Photon Fragmentation Functions
Extracting effective photon fragmentation functions from PYTHIA parton showers and distributing them as LHAPDF grids, for use in prompt-photon predictions.
Photon fragmentation functions describe the production of photons through the fragmentation of energetic quarks and gluons, and are a necessary ingredient in theoretical predictions for prompt-photon production once experimental isolation criteria are applied. Traditional parametrizations (BFG, GRV, GDRG) date back to fixed-order fits and are only weakly constrained by data.
This project investigates the extraction of effective photon fragmentation
functions directly from the PYTHIA parton shower, via a dedicated
Rivet analysis (MC_PHOTONFRAGMENTATION)
that records the flavour-dependent fragmentation distributions as a
function of the photon momentum fraction and fragmentation scale,
separately for quark and gluon channels. The resulting shower-level
estimates are exported as LHAPDF-compatible
grids, alongside LHAPDF conversions of the existing BFG, GRV and GDRG sets,
enabling a direct, like-for-like comparison of interpolation behaviour,
kinematic endpoints and low-z behaviour between the shower extraction and
legacy parametrizations.
Published results
- Photon Fragmentation Functions in LHAPDF: Existing Sets and a Pythia-Based Extraction (arXiv:2608.15944)
Ongoing and future work
- Effective nonperturbative boundary conditions informed by the PYTHIA extraction.
- Investigation of factorization-scheme differences (MS-bar vs. DIS-γ).
- Evolution studies using APFEL++ and GEKO.
- Comparisons with photon-in-jet observables in $e^+e^-$ and $ep$ collisions.