Simulation Status

1
Simulation Status
ALICE Progress Report CERN, April 22,
2002 Andreas Morsch for the ALICE Offline
Group
2
Overview

• Simulation in AliRoot
• Simulation Status Detector by Detector
• Geant4
• FLUKA
• Primary Particle Simulation
• Production
• Conclusions

3
Progress ...

• Usage
• Framework widely used for production and analysis
• Very active development and testing/validation
• PPR
• Updates/consolidation of all detector geometries
  and response simulation for the PPR production
• Summable digits and merging implemented
• First test production successful
• Future Simulation
• G4 in AliRoot Implementation -gt Maintenance
• G4 Physics validation
• First prototype of geometry modeller
• Start of FLUKA interfacing

4
AliRoot
AliRoot is the ALICE off-line framework for
simulation, reconstruction, and analysis. Except
for Geant3 and some remaining legacy code, this
framework is based on OO design and written in
C. It uses the ROOT system as a foundation.

• Framework helps people to move into OO
• CINT C scripting language
• persistent transient object
• Super PAW functionality
• Keeps entropy low and allows to speak a common
  language.
• Coherence of Simulation, Reconstruction and
  Analysis
• Wide use of Interfaces ( base classes)
• Ease of evolution
• Maintainability

5
Root Provides...

• Super PAW functionality
• Histogramming
• Data representation
• Graphical user interface classes
• C scripting language
• Automatic documentation
• Full set of container classes
• Object I/O package

6
(No Transcript)
7
(No Transcript)
8
The Heart of Simulation The Virtual MC
9
AliRootComponents Used in Simulation
(FORTRAN)
10
Simulated Data
Needed for event merging
11
Simulation Status Detector by Detector
12
ITS Geometry
13
ITS Geometry

• PPR Geometry
• Updated material thicknesses
• Detailed Cables and Pipes
• Detailed support structures
• Rails
• Cooling Pipe
• Validation
• Comparison with test-beam
• Understanding detector response

14
SPD Simulation / Test Beam
15
SSD Twin-Peak Puzzle
16
K0 Reconstruction
17
TPC Geometry
18
TPC Geometry and Response
Three versions of the TPC geometry are defined
Version 0 is the coarse geometry, without any
sensitive volumes specified. It is used for the
material budget studies. It is the one of
interest for the outer detectors. Version 1 is
the geometry version for the Fast Simulator. The
sensitive volumes are thin gaseous strips placed
in the S and L sectors, at the pad row centers.
The hits are produced whenever a track crosses
the sensitive volume (pad-row). The energy loss
is irrelevant and thus set to 0. Version 2 is
the geometry version for the Slow Simulator. The
sensitive volumes are S and L sectors. One can
specify either all sectors or only a few of them,
up to 6 S and 12 L-sectors. The hits are
produced at every ionizing collision. The
tracking step is calculated for every collision
from the exponential distribution. The energy
loss is calculated from 1/E2 distribution.
19
Response SimulationPhysics Processes
20
Signal Generation
21
Shaper Response
22
TPC (Response)
23
Recent Modification

• New Geometry
• Inner sectors innermost pad-row has been removed
• Outer sectors 2 sizes
• 1-64 1.0 cm
• 65-96 1.5 cm
• Improved code for cross-talk

24
TPC Occupancy
25
TRD Geometry
26
TRD Geometry
I

• Geometry versions
• With holes in front of PHOS and RICH
• No holes
• Correct material budget ( electronics, pipes, ..)

27
TRD Response
I

• Full Response and digitization implemented
• TR photon yield
• Approximated by analytical solution for foil
  stack
• Adjustment of yield for real radiator including
  foam and fiber layers from test beam data.

28
Response SimulationdE/dx
Generation of Hits The StepManager() function
in AliTRDv1creates along the path of a traversing
charged particle in the drift volume of the
chambers electron clusters. The distance between
the points where the creation of the primary
delta-electrons takes place is set according to a
parametrization of the Bethe-Bloch formula (see
below). The data points are averaged values taken
from GEANT. The plateau value is 1.55. For the
number of produced delta-electrons at the minimum
ionizing point a value of dN1/dxmin 48.0/cm
is used.
29
Response Simulationd-Electrons
The energy distribution of the delta-electrons is
assumed to follow a description given in
V.C.Ermilova et al., Nucl. Instr. and Meth. 145,
555 (1977) (red curve in plot below). Compared to
a 1/E2 distribution (blue curve) the mean
energy is higher (33.93 eV, compared to 19.89 eV)
which results in a higher yield of released
secondary electrons, in accordance with
measurements. The energy of one delta-electron
is given by a random sample from this
distribution subtracted by the first ionization
potential (12.1 eV).
30
TRD Digitization
Digitization The AliTRDdigitzer class
transforms the hits from AliTRDv1 into digits. In
this process the following effects can be
included Effect Defa ult Status
Diffusion ON E x B OFF
Absorbtion OFF Pad response
(1-dim) ON Gas gain gain
fluctuations ON Electronis gain
noise ON Conversion to ADC values ON
All corresponding parameter can be customized
(see the example macro slowDigitsCreate.C). The
default parameter are defined in
AliTRDdigitizerInit(). At the moment we use
only a one-dimensional pad response
function, i.e. it only describes charge sharing
in column direction
The fluctuations in the gas gain are described by
an exponential distribution
31
TRD Response
white normal dE/dx clusters red absorbed TR
photons
32
Comparison with Test Beam Data
33
TOF Geometry Options
34
2001 Detailed Strip Layout
35
RICH Geometry
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
PHOS Geometry
CPV or PPSD
APD
Crystals
41
Hits-gtSummable Digits-gtDigits
42
Comparison with Test Beam Data
43
FMD (Forward Multiplicity Detector)

•  Detailed geometry is ready
• Support structure will be included when
  construction drawings are ready
• Hits /Summable Digits / Digits / Multiplicity
  reconstruction for high occupancy are available
• Reconstruction algorithm should be improved for
  different occupancies
• Digitization will be clarified after beam
  tests. 
•  

44
FMD Geometry
45
FMD Acceptance
46
START

• Detail geometry is ready
• Support structure will be included when
  construction drawings are ready
• Hits /Digits /Fast reconstruction of vertex
  position are available
• Fast simulation issue
• T0 signal as average arrival time for first
  particles hitting left and right arrays
• left-right time-of-flight difference
• Slow simulation will be available next ALICE week

47
START Geometry
New asymmetric geometry Left flight path 69.7
cm Right flight path 350 cm
48
START Performance Simulation
49
PMD

• Geometry
• At new position
• New segmentation
• Hits
• Ok
• SDigits and Digits
• Under development

50
V0

• Geometry
• available
• Hits and Digits
• under development

51
MUON Simulated Data

• Hits
• Impact point
• Energy Loss
• Local momentum vector
• PadHits (summable digit)
• Cluster generation
• Mathieson formalism
• Ongoing work on
• Angular dependence
• Lorentz angle
• Charge correlation

52
(No Transcript)
53
MUON Geometry Status

• Stations 1-2
• conservative material distribution
• Stations 3-5
• detailed geometry
• Trigger Stations
• detailed geometry
• Frames and support structures
• coarse or missing but not very important
• All chambers
• logical segmentation

54
Resolution as a Function of Angle of Incidence
Resolution f 0 with improved response
TC1 Resolution from Beam Test Data
TC1
55
ZDC in AliRoot
1 Calorimeters for spectator neutrons (ZN) and
protons (ZP) 1 E.M. calorimeter (new position)
56
Hijing events Study of correlations with
transverse energy, multiplicity.

• Pb-Pb interaction at 2.7 A TeV
• ZP is almost free from background, while in ZN a
  contamination of gs and secondary particles is
  visible.

57
Event merging for the ZDC
SIGNAL Samples of 104 spectator p and 104
spectator n generated only once, storing
hits. BACKGROUND Simulated with full HIJING
generator. EVENT Merging of SIGNAL and BACKGROUND
hits.
58
New EMCAL
59
First Reconstruction Results
60
Non-Detector Geometries

• Beam-Pipe, flanges, pumps
• New drawings coming soon
• Decision about Be/Al/Steel
• Front and small angle absorber
• close to completion (see next TB)
• very detailed due to importance for muon
  spectrometer
• Space-Frame
• to be updated
• new position of cross-bars
• new profiles

61
New Field Map
62
Geant4 and ALICE

• Decision of September 2001 Offline Board
• Freeze development related to G4 in AliRoot
• Maintain the current implementation of TGeant4

63
Progress During 2001

• Reflections
• General solution for treating reflections (not
  biased to G3toG4 tool in the 4.0 release
  (December 2001)
• G4ReflectionFactory (by I. H.)
• G4ReflectedSolid (by V. Grichin)
• Why problem?
• G4 treats rotation matrices as "pure" rotation
  
• Basic idea Decomposition of general
  transformation and including reflection in a
  solid.
• Known problems (being investigated)
• Reflected G4Polycone -gt stops G4 with exception
• Reflected Boolean solids

64
Progress During 2001 (suite)

• "MANY" in AliRoot
• Required modifications
• STEER AliMCGsbool(const char, const char)
  0
• TGeant3 - dummy implementation
• TGeant4 - call to G3toG4
• Detectors/structures geometries
• SHIL, PIPE - only added Gsbool() calls
• MAG, MUON - geometry modified to fulfil
  limitation ()
• in MAG a part of geometry has to be build in a
  different way in G3 and G4 (8 lines of code)
• TRD - geometry was redefined without MANY
• Not yet done ITS

65
Progress During 2001 (suite)

• TGeant4, AliGeant4 development
• Creating materials
• A new material is created only if it is different
  from the existing ones
• Significantly reduces memory usage
• DigitsHits
• New sub-category introduced in TGeant4, AliGeant4
  in order to eliminate dependence of
  TGeant4/geometry category on Geant4 categories
  "above" geometry (digitshits).
• Needed for TGeant4/AliGeant4 usage with Flugg

66
FLUKA Tracking with G4 GeometryFLUGG

• AliFluka a new category
• Interface to FLUKA using Flugg TGeant4 and
  AliGeant4 subset includes
• TFluka class - implementation of AliMC interface
  using TG4GeometryManager (from TGeant4) only
  geometry methods implemented
• alifluka.cxx - main program equivalent of
  aliroot (for G3) and aligeant4 (for G4)
• Requires different TGeant4 and AliGeant4
  libraries from those for Geant4 (subset of
  classes, includes from Flugg and not Geant4)
• special Makefiles for TGeant4 and AliGeant4
• Perl script for selecting TGeant4 and AliGeant4
  according to needed categories.

67
G4 Physics Verification in ALICE (1/3)

• Geant4 A Benchmark of Hadronic Processes.
  (F. Carminati and I. González Caballero),
  ALICE-INT-2001-041
• GEISHA
• Pre-Compound Model
• So far studied
• Comparisons with thin target experimental data.
• Checks on azimuthal distributions, hadron
  inelastic and charged pion production cross
  sections, energy, momentum, baryon number and
  charge conservation were performed.
• Secondary neutron production.

68
G4 Physics Verification (2/3)
69
Iron and Lead with G4

Iron _at_ 597 MeV
Lead _at_ 800 MeV
jnucleons
70
G4 Physics Verification
GEISHA Pre-compound Model
71
Conclusion for G4 Hadronic Physics Evaluation

• Both models show wrong azimuthal distributions
  non-conservation of basic quantities (energy,
  momentum, baryon number and charge) was observed
  in GHEISHA.
• The pre-compound model produces no pions, while
  the GHEISHA pion production cross sections at the
  energies studied appear inconsistent with
  experimental data.
• The agreement between simulation and data for the
  secondary neutrons produced by the interaction is
  unsatisfactory for both models, especially for
  the high energy and small angle peak of the
  double differential production cross section,
  d2s/dE/dW.

72
Conclusion for G4 Hadronic Physics Evaluation

• The results of these tests point to deficiencies
  of Geant4 in the description of the intermediate
  energy range of hadronic showers. These results
  raise doubts on the possibility to use Geant4 for
  full detector simulation and indicate weaknesses
  in the Geant4 physics validation strategy.

73
Neutron Transport Benchmark

• Simulation of the TIARA experimental set-up
• 43 MeV and 68 MeV protons bombard a 7Li target,
  producing a quasi-mono-energetic source of 40 MeV
  and 65 MeV neutrons. Iron and concrete targets of
  different widths where placed 200 cm away from
  the neutron source.

74
68 MeV Fe
75
68 MeV Concrete
76
The Role of FLUKA

• Special Background Calculation Tasks
• Neutron fluence
• Dose rates
• Front absorber and beam shield calculations
• Beam loss scenarios
• Geant4 in its present state does not replace (as
  claimed by authors) FLUKA

77
ALIFE and Coupling with AliRoot
78
FLUKA in ALICE

• Recent activities
• Catastrophic beam loss scenarios during injection
• Single Event Effects and Neutron Fluences
• Beam halo
• Dose and Neutron Fluence on Electronics Equipment

79
Neutron Fluence
Fluence (cm-2/10y) Ekin gt 20 MeV
80
Misinjection Scenarios
81
Current and Future Activities

• Implement TFluka for direct use of FLUKA inside
  AliRoot
• Use newly developed geometry modeller

82
Primary Particle Simulation Status

• Generator Interface
• Standard Background Event
• Paramterized Particle Cocktails
• External Generators

83
Physics Simulation Strategy

• ALICE should does not rely on result of specific
  event generator but rather on predictions of the
  particle multiplicity and cross-sections of rare
  processes in PbPb collisions.
• Assume worst case scenario
• Highest multiplicity (HIJING, VENUS)
• Smallest cross sections for hard processes
  (Pythia)
• Use Generator Interface (AliGenerator)

84
Generator Interface

• Provide user with
• Easy and coherent way to study variety of
  physics signals
• Testing tools
• Background studies
• Possibility to study
• Full events (event by event)
• Single processes
• Mixture of both (Cocktail events)

85
Standard Background Event

• Up to now
• Parameterized event needed since most studies
  rely on approx. 1 background event
• For PPR
• "Signal Free" underlying event requested
• Hijing Parameterisation
• h-Distribution a la HIJING
• CDF pT distribution

86
Hijing Parameterisation
87
External Generators

• So far "wrapped" and usable through the
  AliGenerator and TGenerator interfaces
• Pythia
• Herwig
• HIJING
• ISAJET
• Pythia
• used with PDF lib
• includes possibility to use nuclear structure
  functions
• Coming soon
• DPMJET III

88
HIJING
89
Particle Cocktail Generator

• Replaces "Shaker"
• Events from user defined particle cocktail
• User has to define via function library
• Particle composition
• Transverse momentum spectrum
• Rapidity distribution
• Implemented up to now
• AliGenMUONlib
• AliGenPHOSlib
• AliGenPMDlib
• AliGenGSIlib
• AliGenSTRANGElib

90
HBT Analyzer
91
Simulation Baseline HI Run

• We need O(107) equivalent central HI events
• One HI central event at dN/dy 8000 24h_at_600MHz
• 300,000 PC's to do the job in one year
• We need to find alternative simulation strategies
• Background merging
• Track parametrisation
• Generate the background with HIJING
  parametrisation
• Pions and Kaons only, write summable digits
• Generate on the flight the signals
• Typically PYTHIA and specific parametrisations
• Read one background event and merge the signals
• Reconstruct and compare
• O(104) background reused O(103) times
• Simulating and creating digits for a signal takes
  1 minute

92
Fast Simulation Activities

• Event merging (all detectors)
• Combined fast and slow tracking (ITS V0 studies)
• Parameterisation of hit resolution(MUON)
• Combinded TPC and EMCAL information for jet
  studies (EMCAL)
• ....

93
HI PPR Test Production Summary

• Entirely AliEn based!
• gt5500 jobs validated (24h each)
• 13 clusters actively used in production, 9 remote
  sites
• GSI, Karlsruhe, Dubna, Nantes, Budapest, Bari,
  Zagreb, Birmingham are joining
• Hijing param 8000/4000/2000 dN/dy
• Hijing centrality bins
• fm 0-5, 0-2, 5-8.6, 8.6-11.2, 11.2-13.2,
  13.2-15, 15-inf.
• HIJING Jet/Photon Trigger
• Minimum Transverse Momentum 25, 50, 75, 100GeV

94
Event Merging
TPC Merging and Region of Interest
95
Merging

• Steering of Digitizing and Merging implemented
  into AliRoot
• Digitizing and Merging available for all
  detectors
• Testing and debugging ongoing

96
2001 Conclusions with 2002 Comments

• ALICE Geometry and simulated data in place to
  allow full event reconstruction including the
  main tracking devices. (More updates and
  consolidation)
• Some detectors are still under development and
  will come late for PPR. (V0?, EMCAL new)
• Comparison with test-beam date is performed in
  many cases, but
• Closer connection of test beam analysis and the
  AliRoot needes (still true !)
• Better documentation of the results and
  activities (still true !)

97
2001 Conclusions with 2002 Comments

• Full event reconstruction is an important
  milestone allowing extensive debugging (proven to
  be true).
• Upcoming PPR will trigger more framework
  development due to
• new requirements
• analysis code
• user interfaces
• Important contributions from outside included in
  2001
• Better documentation needed
• Especially for new users during PPR activity
• Some non documented user requirements are
  undocumented feature.

98
2001 Conclusions with 2002 Comments

• Great effort to integrate Geant4 into AliRoot
  framework (mainly done)
• FLUKA needed for radiation studies
• Integration into AliRoot needed (has started)