1. Development of RICH Detector and Large-area HPD for LHCb Experiment
Apollo Go
CERN/EP
for LHCb Pad HPD group*
*A. Braem, E. Chesi, W. Dulinski, F. Filthaut, A. Go,
C. Joram, G. Lion, J. Sequinot, P. Weilhammer, P. Wicht and T. Ypsilantis
Apollo Go Development of RICH and HPD for LHCb
17/11/98

2. LHCb Experiment
Spectrometer at the LHC collider dedicated to study CP violation in B decays
bb production cross-section peaks in the forward-backward direction  Forward geometry _
Apollo Go Development of RICH and HPD for LHCb
17/11/98

3. Particle ID in LHCb Some of the interested B decays channels:
B0d  p+p-
B0d  J/ KS
B0S  DS K
B0S  J/ 
B0d  D0K*0
Without K/p separation:
B0d  p+p- would be
contaminated with
B0d  Kp,
B0S  Kp,
B0S  K+K-
B0S  DS K would be contaminated with
B0S  DS 
Unable to tag B flavour through K ( b  c  s)
 Need particle identification! _ _ _
Apollo Go Development of RICH and HPD for LHCb
17/11/98

4. Particle ID requirements
Momentum coverage:
(a) Up to 150GeV/c for B0d  p+p- and
B0S  D-Sp+p+ p-
(b) Down to 1GeV/c for kaon tagging
 Use RICH
Goal: K/p separation in 1-150GeV/c range
Apollo Go Development of RICH and HPD for LHCb
17/11/98

5. Particle ID requirements
Momentum and polar angle correlation
 Two separate RICHs:
RICH 1: wider angular coverage for softer momentum tracks, before the magnet
RICH 2: very forward angle coverage but harder momentum tracks, after the magnet
Apollo Go Development of RICH and HPD for LHCb
17/11/98

6. RICH 1 Two radiators: 5cm Silica Aerogel 95cm C4F10 gas
Polar angle coverage: mrad
Mylar window to cut Rayleigh scattered UV photons in Aerogel
Spherical mirrors (190cm rad. of curvature) tilted by 250mrad to focus light onto
60cm x 100cm x2 photodetector area
Apollo Go Development of RICH and HPD for LHCb
17/11/98

7. RICH 2 180cm CF4 gas radiator: Polar angle coverages:
mrad in x (bending plane)
mrad in y (non-bending plane)
Spherical mirrors and flat mirrors to focus light onto
72cm x 120cm x2 photodetector area
Apollo Go Development of RICH and HPD for LHCb
17/11/98

8. Performance Performance:
Particle identification performances will be covered in R. Forty’s talk tomorrow.
Apollo Go Development of RICH and HPD for LHCb
17/11/98

9. Photodetectors Requirements: 3 options under study:
Total of 3m2 coverage, 73% active area
2.5 x 2.5 mm2 granularity, channels
High quantum efficiency in the visible and UV region
3 options under study:
Pad HPD:
127mm tube, 2048 channels
Fountain focusing
Analog readout
Pixel HPD:
80mm tube, 1024 channels
Cross focusing
Binary readout
Multi-anode PMT: (Hammamatsu R )
64 channels (8x8)
2.3x2.3mm granularity
Lenses needed to have comparable active area
Prototype tests will be covered in S. Easo (next talk)
Apollo Go Development of RICH and HPD for LHCb
17/11/98

10. Pad HPD Overview
HPD (Hybrid Photo Diode) = Photocathode + Silicon detector.
127mm diameter glass
envelope with borosilicate
UV-glass window
Bialkali (K2CsSb)
photocathode
4 focusing electrodes
Baseplate with 40
feedthroughs and
V-shaped groove for
cold indium sealing
Silicon sensor, 1x1 mm2,
2048pads
Multiplexed analog
readout
Photocathode
Borosilicate window Uc U1
114mm U2 U3
Focusing electrodes U4
Indium seal
Silicon sensor
baseplate
Groove
Feedthroughs
Apollo Go Development of RICH and HPD for LHCb
17/11/98

11. Silicon Sensor 50mm diameter, 300mm thick. Subdivided into 16 sectors
with 128 1x1mm2 pad sensor.
The sensor is wire bonded to
the printed ceramic with
readout electronics.
Test has been done
with VA3 chip (1-2ms
peaking time) with
10s signal/noise
Next step: fast electronics SCT128A (25ns peaking time) will be used (ENC= 500)
Apollo Go Development of RICH and HPD for LHCb
17/11/98

12. Electron Optics
To map 127mm diameter entrance window area onto 50mm Silicon sensor.
Fountain focussing, 20kV
90% window area can be covered with 3 electrodes
A 4th electrode (bleeder) needed to achieve unique mapping
Simulation with MAFIA and SIMION:
Without bleeder
With bleeder
Apollo Go Development of RICH and HPD for LHCb
17/11/98

13. Electron Optics
Optics has been verified with a non-sealed CsI tube and movable UV light source.
Result: 114mm coverage with 2.7 demagnification, point spread function of 0.35mm
Apollo Go Development of RICH and HPD for LHCb
17/11/98

14. HPD Fabrication Plant A UHV plant was built for
photocathode evaporation
Sealing of envelope and baseplate
4 moveable cariages
Sb source
K, Cs source
baseplate
glow discharge
Heating element to control photocathode temp.
Piston to seal the tube
Entirely covered with heating jacket for bakeout
Monitoring and Control using PC with BridgeView
Apollo Go Development of RICH and HPD for LHCb
17/11/98

15. HPD Fabrication Plant Apollo Go Development of RICH and HPD for LHCb
17/11/98

16. Photocathode Deposition
Bake-out at 250oC for more than 24hrs to reach a vacuum of 10-9 mbar
Cool down to 70oC,
deposit Sb till laser
light (l=632nm)
transmission reduces
to 85%
At 160oC, deposit K
till max. Q.E. is
reached at l=400nm
Deposit Cs also till
max. Q.E. is reached
at l=400nm.
If needed, evaporate K, Cs alternatively to replace re-evaporation loss and to further increase Q.E.
Apollo Go Development of RICH and HPD for LHCb
17/11/98

17. Evaporation Process Apollo Go Development of RICH and HPD for LHCb
17/11/98

18. Photocathode Effeciency
Q.E. (l=400nm) of
22 Photocathodes:
Q.E. of 3 recent
photocathodes:
Apollo Go Development of RICH and HPD for LHCb
17/11/98

19. Cold Indium Sealing
Cold Indium sealing to avoid thermal load and contamination of silicon sensor.
Nickel and Indium are deposited galvanically on the knife and on the groove to improve wetability
High purity (99.999%) Indium wire is pre-melted at 400oC in the groove before mounting
Piston pushes the baseplate onto the envelop with a force of 25kN
One prototype 110mm tube sealed (with metallic anode plate) and stable for 80hrs
Apollo Go Development of RICH and HPD for LHCb
17/11/98

20. Summary & Outlook Individual components tested
Integration of all components is under way
Further Q.E. optimization and stability of photocathode are under study
First 2048 pad HPD with CsI photocathode will soon be produced for test beam at the end of November
First bialkali HPD expected soon
Apollo Go Development of RICH and HPD for LHCb
17/11/98