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Simulation in LHCb


Gauss is the LHCb Simulation software, built on the Gaudi Framework.
It consist of a first phase where the events are generated (e.g. pp collisions at 14 TeV) and a second phase where the particles are propagated trough the LHCb detectors.


The Gauss integration and release manager is Gloria Corti. The list of topics and coordinators/contacts is here.

Gauss Web

The main Gauss web page containing release information and links to user guides and tutorials, is here.



Gauss Tutorial

There are some tutorials for self-teaching. See here.

Gauss User Guide

Information on Generators in Gauss

A collection of information related to the generator part of Gauss can be found DocGen here: links, talks, notes.

Information on Detector simulation (Gauss and Boole)

An updated collection of notes, talks and links related to the description of the status of the simulation and digitization for the different subdetectors can be found here.

Ongoing tasks/projects, open issues


Geometry and mis-alignment for simulation

Last update: 16th April 2009

It was agreed that, ultimately, the 2008 simulation should simulate a realistic detector based on the surveyed detector, not the ideal ("Optimisation TDR") detector simulated in DC06
See here for the various issues

Overlap checking can be done in Gauss for what Geant4 sees with special tool DAVID and DAWN. The list of the overlaps identified with Gauss v37r0(DDDBtag = "head-20090330") has been produced by Marco Pappagallo and can be found here.

Status for MC09 as used by Gauss v37r0, DDDB tag head-20090330 and SIMCOND tag sim-20090402-xx

Detector Contents and Comments Responsible
VELO nominal in DDDB and as installed from survey in SIMCOND, tags for stepping motor for open/close, also tag for 'zero' misalignment David/Marco G/Silvia
TT nominal final geometry in DDDB, survey cannot be used, overlaps ok Jeroen/Cristophe
IT nominal geometry in DDDB, survey cannot be used Vincent/Matt
OT restructured with multiple LV for stations and layers (allow survey in SIMCOND) Jan
RICH ideal and survey geometry. Conditions db filled with measured properties of various things like hpds. Also in dddb, properties for aerogel, rich2 mirror surface. Rich1 and rich2 hpd boxes location survey ? Sajan/Antonis
Calorimeters calo split in 2 halves, real position for plugs and z ? Vladimir/Olivier D.
Muon survey of chamber in DDDB, half stations final positions in DDDB (problem for use in SIMCOND as assemblies, M1 closed Alessia
BCM Ideal in DDDB including cables Magnus
Magnet and Beam Pipe supports as installed in DDDB, no bakeout in RICH2, pumps etc downstream muon and upstread Velo, (not yet done better description of bellow in VELO window and different structure-volume-in-volume) Daria/Gloria/Magnus
Magnetic field map Current and polarity in SIMCOND. Measured maps for one polarity in FieldMap v5r0, other maps in preparation. Multiple field for corrector dipoles to be done Adlene/Magnus
RMS togheter with IT2 already in Kiev(/Vincent/Matt)
Beam scintillators crude description of layers in, real detector once installed Vadim

Conditions for simulation

Last update: 16th April 2009

The simulation (and reconstruction of simulated data) will get a copy of the necessary online conditions from a SIMCOND database.

See here for the various issues

Marco Cl. has provided versions of SIMCOND containing the existing ONLINE data structure, and the conditions included in the latest LHCBCOND tags. Not all alignment conditions are included since they cannot be taken into account correctly by Gauss: in particular no alignment different from zero is set for ST and OT. There will also be a version corresponding to the nominal positions (not the survey) for which the VELO already exist. SIMCOND contains the magnet variables from online and has values for full field up and down and for magnet off. All directory in ONLINE will be copied to SIMCOND once they are available: we will then need to decide what values are set in the variable and the corresponding tags for productions.

The global tags in SIMCOND begin systematically with sim and the date YYYYNN (higher that that of the DDDB tag they are related to (ie. the corresponding geometry to which they apply)

Global tags have then a field used to identify specific values for following variables:

  • perfect or misaligned (including survey) geometry
  • setting for magnetic field
  • motor position for VELO

Beam conditions (including beam energy, bunch filling schema, crossing angle, beta*, beam size, luminosity) are instead set at initialization of Gauss as properties and stored in a DataObject in the /Gen tree. This corresponds to the conditions the simulation is run with. In fact Boole and Brunel should then be configured appropriately based on the SIMCOND tag chosen (eg. number of spillover events unless spillover is moved to Gauss, and field on/off). A dedicated configurable that will provide a translation from a given tag to the configurables of the applications will be available and the translation map distributed externally with the CondDB.

List of available global tags and corresponding variables settings:

Global tag with DDDB Velo alignment Velo motor position Magnetic field
sim-20090402-vc-md100 head-20090330 survey closed down
sim-20090213-vc-md100 head-20090212
sim-20090402-vc-moff head-20090330 survey closed off
sim-20090213-vc-moff head-20090212
sim-20090402-vc-mu100 head-20090330 survey closed up
sim-20090213-vc-mu100 head-20090212
sim-20090402-vo-md100 head-20090330 survey open down
sim-20090213-vo-md100 head-20090212
sim-20090402-vo-moff head-20090330 survey open off
sim-20090213-vo-moff head-20090212
sim-20090402-vo-mu100 head-20090330 survey open up
sim-20090213-vo-mu100 head-20090212
sim-20090402-vci-md100 head-20090330 ideal closed down
sim-20090213-vci-md100 head-20090212

CondDB release notes

A list of SimulationConditions used in productions and for which data are available is listed here with some explanation.

Samples for validation

Last update: 23rd January 2009

A set of samples are necessary for validating a new production version, new versions of Geant4 and of generators. The production of these samples should become automated and the results published on a dedicated web page. This samples are produced by the production system, so that the all chain is exercised. It should also be investigated if the Data Quality/Monitoring infrastructure is suitable for this. Finally a new facility called QMTests is available within the Gaudi context, its suitability for this should also be investigated.

Two different macro-sets are produced depending on what need to be validated:

  • particle-gun, min bias and inclusive samples (sim+digi)
  • physics samples (dst files)

The list of sample to be produced, status of requests and productionIDs for them can be found here.

Validation of generator phase

Plots comparing different generators and Gauss versions can be found here

Validation of simulation phase

Plots comparing different Geant4 and Gauss versions can be found here

MC production histograms: monitoring tools

Instructions to use of the Online Tools (OnlineHistDB, Presenter) for monitoring the MC histograms can be found here.

Radiation Length Scans using G4

Updated version of the material budget scans made using Geant4 can be found here.

Migration to HepMC2

Migration done in Gauss v35r0

Recipies on how to migrate user code from HepMC 1.26 to HepMC 2.03 are available

CLHEP::HepLorentzVector and the new class HepMC::FourVector

Current and future developments

See here for details on topics being worked on or on open list of things to do

Bugs and features

Last update : 22 January 2010

To report new bugs or unexpected feature use the "LHCb Physics software" savannah portal and select "Simulation" as category.

These are known to the Gauss team and being worked on.

  • Work in progress, under construction When using _HP physics list G4 uses NDL cross section data and a long set of warning is issued as for many atoms only neutron cross sections of the natural composition exists and specific atom isotopes are instead used in the LHCb material list.
  • Work in progress, under construction Gauss stops when using a different PDF for Lamdba studies, reported by Raluca, WRONG LHAPDF set number =       20650 given! STOP EXE!, Patrick, Gloria, Raluca investigating. Could be that either chosen PDF is not distributed with Gauss if running remotely or available only in newer version of lhapdf. PDF chosen requires newer LHAPDF, available with Gauss v38r0

Next versions

Last update : 22 January 2010

  • v37r8, based on LHCb v26r3, *AppConfig v3rX*, Gaudi v20r4 and Geant4 v91r3, MC09 production compatible, bug fixes and features for signals. No major further development foreseen.
  • v38r3, based on LHCb v29r0, AppConfig v3rX, Gaudi v21r7 and Geant4 v92r2(pX) (9.2.p02 + MacOS build), developement version for comparison with real data
see the LHCb Tag Collector for details

-- GloriaCorti - 18 Nov 2008

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Topic revision: r67 - 2010-05-28 - GloriaCorti
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