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\(\kt\)-factorised \(\ggff\) process#

The photon transverse momentum-dependant description of this process was previously developed in PPtoLL, and described in [GdSFP+15]. It is defined as the pptoll process in CepGen.

Process-specific options#

method#

This integer allows to switch between the two matrix element definitions:

  • 0: on-shell amplitude,

  • 1: off-shell amplitude.

mode#

This enumeration allows to specify the kinematic regime to generate and the size of the phase space to perform the integration. It can take the following values:

  • ProcessMode.ElasticElastic := 1: elastic emission of photons from the incoming protons (default value if unspecified),

  • ProcessMode.ElasticInelastic := 2 / ProcessMode.InelasticElastic := 3: elastic scattering of one photon and an inelastic/semi-exclusive emission of the other photon, resulting in the excitation/fragmentation of the outgoing proton state,

  • ProcessMode.InelasticInelastic := 4: both protons fragmented in the final state.

pair#

This integer value allows the end-user to specify the PDG identifier of the fermion pair to be produced in the final state.

It can take the following values:

  • PDG.electron := 11: \(e^+e^-\) pair production

  • PDG.muon := 13: \(\mu^+\mu^-\) pair production

  • PDG.tau := 15: \(\tau^+\tau^-\) pair production

  • PDG.down, PDG.up, PDG.strange, PDG.charm, PDG.bottom, PDG.top (or equivalently 1-6): quark pair production.

Full object reference#

class PPtoFF : public FactorisedProcess#

Compute the 2-to-4 matrix element for a CE \(\gamma\gamma\rightarrow f\bar f\) process.

Private Types

enum class Mode#

Values:

enumerator onShell#
enumerator offShell#

Private Functions

inline virtual void prepareFactorisedPhaseSpace() override#

Prepare central part of the Jacobian after kinematics is set.

inline virtual double computeFactorisedMatrixElement() override#

Factorised matrix element (event weight)

double onShellME() const#
double offShellME() const#

Private Members

enum PPtoFF::Mode method_#
PPtoFF::OffShellParameters osp_#
double mf2_ = {0.}#
double qf2_ = {0.}#
std::function<double(double)> g_part1_ = {nullptr}#
std::function<double(double)> g_part2_ = {nullptr}#

Private Static Attributes

static constexpr double kFourPi = 4. * M_PI#
struct OffShellParameters : public SteeredObject<OffShellParameters>#

Parameters for the off-shell matrix element.