[PWGLF] Add finite-width resonance injection and particle definitions

[mjkim525]

This PR adds finite-width support for injected resonances in pp at $\sqrt{s}=13.6$ and $5.36$ TeV with Pythia8.

It also introduces configuration files containing additional particle-data definitions and the resonance lists used for injection.

Additional particle-data definitions

generator_pythia8_LF_rapidity_width.C extends the existing LF resonance-injection implementation by loading the additional particle definitions into both:

• mPythia, which owns the particle-data table used by the combined minimum-bias and injected event; and
• mPythiaGun, which is used to generate and decay the injected resonances.

This initialization is implemented at lines 155–170. The helper function that extracts the particle-data entries from the configuration and loads them into the Pythia objects is implemented at lines 586–629.

When a minimum-bias event is copied into the event used for resonance injection, its particle-data pointer is explicitly rebound to the particle-data table owned by mPythia. This is implemented at lines 578–584.

This rebinding is required for custom resonances that are not included in Pythia’s default particle database, such as $\Xi(1820)$ and $\Omega(2012)$. Without it, copied particles may no longer be associated with valid particle definitions. Consequently, the injected particles can remain with status code 11 and may not be propagated correctly to the AO2D output.

Finite-width mass sampling

Previously, the masses of injected resonances were always taken as fixed values from the generator configuration. As a result, the generated invariant-mass distributions did not reflect the physical decay widths of the resonances.

The new sampleMass() implementation, located at lines 515–527, uses Pythia’s ParticleData::mSel() function whenever a nonzero particle width is defined.

The sampled mass is then used when constructing the injected particles at:

• lines 282–308; and
• lines 392–409.

Consequently, the generated mass distributions now reflect the mass and width information stored either:

• in Pythia’s built-in particle database; or
• in the additional particle definitions supplied through the new configuration files.

The following plot shows the results of the local tests performed with the updates introduced in this PR with pp 13.6 TeV.

Note that $\Omega(2012)$ PDG code is assumed 123334, following previous studies such as [the Run 2 result] (https://journals.aps.org/prd/abstract/10.1103/v4mh-3r8z)

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[mjkim525]

Helper function for sampling the injected resonance mass

[mjkim525]

Use the sampled mass when constructing generator-decayed injected particles

[mjkim525]

Use the same mass-sampling prescription for transport-decayed injected particles

[mjkim525]

Rebind the copied event to mPythia’s particle-data table so that custom particle definitions remain accessible.