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

Development of the RICH Detectors in LHCb  Goals of the LHCb Experiment.  Particle Identification Requirements and RICH Detector Design.  Components of the RICH Detector and Prototype Testing. OUTLINE:  Photo Detectors: HPD as baseline option.  Readout : Binary Readout with Optical Links.  Mirrors.  Radiators: Aerogel, C 4 F 10, CF 4.  Engineering Design.  Summary of the Current Status.

Goals of LHCb Precision Measurements of CP violation in the B Meson System.  Large Sample of Events with B d and B s Mesons. At the beginning of LHC, N b b = 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:  from B 0 d        from B 0 s  D s + K -  from B 0 d  D 0 K *0  K -  + K +   Physics Performances of LHCb: Presentation by R. Forty. LHCb relies on Particle Identification for these measurements.

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

Particle Identification in LHCb Tag the flavour of b-hadrons where b  c  s : Identify the kaon and its charge. B 0 d      B 0 d       (signal) B 0 s       B 0 s         b  p K -    b  p   B 0 s  D s + K - B 0 s  D s -   ( signal) (background)

Particle Identification in LHCb  Upper limit from the pions in B        Lower Limit from the flavour tagging kaons. Momentum Range: Pion Momentum Kaon Momentum Total Range: GeV/c. 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

LHCb-RICH Specifications (Refractive Index-1) vs. Photon Energy RICH1: Aerogel 2  10 GeV/c C 4 F 10 < 70 GeV/c RICH2: CF 4 <150 GeV/c. n=1.03 n= n= Aerogel C 4 F 10 CF 4 L cm  c max mrad  Th GeV/c K Th GeV/c

Side View of Top Half of RICH1. Top View of Half of RICH2 LHCb-RICH Specifications Length units in cm. 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. R=240 cm x z Beam Axis C 4 F 10 Entry window Magnetic Shielding R=860cm

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 mm 2 and single photon sensitivity for 200  600 nm. LHC Speed Readout 40 MHz.  Baseline solution: 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%.

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 mm 2 segmented into 8 subpixels of size X0.5 mm 2 to match the readout chip. HV: - 20 kV  5000 electrons Signal. Cross-focussing. Prototypes with different types of anodes made HPDs in RICH1 + RICH2.  Using LED scans, Demagnification =  PSF from 33 microns on axis to 54 microns at the edge.

Transverse field causes Non-uniform shift. Axial field causes rotation and stretch. Pixel HPD in Magnetic Field 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. Results from Unshielded HPD

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

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. Mean=14.8 mV = 977 e- Mean = 1.7 mV = 112 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. Noise Threshold

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 = . Differential number of firing pixels HPD high voltage (kV) V bias = 80 V Mean= 6.76kV(<1880 e-)  : 0.82 kV (<230 e - ) V bias =80V and HV=19kV. From counting the Fraction of events with zero pixel hits = exp(-  ),  = Poisson fit:  = Mean Threshold < 2000 e-.

LHCb RICH Mirrors  Baseline Solution: 6 mm thick glass coated by 900 nm Al + MgF 2 or SiO 2.  Typical reflectivity= 0.9, Radiation Length = 4.7 % X 0 + 4% X 0 ( RICH2 Panel). + 3% X 0 (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 mm 2.  To reduce the material budget, new ‘light’ materials being sought:  From U.S.A.(CMA):  2 mm thickness, 0.8 % X 0.  Composite: Carbon+ Epoxy.  Reflector: Pure Al + SiO coating.  From Italy (INFN) :  2 mm thickness, <1 % X 0.  Composite: Plexiglass+ Epoxy.  RICH1: With light materials, 4 segments of size 820 mm X 614 mm. RoC=2400 mm. Support frame outside the acceptance.

Testing LHCb Mirrors  Mirror Test Facility at CERN: Image of a point source  Point source with 10  m diameter.  Can be used to measure RoC.  For each RICH2 mirror: Expected Angular resolution=30  rad.  For RICH2: Initial overall alignment < 1.0 mrad.  fter software alignment using data, we expect ~ 0.1 mrad. D 0 = 1.2 to 1.3 mm. Image Diameter( )

LHCb-RICH Gas Radiators and tests usingTestbeams 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.. CF 4 with RICH2 like geometry. C 4 F 10 with RICH1 like geometry. Results compared with full Simulation.

Display of Events from 120GeV/c   Cherenkov Angle Per Photon in rad. CF 4 Radiator in RICH2 setup. 18mm HPD MAPMT MC Data Single Photon Cherenkov Angle resolution in mrad LHCb-RICH TestBeam Ref: NIMA 456(2001)

Display of Events: Using 120GeV/c    Three 83 mm HPDs with external Analogue Readout. Testbeam using C 4 F 10 and Pixel HPDs C 4 F 10 Radiator in RICH1 setup

Display of Events: Ring in HPD1 Using 120GeV/c    Three 83 mm HPDs with external Analogue Readout. LHCb-RICH Test beams C 4 F 10 Radiator in RICH1 setup. Data:  mrad. MC:  0.98mrad. HPD Yield in Data Yield in MC C 4 F 10 Pressure=160 mbar. Photoelectron yield per event Figure of merit = cm -1

LHCb-RICH Radiators: Aerogel Presentation by M.Musy Properties of Aerogel: Quartz-like structure with a density of about 0.15 g/cm 3. The ones we tested came from Novosibirsk : hygroscopic Matsushita : hydrophobic. For two of the tiles from Novosibirsk, n= at 400 nm, C=  m 4 /cm. A= n= at 400 nm, C=  m 4 /cm. A= Quality is improving over time. T = A e (-C t /  4 ) Transmittance: Tested in a testbeam: Typical beam: 9 GeV/c    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 mm 2

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

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.