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Subject: Electron-proton scattering and its role in the proton charge radius puzzle
Speaker:    Marko Horbatsch
York University - Toronto
Date: Friday, December 8, 2017
Time: 11:00 a.m.
Place: CEBAF Center Auditorium
Abstract:Following the very accurate determination of the proton charge radius from the muonic hydrogen Lamb shift previous results from regular hydrogen spectroscopy, as well as the 2010 MAMI e-p scattering analysis were put in question. With recent further spectroscopic evidence from muonic deuterium, and more recently from the regular H(2S-2P) interval it appears that the e-p scattering analysis has to be revisited. After an introduction to the problem a new analysis of MAMI data at intermediate momentum transfer squared (covering up to 70% of the entire set of cross sections) will be presented. This analysis uses information from chiral perturbation theory on higher moments of the electric and magnetic form factors. It reveals that the small charge radius value (0.84 fm) is not excluded by the data and that our derived value for the magnetic charge radius is consistent with the MAMI analysis. It is also shown how using fits with many parameters in this region can lead to a preference for a larger charge radius and larger quartic electric moment, as found by other analyses.

The present work extends findings from several re-analyses at lowest momentum transfer (which agree with the small radius value) to a wider range of MAMI data.


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