Blair Ratcliff. Status Update: the Focusing DIRC Prototype at SLAC. Representing: I. Bedajanek, J Benitez, J. Coleman, C. Field, D.W.G.S. Leith, G. Mazaheri, M. McCulloch, B. Ratcliff, R. Reif, J. Schwiening, K. Suzuki, S Kononov, J. Uher. Focusing DIRC Prototype Goals.
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Representing: I. Bedajanek, J Benitez, J. Coleman, C. Field, D.W.G.S. Leith, G. Mazaheri, M. McCulloch, B. Ratcliff, R. Reif, J. Schwiening, K. Suzuki, S Kononov, J. Uher.
Focusing DIRC Prototype Goals
Typical Scanning System results
Typical Scanning System Results
Beam Test Setup
Start counters, lead glass
Mirror and oil-filled detector box:
Movable bar support and hodoscope
Radiator bar in support structure
PMT with amplifiers
Simulated eventsin GEANT 4
Photodetector coverage in focal plane
Beam Test Data
Occupancy for accepted events in single run, 400k triggers, 28k events
Timing versus Beam Position
Hit time distribution for single PMT pixel in three positions.
hit time (ns)
Example: chromatic growth for one selected detector pixel in position 1
calculate from reco
hit time (ns)
Cherenkov Angle Resolution
Photon detector performance continues to be improved by manufacturers, and is approaching the required level for timing resolution, and single photon efficiency. Burle MCP-PMT detectors with 10 micron holes have acceptable gain and timing resolution in magnetic fields up to 15 KG.
Single photon Cherenkov angular resolution performance of DIRC prototype in timing mode looks fine, and meets MC expectations.
A fast DIRC is operationally challenging. Calibration is and will be a major issue.
We hope that many of the basic performance issues will be addressed during the next year with the prototype.
Many photon detector questions remain:
Geometry, aging, rate capability, cross talk, sensitivity to magnetic field, quantum efficiency, reliability, electronics, number of channels, and cost.
Photon Pathlength in bar [cm]
Most of the data taken in positions 1, 3, 4, 5, 6
Energy (ADC counts)
Lead glass: single track ADC distribution
Hodoscope: single track hit map
x coordinate (cm)
Cherenkov counter: corrected event time
z coordinate (cm)
Corrected time (ns)
Cherenkov Angle Resolution
Position 1, mirror-reflected photons (longest photon path)
θc from time of propagation
θc from time of pixels
Efficiency relative to Photonis PMT, 440nm, H-9500 at -1000V
BABAR-DIRC Resolution Limits
Photon yield:18-60 photoelectrons per track (depending on track polar angle)
Typical PMT hit rates:200kHz/PMT (few-MeV photons from accelerator interacting in water)
Timing resolution:1.7nsper photon (dominated by transit time spread of ETL 9125 PMT)Cherenkov angle resolution:9.6mrad per photon → 2.4mrad per track
Focusing DIRC prototype designed to achieve • 4-5mrad qc resolution per photon,
• 3σπ/K separation up to ~ 5GeV/c
Chromatic effect at Cherenkov photon productioncos qc = 1/n(λ) bn(λ) refractive (phase) index of fused silican=1.49…1.46 for photons observed in BABAR-DIRC (300…650nm)→ qcγ= 835…815mradLargerCherenkov angle at production results in shorter photon path length→ 10-20cm path effect for BABAR-DIRC(UV photons shorter path)
Chromatic time dispersion during photon propagation in radiator barPhotons propagate in dispersive medium with group index ngfor fused silica: n / ng = 0.95…0.99Chromatic variation of ng results in time-of-propagation (ΔTOP) variation
ΔTOP= | –L l dl / c0 · d2n/dl2 |(L: photon path, dl: wavelength bandwidth)→ 1-3ns ΔTOP effect for BABAR-DIRC(net effect: UV photons arrive later)
Precisely measured detector pixel coordinates and beam parameters.→ Pixel with hit (xdet, ydet, thit) defines 3D propagation vector in bar and Cherenkov photon properties (assuming average )x, y, cos cos cos Lpath, nbounces,c, fc , tpropagation