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.

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.

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

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%)

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

Simulation of the Testbeam Setup using GEANT4.

Mirror Rad. of Curvature=1185 mm.Four Pad Hpds are used.

Mirror

Hpd

Aerogel

FilterVessel

Optical Transmission in Aerogel

Green Lines: Photons.

Photons Transmitted without Scattering

Rayleigh Scattered Photons

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 ).

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

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.

Refractive Index of Aerogel

Novosibirsk Tile 7*8*4 cm.At 400 nm,Ref.Index=1.03066.

A Typical event in the Testbeam

Red lines: Charged particleGreen lines : Photons.

Cherenkov Radius on the Photocathode

Peak at 146.4 mm.Tails from Rayleigh Scattered Photons.

Radius in mm.

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.

Photoelectric Effect at the HPD.

Red lines: Charged particlesGreen lines : Photons

HPD Quartz Window,Silicon detector .

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.

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%

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%

?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 )

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.

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

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

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.

RICH1 with a Particle Gun

Pion with 7 GeV/c.Cherenkov PhotonsIn Aerogel and C4F10.

RICH1 Event DisplayXMLàG4àOpenGL

Rayleigh scatteringSwitched off forIllustration.

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.