Aligned polarimetry field of the Λc → p π K decay

This repository contains the source code for “$\Lambdac^+$ polarimetry using the dominant hadronic mode” (2023) by the LHCb Collaboration (10.1007/JHEP07(2023)228). It uses ampform-dpd to formulate symbolic amplitude models for the decay $\Lambda^+c \to p \pi^+ K^-$ that are aligned with Dalitz-plot decomposition. The aligned amplitudes are used to compute polarimeter vector field $\vec\alpha$ over the Dalitz plane. Helicity couplings and other parameter values are taken from a recent study by the LHCb Collaboration[^1] and its supplementary material.

[^1]: Amplitude analysis of the $\Lambda^+c \to p K^- \pi^+$ decay and $\Lambda^+c$ baryon polarization measurement in semileptonic beauty hadron decays (2022) [link]

Installation

All the dependencies required to work on this Repository are managed by Pixi. If you have installed Pixi, you can simply start developing by activating the environment with:

shell pixi shell

This will install uv for managing Python and its dependencies as well as Julia. Then it activates the environment and you can start developing.

Common checks are defined under pixi.toml and can be listed with

shell pixi task list

For example, you build the documentation with executed notebooks with

shell pixi run docnb

Style checks are enforced with Pre-commit. You should install this system-wide once, for instance through uv:

shell uv tool install --with pre-commit-uv pre-commit

You can then install the Git hooks for this repository, so that the checks are run automatically before each commit:

shell pre-commit install

[!TIP] For more information about the local Python developer environment, see here.

This repository also contains Julia source code and Pluto notebooks. Julia can be downloaded here. You then have to activate and instantiated the Julia environment provided in the julia folder. This can be done as follows from the root directory:

shell julia --project=./julia -e 'import Pkg; Pkg.instantiate()'

Documentation dependencies

To build the documentation, you need to install LaTeX and some additional fonts. In Ubuntu, this can be done with:

shell sudo apt-get install -y cm-super dvipng texlive-latex-extra

In addition, for building the documentation as a single PDF file, you need to install XeTeX:

shell sudo apt-get install -y inkscape latexmk make texlive-fonts-extra texlive-xetex xindy

Building the documentation

Having installed the Python environment, you can build the documentation with:[^2]

shell pixi run docnb

This will run all Jupyter notebooks and convert the output to static webpages (view the output under docs/_build/html/index.html). Running all notebooks from scratch (without any available cache) should take around one hour.

If you have installed Julia and instantiated the Julia environment, you can embed the Pluto notebooks as static pages in the documentation with:

shell pixi run docnb-pluto

or, alternatively, by executing all Jupyter and Pluto notebooks (ignoring any existing caches):

shell pixi run docnb-pluto-force

The above commands result in a static HTML webpage. It's also possible to render the notebook as a single PDF file. This can be done as follows:

shell pixi run pdf

Just as above, cell output can be rendered by appending nb:

shell pixi run pdfnb

[^2]: It's also possible have a look at the documentation without cell output (just as a check for the links). This can be done with:

```shell
pixi run doc
```