README.md

Comparison repository for GlueX amplitude models

This repository was created during PWA working group meetings for GlueX at Jefferson Lab, July 31st to August 4th, 2023. Live notes for these discussions can be found here on HackMD. Each meeting was organised like a 'hackathon' and the results of these programming sessions can be found on compwa.github.io/gluex-amplitude.

The main target for the week was to implement a simple intensity function for two-pseudoscalar system with photo-production:

where $Z_{l}^{m}(\Omega,\Phi)=Y_{l}^{m}(\Omega)e^{-i\Phi}$ is a phase-rotated spherical harmonic, $\Omega$ is the solid angle, $\Phi$ is the angle between the production and polarization planes, $P_{\gamma}$ is the polarization magnitude, $[l]$ are the partial wave amplitudes, $m$ is the associated m-projection, $k$ refers to a spin flip ($k=1$) or non-flip ($k=0$) at the nucleon vertex, and $\kappa$ is an overall phase space factor.

The details for this model have been worked out in 10.1103/PhysRevD.100.054017 (2019).

The amplitude model is implemented in AmpTools and symbolically in Python using SymPy with additional tools from amptools (ComPWA Project). Dynamics are not yet included (model-indepedent by binning over energy). So we are just comparing linar combinations of spherical harmonics, but the comparison can be extended by investigating final states with a vector meson and/or parametrizing dynamic lineshapes.

Installation

C++ implementation

This repository comes with AmpTools as a submodule. If you clone this repository as:

git clone https://github.com/compwa/gluex-amplitude --recurse-submodules

you should get AmpTools as well. Navigate to extern/AmpTools for further build instructions. Additionally, you need to have ROOT installed. Official installation instructions can be found here, but alternatively, you can install ROOT in your conda environment (see Python implementation) as follows:

conda activate gluex-amplitude
conda install root -c conda-forge

The benefit of AmpTools as a sub-module and installing ROOT into the conda environment is that you have out-of-the-box language navigation in VSCode.

To build all source code, you first need to compile AmpTools. Either do this by cloning AmpTools and following the instructions, or with:

cd extern/AmpTools
make

You can then compile the code for this repository by navigating back to the root directory (cd ../../) and running:

make

Python implementation

Install Conda (recommended: Miniconda), then just create a Conda environment from environment.yml:

conda env create
conda activate gluex-amplitude
pre-commit install --install-hooks  # optional

The Python implementation mainly consists of Jupyter notebooks located under the docs folder. It's best to view, run, and edit them with VSCode or with

jupyter lab

You can also run all notebooks and render them as static HTML pages with Jupyter Book as follows:

jb build docs/ -W

Open docs/_build/html/index.html to view the resulting HTML pages. In VSCode, you can view the output HTML files by searching for "Live Preview: Start Server" through the command pallette (Ctrl+Shift+P).