ASCIIEventTree

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Latest version: v8317 | Compatible with: Pythia 8.310+ | Authors: Christian Bierlich christian.bierlich@fysik.lu.se 0000-0002-3978-6085

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ASCIIEventTree

A PYTHIA 8 plugin that renders the event record as an ASCII decay tree after each fully-generated event. Uses box-drawing characters to show parent-daughter relationships and supports filtering of parton-shower copy chains, deduplication of shared particles, and annotation of multi-body production vertices.

Bierlich, Christian christian.bierlich@fysik.lu.se

Overview

The ASCIIEventTree plugin prints a human-readable ASCII tree structure of the PYTHIA 8 event record, including:

• Tree structure: Full decay chain from primary beam particles to final-state hadrons.
• Particle information: Name, event-record index, and PDG id for each particle.
• Copy suppression: Optionally collapse single-daughter same-id parton-shower chains (e.g., q → q → q → ... becomes q → ...).
• Deduplication: Optionally print each particle index at most once; repeated occurrences show a cross-reference stub.
• Vertex annotation: Optionally flag multi-body production vertices (hard scatters, string fragmentation, etc.) with {2->N: parent1 + parent2} labels.

Settings

All settings have the prefix ASCIIEventTree:.

• enabled (flag, default off): Enable or disable ASCII tree output.
• nFirst (mode, default 1, range [-1, ∞)): Number of events for which to print the tree. -1 = all events; 0 = none; N > 0 = first N events.
• suppressCopies (flag, default off): Collapse parton-shower copy chains.
• deduplicateShared (flag, default off): Print each particle index at most once.
• markVertices (flag, default off): Annotate multi-body production vertices.

Usage

Load the plugin and configure settings via a command file:

Init:plugins = {libASCIIEventTree.so::EventHooks}
ASCIIEventTree:enabled = on
ASCIIEventTree:nFirst = 10

Run the test program:

./testPlugins ASCIITree-ee.cmnd

Example Output

┌─ Event 1 (192 entries) ─────────────────
├── e- [idx = 1, pid = 11]
│   └── e- [idx = 6, pid = 11]
│       ├── gamma [idx = 9, pid = 22]
│       └── e- [idx = 3, pid = 11]
│           └── Z0 [idx = 8, pid = 23]
│               ├── u [idx = 40, pid = 2]
│               │   └── u [idx = 69, pid = 2]
│               │       ├── rho0 [idx = 74, pid = 113]  {2->N: u + ubar}
│               │       │   ├── pi+ [idx = 121, pid = 211]
│               │       │   └── pi- [idx = 122, pid = -211]
│               │       └── ...
│               └── ubar [idx = 45, pid = -2]
│                   ├── ↩ rho0 [idx = 74, pid = 113]  (see above)
│                   └── ...

• PYTHIA 8 documentation: https://pythia.org/
• Plugin system: See share/Pythia8/xmldoc/Plugins.xml in the PYTHIA 8 source.