Proton radius extraction from transverse charge density

This repository contains all of the code and data necessary to generate the full analysis and plots of our paper:

A. V. Gramolin and R. L. Russell, "Transverse charge density and the radius of the proton", Phys. Rev. D 105, 054004 (2022)

All of the data analyzed come from the A1 Collaboration at Mainz, described in:

J. C. Bernauer et al. (A1 Collaboration), Phys. Rev. Lett. 105, 242001 (2010)
J. C. Bernauer et al. (A1 Collaboration), Phys. Rev. C 90, 015206 (2014)

Requirements

Our analysis scripts require Python 3.6 or above. The Python package dependencies can be installed via:

> pip3 install -r requirements.txt

Running the code

The fit.py script runs the full analysis described in the paper including cross-validation. You can change the model order and regularization parameter from the default "best-fit" ones by command line arguments. Use the --help flag to see how to pass the arguments:

> python3 fit.py --help
usage: fit.py [-h] [--order ORDER] [--reg_param REG_PARAM]

Fit and validate models to cross section data.

optional arguments:
  -h, --help              show this help message and exit
  --order ORDER           order of form factor expansion (default: N=5)
  --reg_param REG_PARAM   regularization parameter (default: lambda=0.02)

You can regenerate all of the plots used in the paper and supplemental material by running the plot.py script.