Photodetector R&D and the Fast Focusing DIRC Prototype at SLAC: A Status Report Blair Ratcliff, SLAC Representing C. Field, T. Hadig, D.W.G.S. Leith, G. Mazaheri, B. Ratcliff, J. Schwiening, J. Uher, J. Va’vra - Motivation - R&D Program Goals - Photon Detector Evaluation -Status of Prototype -Summary
Some PID Detector Design Assumptions and Issues: • Need to maintain radiation length in front of calorimeter to (<20%) at 90 degrees. • Radiation robustness of fused silica is OK (expect ~0.01-1 mega-rad within 10 year lifetime). • Photon Detector Lifetimes must be long and be well understood. • Will have good central tracking ( ~< 1 mrad in dip angle). • There will be good dE/dx from the tracking system (Is this true?). • Backgrounds will be a (the?) major concern. • Present PID performance needs to be maintained (Does physics require that it be enhanced?). 2 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
� A generic DIRC device is well matched to PID needs at a Super-B Factory SLAC group’s strategy: Since a DIRC is intrinsically a 3-D device, we should try to take full advantage of all three dimensions for best performance and background rejection. Background rejection improves ~ directly with time resolution. Other uses for timing (e.g., measuring Cherenkov photon wavelength or making PID competitive angular or TOF measurements) have resolution thresholds in the ~150 ps and ~< 100 ps range respectively. 3 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Fast Focusing DIRC detector - schematic “design” � Goal: true 3D imaging using x,y and time for each photon. � The crucial issue: Is there an adequate photon detector ?? (Many questions including (1) quantum efficiency; (2) noise; (3) cross talk;(4) timing resolution; (5) geometrical considerations; (6) operation in a magnetic field; (7) operational lifetime; (8) cost. 4 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Goals of R&D Program I. Detailed Lab Investigation of Candidate Photon Detectors a. Develop methodology to study timing, efficiency and spatial properties of candidate detectors. b. Evaluate candidate detectors. c. Work with manufacturers to improve product. II. Test detector concepts and candidate photon detectors in a “conceptual” scale prototype a. ~ 400 channels of fast electronics. b. 4m fused silica bar, ~100 ps timing resolution, and spatial resolution similar to BaBar DIRC. c. Demonstrate that (1) detector methodology is understood, and (2) demonstrate correction of chromatic error by timing. d. Test and evaluate performance of photon detector candidates in a “real” detector. e. Evaluate operations issues. 5 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Hamamatsu H-8500 Flat panel MaPMT Hamamatsu Co. data sheet 6 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Burle 85011 MCP-PMT Burle Co. data sheet 7 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Scanning setup to measure PMT response • Light Source - PiLas laser diode operating in single photoelectron mode. - λ = 635 & 430nm (on loan from T. Sumyioshi). - 63 µ m dia. multi-mode fiber, with lenses at both ends; ~150 µ m spot; timing resolution ~ 35 ps. • x-y Stage -Stepper motor moves the end of the fiber equipped with a lens, typical x-step ~ 100 µ m & y-step ~ 1mm. • Data Accumulation - A “hit” must be in the illuminated pad within a time window - Efficiency is relative either to the 2 inch dia. Photonis XP 2262B PMT. ( or the DIRC PMT, ETL 9125FLB17). - Typical DAQ trigger rate: 20kHz. 8 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Resolution of the scanning system Hamamatsu Flat Panel H8500 MaPMT #2 Micro-structure of the dynode electrodes: � Clearly see the details of the dynode electrode structure. Spatial resolution of the system is less than 150 µ m, for a step size of 25 µ m. 9 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Typical Scan: The Relative Spatial Response Along a Line Across 8 Pads Hamamatsu H8500 Flat Panel-PMT #2 Burle 85011-501 MCP-PMT #3 � In this example, the Hamamatsu MaPMT uniformity is ~1:2.5 and the Burle MCP-PMT uniformity is ~1:1.5. 10 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Typical MCP Photo-detector (Burle) Scans 635 nm: 430nm: Burle MCP- PMT #3 Burle MCP- PMT #4 Burle MCP- PMT #10 Burle MCP- PMT #8 � Typical relative efficiency is 50-60% of the 2 inch dia. Photonis XP 2262B PMT at 430nm. The efficiency drops to 30-50% around the edges at 430nm. 11 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Typical Flat PMT (Hamamatsu) Scans 635 nm: 430nm: Hamamatsu MaPMT #1 Hamamatsu MaPMT #2 Hamamatsu MaPMT #4 � Hamamatsu Flat Panel MaPMT relative efficiency is 50-70% of the Photonis XP 2262B PMT at 430nm. The efficiency drops to 30-50% around the edges at 430nm. 12 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Timing studies in MaPMT and MCP-PMT Light source: Use the 635nm PiLas laser diode in single photoelectron mode. Hamamatsu Flat MaPMT #2 Panel H8500 PMT Burle 85011-501 MCP-PMT MCP #3 � Double Gaussian fit. � Hamamatsu Flat Panel MaPMT timing resolution is sufficient to correct chromatic term. � Burle MCP-PMT #3 has a very long tail due to recoil electrons from the MCP top surface (the tail contains ~20% of all events !). The MCP-to-cathode distance is 6mm. 13 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Dependence of timing resolution on the Burle MCP PMT design Light source: Use the 635nm PiLas laser diode in single MCP #3 photoelectron mode. Former design (85011-501 ) MCP-to-Cathode distance = 6 mm; 8x8 pads; one pad selected New design (85011-430) MCP-to-Cathode distance MCP #16 = 0.75 mm; 8x8 pads; one pad selected � Double Gaussian fit. � The reduction of the MCP-to-Cathode distance to 0.75mm limits the rate of recoiling photoelectrons from the MCP surface, which reduces the tail in the timing spectrum. These electrons are, however, lost from the detection efficiency, but the spectrum is more Gaussian. 14 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Compare timing distributions on two different pads MCP #16, Pad 14: MCP #16, Pad 24: � Single Gaussian fit to the timing distribution generated at each laser head location. � Measure typically σ = 70-80ps in the central pad region, slightly worse near the boundary. � Worse timing resolution around edges is due to the charge sharing which causes lower pulse height, and possibly cross-talk from hits in neighboring pads. 15 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Focusing DIRC prototype Focal plane Calibration Fiber Detector Mirror Filled with KamLand mineral oil Fused Silica bar � 3D imaging: x,y, and time. � Photon propagation time measured to σ ~100ps : allows timing to be used directly in separation; the correction of the chromatic error contribution to the Cherenkov angle error; and efficient background suppression. � Mirror focusing: removes bar exit aperture from the angular resolution. � Expected angular performance similar to present BaBar DIRC: defined by chosing focal length and pixel size (6x6 mm at present). 16 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Status of Photo-Detector Testing Program • Have developed and are utilizing a bench top system capable of measuring spatial and timing characteristics of photodetectors to better than ~150 um in space and ~ 50 ps in time. • Have characterized a substantial number of candidate PMTs, especially the Hamamatsu Flat Panel MaPMT and the Burle MCP-PMT. Are working with the manufacturers to improve performance. • Typical relative eff (compared to a standard PMT) at 430 nm is ~50-60% for the BURLE MCP-PMT, and ~ 60- 70% for the Hamamatsu MaPMT. The efficiency varies significantly near the edges and across pads. • There are still substantial non-Gaussian tails in timing distributions. To be useful for the most challenging applications, these must be reduced substantially • Many real world issues are still to be understood, especially aging, and performance in a magnetic field. • Basic performance should allow reasonable performance from a prototype, but there is little margin for error or efficiency loss. • As for the future: Is the glass ½ empty or ½ full? 17 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
Elements of the prototype Mirror 4m-long fused silica DIRC bar Photon detectors at the focal Detector box filled with oil plane 18 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
The DIRC Prototype in the Test Beam 4m-long DIRC bar + Photon 3 MCP-PMTs and 2 detector MaPMTs: 320 ch. In test beam (ESA SLAC) 32-channel SLAC CFD/TAC board 19 B. Ratcliff, Super B Factory Workshop, April 20-22, 2005
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