Compton scattering from the deuteron above pion-production threshold

Abstract

The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this article, the first measurement of the cross section for Compton scattering on the deuteron above the pion-production threshold is presented.

Deuteron Compton Scattering Above Pion Threshold

“…This measurement was conducted at the former Tagged Photon Facility (TPC) at the MAX IV laboratory in Lund, Sweden [7]. The pertinent details of the experiment are described below; the reader is referred to [1] for additional information.…”

“…This work [1] represents a continuation of the study of the electric and magnetic polarizabilities (α n and β n , respectively) of the nucleon. There has been much progress in the experimental study of the nucleon static and spin polarizabilities over the past few decades.…”

Near-threshold π− photoproduction on the deuteron

“…Cosmicray muons that traversed the detectors during data taking were identified with the annulus scintillators by requiring coincident signals in opposing annular segments. The pulse-height variations of identified cosmic-ray muon events registered by the PMTs were used to correct for PMT gain instabilities [19]. After calibration procedures, the NaI(Tl) detectors had an energy resolution of ∼3 MeV (full width at half maximum).…”

“…The simulated RC spectrum was obtained by first matching the Monte Carlo inbeam data to the experimental in-beam data as described in Refs. [19,31]. Then, photons with energies sampled from the theoretical RC spectrum and an isotropic angular distribution were generated in the LD 2 target into 4π solid angle.…”

“…The cross-section data from Refs. [19,32] were extrapolated to produce conservative scattering-contamination estimates. These indicated that the effect on the extracted π − cross section was typically ±3% (maximum of 5.5% at lowest E γ ).…”