SimpleCluster

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Latest version: v8317.00 | Compatible with: Pythia 8.317+ | Authors: Stephen Mrenna mrenna@fnal.gov

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Documentation

This plugin provides an alternate hadronization model based on the idea of cluster fragmentation. This model is home-grown and not as sophisticated as the developments to be found in Herwig and Sherpa -- hence the name SimpleCluster.

Package Description

The core idea is that hadronization should be as simple as possible. At the end of the parton shower, all gluons are split into quark-antiquark pairs carrying the large-N_c-limit color tags. Quarks and anti-quarks with matching color and anti-color tags are formed into color neutral clusters. These clusters subsequently undergo two-body decays to hadrons according to the given quantum numbers.

In practice, the sophisticated cluster models are far from simple, and a naive implementation will produce too many high-mass clusters. To alleviate this problem, fissioning of high-mass clusters into multiple low-mass ones is allowed.

In this implementation, a parton shower-like algorithm is used to transform the color singlet systems that exist at the end of the parton shower into quark-antiquark pairs. These pairs are then hadronized using the MiniString fragmentation implementation that already exists in Pythia.

Currently, a number of warnings are produced indicating that many MiniString clusters are too low in mass. In these cases, the hadronization is attempted again.

Since the event multiplicity is related to the number of quark-antiquark pairs, some work should be done on the gluon splitting algorithm. Some parameters, such quark masses might need to be adjusted. Finally, some aspects of the MiniString model might need to be reconsidered, especially for the case of heavy quark fragmentation.

The current implementation has been tested only for simple partonic final states. Junctions have not yet been explored.

Package Authors

Stephen Mrenna mrenna@fnal.gov

Package Dependencies

This package has no external dependencies other than Pythia 8.

How to use

Once you have checked-out the plugin, you must configure it to point to a Pythia8 installation.

./configure --with-pythia8=DESIRED_PYTHIA8_PATH

Then, build the plugin using:

make -j

To test the plugin, navigate to the examples directory:

cd share/SimpleCluster/examples/

Then, make and run:

make testPlugins
./testPlugins UserFrag.cmnd testPlugins.cmnd 

You can modify testPlugins.cmnd to explore other physics scenarios.

Any additional documentation will be added here.