Minutes – LHCHWG Meeting: K-Factor Updates
Date:March 6, 2026
Presenter: Mohit Srivastav

Summary

• The ggH k-factor is computed using HNNLO, deriving corrections from LO → NLO and LO → NNLO, with NLO → NNLO obtained implicitly.

• Updated PDF sets are used and mass points are evaluated from 100 GeV to 6 TeV.

• Systematic uncertainties include QCD scale variations, PDF uncertainties, and αs variations, requiring large computing resources (~50k jobs).

• For qq → ZZ, the calculation is performed with MATRIX.

• A key issue was EW photon emission (ISR/FSR) distorting the (m_{4\ell}) distribution; after discussions with the authors, the treatment was updated and a ΔR = 0.5 photon–lepton merging (consistent with the analysis) will be used.

• Current k-factors are derived as a function of (m_{4\ell}), with combined QCD + EW corrections preferred.

Next Steps

• Produce NLO samples with POWHEG for gluon-fusion signal, background, and interference to improve the modeling and potentially reduce the current ~10% uncertainty.

• Continue interaction with the MATRIX authors to streamline photon treatment and speed up high-precision calculations.

• Finalize systematic variations for the ggH k-factor and validate the implementation for Run-3 analyses.