g.corti lhcb week in st. petersburg, 29th june 2010 1 simulation developments choice of few topics...

LHCb Week in St. Petersburg, 29th June 2010

1G.Corti

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

Simulation Developments - 2LHCb Week in St. Petersburg, 29th June 2010

Generator TuningPythia6 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



Generator tuningActivity 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 toolsSupport 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 GaussFollow them all the way to compare with data as to feed tuning for minimum bias and beauty/charm production into generatorsDetailed instructions on how to use the Online Tools for MC Monitoring provided

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


Validation and tuning toolsExample of comparison of 2 small samples - 100evts minbias each - using LHCb (ref) and Perugia-0 tune


EvtGenA 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 timeE.g. new model for rare radiative leptonic B-mesons decay recently introduce by Nikolai Nikitin and Daria Savrina

Decay files and EvtGen maintenanceDECAY.DEC last updated in 2009 with PDG 2008 BFsPlenty of new decay files using available modelsEvtGen is looked after within LHCb, by Paul Harrison and Mark WhiteheadHowever, 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 issuesGenerators 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 formatPossibility to have MCParticles/MCVertices filled with generator information exist: need to introduce easy Gauss() configurable controlNeed 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 issuesBeam 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 studiescurrent 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


Future GeneratorsFortran 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)




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.


Pythia8Status:

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 Pythia6Improved shower modelString 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 Pythia6Charmonium + Bottomonium prompt productionDiffractive + elastic


Pythia8 in LHCb

Interface available and used for physics studies

Ks0 production studies

Pythia6 model (not developed anymore) Pythia8 model

(actively developed)

3.0 < y < 3.5

(P.Robbe and student) (R.Muresan)


SherpaMulti-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 orderedSome QCD NLO matrix elementsCluster fragmentation model for hadronization

No complete generation of Minimum Bias yet:Missing elastic scattering, single diffraction, double diffraction.Under development, but soon availableImplementation 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.


Sherpa in GaussInterface 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 eventsDecay kinematics generated according to amplitudes (and form factors)Allow spin correlations and correct angular distributionsTreatment of neutral B mixingAllow generation of signal sample by forcing particle to a given decay modeDecay tables for ~400 hadrons, ~2500 decay channels, ~400 decay modes with specific amplitudes

Few remaining issues for LHCb decaysCP violation in signal B not yet implementedMass smearing problem for broad resonances,

technical problem due to the separation in Gauss of production and decay


Sherpa in Gauss


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

Simulation Developments - 17

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


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.


PHOTOSUsed 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/Geant4are our choices of physics list and cuts adequate?

Comparison with dataonce we are comparing apples with apples (i.e. the same class of events) do we understand where discrepancies come from?


Geant4 hadronic physics

Hadronic’s cross sections and physics listsStudy 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

/ππ,/KK,pp/

/,/KK,pp/


Geant4 EM physicsEM ‘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 backgroundnot applied: bunches now very far away but neutrons component can be very slowlast parametrization for 14 TeV collisions…


Detector geometry and conditionsRICH refractive index calibration

from DDDB to SIMCOND (and LHCBCOND) to be regularly updatedas for dead strips need to define which set to use for massive production

Missing materialVelo recently updated RF foil thicknessSome parts of the cable supports in the beam pipe not yet described nor its outer support frame

Material that should NOT be therePass detector elements one by one to take into account alignment

Needed to VELO open/close BUT Velo-Envelope with vacuum not thereRestructuring of how geometry is passed to G4 needed to fix this


SummarySimulation 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 G4material is well described

Make sure it is ready for the futuremake 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

g.corti lhcb week in st. petersburg, 29th june 2010 1 simulation developments choice of few topics...

Documents

lhcb tune

corti lhcb week

validation tools

mc tuning

lhcb online tools customized

lhcb ref

simulation developments

generator tuning activity