuteron is modo grosso an iso-scalar target, the iso-scalar polarisabilities α It has been noticed by various authors, e.g. [3,4] and [23], that the Compton scattering data on the deuteron taken by the SAL group at ω Lab = 95 MeV [24] seem to prefer a static iso-scalar magnetic dipole polarisabilityβ (s) M ≈ 7 × 10 −4 fm 3 which deviates strongly from dispersion analysis predictions and from the proton values, while the static iso-scalar electric dipole polarisabilityᾱ (s) E ≈ 11 × 10 −4 fm 3 is of the expected size. This leads also to a significant violation of the Baldin sum rule, if the values extracted are taken as the static dipole polarisabilities.…”

“…In view of the leading order HBχPT result discussed in the last section, one may speculate these findings to be a sign that the dispersive effects in the iso-scalar single nucleon amplitudes might not be under full control, as the leading order chiral calculation actually hints at a basically unchanged α M 1 (ω) with energy, albeit on a much smaller scale. Partially, such dispersive effects have of course been taken into account in [3,4]. Likewise, Ref.…”

“…The most recent global analysis of the world data for the proton [2] givesᾱ p = (11.9 ± 0.5 ∓ 0.5) × 10 −4 fm whereas the neutron polarisabilities are less well determined, with sometimes conflicting experiments, see e.g. recently [3,4] and references in [5] α n = [0 . .…”

Effective theory of theΔ(1232)resonance in Compton scattering off the nucleon

“…During the past decade a number of excellent experimental programs have been dedicated to these two processes (see Refs. [1][2][3][4][5] and [6][7][8][9][10], respectively). At low photon energies, these experiments probe the static properties of the nucleon, such as its electric charge, magnetic moment, and polarizabilities.…”