Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20061

Status Update: the Status Update: the Focusing DIRC Prototype at Focusing DIRC Prototype at

SLACSLAC Blair RatcliffBlair Ratcliff

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.

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20062

Focusing DIRC Prototype GoalsFocusing DIRC Prototype GoalsWork with manufacturers to develop and characterize one or more fast, pixelated photon detectors including;

• basic issues such as cross talk, tube lifetime, and absolute efficiency• operation in 15 KG field

Measure single photon Cherenkov angular resolution in a test beam• use a prototype with a small expansion region and mirror focusing, instrumented with a

a number of candidate pixelated photon detectors and fast (25 ps) timing electronics.• demonstrate performance parameters• demonstrate correction of chromatic production term via precise timing• measure N0 and timing performance of candidate detectors.

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20063

Prototype OpticsPrototype Optics

Radiator• 3.7m-long bar made from three spare high-quality

BABAR-DIRC barsExpansion region

• coupled to radiator bar with small fused silica block• filled with mineral oil (KamLand experiment) to match

fused silica refractive index • include optical fiber for electronics calibration• would ultimately like to used solid fused silica block

Focusing optics• spherical mirror from SLD-CRID detector (focal length 49.2cm)

Photon detector• placed in fixed slots allowing easy replacement.• typically using 2 Hamamatsu flat panel PMTs and 3 Burle MCP-PMTs in focal plane• readout to CAMAC/VME electronics with 25 ps resolution. Limited number of channels available.

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20064

Burle 85011-501 MCP-PMT• bialkali photocathode• 25μm pore MCP• gain ~5×105

• timing resolution ~70ps• 64 pixels (8×8), 6.5mm pitch

Typical Scanning System results Typical Scanning System results (Burle 85011-501)(Burle 85011-501)

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20065

Typical Scanning System Results Typical Scanning System Results (Hamamatsu H-8500)(Hamamatsu H-8500)

Hamamatsu H-8500 Flat Panel Multianode PMT• bialkali photocathode• 12 stage metal channel dynode• gain ~106

• timing resolution ~140ps• 64 pixels (8×8), 6.1mm pitch

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20066

Beam Test SetupBeam Test Setup• 10 GeV/c e- beam in End Station A at SLAC.

• Beam enters bar at 90º angle.

• 10 Hz pulse rate, approx. 0.1 particle per pulse

• Bar contained in aluminum support structure

• Beam enters through thin aluminum foil windows

• Bar can be moved along long bar axis to measure photon propagation time for various track positions

• Trigger signal provided by accelerator

• Fiber hodoscope (16+16 channels, 2mm pitch) measures2D beam position and track multiplicity

• Cherenkov counter and scintillator measure event time

• Lead glass calorimeter selects single electrons

• All beam detectors read out via CAMAC (LeCroy ADCs and TDCs, Philips TDC, 57 channels in total)

Mirror and oil-filled detector box:Movable bar support and hodoscope Start counters, lead glass

Hodoscope

Scintillator

Cherenkovcounter

Calorimeter

Radiator bar in support structure

Prototype

e– beam

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20067

Prototype ReadoutPrototype Readout

Photodetector backplanePMT with amplifiers

• For 2005 beam test read out two Hamamatsu Flat PanelPMTs and three Burle MCP-PMTs (total of 320 pads).

• Elantec 2075EL amplifier (130x) on detector backplane

• SLAC-built constant fraction discriminator

• Eight Philips 7186 TDCs (25ps/count) for 128 channels

• Four SLAC-built TDC boards: TAC & 12 bit ADC (~31ps/count) for 128 channels

• Connect only pads close to expected hit pattern of Cherenkov photons

• Calibration with PiLas laser diode (~35ps FWHM) to determine TDCs/ADCs channel delays and PMT uniformity

Photodetector coverage in focal plane

Simulated events

in GEANT 4

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20068

Beam Test DataBeam Test Data

• In July, August, and November 2005 we took beam data during five periods, lasting from few hours to several days.

• Total of 4.1M triggers recorded, 10 GeV/c e–

• Reconstructed 201k good single-track events

• Beam entered the radiator bar in 7 different locations.

• Recorded between 100k and 700k triggers in each beam location.

• Photon path length range: 0.75m – 11m.

Occupancy for accepted events in single run, 400k triggers, 28k events

Mirror

Expansion region

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 20069

Timing versus Beam PositionTiming versus Beam Position

Hit time distribution for single PMT pixel in three positions. Position 1

direct

mirrorreflection

Position 4

Position 6

hit time (ns)Mirror

Expansion region

Position 1

Position 4

Position 6

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200610

Chromatic BroadeningChromatic Broadening

ΔTOP (ns)

ΔTOP (ns)

hit time (ns)

Example: chromatic growth for one selected detector pixel in position 1

75cm path

870cmpath

σnarrow≈170ps

σnarrow≈420ps

• First peak ~75cm photon path length

• Second peak ~870cm photon path length

• Important: careful calibration of all TDCchannels to translate counts into ps

• Use accelerator trigger signal as event time

• Calculate the time of propagation assuming average <λ>≈410nm

• Plot ΔTOP: measured minus expected time of propagation

• Fit to double-Gaussian

• Observe clear broadening of timing peak for mirror-reflected photons

calculate from reco

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200611

Cherenkov Angle ResolutionCherenkov Angle Resolution

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200612

Burle MCP-PMT with 10 micron holes: sensitivity to magnetic field angular rotation

wrt z axis ( B = 15kG)

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200613

Timing in Magnetic Field Timing in Magnetic Field (B=15 Kg)(B=15 Kg)

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200614

SummarySummary 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.

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200615

Additional SlidesAdditional Slides

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200616

Data SetData Setrun 1position 4 5,590 tracks

run 4position 7 8 tracks

run 7position 131,561 tracks

run 10position 5 5,107 tracks

run 13position 336,880 tracks

run 2position 4 4,650 tracks

run 3position 1 9,651 tracks

run 6position 622,911 tracks

run 9position 3 5,058 tracks

run 12position 131,914 tracks

run 5position 7 4,126 tracks

run 8position 2 6.232 tracks

run 11position 420,414 tracks

run 14position 517,475 tracks

Photon Pathlength in bar [cm]

Most of the data taken in positions 1, 3, 4, 5, 6

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200617

Beam DetectorsBeam Detectors

z coordinate (cm)

x co

ordi

nate

(cm

)

Hodoscope: single track hit map

Cherenkov counter: corrected event time

Lead glass: single track ADC distribution

Corrected time (ns)

Energy (ADC counts)

doubles

π –

e –

σnarrow≈50ps

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200618

Cherenkov Angle ResolutionCherenkov Angle Resolution

θc from time of propagation

θc from time of pixels

σnarrow≈7.1mrad

σ≈13mrad

Position 1, mirror-reflected photons (longest photon path)

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200619

Hamamatsu H-9500Hamamatsu H-9500

Hamamatsu H-9500 Flat Panel Multianode PMT• bialkali photocathode• 12 stage metal channel dynode• gain ~106

• typical timing resolution ~220ps

• 256 pixels (16×16), 3 mm pitch• custom readout board – read out as 4×16 channels

σnarrow ≈220ps

Efficiency relative to Photonis PMT, 440nm, H-9500 at -1000V

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200620

BABAR-DIRC Resolution LimitsBABAR-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: 1.7ns per photon (dominated by transit time spread of ETL 9125 PMT)

Cherenkov angle resolution: 9.6mrad per photon → 2.4mrad per track

Limited byLimited by BABAR-DIRCBABAR-DIRC Improvement strategyImprovement strategy

Size of bar imageSize of bar image ~ 4.1mrad~ 4.1mrad Focusing opticsFocusing opticsSize of PMT pixelSize of PMT pixel ~ 5.5mrad~ 5.5mrad Smaller pixel sizeSmaller pixel size

Chromaticity (n=n(Chromaticity (n=n()))) ~ 5.4mrad~ 5.4mrad Better timing resolutionBetter timing resolution

Focusing DIRC prototype designed to achieve

• 4-5mrad c resolution per photon,

• 3σ π/K separation up to ~ 5GeV/c

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200621

Chromatic EffectsChromatic Effects

Chromatic effect at Cherenkov photon production cos c = 1/n(λ)

n(λ) refractive (phase) index of fused silica n=1.49…1.46 for photons observed in BABAR-DIRC (300…650nm)

→ cγ = 835…815mrad

Larger Cherenkov 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 bar

Photons 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 d/ c0 · d2n/d2 |

(L: photon path, dwavelength bandwidth)

→ 1-3ns ΔTOP effect for BABAR-DIRC (net effect: UV photons arrive later)

Refractive Indices and Dispersion versus Wavelength for SiO2

1.4

1.5

1.6

1.7

1.8

1.9

2

0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7

Photon Wavelength (microns)

Refra

ctiv

e In

dex

0.01

0.1

1

10

Disp

ersi

on, -

dn/d

n(phase) n (group)

Dispersion [n (phase)] Dispersion [n (group)]

Dispersion [n (group)]/ Dispersion [n (phase)]

Blair Ratcliff2nd Workshop on SuperB, Frascati, March 200622

ReconstructionReconstruction

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, c , tpropagation