Proton Charge Radius from Electron Scattering

Sick, I.

doi:10.3390/atoms6010002

Cited by 33 publications

(41 citation statements)

References 122 publications

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“…Interestingly, the data points below 0.01 GeV 2 do not contribute towards a strong statement (as anticipated in Ref. [18]). This is not immediately obvious from Fig.…”

Section: Introductionsupporting

confidence: 64%

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Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

Horbatsch

2020

Physics Letters B

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Recently published data on the Sachs electric form factor by the PRad collaboration (Nature 575, 147-151) are analyzed to investigate their consistency with the known proton charge radius from muonic and electronic hydrogen spectroscopy, as well as theoretical predictions from dispersively improved chiral perturbation theory. It is shown that the latter is fully consistent with the data, and pointers are given how future e − p scattering experiments can lead to an improvement of our knowledge of the form factor in the low-momentum-transfer regime. * marko@yorku.ca arXiv:1912.01735v4 [nucl-ex] 1 Feb 2020 R E = 0.879(8) fm. The radius R E enters the spectroscopic analysis via the slope of the Sachs electric form factor at zero momentum transfer squared Q 2 . The fact that hydrogen spectroscopy and e − p scattering are determining the same quantity is documented well in the literature [5].Since then, numerous efforts were undertaken to resolve the puzzle: (i) measurements on muonic deuterium [6] combined with the isotope shift, (ii) a fluorescence-based determination of the regular hydrogen 2S − 4P fine structure intervals [7], and (iii) a high-accuracy measurement of the Lamb shift in regular hydrogen [8] all pointed to a confirmation of the muonic hydrogen result; on the other hand (iv) a high-precision re-measurement of the 1S − 3S interval by the Paris group [9] continued to support the original higher value for the charge radius; this latter work is being contested by current fluorescence-detection work in Garching, which is achieving substantially higher precision.In more recent e − p scattering experiments both the Mainz group through a different method, based on intermediate-state radiation (ISR) [10] found consistency with the muonic charge radius (albeit with insufficient accuracy to make a strong case, so far), as did the PRad collaboration [11] which employed a gas jet target and measured projectile deflections directly.The situation still has the attention of both the spectroscopy and scattering communities, but the originally spread ideas that there could be new physics, i.e., that muons and electrons might behave differently have been damped by these developments.The significance of resolving the puzzle is not just academic, i.e., eventually, lattice gauge calculations within quantum chromodynamics will be able to compute at least certain aspects of the electric and magnetic form factors, and it will be good to have a solid understanding of the charge and current distributions of the proton based on experimental data. In addition, the determination of the charge radius leads to a significant change in the Rydberg constant

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“…Interestingly, the data points below 0.01 GeV 2 do not contribute towards a strong statement (as anticipated in Ref. [18]). This is not immediately obvious from Fig.…”

Section: Introductionsupporting

confidence: 64%

“…Different analyses of the MAMI data led authors to believe that the fourth moment r 4 should be of order 2.0 fm 4 or bigger [17,18]. Pure chiral perturbation theory (with pions, or with pions and Delta resonances as degrees of freedom) predicts values below 1.0 fm 4 [19].…”

Section: Introductionmentioning

confidence: 99%

Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

Horbatsch

2020

Physics Letters B

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“…The msr depends on a single-proton and a single-neutron size through the second and the third term of the above equation. They are not in a negligible order, but unfortunately, it seems that their experimental values are still under discussion [28]. We note, however, that their contributions to the msr is almost eliminated in taking the difference between the values for two nuclei, for example, in discussing isotope and isotone shift, or mirror nuclei.…”

Section: Relativistic Expression Of the N-th Order Momentmentioning

confidence: 83%

“…Finally, we note that a precise determination of the proton and the neutron size [28] is necessary for more detailed discussions of the moment as to the nuclear charge density.…”

Section: Discussionmentioning

confidence: 99%

The nth-order moment of the nuclear charge density and contribution from the neutrons

Kurasawa

Suzuki

2019

Progress of Theoretical and Experimental Physics

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The relativistic expression for the n-th order moment of the nuclear charge density is presented. For the mean square radius(msr) of the nuclear charge density, the non-relativistic expression, which is equivalent to the relativistic one, is also derived consistently up to 1/M 2 with use of the Foldy-Wouthuysen transformation. The difference between the relativistic and non-relativistic expressions for the msr of the point proton density is also discussed. The n( ≥ 4)-th order moment of the nuclear charge density depends on the point neutron density. The 4-th order moment yields a useful information on the msr of the point neutron density, and is expected to play an important role in electron scattering off neutron-rich nuclei. * kurasawa@faculty.chiba-u.jp accuracy, aiming to determine a small difference 0.03 ∼ 0.05 fm between the root mean square radii of point-proton and -neutron distributions [11]. In order to respond to these challenges, it is necessary for nuclear models to make clear a role of each element in the nuclear charge density. Although main contribution to the charge density comes from the point proton density, it is not obvious whether or not other elements are always negligible. One of the purposes of the present paper is to explore the contribution of each element in the nuclear charge density to the msr.Another purpose is to propose a complementary method to the previous ones[11] for investigating the neutron density of nuclei. It is one of the fundamental problems in nuclear physics how the protons and neutrons are distributed in nuclei. In contrast to the proton distribution, however, the neutron distribution is not well known yet, since there is no simple way to explore it experimentally. For example, in elastic electron scattering, the cross section is strongly dominated by the proton charge distribution, and the contribution from the neutrons is hidden behind the one from protons. As a result, it is hard to extract information on the neutron density by the analysis of the charge density profile. In hadron scattering [12], there is a different kind of difficulties. Although contributions to the cross section from neutrons and protons are comparable, they are not distinguishable from each other, because in the strong interaction, the reaction mechanism is not well understood, and the physical meaning of the parameters employed in the analyses is not obvious [11]. As a unique experiment to observe directly the neutron weak charge density, the measurement of the parity-violating asymmetry in the polarized-electron scattering has recently been performed [13,14]. It is a promising, but very difficult and time-consuming experiment. At present, the value of the form factor is available only for 208 Pb at a single value of the momentum transfer, q = 0.475 fm −1 , with the error of about 10%. Thus, it does not seem that the neutron density profiles are extracted soon from experiment without the help of nuclear models. In the present paper, it will be shown that instead of discussing the charge den...

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“…Although great theoretical and experimental efforts have been devoted to improving our knowledge of the nucleon structure, there are several unsolved problems associated with fundamental properties of the proton and neutron. The proton radius puzzle, where highprecision measurements of the proton's electric charge radius from the muonic hydrogen Lamb shift [2,3] disagree with well established results of both electron-proton scattering and hydrogen spectroscopy [4], is currently one of the most intriguing problems in this field [5]. The neutron lifetime puzzle, where the discrepancy between the results of beam experiments and storage experiments remains unsolved, is another open question that deserves further investigation in terms of the nucleon axial-vector coupling g A [6].…”

Section: Introductionmentioning

confidence: 99%

Nucleon form factors on a large volume lattice near the physical point in 2+1 flavor QCD

et al. 2018

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We present results for the isovector nucleon form factors measured on a 96 4 lattice at almost the physical pion mass with a lattice spacing of 0.085 fm in 2+1 flavor QCD. The configurations are generated with the stout-smeared O(a)-improved Wilson quark action and the Iwasaki gauge action at β=1.82. The pion mass at the simulation point is about 146 MeV. A large spatial volume of (8.1 fm) 3 allows us to investigate the form factors in the small momentum transfer region. We determine the isovector electric radius and magnetic moment from nucleon electric (GE) and magnetic (GM ) form factors as well as the axial-vector coupling gA. We also report on the results of the axial-vector (FA), induced pseudoscalar (FP ) and pseudoscalar (GP ) form factors in order to verify the axial Ward-Takahashi identity in terms of the nucleon matrix elements, which may be called as the generalized Goldberger-Treiman relation.

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Proton Charge Radius from Electron Scattering

Cited by 33 publications

References 122 publications

Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

The nth-order moment of the nuclear charge density and contribution from the neutrons

Nucleon form factors on a large volume lattice near the physical point in 2+1 flavor QCD

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Proton Charge Radius from Electron Scattering

Cited by 33 publications

References 122 publications

Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

The nth-order moment of the nuclear charge density and contribution from the neutrons

Nucleon form factors on a large volume lattice near the physical point in 2+1 flavor QCD

Contact Info

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Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy

Properties of the Sachs electric form factor of the proton on the basis of recent e − p scattering experiments and hydrogen spectroscopy