First extraction of the scalar proton dynamical polarizabilities from real Compton scattering data

Pasquini, B.; Pedroni, P.; Sconfietti, S.

doi:10.1103/physrevc.98.015204

Cited by 20 publications

(32 citation statements)

References 54 publications

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“…This behavior was already observed in the extraction of the scalar dipole dynamical polarizabilities in Ref. [16]. We also note a large and negative (positive) correlation between γ π and β M 1 (α E1 ).…”

Section: Discussionsupporting

confidence: 85%

“…4. The scientific community has not reach so far a common agreement on the definition of the data set of proton RCS below pion-production threshold [16,24,25]. As pointed out in Ref.…”

Section: B Resultsmentioning

confidence: 99%

“…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.…”

mentioning

confidence: 96%

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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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Section: Discussionsupporting

confidence: 85%

“…4. The scientific community has not reach so far a common agreement on the definition of the data set of proton RCS below pion-production threshold [16,24,25]. As pointed out in Ref.…”

Section: B Resultsmentioning

confidence: 99%

mentioning

confidence: 96%

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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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“…The joint experimental and theoretical efforts in the last years have allowed us to identify a set of response functions that can be extracted from the Compton scattering process at different energy scales and in different kinematical conditions, and have a clear interpretation in terms of structure properties of the nucleon. Low-energy Compton scattering provides information on global as well as spatially resolved electromagnetic properties of the nucleon in terms of static and generalized polarizabilities, and, with increasing energy, allows us to study the effects of the nucleon excitation spectrum through dynamical (energy dependent) polarizabilities [104][105][106]. Furthermore, the variation of the initial photon virtuality Q 2 allows one to probe a wide range of distance scales, interpolating between hadronic degrees of freedom at low virtuality and partonic degrees of freedom at large virtuality.…”

Section: Theoretical Frontmentioning

confidence: 99%

Virtual Compton scattering and nucleon generalized polarizabilities

Fonvieille

Pasquini

Sparveris

2020

Progress in Particle and Nuclear Physics

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This review gives an update on virtual Compton scattering (VCS) off the nucleon, γ * N → N γ, in the low-energy regime. We recall the theoretical formalism related to the generalized polarizabilities (GPs) and model predictions for these observables. We present the GP extraction methods that are used in the experiments: the approach based on the low-energy theorem for VCS and the formalism of Dispersion Relations. We then review the experimental results, with a focus on the progress brought by recent experimental data on proton GPs, and we conclude by some perspectives in the field of VCS at low energy. Theoretical frameworkThis section reviews the formalism related to the nucleon GPs. We first outline some basic properties of polarizabilities and their generalization to finite Q 2 (Sect. 3.1). Then the main ingredients of the low-energy theorem in VCS are summarized in Sect. 3.2. A synthetic overview of model predictions for GPs is given in Sect. 3.3, and the DR formalism is presented in more details in Sect. 3.4. We then move closer to experimental aspects with Sects. 3.5 to 3.7. From real to virtual Compton scatteringThe polarizabilities of a composite object are fundamental characteristics of the system, just as its mass or shape. Among all the known properties of the nucleon, polarizabilities have the unique status of characterizing the nucleon dynamical response to an external electromagnetic (EM) field, describing how easy the charge and magnetization distributions inside the nucleon are distorted by the EM field. Real Compton scattering (RCS) experiments, performed since more than 50 years, have accumulated an 1 Note that this is up to a rotation of the leptonic plane by the azimuthal angle ϕ ′ e lab of the scattered electron. If specified, ϕ ′ e lab is then a sixth independent variable. 2 Other sets of variables are sometimes used, such as (k lab , k ′ lab , θ ′ e lab ) or (Q 2 , √ s, ǫ) for the leptonic vertex, and t instead of cos θ cm . 3 We also findQ = Q2 , andq 0cm defined in the Appendix. 4 This is for instance the case for all experimental values of Q 2 in Sect. 4. 2 qcm √ Q 2 q 0

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“…It has been suggested recently in a partial wave analysis of proton RCS data below the pion production threshold [25] that this difference might be a problem of the experimental database, see also refs. [26,27]. This could be further tested when the new RCS data become available [28,29,30].…”

Section: Nucleon Rcs and Polarisabilities In Bχptmentioning

confidence: 99%

Polarisabilities of the nucleon in baryon chiralperturbation theory and beyond

Lensky¹,

Pascalutsa²

2020

Proceedings of the 9th International Workshop on Chiral Dynamics — PoS(CD2018)

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We review the recent baryon chiral perturbation theory results for the nucleon polarisabilities that describe the different regimes of nucleon Compton scattering -real, virtual, and doubly virtual. We stress the importance of the empirical verification of the theory in the context of the calculation of the inelastic nucleon structure corrections, such as the two-photon exchange contributions. We also discuss the recently obtained constraints that relate the different regimes of nucleon Compton scattering and can provide additional information on the nucleon structure.

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First extraction of the scalar proton dynamical polarizabilities from real Compton scattering data

Cited by 20 publications

References 54 publications

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

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

Virtual Compton scattering and nucleon generalized polarizabilities

Polarisabilities of the nucleon in baryon chiralperturbation theory and beyond

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