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.
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.
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
Occupancy for accepted events in single run, 400k triggers, 28k events
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)
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.Summary
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)
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
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 production cos qc = 1/n(λ) bn(λ) refractive (phase) index of fused silica n=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 ng for fused silica: n / ng = 0.95…0.99 Chromatic 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