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Development of RICH Detectors in LHCb: Improving Particle Identification for LHCb-RICH Group

This presentation outlines the goals and design of the RICH Detectors for the LHCb Experiment, focusing on particle identification requirements. It covers components, prototype testing, photo detectors, readout methods, mirrors, radiators (aerogel, C4F10, CF4), and engineering design. The current status, goals of LHCb, CP violation measurements in B Meson system, and physics performances are explored. Specifications, momentum ranges, refractive index charts, photo detectors, and readout chip details are discussed, emphasizing the need for precise and efficient particle identification in the LHCb experiment environment.

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Development of RICH Detectors in LHCb: Improving Particle Identification for LHCb-RICH Group

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  1. Developmentof the RICH Detectors in LHCb For the LHCb-RICH Group RICH2002 PYLOS, GREECE S. Easo Rutherford-Appleton Laboratory June 5, 2002

  2. Development of the RICH Detectors in LHCb OUTLINE: • Goals of the LHCb Experiment. • Particle Identification Requirements and RICH Detector Design. • Components of the RICH Detector and Prototype Testing. • Photo Detectors: HPD as baseline option. • Readout : Binary Readout with Optical Links. • Mirrors. • Radiators: Aerogel, C4F10 , CF4 . • Engineering Design. • Summary of the Current Status.

  3. Goals of LHCb Precision Measurements of CP violation in the B Meson System. • Large Sample of Events with Bd and Bs Mesons. At the beginning of LHC , Nb b = 1012 per year. • 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. Examples: • a from B0d p+ p- • gfrom B0sDs+K- • g from B0d D0K*0 K-p+ K+p- Physics Performances of LHCb: Presentation by R. Forty. LHCb relies on Particle Identification for these measurements.

  4. LHCb Experiment This design is being modified,to optimize the performance of LHCb.

  5. Particle Identification in LHCb • B0d p+ p- B0d K+ p- • (signal) B0s K- p+ • B0s K+ K- • Lb  p K- • Lb  p p- B0sDs+K- B0sDs- p+ ( signal) (background) Tag the flavour of b-hadrons where bcs : Identify the kaon and its charge.

  6. Particle Identification in LHCb Momentum Range: • Upper limit from the pions in Bp+p- . • Lower Limit from the flavour tagging kaons. Pion Momentum Total Range: 1-150 GeV/c. Kaon Momentum Acceptance in Polar Angle: RICH1 : For small momentum particles, Full acceptance. Upstream of magnet. RICH2 : For high momentum particles, Lower acceptance. Downstream of magnet. Polar Angle vs. Momentum for charged tracks

  7. LHCb-RICH Specifications (Refractive Index-1) vs. Photon Energy RICH1: Aerogel 210 GeV/c C4F10< 70 GeV/c RICH2: CF4 <150 GeV/c. n=1.03 n=1.0014 Aerogel C4F10 CF4 L 5 86 196 cm qcmax 242 53 32 mrad pTh 0.6 2.6 4.4 GeV/c KTh 2.0 9.3 15.6 GeV/c n=1.0005

  8. LHCb-RICH Specifications Side View of Top Half of RICH1. Top View of Half of RICH2 Magnetic Shielding x z R=240 cm C4F10 Entry window Length units in cm. Beam Axis R=860cm • Spherical Mirrors: Tilted to Keep the Photo Detectors outside the Acceptance. • Plane Mirrors: to reduce the overall length of the Detector. • BeamPipe Limit : 25 mrad at RICH1, 15 mrad for RICH2.

  9. LHCb-RICH Photo Detectors • To Cover an Area of 2.6 m 2 with large Active area fraction (>73 %) . • Granularity of 2.5 X 2.5 mm2 and single photon sensitivity for 200600 nm. • LHC Speed Readout 40 MHz. • Baselinesolution: Hybrid Photo Diode with Silicon Pixels (Pixel HPD). • Backup solution: MultiAnode PMT : Presentation by F. Muheim. Pixel HPD: In collaboration with DEP. S20 photocathode with QE >20%.

  10. Pixel HPD • Photocathode Active Diameter: 72 mm, Overall Diameter 83 mm. • Anode 32 X 32 arrray of Silicon pixels. Pixel: 0.5 X 0.5 mm2 segmented into • 8 subpixels of size 0.0625X0.5 mm2 to match the readout chip. • HV: - 20 kV  5000 electrons Signal. • Cross-focussing. • Prototypes with different types of anodes made. • 168 + 262 HPDs in RICH1 + RICH2. • Using LED scans, Demagnification = 0.216 . • PSF from 33 microns on axis to 54 microns at the edge.

  11. Pixel HPD in Magnetic Field Results from Unshielded HPD Axial field causes rotation and stretch. • Distortions up to 10 Gauss tolerable. • Tests repeated with 0.9 mm cylindrical • Mu Metal shield: up to 30 Gauss tolerable. • In LHCb : individual Mu Metal shield + • large overall soft iron structures around • HPD arrays to shield up to 150300 Gauss. Transverse field causes Non-uniform shift.

  12. Pixel HPD Readout Chip • Developed at CERN for LHCb-RICH and ALICE Silicon Tracking detectors. Architecture compatible for both detectors. • 0.25 m m CMOS technology: Radiation Hard. • 9 million transistors in 15mm X 14mm. • 256 X 32 pixel cells. • cell size: 50m m X 425 m m. • Threshold: global+ individual adjust • LHCb Mode: 8 cells in a column  Super Pixel • Total Power consumption: 0.9 W Chip Prototype on a Carrier Schematic diagram of the pixel Readout Chip Cell

  13. Pixel Readout Chip Performance • Requirements: Threshold <2000 e- , Noise<250 e- , 40 MHz. • Lab tests on Prototype Chips: Bare Chip glued to a PCB and wire-bonded. Noise Threshold Mean = 1.7 mV = 112 e- Mean=14.8 mV = 977 e- • After Bump-bonding , Mean Threshold=1150 e-. • Threshold Width = 182 e- without the 3-bit adjustment of individual Thresholds. • New version of the chip prototype, received recently: works at 40 MHz. • Extensive programme of Chip testing being setup.

  14. Pixel HPD with the Pixel Chip • First prototype was made recently. • Tests done to verify its characteristics using LED. • Average number of pixels fired per LED pulse = . Vbias = 80 V Vbias=80V and HV=19kV. Poisson fit:  = 1.744 • Mean= 6.76kV(<1880 e-) Differential number of firing pixels •  : 0.82 kV (<230 e-) From counting theFraction of events with zero pixel hits = exp(- ) ,  = 1.741 HPD high voltage (kV) Mean Threshold < 2000 e-.

  15. LHCb RICH Mirrors • Baseline Solution: 6 mm thick glass coated by 900 nm Al + MgF2 or SiO2 . • Typical reflectivity= 0.9, Radiation Length = 4.7 % X0 + 4% X0 ( RICH2 Panel) . + 3% X0 (RICH1supports). • RICH2: 42 Hexagonal segments + 14 Half Hexagonal segments. Segment Size 510 mm (diagonal length) . RoC=8600mm. Plane Mirror: 40 rectangles of size 410 X 380 mm2 . • To reduce the material budget, new ‘light’ materials being sought: • From U.S.A.(CMA): • 2 mm thickness, 0.8 % X0 . • Composite: Carbon+ Epoxy. • Reflector: Pure Al + SiO coating. • From Italy (INFN) : • 2 mm thickness, <1 % X0 . • Composite: Plexiglass+ Epoxy. • RICH1: With light materials, 4 segments of size 820 mm X 614 mm. RoC=2400 mm. Support frame outside the acceptance.

  16. Testing LHCb Mirrors • Mirror Test Facility at CERN: Image of a point source D0 = 1.2 to 1.3 mm. Image Diameter( ) • Point source with 10 m m diameter. • Can be used to measure RoC. • For each RICH2 mirror: Expected Angular resolution=30 m rad. • For RICH2: Initial overall alignment < 1.0 mrad . After software alignment using data, we expect ~ 0.1 mrad.

  17. LHCb-RICH Gas Radiators and tests usingTestbeams • CF4 with RICH2 like geometry. • C4F10 with RICH1 like geometry. • Results compared with full Simulation. . • HPD: 18 mm diameter • Proximity focussing, • 61-pixel anode, Analogue Readout . • MAPMT: 64-pixel, Analogue Readout. • HPD: 40 mm diameter, • Cross-focussing, • 2048-pixel anode, Binary Readout. • HPD: 83 mm diameter, • Cross-focussing , • 61-pixel anode, Analogue Readout.

  18. Display of Events from 120GeV/c p- LHCb-RICH TestBeam CF4 Radiator in RICH2 setup. Cherenkov Angle Per Photon in rad. Single Photon Cherenkov Angle resolution in mrad Ref: NIMA 456(2001) 233-247

  19. Testbeam using C4F10 and Pixel HPDs C4F10 Radiator in RICH1 setup Display of Events: Using 120GeV/c p-.. Three 83 mm HPDs with external Analogue Readout.

  20. Yield in MC LHCb-RICH Test beams C4F10 Radiator in RICH1 setup. Data: s=1.02mrad. MC: s=0.98mrad. Yield in Data HPD C4F10 Pressure=160 mbar. Display of Events: Ring in HPD1 Using 120GeV/c p-.. Three 83 mm HPDs with external Analogue Readout. Photoelectron yield per event Figure of merit = 202 + 16 cm-1

  21. LHCb-RICH Radiators: Aerogel Properties of Aerogel: • Quartz-like structure with a density of about 0.15 g/cm3 . • The ones we tested came from Novosibirsk : hygroscopic • Matsushita : hydrophobic. • For two of the tiles from Novosibirsk, • n=1.03066 at 400 nm, C=0.00719 mm4/cm. A=0.9368 • n=1.02982 at 400 nm, C=0.00673 mm4/cm. A=0.9589 • Quality is improving over time. T = A e (-C t / l4) Transmittance: • Tested in a testbeam: • Typical beam: 9 GeV/c p - . • Using HPD prototypes made at CERN: . • Bialkali Photocathodes, • 114 mm active input diameter, ( 127 mm overall diameter) • Fountain Focussing, • 2048 Silicon Pads of size 1X 1 mm2 Presentation by M.Musy

  22. LHCb-RICH2 Engineering Design magnetic shield box to shield against magnetic stray field of ~150 Gauss exit window low mass frame Plane mirrors spherical mirrors on supporting planes beam pipe envelope supported by windows entry window low mass photodetectors with individual magnetic shields

  23. Summary of the Current Status • The Design of the RICH detectors is well advanced. • The development of the HPD and its readout chip are two • of the major projects that required lot of efforts. • The RICH2 has passed the Engineering Design Review. • The RICH1 Engineering Design continuing.

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