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

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. http://indico.cern.ch/conferenceDisplay.py?confId=93939 http://indico.cern.ch/conferenceDisplay.py?confId=73578

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

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 https://twiki.cern.ch/twiki/bin/view/LHCb/McMonitor

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

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.

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 http://lhcb-release-area.web.cern.ch/LHCb-release-area/DOC/gauss/doc/UsersGuideStatMC09.php

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

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) http://indico.cern.ch/conferenceDisplay.py?confId=93939 http://indico.cern.ch/conferenceDisplay.py?confId=73578

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.

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

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

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.

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

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

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

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

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.

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.

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?

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

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 9.2...) Muon low energy background not applied: bunches now very far away but neutrons component can be very slow last parametrization for 14 TeV collisions…

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

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