The histogram package

If you would like to project the generated events directly into histograms, you should choose the option "histo" in the input file "parameter.indat" and define your histograms in the file "param_histo.indat".

In this file, you can define cuts on the rapidity and transverse momentum of the photons/hadrons. Note that some rough cuts can already be defined at the grid level in "parameter.indat".

In the second part of "param_histo.indat", you can define the histograms you would like to be produced. You can define histograms with equidistant or non-equidistant bins. There is also the possibility to specify several additional cuts for each histogram. Further details are given in the file "param_histo.indat" itself.

There is a certain predefined set of observables which can be histogrammed. In the case of identical particles, these are

• mass_gamma_gamma: invariant mass between the two photons
• pt_gamma: transverse momentum of each photon (double entries)
• pt_pair: transverse momentum of the photon pair
• phi_gamma_gamma: azimuthal angle between the two photons
• y_gamma: rapidity of one photon (double entries)
• y_boost: half sum of the photon rapidities
• y_star: half difference of the photon rapidities
• y_gamma_gamma: rapidity of the photon-photon pair
• cos_theta_star: cosine of polar angle in the partonic center-of-mass
• p_out: out-of-plane momentum (double entries)
• pt_balance: pt balance between the two photons (double entries)

In the case of non identical particles, similar observables also exist (see "param_histo.indat").

If you want to define new observables, you have to define them in the Fortran file "histo_selection.f" in the directory "src/histo". But note that the script "start.pl" also has to be modified accordingly.

A summary of the cuts and histograms which have been defined will be written to the file "histoNameHisto.outdat".
The resulting *.dat files for the histograms will be stored in the directory "pawres".

Note that 'NLO' in the definition of the histograms means 'Born + higher orders', i.e. your histogram represents already the sum of leading order and higher order contributions.

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