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MILOU is a Monte Carlo generator for deeply virtual Compton scattering (DVCS), ep → eYγ, developed by E. Perez, L. Schoeffel and L. Favart [1]. It is based on generalised parton distributions (GPDs) evolved to next-to-leading order.


The MILOU code is written in Fortran. GPDs, evolved to next-to-leading order, provide the real and imaginary parts of Compton form factors (CFFs), which are used to calculate cross sections for DVCS and DVCS-BH interference. The package BASES/SPRING [2] is used to generate events from these cross sections. First, the differential cross sections are integrated by the numerical integration package BASES to yield probability distributions. These distributions are used by the event generation package SPRING to generate the DVCS events. Proton dissociation (ep → eYγ) can be included, with hadronisation of the system Y performed by PYTHIA. The generated events are saved to a PAW ntuple.

Running MILOU

A 32-bit installation of MILOU can be found in the EIC AFS region at


The generator options are set via a "steering card" dvcs.steer. The options are described in [1].

The program is run via the command


This generates a PAW file named bookhis_form_modif.ntp, which contains an ntuple with the event information. If a ROOT file is preferred, the programme h2root can be used to produce a ROOT ntuple from the PAW ntuple:

h2root bookhis_form_modif.ntp <rootFileName>

Output file structure

the output file is in a text format, asc.out, which has the following structure:

  • 1st line: "generator name" (i.e. MILOU32); "name of the person generating the sample"; "Name of the Istitution"
  • 2st line: MILOU EVENT FILE
  • 3nd line: "============================================"

  • 4rd line: Information on event wise variables stored in the file
I: 0 (line index)
ievent: eventnumber running from 1 to XXX
linesnum: numbers of particles in the event (max value of line index); =5 if no radiative corrections applied, =6 otherwise
weight: applied weight, default is 1.00000000
genprocess: generated process (1=BH, 2=DVCS, 3=Interaction(btw BH and DVCS), 4=BH+DVCS+Interaction, 5=SSA without TW3)
radcorr: radiative corrections (0= NO correction; 1= Initial State Radiation(ISR) )
truex, trueQ2, truey, truet, truephi: are the kinematic variables of the event.
phibelgen: azimuthal angle between the production and the scattering plane.
phibelres: azimuthal angle (see above) resolution.
phibelrec: reconstructedazimuthal angle between the production and the scattering plane.
If radiative corrections are turned on they are different from what is calculated from the scattered lepton.
If radiative corrections are turned off they are the same as what is calculated from the scattered lepton

  • 5th line: "============================================"

  • 6th line: Information on track wise variables stored in the file
I: line index, runs from 1 to Nr. of particles
K(I,1): status code KS (1: stable particles 10x:beam particles)
K(I,2): particle KF code (11: electron, 22: photon, 2212: proton)
K(I,3): line number of parent particle
K(I,4): normally the line number of the first daughter; it is 0 for an undecayed particle or unfragmented parton
K(I,5): normally the line number of the last daughter; it is 0 for an undecayed particle or unfragmented parton.
P(I,1): px of particle
P(I,2): py of particle
P(I,3): pz of particle
P(I,4): Energy of particle
P(I,5): mass of particle
V(I,1): x vertex information
V(I,2): y vertex information
V(I,3): z vertex information
  • 7th line: "============================================"
  • 8th line: event information for first event
  • 9th line: "============================================"
  • 10th to X-1 line: trackwise info of 1st event
  • Xth line "=============== Event finished ==============="

the information from line 8 to X repeats for each event.


(1) "MILOU: a Monte-Carlo for Deeply Virtual Compton Scattering", E. Perez, L. Schoeffel and L. Favart, hep-ph/0411389v1.

(2) "A New Monte Carlo Generator for High Energy Physics", S. Kawabata, Comp. Phys. Comm. 41, 127 (1986).