CMPPlugin 
=========

/// Implementation of the CMP flavoured anti-kt algorithm

This code provides an implementation of the flavoured anti-kt algorithm
from

> Infrared-safe flavoured anti-kT jets,
> by Michal Czakon, Alexander Mitov and Rene Poncelet
> https://arxiv.org/pdf/2205.11879 (v2)

including modifications to ensure IR-safety suggested in

> Flavoured jets with exact anti-kt kinematics and tests of infrared and collinear safety,
> by Fabrizio Caola, Radoslaw Grabarczyk, Maxwell Hutt, Gavin P. Salam, Ludovic Scyboz, and Jesse Thaler
> https://arxiv.org/abs/2306.07314

To learn how to use the library, the [`example-CMP.cc`](example-CMP.cc) code is
a good place to get started.

Main principles of CMP
----------------------

The CMP algorithm provides a anti-kT-like flavour safe jet clustering algorithm.
IR safety is ensured through a modified pseudojet distance for "soft"
flavour-anti-flavour pairs. Through this modification the clustering sequence is
not exactly anti-kT. The modification can be steered by a parameter a (the limit
a->0 recovers the IR flavour unsafe anti-kT algorithm).

Code Structure
--------------

The main interface to the CMP algorithm is in [`CMPPlugin.hh`](CMPPlugin.hh):
```cpp
// create an CMPPlugin for a given a  and jetradius R
double a = 0.1;
double R = 0.4;
JetDefinition jet_def(new CMPPlugin(R,a));
jet_def.delete_plugin_when_unused();
```

The plugin can be used as standard with the FastJet package, e.g.:
```cpp
vector<PseudoJet> particles;
// ... fill the particles ...
auto jets = jet_def(particles);
for (const auto & jet : jets) {
  cout << "jet pt = " << jet.pt() 
       << ", flav = " << FlavHistory::current_flavour_of(jet) << endl;
}
```