Jet Reconstruction ​

This package implements sequential Jet Reconstruction (clustering) algorithms, which are used in high-energy physics as part of event reconstruction for $pp$ and $e^{+}{e}^{-}$ colliders.

Algorithms ​

Algorithms used are based on the C++ FastJet package (https://fastjet.fr, hep-ph/0512210, arXiv:1111.6097), reimplemented natively in Julia.

The algorithms include $\text{anti}-k_{\text{T}}$, Cambridge/Aachen and inclusive $k_{\text{T}}$.

Reconstruction Interface ​

The main interface for reconstruction is jet_reconstruct, called as, e.g.,

jet_reconstruct(particles; p = -1, R = 1.0)

Where particles is a collection of 4-vector objects to reconstruct.

The object returned is a ClusterSequence, which internally tracks all merge steps.

Strategy ​

Three strategies are available for the different algorithms:

Generally one can use the jet_reconstruct interface, shown above, as the Best strategy safely as the overhead is extremely low. That interface supports a strategy option to switch to a different option.

Another option, if one wishes to use a specific strategy, is to call that strategy's interface directly, e.g.,

# For N2Plain strategy called directly
plain_jet_reconstruct(particles::Vector{T}; p = -1, R = 1.0, recombine = +)

Note that there is no strategy option in these interfaces.

Inclusive and Exclusive Selections ​

To obtain final jets both inclusive ($p_T$ cut) and exclusive ($n_{jets}$ or $d_{ij}$ cut) selections are supported:

• inclusive_jets(clusterseq::ClusterSequence, ptmin = 0.0)

• exclusive_jets(clusterseq::ClusterSequence; dcut = nothing, njets = nothing)

Sorting ​

Sorting vectors is trivial in Julia, no special sorting methods are provided. As an example, to sort exclusive jets of $>5.0$ (usually GeV, depending on your EDM) from highest energy to lowest:

sorted_jets = sort!(inclusive_jets(cs::ClusterSequence; ptmin=5.0), 
  by=JetReconstruction.energy, rev=true)

Plotting and Animation ​

To visualise the clustered jets as a 3d bar plot (see illustration above) we now use Makie.jl. See the jetsplot function in ext/JetVisualisation.jl and its documentation for more. There are two worked examples in the examples directory.

The plotting code is a package extension and will load if the one of the Makie modules is loaded in the environment.

The animatereco function will animate the reconstruction sequence, given a ClusterSequence object. See the function documentation for the many options that can be customised.

Serialisation ​

The package also provides methods such as loadjets, loadjets!, and savejets that one can use to save and load objects on/from disk easily in a very flexible format. See documentation for more.

Reference ​

Although it has been developed further since the CHEP2023 conference, the CHEP conference proceedings, 10.1051/epjconf/202429505017, should be cited if you use this package:

@article{refId0,
    author = {{Stewart, Graeme Andrew} and {Gras, Philippe} and {Hegner, Benedikt} and {Krasnopolski, Atell}},
    doi = {10.1051/epjconf/202429505017},
    journal = {EPJ Web of Conf.},
    pages = {05017},
    title = {Polyglot Jet Finding},
    url = {https://doi.org/10.1051/epjconf/202429505017},
    volume = 295,
    year = 2024,
    eprint={2309.17309},
    archivePrefix={arXiv},
    primaryClass={hep-ex}
}

The original paper on arXiv is:

@misc{stewart2023polyglot,
      title={Polyglot Jet Finding}, 
      author={Graeme Andrew Stewart and Philippe Gras and Benedikt Hegner and Atell Krasnopolski},
      year={2023},
      eprint={2309.17309},
      archivePrefix={arXiv},
      primaryClass={hep-ex}
}

Authors and Copyright ​

Code in this package is authored by:

• Atell Krasnopolski <delta_atell@protonmail.com>

• Graeme A Stewart <graeme.andrew.stewart@cern.ch>

• Philippe Gras <philippe.gras@cern.ch>

and is Copyright 2022-2024 The Authors, CERN.

The code is under the MIT License.