Evaluation of the forward Compton scattering off protons: Spin-independent amplitude

Gryniuk, Oleksii; Hagelstein, Franziska; Pascalutsa, Vladimir

doi:10.1103/physrevd.92.074031

Cited by 36 publications

(68 citation statements)

References 29 publications

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“…We propose to widen the accessed energy range and improve on the precision of Based on the fits of the total photo-production cross section, by using a once-subtracted dispersion relation, we construct e[T ]. We discuss the impact of various fits for low- [44] and high-energy [45,46] data and argue the need for a new direct amplitude assessment. We present an estimate of the forward-backward asymmetry to the γp → e − e + p process for low values of momentum transfer −t and lepton pair mass M ll , which results from interchanging the leptons in the interference between the time-like Compton and the Bethe-Heitler mechanisms.…”

Section: Guzeymentioning

confidence: 99%

Nucleon and Nuclear Structure Through Dilepton Production

Anikin¹,

Baltzell²,

Boër³

et al. 2018

Acta Phys. Pol. B

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Transverse momentum distributions and generalized parton distributions provide a comprehensive framework for the three-dimensional imaging of the nucleon and the nucleus experimentally using deeply virtual semi-exclusive and exclusive processes. The advent of combined high luminosity facilities and large acceptance detector capabilities enables experimental investigation of the partonic structure of hadrons with time-like virtual probes, in complement to the rich on-going space-like virtual probe program. The merits and benefits of the dilepton production channel for nuclear structure studies are discussed within the context of the International Workshop on Nucleon and Nuclear Structure through Dilepton Production taking place at the European Center for Theoretical Studies in Nuclear Physics and Related Areas (ECT ) of Trento. Particularly, the double deeply virtual Compton scattering, the time-like Compton scattering, the deeply virtual meson production, and the Drell-Yan processes are reviewed and a strategy for high impact experimental measurements is proposed.PACS. 13.40-f Electromagnetic processes and properties -13.60.Fz Elastic and Compton scattering -13.60.Le Meson production a Corresponding author: voutier@ipno.in2p3.fr physics. After decades of theoretical and experimental efforts in elastic and deep inelastic lepton scatterings, a new formulation of the hadron structure [1-3] emerges that builds any hadron from the correlations between its inner partons. This powerful approach provides not only a tomographic image [4][5][6] of the nucleon and the nucleus, but also a comprehensive description of their internal dy-arXiv:1712.04198v2 [nucl-ex]

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Section: Guzeymentioning

confidence: 99%

Nucleon and Nuclear Structure Through Dilepton Production

Anikin¹,

Baltzell²,

Boër³

et al. 2018

Acta Phys. Pol. B

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“…In particular, we used the empirical amplitudes from the fit I of Refs. [35,49], that are tabulated from E γ = 50 MeV and correspond to α E1 + β M 1 = 14.29 ± 0.27 and γ 0 = −0.929 ± 0.105. We observe a remarkable agreement between the two analysis.…”

Section: Available Extractions Of Rcs Scalar Dipole Static Polarimentioning

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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“…The empirical evaluation of the forward amplitudes f (ν) and g(ν) for proton CS has recently been performed in [22] and [23], respectively. Thus, the sum rules provide two linear relations on the multipole amplitudes.…”

Section: B Linear Relations: Sum Rulesmentioning

confidence: 99%

“…However, a modelindependent Compton PWA has not done until now, mainly due to the lack of accurate data. The latter problem is compensated in our analysis by the recent empirical determination of the forward Compton amplitudes through the sum rules involving the photoabsorption cross sections [22,23]. The sum rules yield two independent linear relations between the multipole amplitudes at each energy.…”

Section: Introductionmentioning

confidence: 99%

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

2018

Self Cite

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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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Evaluation of the forward Compton scattering off protons: Spin-independent amplitude

Cited by 36 publications

References 29 publications

Nucleon and Nuclear Structure Through Dilepton Production

Nucleon and Nuclear Structure Through Dilepton Production

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

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

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