Proton Compton Scattering from Linearly Polarized Gamma Rays

Abstract

Differential cross sections for Compton scattering from the proton have been measured at scattering angles of 55°, 90°, and 125°in the laboratory frame using quasimonoenergetic linearly (circularly) polarized photon beams with a weighted mean energy value of 83.4 MeV (81.3 MeV). These measurements were performed at the High Intensity Gamma-Ray Source facility at the Triangle Universities Nuclear Laboratory. The results are compared to previous measurements and are interpreted in the chiral effective field theory framework to extract the electromagnetic dipole polarizabilities of the proton, which gives α p E1 = 13.8 ± 1.2stat ± 0.1BSR ± 0.3 theo , β p M 1 = 0.2 ∓ 1.2stat ± 0.1BSR ∓ 0.3 theo in units of 10 −4 fm 3 .

Recent Results on Proton Charge Radius and Polarizabilities

“…(1) Proton Compton scattering from linearly polarized Gamma rays [51]: The experimental configuration is shown in Fig. 15, which includes a liquid hydrogen target and eight medium-size NaI(Tl) cire detectors in the HIγS NaI Detector Array (HINDA).…”

Proton electromagnetic generalized polarizabilities

“…The two static polarizabilities of the proton were determined as α E = (10.99 ± 0.16 ± 0.47 ± 0.17 ± 0.34) 10 -4 fm 3 and β M = (3.14 ± 0.21 ± 0.24 ± 0.20 ± 0.35) 10 -4 fm 3 . The second experiment [15] was performed at the High Intensity Gamma-Ray Source (HIGS) facility at the Triangle Universities Nuclear Laboratory, reporting for two polarizabilities α E = (13.8 ± 1.2 ± 0.1 ± 0.3) 10 -4 fm 3 and β M = (0.2 ± 1.2 ± 0.1 ± 0.3) 10 -4 fm 3 . The tensions between the MAMI and HIGS measurements illustrate the difficulty in conducting these experiments and highlight the need to be cautious in the treatment of the experimental uncertainties.…”

First concurrent extraction of the leading-order scalar and spin proton polarizabilities

“…In particular, real Compton scattering (RCS) at low energies is parametrized by polarizabilities that describe the response of the charge and magnetization distributions inside the nucleon to an applied quasistatic electromagnetic field. These structure constants are fundamental properties of the nucleon and their determination has driven a relevant experimental effort in the last few years [1][2][3][4][5].…”

“…For the low-energy set, in addition to the new data from Refs. [4,5], we used the same selection extensively discussed in a previous work by Pasquini et al [14], which includes datasets from Refs. [28][29][30][31][32][33][34][35][36][37][38][39].…”

“…The polarization observables have enhanced sensitivity to the spin polarizabilities [23,51], hence are crucial for the extraction of these structure constants. The adopted datasets include three different polarization observables: Σ 2x [1], Σ 2z [3], and Σ 3 both below [2,4,5] and above [48] pion photoproduction threshold. Although the data for the photon asymmetry Σ 3 above threshold are from the same dataset of the LEGS unpolarized cross section, they are consistent with the available MAMI results for both the pπ 0 and the nπ + photoproduction channels [50].…”