Reduction of the proton radius discrepancy by 3σ

Physical Review D, 2014

We combine constraints from analyticity with experimental electron-proton scattering data to determine the proton magnetic radius without model-dependent assumptions on the shape of the form factor. We also study the impact of including electron-neutron scattering data, and ππ → NN data. Using representative datasets we find for a cut of Q 2 ≤ 0.5 GeV 2 , r p M = 0.91 +0.03 −0.06 ± 0.02 fm using just proton scattering data; r p M = 0.87 +0.04 −0.05 ± 0.01 fm adding neutron data; and r p M = 0.87 +0.02 −0.02 fm adding ππ data. We also extract the neutron magnetic radius from these data sets obtaining r n M = 0.89 +0.03 −0.03 fm from the combined proton, neutron, and ππ data.

EPJ Web of Conferences

Higher-order QED radiative corrections to elastic electron-proton scattering are discussed. It is shown that they are relevant for high-precision experiments on proton form factor measurements. Analytic result are obtained for next-to-leading second order corrections to the electron line. Light pair corrections are taken into account. The role of the hadronic contribution to vacuum polarization is discussed. Numerical results are given for the conditions of the experiment on proton form factors performed by A1 Collaboration. Preliminary results are also shown for the set-up with reconstruction of momentum transfer from the recoil proton momentum.

Physics Letters B, 2000

Recent values of the proton charge radius derived from the Lamb shift in electronic hydrogen tend to be larger than those from electron scattering. Therefore low-momentum-transfer scattering data from different groups and laboratories have been reanalyzed with Coulomb and recoil corrections included. This was done by calculating at each scattering angle and scattering energy the corresponding correction obtained from a partial wave program which includes recoil approximately. Corrections due to magnetic scattering were also made before the rms-radius was determined by a fit which allows free normalization for each experiment. It is shown that an analysis of electron scattering data including Coulomb corrections lowers the χ 2 of the fit and increases the proton radius by about (0.008 − 0.013) fm depending on the fit strategy. A value of r p = 0.880 (15) fm is obtained which is in good agreement with the one extracted from Lamb shift measurements.

The recent values of the proton charge radius obtained by means of muonic-hydrogen laser spectroscopy are about $4\%$ different from the electron scattering data. It has been suggested that the proton radius is actually measured in different frames and that, starting from a non relativistic quark model calculation, the Lorentz transformation of the form factors accounts properly for the discepancy. We shall show that the relation between the charge radii measured in different frames can be determined on very general grounds by taking into account the Lorentz transformation of the charge density. In this way, the discrepancy between muonic-hydrogen laser spectroscopy and electron scattering data can be removed.

Physical Review C

To extract the charge radius of the proton, r p , from the electron scattering data, the PRad collaboration at Jefferson Lab has developed a rigorous framework for finding the best functional forms-the fitters-for a robust extraction of r p from a wide variety of sample functions for the range and uncertainties of the PRad data. In this paper we utilize and further develop this framework. Herein we discuss methods for searching for the best fitter candidates as well as a procedure for testing the robustness of extraction of the deuteron charge radius, r d , from parametrizations based on elastic electron-deuteron scattering data. The ansatz proposed in this paper for the robust extraction of r d , for the proposed low-Q 2 DRad experiment at Jefferson Lab, can be further improved once there are more data.

arXiv (Cornell University), 2017

High-precision measurements of the proton radius from laser spectroscopy of muonic hydrogen demonstrated up to six standard deviations smaller values than obtained from electron-proton scattering and hydrogen spectroscopy. The status of this discrepancy, which is known as the "proton radius puzzle" will be discussed in this paper, complemented with the new insights obtained from spectroscopy of muonic deuterium.

Bulletin of the American Physical Society, 2015

The proton is a fundamental constituent of matter. It is an extended object with finite size that can be inferred with some degree of accuracy from several measurements. Using constraints from the analytic behavior of the form factors we present here a model-independent study that extracts the proton magnetic radius from scattering data. From electronproton scattering data we find r M = 0.91 +0.03 −0.06±0.02 fm. When we include electron-neutron scattering data and ππ data, we find r M = 0.87 +0.04 −0.05±0.01 fm and r M = 0.87 +0.02 −0.02 fm respectively. The neutron magnetic radius is extracted as r M = 0.89 +0.03 −0.03 fm combining all three data sets.

2013

The Proton Radius Puzzle is the inconsistency between the proton radius determined from muonic hydrogen and the proton radius determined from atomic hydrogen level transitions and ep elastic scattering. No generally accepted resolution to the Puzzle has been found. Possible solutions generally fall into one of three categories: the two radii are different due to novel beyond-standardmodel physics, the two radii are different due to novel aspects of nucleon structure, and the two radii are the same, but there are underestimated uncertainties or other issues in the ep experiments.

2019

The proton charge radius can be determined by measuring the slope of the electric form-factor $G_E$ at small four-momentum transfer squared $Q^2$. Numerous elastic-scattering and laser-spectroscopy measurements of the proton radius have been performed with contradicting results, often referred to as the proton-radius puzzle. We propose to measure the proton charge radius in high-energy elastic muon-proton scattering at the M2 beam line of CERN's Super Proton Synchrotron (SPS) in 2022. A high-precision measurement at low $Q^2$, performed with a high-pressure hydrogen-filled time-projection chamber (TPC), can contribute to the resolution of the puzzle, especially due to the different systematic effects of this approach compared to those of electron-proton scattering. In 2018, we performed a test measurement with silicon tracking detectors up- and downstream of a prototype TPC to study the feasibility of the measurement concept. We present initial results of the on-going analysis o...

The European Physical Journal A, 2012

We analyze the recent electron-proton scattering data from Mainz using a dispersive framework that respects the constraints from analyticity and unitarity on the nucleon structure. We also perform a continued fraction analysis of these data. We find a small electric proton charge radius, r p E = 0.84 +0.01 -0.01 fm, consistent with the recent determination from muonic hydrogen measurements and earlier dispersive analyses. We also extract the proton magnetic radius, r p M = 0.86 +0.02 -0.03 fm, consistent with earlier determinations based on dispersion relations.