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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 3 tutorials for self-teaching. See here.

Gauss User Guide

Ongoing tasks/projects, open issues


Documentation of the 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 subcomponents can be found here.

Survey geometry for simulation

Last update: 8th July 2008

It is 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 v35r1 and DDDB-SIMCOND head-20081002 has been prodcued by Marco Pappagallo and can be found here.


Detector SQLDDDB tags Gauss version Contents and Comments Responsible
VELO velo-20080611 Gauss v33r2 (changing options) Marco Cl. received some recently from Marco G., it should be final one: is it perfect in DDDB and survey in LHCBCOND, stepping motor status in ONLINE not yet ready David/Marco G/Silvia
TT     Ideal final geometry in DDDB, Survey cannot be used, overlaps ok for LHCb and G4 Jeroen/Cristophe
IT it-20080613, it-20080715 v34r0, v34r1 Ideal geometry in DDDB. Survey cannot be used, overlaps ok for LHCb, to be checked for g4, some fixes in latest it-20080715 Vincent/Matt
OT     Restructuring with multiple LV for stations and layers, overlaps ok in LHCb (jan), to do for G4 Jan
RICH     Still small work, ideal and survey. The conditions db being filled with measured properties of various things like hpds. Also in dddb, the properties are being added for aerogel, rich2 mirror surface. For the rich1 and rich2 hpd boxes location survey info not available yet. We may add them in dddb or condb depending upon the situation. Sajan/Antonis
Calorimeters calo-20080708 v34r1 calo split in 2 halves done, real position for plugs and z ?, overlaps ok in LHCb. to be done in G4 Vladimir/Olivier D.
Muon     survey of chamber to bein DDDB, half stations final positions in SIMCOND, M1 open to be in DDDB(all chambers there), off in SIMCOND Simone/Alessia
BCM head-20080603 not used Ideal in DDDB, cables? Magnus
Magnet and Beam Pipe     To do as installed in DDDB: Bakeout in RICH removed, collars in magnet, bellow in VELO window, and clear overlaps. Daria/Gloria
Magnetic field map     Current and polarity in CondDB to be in SIMCOND first implementation, to be taken in MagneticFieldSvc. Measured maps for one polarity in FieldMap v5r0, other maps in preparation Adlene
RMS     togheter with IT2 already in Kiev(/Vincent/Matt)

Conditions for simulation

Last update: 3rd February 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 a first version 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 DDDB YYYYNN tag they relate 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 Velo alignment Velo motor position Magnetic field
sim-20090212 & sim-20090213-vc-md100 survey closed down
sim-20090213-vc-moff survey closed off
sim-20090213-vc-mu100 survey closed up
sim-20090213-vo-md100 survey open down
sim-20090213-vo-moff survey open off
sim-20090213-vo-mu100 survey open up
sim-20090213-vci-md100 ideal closed down

CondDB release notes

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

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

Next versions

Last update : 21 January 2009

  • v36r2, based on LHCb v26r2, Gaudi v20r4 and Geant4 v91r3 (9.1.p03)
  • v37r2, identical to v36r2 but built on Geant4 v92r0 (i.e. G4 9.2)
see the LHCb Tag Collector for details

-- GloriaCorti - 18 Nov 2008

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Topic revision: r33 - 2009-02-24 - SilviaMiglioranzi
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