![[DecayLanguage](https://github.com/scikit-hep/decaylanguage)](https://github.com/scikit-hep/decaylanguage/raw/master/images/DecayLanguage.png)

DecayLanguage implements a language to describe and convert particle decays between digital representations, effectively making it possible to interoperate several fitting programs. Particular interest is given to programs dedicated to amplitude analyses.

DecayLanguage provides tools to parse so-called .dec decay files, and manipulate and visualize decay chains.

Installation

Just run the following:

pip install decaylanguage

You can use a virtual environment through pipenv or with --user if you know what those are. Python 2.7 and 3.4+ are supported.

Usage

This is a quick user guide. For a full API docs, go here.

DecayLanguage is a set of tools for building and transforming particle decays. The parts are:

Particles

Particles are a key component when dealing with decays. Refer to the particle package for how to deal with particles and PDG identification codes.

Decay files

Decay .dec files can be parsed simply with

from decaylanguage import DecFileParser

parser = DecFileParser('my-decay-file.dec')
parser.parse()

# Inspect what decays are defined
parser.list_decay_mother_names()

# Print decay modes, etc. ...

A copy of the master DECAY.DEC file used by the LHCb experiment is provided here for convenience.

The DecFileParser class implements a series of methods giving access to all information stored in decay files: the decays themselves, particle name aliases, definitions of charge-conjugate particles, variable and Pythia-specific definitions, etc.

It can be handy to parse from a multi-line string rather than a file:

s = """Decay pi0
0.988228297   gamma   gamma                   PHSP;
0.011738247   e+      e-      gamma           PI0_DALITZ;
0.000033392   e+      e+      e-      e-      PHSP;
0.000000065   e+      e-                      PHSP;
Enddecay
"""

parser = DecFileParser.from_string(s)
parser.parse()

The class DecayChainViewer allows the visualization of parsed decay chains:

from decaylanguage import DecayChainViewer

# Build the D*+ decay chain representation setting the D+ and D0 mesons to stable,
# to avoid too cluttered an image
d = parser.build_decay_chain('D*+', stable_particles=['D+', 'D0'])
DecayChainViewer(d)  # works in a notebook

Decay modeling

The most common way to create a decay chain is to read in an AmpGen style syntax from a file or a string. You can use:

from decaylanguage.modeling import AmplitudeChain
lines, parameters, constants, states = AmplitudeChain.read_ampgen(text='''
EventType D0 K- pi+ pi+ pi-

D0[D]{K*(892)bar0{K-,pi+},rho(770)0{pi+,pi-}}                            0 1 0.1 0 1 0.1

K(1460)bar-_mass  0 1460 1
K(1460)bar-_width 0  250 1

a(1)(1260)+::Spline::Min 0.18412
a(1)(1260)+::Spline::Max 1.86869
a(1)(1260)+::Spline::N 34
''')

Here, lines will be a list of AmplitudeChain lines (pretty print supported in Jupyter notebooks), parameters will be a table of parameters (ranged parameters not yet supported), constants will be a table of constants, and states will be the list of known states (EventType).

Converters

You can output to a format (currently only GooFit supported, feel free to make a PR to add more). Use a subclass of DecayChain, in this case, GooFitChain. To use the GooFit output, type from the shell:

python -m decaylanguage -G goofit myinput.opts

Acknowledgements

DecayLanguage is free software released under a BSD 3-Clause License. It was originally developed by Henry Schreiner.

Changelog

Version 0.3.1 (2019-07-18)

• Parsing of decay files (aka .dec files):
  • Update to latest LHCb DECAY.DEC file.
• Visualisation of decay chains:
  • DecayChainViewer class made more robust.
  • Better tests.
• Miscellaneous:
  • Demo notebook updated.
  • README updated with latest package functionality.
  • Python wheels generation added.
  • Zenodo DOI badge added to README.

Version 0.3.0 (2019-06-26)

• Decays modelling:
  • Updates to Mint related particle data files.
• Parsing of decay files (aka .dec files):
  • Lark parser files added, for .dec decay files.
  • DecFileParser class introduced, with documentation and test suite.
  • Various .dec test decay files added.
• Visualisation of decay chains:
  • DecayChainViewer class introduced, with documentation and test suite.
• Universal representation of decay chains:
  • First "building block" classes DaughtersDict and DecayMode introduced, with documentation and test suite.
• Package dependencies:
  • Package made dependent on Scikit-HEP's Particle package.
  • Redundant code removed.
• Continuous integration:
  • CI with Azure pipelines introduced.
  • CI with Travis and AppVeyor removed.
• Miscellaneous:
  • Demo notebook added, with a launcher for Binder.
  • Copyright statements added to repository files.
  • General clean-up and minor bug fixes.

Version 0.2.0 (2018-08-02)

• First release as part of Scikit-HEP.
• Using new data package with importlib_resources (or importlib.resources on Python 3.7).
• Better docs and examples.
• Some method renaming.
• Generalized converter script.

Version 0.1.0 (2018-03-13)

• First release on PyPI.