gamma2MC version 1.1

A program to compute the di-photon cross section at Next-to-Leading order (NLO) in QCD at hadronic colliders.
See Ref. [1] for details and results.

In this program the di-photon cross section, p p(bar) --> gamma gamma X, can be computed through three distinct subprocesses:

  1. Through the Higgs resonance: g g --> H X, followed by H --> gamma gamma. The production cross section of the Higgs boson is through gluon-gluon fusion (with all associated channels at NLO) in the heavy top quark limit (top quark mass dependence is included only in the LO prefactor). The branching ratio to gamma gamma is not included. It can be obtained elsewhere, such as from the program HDECAY [2].

  2. Through the (formally NNLO) process g g --> gamma gamma X, which occurs at one loop. This box contribution is then treated as the LO part of a NLO calculation, where only gluon-gluon initial-states are considered.

  3. Through q qbar --> gamma gamma X , as well as all associated channels through NLO. This process at NLO has a collinear singularity when the photon and a final-state quark are collinear. This singularity has been MSbar-subtracted, so that the calculation should be finite for any isolation cuts. However, no fragmentation processes are included, so only a calculation with an IR-safe isolation (such as Frixione's smooth isolation cut [3]) has any physical meaning at NLO. (I.e, the calculation with the IR-safe isolation cut does not depend on the subtraction prescription and does not get any contribution from photon fragmentation processes.) A complementary program that does contain fragmentation processes in di-photon production is DIPHOX [4].

  1. The source code can be obtained here: gamma2MC_1.1.tar.gz .
  2. Click here for the installation guide .
  3. Click here for the program manual and input-file guide .
  4. This introductory page, as well as the installation guide and program manual/input-file guide, is also included in the source code distribution.
  5. The program uses the LHAPDF (Les Houches Accord PDF) interface to access various up-to-date parton distribution function sets. More information on downloading the LHAPDF libraries and the various PDF sets can be found at
  6. Please send questions or comments to


  1. gamma2MC_1.1: Updated to use LHAPDFs. (Current version)
  2. gamma2MC_1.0(beta)


  1. Z. Bern, L. Dixon, and C. Schmidt, Phys. Rev. D66 (2002) 074018.

  2. A. Djouadi, J. Kalinowski and M. Spira Comput. Phys. Commun. 108 (1998) 56.

  3. S. Frixione, Phys. Lett. B429 (1998) 369.

  4. T. Binoth, J.P. Guillet, E. Pilon and M. Werlen, Eur. Phys. J. C16 (2000) 311.