Reinterpretation of Classic Proton Charge Form Factor Measurements

Mihovilovič, M.; Higinbotham, D. W.; Bevc, Melisa; Širca, S.

doi:10.3389/fphy.2020.00036

“…Apparent discrepancies between the different extraction methods (the "proton radius puzzle") have engendered intense experimental and theoretical efforts, including dedicated new elastic scattering experiments at low Q 2 with electron and muon beams [11,12]. Most recent experiments and reanalyses have converged around r p E = 0.84 fm [11,[13][14][15][16][17][18][19][20][21][22][23][24], while some have obtained larger values [25][26][27][28]; the CODATA Task Group and the Particle Data Group have now adopted 0.84 fm as the recommended value [29,30]. The proton magnetic radius can only be extracted from elastic FF measurements (a method using atomic measurements was proposed in Ref.…”

Section: Introductionmentioning

confidence: 99%

Precise determination of the proton magnetic radius from electron scattering data

Alarcón

¹

,

Higinbotham

²

,

Weiß

³

2020

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We extract the proton magnetic radius from high-precision electron-proton elastic scattering cross section data. Our theoretical framework combines dispersion analysis and chiral effective field theory and implements the dynamics governing the shape of the low-Q 2 form factors. It allows us to use data up to Q 2 ≈ 0.5 GeV 2 for constraining the radii and overcomes the difficulties of empirical fits and Q 2 → 0 extrapolation. We obtain a magnetic radius r p M = 0.850 ± 0.001 (1σ fit uncertainty) +0.009 −0.004 (full-range theory uncertainty) fm, significantly different from earlier results obtained from the same data using empirical fits, and close to our extracted electric radius r p E = 0.842 ± 0.002 (1σ fit uncertainty) +0.005 −0.002 (full-range theory uncertainty) fm.

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“…This discrepancy triggered the "proton radius puzzle" [4,5]. The puzzle prompted new scattering experiments [6,7,8] and numerous reanalyses of existing electron scattering data [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23].…”

Section: Introductionmentioning

confidence: 99%

Elastic positron–proton scattering at low Q$$^2$$

Hague

¹

,

Dutta

²

,

Higinbotham

³

et al. 2021

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Systematic differences in the the proton's charge radius, as determined by ordinary atoms and muonic atoms, have caused a resurgence of interest in elastic lepton scattering measurements. The proton's charge radius, defined as the slope of the charge form factor at Q 2 =0, does not depend on the probe. Any difference in the apparent size of the proton, when determined from ordinary versus muonic hydrogen, could point to new physics or need for the higher order corrections. While recent measurements seem to now be in agreement, there is to date no high precision elastic scattering data with both electrons and positrons. A high precision proton radius measurement could be performed in Hall B at Jefferson Lab with a positron beam and the calorimeter based setup of the PRad experiment. This measurement could also be extended to deuterons where a similar discrepancy has been observed between the muonic and electronic determination of deuteron charge radius. A new, high precision measurement with positrons, when viewed alongside electron scattering measurements and the forthcoming MUSE muon scattering measurement, could help provide new insights into the origins of the proton radius puzzle, and also provide new experimental constraints on radiative correction calculations.

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“…Apparent discrepancies between the different extraction methods (the "proton radius puzzle") have engendered intense experimental and theoretical efforts, including dedicated new elastic scattering experiments at low Q 2 with electron and muon beams [11,12]. Most recent experiments and reanalyses have converged around r p E = 0.84 fm [11,[13][14][15][16][17][18][19][20][21][22][23][24], while some have obtained larger values [25][26][27][28]; the CODATA Task Group and the Particle Data Group have now adopted 0.84 fm as the recommended value [29,30]. The proton magnetic radius can only be extracted from elastic FF measurements (a method using atomic measurements was proposed in Ref.…”

Section: Introductionmentioning

confidence: 99%

Precise determination of proton magnetic radius from electron scattering data

Alarcón¹,

Higinbotham²,

Weiß³

2020

IWHSS 2020 (17th International Workshop on Hadron Structure and Spectroscopy), Trieste, Italy (Virtual), November 16, 2020

0

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We extract the proton magnetic radius from high-precision electron-proton elastic scattering cross section data. Our theoretical framework combines dispersion analysis and chiral effective field theory and implements the dynamics governing the shape of the low-Q 2 form factors. It allows us to use data up to Q 2 ≈ 0.5 GeV 2 for constraining the radii and overcomes the difficulties of empirical fits and Q 2 → 0 extrapolation. We obtain a magnetic radius r p M = 0.850 ± 0.001 (1σ fit uncertainty) +0.009 −0.004 (full-range theory uncertainty) fm, significantly different from earlier results obtained from the same data using empirical fits, and close to our extracted electric radius r p E = 0.842 ± 0.002 (1σ fit uncertainty) +0.005 −0.002 (full-range theory uncertainty) fm.

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Reinterpretation of Classic Proton Charge Form Factor Measurements

Cited by 7 publications

References 44 publications

Precise determination of the proton magnetic radius from electron scattering data

Precise determination of the proton magnetic radius from electron scattering data

Elastic positron–proton scattering at low Q$$^2$$

Precise determination of proton magnetic radius from electron scattering data

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