status of geant4 in lhcb s. easo, ral, 30-9-2002 the ... · rich1: aerogel 2à10 gev/c c 4 f 10...
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Status of GEANT4 in LHCbS. Easo, RAL, 30-9-2002
• The LHCb experiment.
• GEANT4 is used for simulating: RICH testbeam data,HCAL testbeam data.
• GAUSS Project: LHCb Simulation using GEANT4 with GAUDI.
• Summary.
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LHCb Experiment
Precision Measurements of CP violation in the B Meson System.§ Large Sample of Events with Bd and Bs Mesons. §Most of the b hadrons are produced at small polar angles.
LHCb: Single Forward Arm Spectrometer with Open Geometry.§ From the CP asymmetries in the final states of B-meson decays,
Measure CKM Angles.
This design isbeing modifiedto optimize theperformance of LHCb.
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RICH detectors in LHCb
• To identify charged particles in the momentum range 1-150 GeV/c.• Two detectors: RICH1, RICH2.
RICH1: Aerogel 2à10 GeV/cC4F10 < 70 GeV/c
RICH2: CF4 <150 GeV/c.
• Photo Detectors: Baseline solution- HybridPhotodiodes (HPD).
• RICH test beam presented: To test the performance of theAerogel radiator.
Momentum range
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Test beam Set-up at CERNTestTest beam Set-up at CERN
Beam from CERN-PS: p¯and p/p in the range 6 – 10 GeV/c (? p/p = 1%)
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Quantum Efficiency of the 4 photocathodes > 20% (λ=280-380nm)
• Bialkali photocathode, K2CsSb• Fountain shaped electric field,
demagnification factor ˜ 2.3• Silicon pad sensor 2048 pixels
(16 sectors x 128 pads 1x1 mm²2.3x2.3 mm² granularity on ph.cathode)
Hybrid Photo Detectors
Hybrid Photo Detectors
AEROGEL test beam
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Simulation of the Testbeam Setup using GEANT4.
Mirror Rad. of Curvature=1185 mm.Four Pad Hpds are used.
Mirror
Hpd
Aerogel
FilterVessel
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Optical Transmission in Aerogel
Green Lines: Photons.
Photons Transmitted without Scattering
Rayleigh Scattered Photons
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Verification of Aerogel and Filter TransmissionsGenerate Photons: • With a uniform wavelength distribution from 170 to 950 nm.• Uniform X and Y coordinates of origin.• With Z coordinate of origin at 180mm (upstream of Aerogel).• With direction along the Z axis.
An Aerogel Tile simulated with: A=0.9368, C=0.00719 micrometer**4/cm.
C=Clarity, A=Surface scattering constant.Transmission = A exp(-C * thickness/ wavelength **4 ).
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Verification of Aerogel Transmission
Red: Photons incidenton Aerogel Tile
Blue: Photons transmittedout of aerogel fromthe opposite side, but in thesame direction.
Black: Blue/Red
Green: ExpectedTransmission .
nm
nmPhoton wavelength in nm
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Cherenkov Radiation in Aerogel
• Typical Run Configuration in the Testbeam:
• 9 GeV/c Pions.• One Novosibirsk Aerogel Tile with thickness = 4 cm.• Filter: Glass D263.
• Nitrogen Gas at 1 bar and 292 Kelvin in the Vessel.
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Refractive Index of Aerogel
Novosibirsk Tile 7*8*4 cm.At 400 nm,Ref.Index=1.03066.
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A Typical event in the Testbeam
Red lines: Charged particleGreen lines : Photons.
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Cherenkov Radius on the Photocathode
Peak at 146.4 mm.Tails from Rayleigh Scattered Photons.
Radius in mm.
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Photoelectric Effect at the HPD.
•Standard Geant4 processes not applicable in this case.
•A Special class created to generate the photoelectrons, which is derived from a GEANT4 base class.
•This process uses the quantum efficiency data and the results of Fountain focussing tests. Electron Energy: High Voltage applied.Direction: From Fountain focussing.
• The quantum efficieny data includes the loss of photons byreflection at the Hpd quartz window surface.
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Photoelectric Effect at the HPD.
Red lines: Charged particlesGreen lines : Photons
HPD Quartz Window,Silicon detector .
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Hit Creation in the Si Detector.
• Implemented using a special process class since the standardGeant4 procedure somewhat too complicated for this purpose.
• The Photoelectrons loose all their energy in the Silicon.
• The backscattering causes a loss of efficiency in creating hits.
• Efficiency = 1.0 - B* N/S where N = threshold cut in terms of width of the pedestal = 4
S= Signal to noise ratio=10B= backscattering probability=0.18.
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Sector #4
Sector #8
Ring region
Out of ring
sect 4
sect 8
Test beam resultsTest beam resultsTest beam results• 9 Gev/c p¯ beam• 4 cm aerogel Novosibirsk• noise/pad < 2%
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Photoelectron YieldPhotoelectron YieldPhotoelectron Yield
Contributions to total error in real data per HPD• background subtraction (±1s ): 1->8% • inefficient or noisy pads : 2->7%• Extrapolation to full ring : 5%• separation of on-ring/off-ring (±2mm): 5%• signal losses outside ADC thresholds (±1s ): 2%
DataMC
results are normalised to 2p acceptance
0.67 ± 0.110.55 ± 0.06
1.13±0.21 0.87 ± 0.09
4 cm(off-ring)
1.25 ± 0.210.94 ± 0.10
1.38 ± 0.231.34 ± 0.15
8 cm(off-ring)
results are in units of 10¯²/cm²
6.3 ± 0.77.4 ± 0.8
9.7 ± 1.0 11.5 ± 1.2
4 cm
9.4 ± 1.010.1 ± 1.1
12.2 ± 1.314.7 ± 1.6
8 cm
Filter D263No FilterNovosibirsk
Contributionsto the total error in MC.
• QE (+- 10%) 10%• ref. Index variation (+- 5%) 3%• backscattering (+- 2% ) 2%• clarity (+- 2%) 2%• beam divergence (+-1%) 1%
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?c s ??c s ?
245.4 4.8243.7 3.0
247.1 5.0246.8 3.1
Filter D263
250.0 5.4248.7 4.0
4 cm
246.8 5.8245.0 3.9
8 cm
No filterThickness
DataMC Aerogel from
Novosibirsk
• Results per single photoelectronsingle photoelectron in (mrad):
DataMC
Cherenkov Angle reconstruction
Components of s ? in mrad for the case with filter.Pixel size : 1.3Chromatic: 2.5Emission Pt: 1.1
Beam divergence: 0.7
Alignment: 2->4 (not included in s ? MC )
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HCAL Test beam
• HCAL is a sampling device made out of steel as absorber and scintillating tiles are active material.
• The scintillating tiles run parallel to the beam axis.
• It will provide data for the LHCb hadron trigger.
• Using testbeams , the response to particles incident at various angles is studied and is being compared those fromsimulation.
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Energy Response in HCAL
Response to 50 GeV/c Pions
• Testbeam Data , GEANT3 (MICAP +FLUKA).
• HCAL TDR.
•Testbeam Data, GEANT4.
Histogram : Real DataDots: Simulation
I.Belyaev+A.Berdiouguine et. al
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Energy Resolution of HCAL
• Testbeam Data, GEANT3• GEANT3 with GEISHA, FLUKA,MICAP
• Testbeam Data , GEANT4• G4+GEISHA agrees with G3+GEISHA.• Need help to understand and use
G4 with QGS+CHIPS
• Data§ G4 (QGS+CHIPS)
G4(GEISHA)
Data and G3
Data and G4
I.Belyaev + A. Berdiouguine et. al
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Status of the GAUSS Project
• Current MC productions in LHCb use GEANT3.
• GAUSS: To simulate LHCb using GEANT4 .
• GIGA interface: to use GEANT4 with the GAUDI Framework.Ref: Presentation by W. Pokorski on Wednesday.
• Geometry Input: XML database. A version available for allthe detectors in LHCb.
• Input events: From Pythia or other similar programs through the HEPMC interface into GEANT4.
• A first version of the whole Simulation chain is now working.
• Starting to study the response of the detectors in detail.
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RICH1 with a Particle Gun
Pion with 7 GeV/c.Cherenkov PhotonsIn Aerogel and C4F10.
RICH1 Event DisplayXMLàG4àOpenGL
Rayleigh scatteringSwitched off forIllustration.
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Summary
• RICH testbeam simulation is performed using GEANT4.
• Results of this simulation is compared with Real Data.
• HCAL test beam data comparison with GEANT4 in progress.
• A Project to perform the LHCb simulation using GEANT4 has started.
• We are expecting lot of interactions between the GEANT4collaboration and LHCb in the coming years.