Impact of the Delta (1232) resonance on neutral pion photoproduction in chiral perturbation theory

Cawthorne, Lloyd; McGovern, Judith A.

doi:10.48550/arxiv.1510.09136

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“…Most physical constants that enter are taken from the Review of Particle Physics [26]; the γN ∆ coupling constants are close to those determined from photoproduction in ref. [27] but are adjusted slightly to fit the strength of the unpolarised differential Compton cross section at the Delta peak [4] (see also [28]). At O(e 2 δ 4 ), there are two Compton-specific low-energy constants δα E1 and δβ M 1 for each nucleon; these encode short-distance contributions to the scalar polarisabilities and have been fit to unpolarised Compton scattering data.…”

Section: Compton Scattering On One Nucleon In χEftmentioning

confidence: 99%

Comprehensive study of observables in Compton scattering on the nucleon

2018

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We present an analysis of 13 observables in Compton scattering on the proton. Cross sections, asymmetries with polarised beam and/or targets, and polarisationtransfer observables are investigated for energies up to the ∆(1232) resonance to determine their sensitivity to the proton's dipole scalar and spin polarisabilities. The Chiral Effective Field Theory Compton amplitude we use is complete at N 4 LO, O(e 2 δ 4 ), for photon energies ω ∼ m π , and so has an accuracy of a few per cent there. At photon energies in the resonance region, it is complete at NLO, O(e 2 δ 0 ), and so its accuracy there is about 20%. We find that for energies from pion-production threshold to about 250 MeV, multiple asymmetries have significant sensitivity to presently ill-determined combinations of proton spin polarisabilities. We also argue that the broad outcomes of this analysis will be replicated in complementary theoretical approaches, e.g., dispersion relations. Finally, we show that below the pionproduction threshold, 6 observables suffice to reconstruct the Compton amplitude, and above it 11 are required. Although not necessary for polarisability extractions, this opens the possibility to perform "complete" Compton-scattering experiments. An interactive Mathematica notebook, including results for the neutron, is available from judith.mcgovern@manchester.ac.uk.

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Section: Compton Scattering On One Nucleon In χEftmentioning

confidence: 99%