Speaker
Judith McGovern
(University of Manchester)
Description
We have recently completed a high-precision extraction of the proton spin-independent polarisabilities from the world database of low-energy Compton scattering experiments, within the framework of chiral effective field theory (χEFT) with pions, nucleons, and the Delta(1232) as explicit degrees of freedom [1]. Our Baldin-sum-rule-constrained results are [2]
α_p = 10.65 ± 0.35(stat) ± 0.2(Baldin) ± 0.3(theory),
β_p = 3.15 ± 0.35(stat) ± 0.2(Baldin) ± 0.3(theory).
These were obtained in the heavy-baryon formulation, but almost identical results have been obtained in a covariant calculation [3]. With the publication this year by Myers et al. of the results of the deuteron Compton scattering experiment using the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden, the world γ-d database has doubled in size, allowing the extraction of the isoscalar polarisabilities with unprecedented accuracy, and combined with the proton results we obtain [4]
α_n = 11.65 ± 1.25(stat) ± 0.2(Baldin) ± 0.8(theory),
β_n = 3.55 ± 1.25(stat) ± 0.2(Baldin) ± 0.8(theory).
A new generation of experiments with polarised beams have been performed at the Mainz Microtron, with the first results published this year by Martel et al. [5]. These experiments are sensitive to the spin polarisabilities, and we will discuss the predictions of χEFT for the relevant cross sections cross sections and asymmetries.
References
1. H. W. Griesshammer, J. A. McGovern, D. R. Phillips and G. Feldman, Prog. Part. Nucl. Phys. 67 (2012) 841 [arXiv:1203.6834 [nucl-th]].
2. J. A. McGovern, D. R. Phillips and H. W. Griesshammer, Eur. Phys. J. A 49 (2013) 12 [arXiv:1210.4104 [nucl-th]].
3. V. Lensky and J. A. McGovern, Phys. Rev. C 89 (2014) 032202. [arXiv:1401.3320 [nucl-th]].
4. L. S. Myers et al. COMPTON@MAX-lab Collaboration], Phys. Rev. Lett. 113 (2014) 26, 262506 [arXiv:1409.3705 [nucl-ex]].
5. P. P. Martel et al. [A2 Collaboration], Phys. Rev. Lett. 114 (2015) 11, 112501 [arXiv:1408.1576 [nucl-ex]].
