Status of GEANT4 in LHCb S. Easo, RAL, 30-9-2002 The LHCb - - PowerPoint PPT Presentation

Status of GEANT4 in LHCb

• S. 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 is being modified to optimize the performance of LHCb.

RICH detectors in LHCb

• To identify charged particles in the momentum range 1-150 GeV/c.
• Two detectors: RICH1, RICH2.

RICH1: Aerogel 210 GeV/c C4F10 < 70 GeV/c RICH2: CF4 <150 GeV/c.

• Photo Detectors: Baseline solution- HybridPhotodiodes (HPD).
• RICH test beam presented: To test the performance of the

Aerogel radiator. Momentum range

Test beam Set-up at CE RN Test Test beam Set-up at CE RN

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 mm² 2.3x2.3 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 Filter Vessel

Optical Transmission in Aerogel

Green Lines: Photons. Photons Transmitted without Scattering Rayleigh Scattered Photons

Verification of Aerogel and Filter Transmissions Generate 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 incident

• n Aerogel Tile

Blue: Photons transmitted

• ut of aerogel from

the opposite side, but in the same direction. Black: Blue/Red Green: Expected Transmission . nm nm Photon 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 particle Green 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 by

reflection at the Hpd quartz window surface.

Photoelectric Effect at the HPD.

Red lines: Charged particles Green lines : Photons HPD Quartz Window, Silicon detector .

Hit Creation in the Si Detector.

• Implemented using a special process class since the standard

Geant4 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=10 B= backscattering probability=0.18.

Sector #4 Sector #8

Ring region Out of ring

sect 4 sect 8

Test beam results Test beam results Test beam results

• 9 Gev/c p¯ beam
• 4 cm aerogel Novosibirsk
• noise/pad < 2%

Photoelectron Yield Photoelectron Yield Photoelectron 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%

Data MC

results are normalised to 2p acceptance

0.67 ± 0.11 0.55 ± 0.06 1.13± 0.21 0.87 ± 0.09 4 cm

(off-ring)

1.25 ± 0.21 0.94 ± 0.10 1.38 ± 0.23 1.34 ± 0.15 8 cm

(off-ring)

results are in units of 10¯²/cm²

6.3 ± 0.7 7.4 ± 0.8 9.7 ± 1.0 11.5 ± 1.2 4 cm 9.4 ± 1.0 10.1 ± 1.1 12.2 ± 1.3 14.7 ± 1.6 8 cm

Filter D263 No Filter

Novosibirsk

Contributions

to 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 4.8 243.7 3.0 247.1 5.0 246.8 3.1

Filter D263

250.0 5.4 248.7 4.0 4 cm 246.8 5.8 245.0 3.9 8 cm

No filter

Thickness

Data MC

Aerogel from Novosibirsk

• Results per single photoelectron

single photoelectron in (mrad):

Data MC

Cherenkov Angle reconstruction Components of s? in mrad for the case with filter. Pixel size : 1.3 Chromatic: 2.5 Emission 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 from simulation.

Energy Response in HCAL Response to 50 GeV/c Pions

• Testbeam Data , GEANT3

(MICAP +FLUKA).

• HCAL TDR.
• Testbeam Data, GEANT4.

Histogram : Real Data Dots: 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 all

the 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 Photons In Aerogel and C4F10. RICH1 Event Display XMLG4OpenGL Rayleigh scattering Switched off for Illustration.

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 GEANT4

collaboration and LHCb in the coming years.