GEANT4 is used for simulating: RICH testbeam data, HCAL testbeam data. GAUSS Project: LHCb Simulation using GEANT4 with GAUDI.

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1 Status of GEANT4 in LHCb S. Easo, RAL, The LHCbexperiment. GEANT4 is used for simulating: RICH testbeam data, HCAL testbeam data. GAUSS Project: LHCb Simulation using GEANT4 with GAUDI. Summary.

2 LHCb Experiment Precision Measurements of CP violation in the B Meson System. Large Sample of Events with B d and B s 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.

3 RICH detectors in LHCb To identify charged particles in the momentum range GeV/c. Two detectors: RICH1, RICH2. Momentum range RICH1: Aerogel 2 10 GeV/c C 4 F 10 < 70 GeV/c RICH2: CF 4 <150 GeV/c. Photo Detectors: Baseline solution- HybridPhotodiodes (HPD). RICH test beam presented: To test the performance of the Aerogel radiator.

4 Test beam Set-up at CERN Beam from CERN-PS: p and p/p in the range 6 10 GeV/c (? p/p = 1%)

5 Hybrid Photo Detectors 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) AEROGEL test beam Quantum Efficiency of the 4 photocathodes > 20% (λ= nm)

6 Simulation of the Testbeam Setup using GEANT4. Mirror Rad. of Curvature=1185 mm. Four Pad Hpds are used. Hpd Mirror Vessel Aerogel Filter

7 Optical Transmission in Aerogel Rayleigh Scattered Photons Green Lines: Photons. Photons Transmitted without Scattering

8 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= micrometer**4/cm. C=Clarity, A=Surface scattering constant. Transmission = A exp(-c * thickness/ wavelength **4 ).

9 Verification of Aerogel Transmission Red: Photons incident on Aerogel Tile Blue: Photons transmitted out of aerogel from the opposite side, but in the same direction. nm Black: Blue/Red Green: Expected Transmission. Photon wavelength in nm nm

10 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.

11 Refractive Index of Aerogel Novosibirsk Tile 7*8*4 cm. At 400 nm, Ref.Index=

12 A Typical event in the Testbeam Red lines: Charged particle Green lines : Photons.

13 Cherenkov Radius on the Photocathode Peak at mm. Tails from Rayleigh Scattered Photons. Radius in mm.

14 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.

15 Photoelectric Effect at the HPD. Red lines: Charged particles Green lines : Photons HPD Quartz Window, Silicon detector.

16 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 = 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.

17 Test beam results 9 Gev/c p beam 4 cm aerogel Novosibirsk noise/pad < 2% Ring region sect 8 Sector #4 sect 4 Out of ring Sector #8

18 Novosibirsk 4 cm Photoelectron Yield No Filter 9.7 ± ± 1.2 Filter D ± ± 0.8 Data MC 8 cm 12.2 ± ± ± ± 1.1 results are normalised to 2p acceptance 4 cm (off-ring) 8 cm (off-ring) 1.13± ± ± ± ± ± ± ± 0.10 results are in units of 10 ²/cm² 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% 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%

19 Cherenkov Angle reconstruction Results per single photoelectron in (mrad): Thickness No filter Filter D263 4 cm 8 cm?c s? ?c s? Data MC Data MC Aerogel from Novosibirsk Components of s? in mrad for the case with filter. Pixel size : 1.3 Beam divergence: 0.7 Chromatic: 2.5 Emission Pt: 1.1 Alignment: 2->4 (not included in s? MC )

20 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.

21 Response to 50 GeV/c Pions Histogram : Real Data Dots: Simulation Energy Response in HCAL Testbeam Data, GEANT3 (MICAP +FLUKA). HCAL TDR. Testbeam Data, GEANT4. I.Belyaev+A.Berdiouguine et. al

22 Data and G3 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 and G4 Data G4 (QGS+CHIPS) G4(GEISHA) I.Belyaev + A. Berdiouguine et. al

23 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.

24 RICH1 with a Particle Gun RICH1 Event Display XML G4 OpenGL Pion with 7 GeV/c. Cherenkov Photons In Aerogel and C 4 F 10. Rayleigh scattering Switched off for Illustration.

25 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.