Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ Σ 3 in Compton scattering

Sokhoyan, V.; Downie, E. J.; Mornacchi, E.; McGovern, Judith A.; Krupina, Nadiia; Afzal, F.; Ahrens, J.; Akondi, C. S.; Annand, J. R. M.; Arends, H. J.; Beck, R.; Braghieri, A.; Briscoe, W. J.; Cividini, F.; Collicott, C.; Costanza, S.; Denig, A.; Dieterle, M.; Ferretti, M.; Gardner, S.; Garni, S.; Glazier, D. I.; Glowa, D.; Gradl, W.; Gurevich, G. M.; Hamilton, D.; Hornidge, D.; Huber, G. M.; Käser, A.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Krusche, B.; Lensky, Vadim; Linturi, J. M.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Macrae, R.; Manley, D. M.; Martel, P. P.; Middleton, D. G.; Miskimen, R.; Mushkarenkov, A.; Neiser, A.; Oberle, M.; Spina, H. Ortega; Ostrick, M.; Ott, P. S.; Otte, P. B.; Oussena, B.; Paudyal, D.; Pedroni, P.; Polonski, A.; Prakhov, S.; Rajabi, A. A.; Rostomyan, T.; Sarty, A. J.; Schumann, S.; Spieker, K.; Steffen, O.; Strakovsky, I. I.; Strandberg, B.; Strub, Th.; Supek, I.; Thiel, A.; Thiel, M.; Thomas, A.; Unverzagt, M.; Wagner, S.R.; Watts, D. P.; Wettig, J.; Witthauer, L.; Werthmüller, D.; Wolfes, M.; Zana, L.

doi:10.1140/epja/i2017-12203-0

Cited by 27 publications

(40 citation statements)

References 33 publications

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“…Hopefully, the currently running A2/MAMI experiment will improve the accuracy for this observable, and thus play a crucial role in an accurate determination the magnetic polarizability β M1 [44]. At present we only verify that all our fits are in agreement with the pilot data [43], see Fig. 3.…”

Section: Cs Database and Fitting Strategymentioning

confidence: 56%

“…Also, the points of Federspiel et al [35] are treated as described in the footnote (i.e., omitting them below 50 and at 65.8 MeV), rather than [14], DR calculations [15,39] (note that only α E1 + β M1 is calculated in DR, with their difference fitted to CS data), and an experimental extraction of spin polarizabilities at MAMI [40] (performed using subtracted DRs [9]). We do not include the data on beam asymmetry in our fits, since the only data (below pion-production threshold), coming from the pilot experiment at MAMI [43], are of significantly poorer quality compared to the unpolarized data. Hopefully, the currently running A2/MAMI experiment will improve the accuracy for this observable, and thus play a crucial role in an accurate determination the magnetic polarizability β M1 [44].…”

Section: Cs Database and Fitting Strategymentioning

confidence: 99%

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Partial-wave analysis of proton Compton scattering data below the pion-production threshold

2018

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Low-energy Compton scattering off the proton is used for determination of the proton polarizabilities. However, the present empirical determinations rely heavily on the theoretical description(s) of the experimental cross sections in terms of polarizabilities. The most recent determinations are based on either the fixed-t dispersion relations (DR) or chiral perturbation theory in the single-baryon sector (χPT). The two approaches obtain rather different results for proton polarizabilities, most notably for β M1 (magnetic dipole polarizability). We attempt to resolve this discrepancy by performing a partial-wave analysis of the world data on proton Compton scattering below threshold. We find a large sensitivity of the extraction to a few "outliers", leading us to conclude that the difference between DR and χPT extraction is a problem of the experimental database rather than of "modeldependence". We have specific suggestions for new experiments needed for an efficient improvement of the database. With the present database, the difference of proton scalar polarizabilities is constrained to a rather broad interval: α E1 − β M1 = (6.8 . . . 10.9) × 10 −4 fm 3 , with their sum fixed much more precisely [to 14.0(2)] by the Baldin sum rule. II. MULTIPOLE EXPANSION AND (BI-)LINEAR EMPIRICAL CONSTRAINTSThe general formalism of the multipole expansion for nucleon CS is given in [18,24], and concisely summarized in [5, Sec. 2]. The idea is that, using the rotational and discrete symmetries, the CS helicity amplitudes T σ λ ,σ λ (s,t), with σ (σ ) the helicity of initial (final) photon and λ (λ ) for the helicity arXiv:1712.05349v2 [nucl-th]

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Section: Cs Database and Fitting Strategymentioning

confidence: 56%

Section: Cs Database and Fitting Strategymentioning

confidence: 99%

Partial-wave analysis of proton Compton scattering data below the pion-production threshold

2018

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“…Future measurements planned by the A2 collaboration at MAMI below pion-production threshold [50,51] hold the promise to improve the accuracy and the statistic of the available data set and will help to extract with better precision the values of the proton scalar dipole polarizabilities. In the bootstrap framework, the correlation coefficients ρ among the fit parameters are obtained from the reconstructed probability distribution in the parameters space.…”

Section: Discussionmentioning

confidence: 99%

Proton scalar dipole polarizabilities from real Compton scattering data using fixed-t subtracted dispersion relations and the bootstrap method

Pasquini¹,

Pedroni²,

Sconfietti³

2019

J. Phys. G: Nucl. Part. Phys.

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We perform a fit of the real Compton scattering (RCS) data below pion-production threshold to extract the electric (αE1) and magnetic (βM1) static scalar dipole polarizabilities of the proton, using fixed-t subtracted dispersion relations and a bootstrap-based fitting technique. The bootstrap method provides a convenient tool to include the effects of the systematic errors on the best values of αE1 and βM1 and to propagate the statistical errors of the model parameters fixed by other measurements. We also implement various statistical tests to investigate the consistency of the available RCS data sets below pion-production threshold and we conclude that there are not strong motivations to exclude any data point from the global set. Our analysis yields αE1 = (12.03 +0.48 −0.54 ) × 10 −4 fm 3 and βM1 = (1.77 +0.52 −0.54 ) × 10 −4 fm 3 , with p-value = 12%. I. INTRODUCTIONThe electric and magnetic static scalar dipole polarizabilities, α E1 and β M 1 , respectively, are fundamental structure constants of the proton that can be accessed via real Compton scattering (RCS). In the low-energy expansion of the Compton amplitude, they correspond to the leading-order contributions beyond the structure independent terms that describe the scattering process as if the proton were a pointlike particle with anomalous magnetic moment. When approaching the pion-production threshold, also higher-order terms start competing with the scalar dipole polarizabilities. Therefore, one has to resort to reliable theoretical frameworks for extracting the scalar dipole polarizabilities from experimental data. The most accredited theories, which have been used sofar, are fixed-t dispersion relations (DRs), in the unsubtracted [1-3] and subtracted [4][5][6][7][8] formalism, and chiral perturbation theory (χPT) with explicit nucleons and Delta's, in the variant of heavy-baryon χPT (HBχPT) [9-11] and manifestly covariant [12,13] χPT (BχPT) 1 . Based on these theoretical frameworks, extractions of the scalar dipole polarizabilities have been obtained by fitting different data sets for the unpolarized RCS cross section, and adopting a statistical approach based on the conventional χ 2 -minimization procedure. Recently, a new statistical method has successfully been applied in Ref. [16] to analyze RCS data at low energies and extract values for the energy-dependent scalar dipole dynamical polarizabilities [17,18]. The method is based on the parametric-bootstrap technique, and it is adopted in this work to extract the scalar dipole static polarizabilities, using the updated version of fixed-t subtracted DRs formalism [8] as theoretical framework. Although the bootstrap method is rarely used in nuclear physics [16,[19][20][21][22], it has high potential and advantages [23]. In particular, we will show that it allows us to include the systematic errors in the data analysis in a straightforward way and to efficiently reconstruct the probability distributions of the fitted parameters. We will also pay a special attention to discuss the available sets of ...

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“…Instead of fixing the polarizability values, they can be fitted directly to the Σ 3 data. The fit was performed using only the new data on Σ 3 presented [8], blue dotted curve: HBChPT calculation [9], magenta dash-dotted curve: DR calculation [10], all fixing α E1 = 10.65 × 10 −4 fm −3 and β M1 = 3.15 × 10 −4 fm −3 [7]. Figure 3: Results of the fit within BChPT framework [8] obtained by averaging over angle and energy.…”

Section: Beam Asymmetry σmentioning

confidence: 99%

“…2 [7]. in this work [7] within the BChPT [8] and HBChPT [9] frameworks and it was constrained by Baldin sum rule. Figure 3 shows the BChPT result (very similar plot is obtained for the HBChPT fit).…”

Section: Beam Asymmetry σmentioning

confidence: 99%

Measurement of the proton scalar polarizabilities at MAMI

Mornacchi¹

2018

Proceedings of XVII International Conference on Hadron Spectroscopy and Structure — PoS(Hadron2017)

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The electric (α E1 ) and magnetic (β M1 ) scalar polarizabilities are fundamental properties related to the internal structure of the nucleon. They play a crucial role not only in our understanding of the nucleon, but also in other areas, such as atomic physics. In the past, the values of α E1 and β M1 were determined from the unpolarized differential cross-section of Compton scattering γ p → γ p. The measurement of the beam asymmetry Σ 3 provides an alternative approach to the extraction of the scalar polarizabilities with different sensitivity and systematics compared to the unpolarized cross-section. This asymmetry was measured for the first time below the pion photoproduction threshold by the A2 Collaboration with the Crystal Ball/TAPS experiment at MAMI (Mainz, Germany). A linearly polarized photon beam impinged on a liquid hydrogen target and the scattered photons were detected with the Crystal Ball/TAPS setup, providing almost 4π coverage. A new high precision measurement of both unpolarized cross-section and beam asymmetry Σ 3 will be performed in the near future and polarizabilities α E1 and β M1 will be extracted with unprecedented precision.

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Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ Σ 3 in Compton scattering

Cited by 27 publications

References 33 publications

Partial-wave analysis of proton Compton scattering data below the pion-production threshold

Partial-wave analysis of proton Compton scattering data below the pion-production threshold

Proton scalar dipole polarizabilities from real Compton scattering data using fixed-t subtracted dispersion relations and the bootstrap method

Measurement of the proton scalar polarizabilities at MAMI

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