MILOU


About

MILOU is a Monte Carlo generator for deeply virtual Compton scattering (DVCS), ep → eYγ, developed by E. Perez, L. Schoeffel and L. Favart1. It is based on generalized parton distributions (GPDs) evolved to next-to-leading order.

Currently hosted on GitLab

Contact (for this version)

Overview

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/SPRING2 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 hadronization of the system Y performed by PYTHIA.

Running MILOU

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

$EICDIRECTORY/PACKAGES/milou

The generator options are set via a “steering card” dvcs.steer. The options are described in the manual1.

Note that the executables expect the .dat files and the dvcs.steer file in the directory of execution. Easiest way to achieve this is a softlink (adapt to your location)

cp $EICDIRECTORY/PACKAGES/milou/dvcs.steer .
ln -s $EICDIRECTORY/PACKAGES/milou/*.dat .

You can then run with:

$EICDIRECTORY/bin/milou

The generated events are saved to a PAW ntuple, as well as to an ascii file compatible with eicsmear. The output file names are hard-coded to 15x50_dvcs.ntp and asc_15x50_dvcs.out, respectively.

The program h2root can be used to produce a ROOT ntuple from the PAW ntuple:

h2root 15x50_dvcs.ntp <rootFileName>

Output file structure

The ascii output, asc_15x50_dvcs.out, has the following structure:

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


I: line index, runs from 1 to number of particles
K(I,1): status code KS (1: stable particles 11: particles which decay 55; radiative photon)
K(I,2): particle KF code (211: pion, 2112:n, ….)
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


The information from line 8 to X-1 repeats for each event.

Known Issues

Cannot currently be built with 64 bits. This is most likely fixable (it does compile, but the output contains NaNs).

References

  1. “MILOU: a Monte-Carlo for Deeply Virtual Compton Scattering”, E. Perez, L. Schoeffel and L. Favart, (hep-ph/0411389v1)[http://arxiv.org/abs/hep-ph/0411389v1].  2

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