1. Simulation Developments
Choice of few topics to have production version(s) for the 2010 data in autumn and longer term developments
focus on Generators, Geant4 Physics
LHCb Week in St. Petersburg, 29th June 2010

2. LHCb Week in St. Petersburg, 29th June 2010
Generator Tuning
Pythia6 not expected to evolve significantly but its tuning (to LHC data) yes
Use other generators for specific events, e.g. Pythia8 for diffractive
Important to understand the MinBias (most part of the events are extracted from them)
Need to have soon a proper Pythia tuning (comparison of key distributions using LHCb tune, Perugia-0 tune, Atlas tunes...)
Contribution to the LPCC MB and UE working group
A first attempt to review ongoing projects for the MC tuning (from generators and validation tools to first comparisons/plans for physics results) at the simulation workshop on Jun 2nd.
Report on available tools and first idea by Silvia Miglioranzi at June software week.

3. Generator tuning Activity starting in LHCb
LHCb Week in St. Petersburg, 29th June 2010
Generator tuning
Activity starting in LHCb
few people looking into Minimum Bias tuning
defining appropriate data sample and MC samples to compare
general reasonable agreement between data and MC
David Voong presentation
idea on b production studies and tuning
Rolf Oldeman presentation
B/B*/B** can be tuned in Pythia, affect Flavour Tagging
Not much room in Pythia to tune B spectra expect changing fragmentation function parameters

4. Validation and tuning tools
LHCb Week in St. Petersburg, 29th June 2010
Validation and tuning tools
Support for tuning as joint effort between LCG Generator Service and the LPCC for tuning tools support
Repository of tools
Professor, Rivet, HepMC Analysis Tools
Web resources for validation of different tunes
In LHCb Online tools customized to perform the MC Data Quality Monitoring
by Silvia Miglioranzi
Online Histogram DataBase, Online Presenter and OMAlib (Online Histogram Analysis Tools)
Define and monitor key reference distribution in Gauss
Follow them all the way to compare with data as to feed tuning for minimum bias and beauty/charm production into generators
Detailed instructions on how to use the Online Tools for MC Monitoring provided

5. Validation and tuning tools
LHCb Week in St. Petersburg, 29th June 2010
Validation and tuning tools
Example of comparison of 2 small samples - 100evts minbias each - using LHCb (ref) and Perugia-0 tune

6. LHCb Week in St. Petersburg, 29th June 2010
EvtGen
A merge of features developed by BaBar/Belle/CDF/LHCb since 2003 adopted last year
Needed to re-implement some of the modified to handle the situation at LHC(b)
Different description of Mixing and CP-violation
Handle the fact that Pythia is used to produce the (wider variety) of b-hadrons
New models can be added at run time
E.g. new model for rare radiative leptonic B-mesons decay recently introduce by Nikolai Nikitin and Daria Savrina
Decay files and EvtGen maintenance
DECAY.DEC last updated in 2009 with PDG 2008 BFs
Plenty of new decay files using available models
EvtGen is looked after within LHCb, by Paul Harrison and Mark Whitehead
However, the continuing development, validation and maintenance is also the primary responsibility of the physicist-users within the collaboration.
Always test the generator for your mode before using it!
Let them know of problems, and they will help you fix them.

7. General issues Generators statistics
LHCb Week in St. Petersburg, 29th June 2010
General issues
Generators statistics
Printing of all steps in generation (selection, cuts, flipping) in log files. A dedicated script used to extract and compile information
Migrate to FSR (File Summary Record)
similar to luminosity information
manpower need to be identified
Central production for generator level studies ?
Easy Gauss configuration exist to have only generator content in HepMC format
Possibility to have MCParticles/MCVertices filled with generator information exist: need to introduce easy Gauss() configurable control
Need to define file types for them and make them known to the production system

8. Generators: open issues
LHCb Week in St. Petersburg, 29th June 2010
Generators: open issues
Beam parameters for collisions
now can be configured via options of many tools
define event data class as single stored source of information
Hijing for beam gas generator for luminosity studies
current version not working on slc5
LCG will install ALICE version in near future
will need to pick it up and do some validation in our system
Machine induced background (far away)
need new files of losses at 3.5 TeV on TCT
estimates to be provided by LBS
event types to be defined
merging with physics events to be provided in Gauss() configurable

9. LHCb Week in St. Petersburg, 29th June 2010
Future Generators
Fortran generators are at their end-of-life. Authors will not update them anymore, all developments will be in C++ from now on.
Very productive workshop on Jun 2nd 2010
Summary Report by Patrick Robbe at June software week
Invited talks from authors of C++ generators:
Pythia8: Peter Skands (CERN)
Sherpa: Frank Siegert (Durham)
Herwig++: Mike Seymour (Manchester)
Photos/Taula: Zbiegniew Was (Krakow)
Presentations from LHCb (interfaces to these generators):
Pythia8: Raluca Muresan (EPFL)
Sherpa: Julian Wishahi, Tobias Brambach (Dortmund)

10. C++ generators Amongst C++ generators, 5 are interesting for LHCb:
LHCb Week in St. Petersburg, 29th June 2010
C++ generators
Amongst C++ generators, 5 are interesting for LHCb:
« Production »: Pythia8, Herwig++ and Sherpa
« Decay »: Sherpa, Photos and Tauola (even though Pythia8 and Herwig++ have interesting decay engines, but which will not be as detailed as EvtGen or Sherpa)
Advantages of C++:
Easier maintenance inside LHCb software,
Modular interface (can re-use easily other parts of software – random numbers, ...)
Possibility to have 2 separate instances of the same generator: for example, one for signal, the other for pile-up.

11. Pythia8 Status: All « LHCb » processes available:
LHCb Week in St. Petersburg, 29th June 2010
Pythia8
Status:
Ready and tuned for Minimum Bias
multiple parton-parton interactions, with an improved model (pT ordered, similar to the one we use with Pythia6)
Diffractive description better than Pythia6
Improved shower model
String fragmentation: Lund fragmentation for light quarks, with Bowler modification for c/b quarks
[NB: this is the part where the B spectra may be tuned]
But problem with underlying event (which would not affect the majority of events generated in LHCb)
All « LHCb » processes available:
All 2  2 processes that we use in LHCb with Pythia6
Charmonium + Bottomonium prompt production
Diffractive + elastic

12. Pythia8 in LHCb Interface available and used for physics studies
LHCb Week in St. Petersburg, 29th June 2010
Pythia8 in LHCb
Interface available and used for physics studies
(P.Robbe and student)
(R.Muresan)
Ks0 production studies
Pythia6 model (not developed anymore)
Pythia8 model (actively developed)‏
3.0 < y < 3.5

13. LHCb Week in St. Petersburg, 29th June 2010
Sherpa
Multi-purpose generator, which can be used as a production generator, but also as a decay generator.
Multiple interaction model similar to Pythia, parton showers kT ordered
Some QCD NLO matrix elements
Cluster fragmentation model for hadronization
No complete generation of Minimum Bias yet:
Missing elastic scattering, single diffraction, double diffraction.
Under development, but soon available
Implementation will aim at complement underlying event simulation,
2  2 QCD matrix elements,
Goal is to have a complete description of QCD,
Work partly motivated by LHCb
Detailed hadron decay module, including generation of QED corrections for decay
Authors have plans to develop a large number of different decay models to describe D, B, and tau decays.

14. LHCb Week in St. Petersburg, 29th June 2010
Sherpa in Gauss
Interface available, both for production and decay tool.
A lot of interaction and support between authors and Julian Wishahi and Tobias Brambach who are integrating Sherpa inside Gauss.
Some parts of Sherpa have been tuned for LHCb technical needs.
To be released in near future
Working already fine to generate inclusive b and signal events
Decay kinematics generated according to amplitudes (and form factors)
Allow spin correlations and correct angular distributions
Treatment of neutral B mixing
Allow generation of signal sample by forcing particle to a given decay mode
Decay tables for ~400 hadrons, ~2500 decay channels, ~400 decay modes with specific amplitudes
Few remaining issues for LHCb decays
CP violation in signal B not yet implemented
Mass smearing problem for broad resonances,
technical problem due to the separation in Gauss of production and decay

15. LHCb Week in St. Petersburg, 29th June 2010
Sherpa in Gauss

16. LHCb Week in St. Petersburg, 29th June 2010
Herwig++
Multi-purpose event generator, successor of Fortran HERWIG generator.
Fortran version development stopped, C++ version is now the main one.
Current C++ version provides a full simulation of hadron-hadron collisions, with many improvements with respect to Fortran version:
Angular ordered parton shower,
Many processes at NLO,
Gives a good description of B hadron fragmentation function.
Improvements in hadronization, designed to improve the simulation of bottom and charm hadrons
flavour specific parameters in hadronization (not available in Pythia)
Improved simulation of hadron, tau and B decays.
General properties of heavy mesons and baryons: no CP violation or mixing

17. Herwig++, Event Shapes
B hadron fragmentation function compared to SLD/LEP data.

18. LHCb Week in St. Petersburg, 29th June 2010
Herwig++ in Gauss
An old interface to Fortran Herwig, but not maintained, exists in Gauss.
Interest from Cambridge group to interface Gauss to Herwig.
Development will consider directly C++ Herwig++ version (and leave Fortran Herwig).
Herwig++ authors are willing to help and provide support when implementing Gauss interface to Herwig.

19. LHCb Week in St. Petersburg, 29th June 2010
PHOTOS
Used in LHCb to generate QED radiation from all decays to charged particles.
Is called from EvtGen, we use for the moment FORTRAN version.
C++ version under development, will be released end of summer.
Will be able to call it from outside EvtGen:
PHOTOS will read a HepMC event record with its full structure.
It will then add automatically all necessary radiation photons to decay of particles.
Then we will be able to have it as a « universal » tool inside LHCb generation software.

20. Geant4 and Detectors Physics processes in Gauss/Geant4
LHCb Week in St. Petersburg, 29th June 2010
Geant4 and Detectors
Physics processes in Gauss/Geant4
are our choices of physics list and cuts adequate?
Comparison with data
once we are comparing apples with apples (i.e. the same class of events) do we understand where discrepancies come from?

21. Geant4 hadronic physics
LHCb Week in St. Petersburg, 29th June 2010
Geant4 hadronic physics
Hadronic’s cross sections and physics lists
Study by Silvia Miglioranzi on cross sections
all physics lists looked at have the same cross sections
but different multiplicities (study in progress)
New physics list prepared by Geant4 for LHCb
better cross section for
reference tag last week Geant4 9.3.ref05
we are currently using Geant4 9.2.p03
development version of Gauss in nightlies to be based on this to allow its investigation over the summer

22. Geant4 EM physics EM ‘old’ issues to be checked and revisited
LHCb Week in St. Petersburg, 29th June 2010
Geant4 EM physics
EM ‘old’ issues to be checked and revisited
Delta rays switched on everywhere: is OT simulation fine?
Multiple scattering
lateral displacement in muon filters much better (side effect of switching on delta rays) but need to be re-checked with latest version
slopes pull issue in tracking still there? New MS model used since DC06, but effect not verified
Production and tracking cuts
are they responsible for some of the MC/data difference in clusters multiplicities?
one of the major influence on CPU
Review dE/dx in thin layers
it has been getting better, again check latest version
are muons still different from other particles
Calorimeters calibration done last for MC09 (G4 9.1 now at )
Muon low energy background
not applied: bunches now very far away but neutrons component can be very slow
last parametrization for 14 TeV collisions…

23. Detector geometry and conditions
LHCb Week in St. Petersburg, 29th June 2010
Detector geometry and conditions
RICH refractive index calibration
from DDDB to SIMCOND (and LHCBCOND) to be regularly updated
as for dead strips need to define which set to use for massive production
Missing material
Velo recently updated RF foil thickness
Some parts of the cable supports in the beam pipe not yet described nor its outer support frame
Material that should NOT be there
Pass detector elements one by one to take into account alignment
Needed to VELO open/close BUT Velo-Envelope with vacuum not there
Restructuring of how geometry is passed to G4 needed to fix this

24. Summary Simulation is an essential ingredient of the analysis
LHCb Week in St. Petersburg, 29th June 2010
Summary
Simulation is an essential ingredient of the analysis
Make sure it matches as much as possible what we measure and it is stable
tools in place to help
generators tuning
appropriate physics choice and cuts in G4
material is well described
Make sure it is ready for the future
make it easier to use for private studies
(adopt), commission and follow evolution of new (C++) generators
they can already suit LHCb needs
a lot of interesting work needed to validate them in LHCb
follow Geant4 and detectors evolution