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Description
We present the results of a partial wave analysis of the global real Compton scattering (RCS) database, extracting the leading scalar and spin polarisabilities of the proton.
Exploring the nucleon using electromagnetic probes reveals a fine and intricate interplay between its various structural properties. As an example, the nucleon polarisabilities encode the two-photon response, such as measured in RCS [1, 2]. On the other hand, their precise knowledge is very important for the analysis of atomic spectra, especially in muonic atoms [3], which serves to constrain the details of the nucleon charge distribution such as the charge radius.
The polarisabilities are introduced as the coefficients in the low-energy expansion (LEX) of the RCS amplitudes, and can, in principle, be extracted using the LEX to analyse the RCS data [1, 4]. However, the energies where quality experimental data are available are too high to use the LEX for an analysis, forcing one to use a more sophisticated framework such as effective field theories [5, 6], dispersion relations [7], or partial wave analysis [8]. We use the latter framework here, include the most recent RCS data from MAMI [9] and HIGS [10], and introduce a few further modifications in the formalism. The results of our refined analysis are presented in this contribution.
[1] D. Babusci et al., Phys. Rev. C 58, 1013–1041 (1998).
[2] B. R. Holstein et al., Phys. Rev. C 61, 034316 (2000).
[3] K. Pachucki et al., Rev. Mod. Phys. 96, 015001 (2024).
[4] N. Krupina and V. Pascalutsa, Phys. Rev. Lett. 110, 262001 (2013).
[5] H. W. Griesshammer et al., Prog. Part. Nucl. Phys. 67, 841–897 (2012).
[6] V. Lensky and J. A. McGovern, Phys. Rev. C 89, 032202 (2014).
[7] E. Mornacchi et al., Phys. Rev. Lett. 129, 102501 (2022).
[8] N. Krupina et al., Phys. Lett. B 782, 34–41 (2018).
[9] E. Mornacchi et al. (A2 Collaboration at MAMI), Phys. Rev. Lett. 128, 132503 (2022).
[10] X. Li et al., Phys. Rev. Lett. 128, 132502 (2022).
