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Heavy-quark box-loop corrections to $q\bar q \to Zγ$ at two loops in QCD

Dario Kermanschah, Matilde Vicini

Abstract

We numerically compute the two-loop QCD corrections to $Zγ$ production at the LHC mediated by light- and heavy-quark box loops. The calculation employs the pipeline of refs. arXiv:2407.18051 and arXiv:2510.18801, which performs Monte Carlo integration over spatial loop momenta after local subtraction of infrared, ultraviolet, and threshold singularities. We validate our results for partonic squared matrix elements with massless-quark loops against known benchmarks, extend them to include heavy-quark contributions, and compute the double-virtual corrections to $pp\to Zγ$ by performing the loop and phase space integrations simultaneously. This computation demonstrates the flexibility of the approach in handling both massless and massive final-state bosons, as well as additional mass scales in the loop.

Heavy-quark box-loop corrections to $q\bar q \to Zγ$ at two loops in QCD

Abstract

We numerically compute the two-loop QCD corrections to production at the LHC mediated by light- and heavy-quark box loops. The calculation employs the pipeline of refs. arXiv:2407.18051 and arXiv:2510.18801, which performs Monte Carlo integration over spatial loop momenta after local subtraction of infrared, ultraviolet, and threshold singularities. We validate our results for partonic squared matrix elements with massless-quark loops against known benchmarks, extend them to include heavy-quark contributions, and compute the double-virtual corrections to by performing the loop and phase space integrations simultaneously. This computation demonstrates the flexibility of the approach in handling both massless and massive final-state bosons, as well as additional mass scales in the loop.
Paper Structure (6 sections, 21 equations, 1 figure, 4 tables)

This paper contains 6 sections, 21 equations, 1 figure, 4 tables.

Table of Contents

  1. Introduction
  2. Calculation
  3. IR and UV subtraction
  4. Loop-energy integration and threshold subtraction
  5. Numerical results
  6. Conclusion

Figures (1)

  • Figure 1: Planar and non-planar double box Feynman diagrams and their Cutkosky cuts identifying the threshold singularities. The diagrams with reversed charge flow are not shown.