See, e.g., Abouzaid, et al., "A Measurement of the K0 Charge Radius and a CP Violating Asymmetry Together with a Search for CP Violating E1 Direct Photon Emission in the Rare Decay KL->pi+pi-e+e-", Phys. Rev. Lett. 96:101801 (2006) DOI: 10.1103/PhysRevLett.96.101801 https://arxiv.org/abs/hep-ex/0508010 (determining that the neutral kaon has a negative mean squared charge radius of -0.077 ± 0.007(stat) ± 0.011(syst)fm2).
Rutherford, E. (1911), „The Scattering of α and β Particles by Matter and the Structure of the Atom“, Phil. Mag., 6th Series, 21-jild, № 125, 669–88-bet, doi:10.1080/14786440508637080.
Antognini, A.; Nez, F.; Schuhmann, K.; Amaro, F. D.; Biraben, F.; Cardoso, J. M. R.; Covita, D. S.; Dax, A.; Dhawan, S. (2013). „Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen“. Science. 339-jild, № 6118. 417–420-bet. Bibcode:2013Sci...339..417A. doi:10.1126/science.1230016. PMID23349284.
Antognini, A.; Nez, F.; Schuhmann, K.; Amaro, F. D.; Biraben, F.; Cardoso, J. M. R.; Covita, D. S.; Dax, A.; Dhawan, S. (2013). „Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen“. Science. 339-jild, № 6118. 417–420-bet. Bibcode:2013Sci...339..417A. doi:10.1126/science.1230016. PMID23349284.
nih.gov
pubmed.ncbi.nlm.nih.gov
Antognini, A.; Nez, F.; Schuhmann, K.; Amaro, F. D.; Biraben, F.; Cardoso, J. M. R.; Covita, D. S.; Dax, A.; Dhawan, S. (2013). „Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen“. Science. 339-jild, № 6118. 417–420-bet. Bibcode:2013Sci...339..417A. doi:10.1126/science.1230016. PMID23349284.
See, e.g., J. Byrne, "The mean square charge radius of the neutron", Neutron News Vol. 5, Issue 4, pg. 15-17 (1994) (comparing different theoretical explanations for the neutronʼs observed negative squared charge radius to the data) DOI:10.1080/10448639408217664 http://www.tandfonline.com/doi/abs/10.1080/10448639408217664#.U3GYaPldVUA