Timing and cross-talk properties of Burle
multi-channel MCP PMTs
Peter Križan
University of Ljubljana and J. Stefan Institute
RICH07, October 15-20, 2007
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Contents
Motivation for fast single photon detection in high B fields
MCP PMTs
Cross talk sources and modeling, impact on timing
Bench test set up
Sensitivity and timing – position dependence
Summary
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Hot topics in photon detection for RICHes
For improved PID in super B factories:
• Belle PID upgrade in the barrel and forward regions
• DIRC upgrade for Super B in Frascati
Single photon detection with:
Operation in high magnetic field (1.5T)
Excellent timing (time-of-arrival information)
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Proximity focusing RICH in the forward region
talk by Toru Iijima
Requirements and constraints:
● ~ 5 s K/p separation @ 1-4 GeV/c
● operation in magnetic field 1.5T
● limited available space ~250 mm
Proximity focusing
aerogel RICH
- n = 1.05
- qc(p) ~ 308 mrad @ 4 GeV/c
- qc(p)– qc(K) ~ 23 mrad
- pion threshold 0.44 GeV/c,
- kaon threshold 1.54 GeV/c
October 18, 2007
- time-of-flight difference (2m):
t(K) - t(p) = 180 ps @ 2 GeV/c
45 ps @ 4 GeV/c
RICH07, Trieste
Peter Križan, Ljubljana
Beam tests
pion beam (p2) at KEK
Clear rings, little background
Photon detector: array of 16
H8500 (flat pannel) PMTs
October
This18,photon
detector does
not work in magnetic
field
2007
RICH07, Trieste
Peter Križan, Ljubljana
Photon detectors for the aerogel RICH
Photon detector candidates for 1.5T:
• BURLE 85011 microchannel plate (MPC) PMT
• Multichannel H(A)PD – R+D with Hamamatsu
 talk by Shohei Nishida
• SiPM (G-APD)
October 18, 2007
 talk by Samo Korpar
RICH07, Trieste
Peter Križan, Ljubljana
Photon detector candidate for 1.5 T: MCP-PMT
BURLE 85011 microchannel plate (MCP) PMT: multi-anode
PMT with two MCP stages
excellent performance in beam and bench tests
 very fast (s=50ps for single photons)
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Basic parameters of BURLE MCP-PMTs
multi-anode PMT with two
MCP steps
 bialkali photocathode
6
 gain ~ 0.6 x 10
 collection efficiency ~ 60%
2
 box dimensions 71x71mm
 active area fraction ~ 52%
 2mm quartz window

BURLE 85011 MCP-PMT
64 (8x8) anode pads
 pitch ~ 6.5mm, gap ~ 0.5mm
 25 mm pores

October 18, 2007
BURLE 85001 MCP-PMT
4 (2x2) anode pads
 pitch ~ 25mm, gap ~ 1mm
10 mm pores

RICH07, Trieste
Peter Križan, Ljubljana
Beam tests of Burle MCP PMT
NIM A567 (2006) 124
Tested in pion beam combination
with multi-anode PMTs.
Stable operation, very good
performance
MCP-PMT
multi-anode PMTs
October 18, 2007
Results:
s ~13 mrad (single cluster)
J
 number of clusters per track N~ 4.5
 s ~ 6 mrad (per track)
J
→ ~ 4 s p/K separation at 4 GeV/c
To do list:
improve collection efficiency and
active area fraction higher
number of det. photons  done
aging study
RICH07,
Trieste
Peter Križan, Ljubljana
MCP-PMT timing properties
Bench tests with pico-second laser:
amplifier ORTEC FTA820A
 discriminator PHILIPS 308
 CAMAC TDC Kaizu works KC3781A,
25ps LSB
 CAMAC charge sensitive ADC

Time resolution as a function of the number
of October
detected
photons.
18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Beam test: time-of-flight measurement
Time-of-flight with Cherenkov photons from aerogel radiator
and PMT window
Cherenkov photons
from aerogel
START
track
STOP
MCP PMT
Cherenkov photons
from PMT window
aerogel
MCP-PMT
talk by Toru Iijima
NIM A572 (2007) 432
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
New bench tests: cross-talk and timing properties
Burle MCP PMT has excellent timing properties, a promising
photon detector also for very precise time measurements.
Additional bench tests needed: study detailed timing properties
and cross-talk.
Determine their influence on the
position resolution and
time resolution
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Scanning setup: optical system
Outside dark box:
 PiLas diode laser system EIG1000D
(ALS)
 404nm laser head (ALS)
 filters (0.3%, 12.5%, 25%)
 optical fiber coupler (focusing)

optical fiber (single mode,~4mm core)
Inside dark box mounted on 3D stage:
 optical fiber coupler (expanding)
 semitransparent plate
 reference PMT (Hamamatsu H5783P)
 focusing lens (spot size s ~ 10mm)
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Scanning setup: read-out
NIM
amplifier
ORTEC
FTA820A
discriminator
Philips
signal splitter model 806
passive 3-way
laser rate 2kHz (~DAQ rate)
 amplifier: 350MHz (<1ns rise time)
 discriminator: leading edge, 300MHz
 TDC: 25ps LSB(s~11ps)
 QDC: dual range 800pC, 200pC
 HV 2400V

October 18, 2007
RICH07, Trieste
TDC
Kaizu works
KC3781A
CAMAC
QDC
CAEN
V965
VME
ALS
PiLas
controller
PC
LabWindows
CVI
Peter Križan, Ljubljana
Time walk correction
ADC
TDC vs. ADC correlation is fitted
with
P2
TDC  P1 
ADC  P3
and used for TDC correction
raw TDC
raw TDC
ADC
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Corrected TDC
s = 40ps
s = 37ps
s = 39ps
s = 38ps
Corrected TDC distributions
for all pads
70%
20%
10%
October 18, 2007
Response:
 prompt signal ~ 70%
 short delay ~ 20%
 ~ 10% uniform distribution
RICH07, Trieste
Peter Križan, Ljubljana
Photon electron detection:
modeling
Parameters used:
 U = 200 V
 l = 6 mm
 E = 1 eV
0
2
 m = 511 keV/c
e
-19 As
 e = 1.6 10
0
d0
g
Photo-electron:
 d
0,max ~ 0.8 mm
 t ~ 1.4 ns
0
 Δt ~ 100 ps
0
−
a
e
l
d1
g
Backscattering:
 d
1,max ~ 12 mm
 t
1,max ~ 2.8 ns
−
e
b
Charge sharing
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
l
Photo-electron:
simple estimates
2me
t0  l
Ue0
E0
d 0  2l
cos a
Ue0
Distributions assuming
that photo-electron is
emitted at angle a
uniformly over the solid
angle
d0
~ 90ps
~ 0.8mm
t0
October 18, 2007
Maximum variation of
photo-electron
travel
time.
t0  t0
RICH07, Trieste
E0
l

2me E0
Ue0 Ue0
Peter Križan, Ljubljana
Timing resolution, contributions
Laser: 15ps (rms)
Electronics: 12ps (rms)
TTS of photo-electron (blue): 26ps (rms)
Sum in squares: 32ps  very close to 37-40ps

s = 40ps
s = 39ps
October 18, 2007
s = 37ps
s = 38ps
RICH07, Trieste
Time resolution of the
main peak seems to
be dominated by the
photo-electron time
spread
Peter Križan, Ljubljana
Elastic back-scattering
~ 12mm
d1
g
2.8ns
−
e
b
l
Travel time t1 vs.
travel distance d1
Distributions assuming
that back-scattering by
angle b is uniform over
the solid angle
~ 2.8ns
t1  2t0 sin b
October 18, 2007
RICH07, Trieste
~ 12mm
d1  2l sin 2b
Peter Križan, Ljubljana
Understanding time-of-arrival distribution
Normal photo-electrons
70%
Inelastically scattered
photo-electrons?
20%
10%
October 18, 2007
Elastically scattered
photo-electrons
RICH07, Trieste
Peter Križan, Ljubljana
Photon detection uniformity
Number of detected events at different positions of light spot
– sum of all 4 channels
 double counting at pad boundaries due to charge sharing

October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Photon detection uniformity –
single pad
number of all detected events
maximum signal detected by the pad

with
number of events with maximum signal
detected by other pads

number of delayed events with maximum
signal detected by the pad

October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Charge sharing
Fraction of the signal detected on
channel 1 vs. x position of light spot
sizable charge sharing in
~2mm wide boundary area
 can
be used to improve
position resolution

October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Charge sharing
red
blue
Comparison of the
charge
sharing
effect for red (635
nm) and blue (405
nm) laser
red
blue
As expected:
more photo-electron
initial energy for
photons
October 18, 2007
RICH07, Trieste
Peterblue
Križan, Ljubljana
Detailed 1D scan
all events with maximum
signal on channels 1 and 2
1
1
2
delayed (>1.1ns) events with
maximum signal on channels 1
and 2
2
1
2
2x12 mm
= range
photo-electrons
Octoberof
18,back-scatterd
2007
RICH07, Trieste
2x12
mm Ljubljana
Peter Križan,
Timing uniformity
1
1
2
Time of arrival vs. x
good uniformity over
most of the surface
large deviation at active area edge
small deviation at pad boundaries
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
MCP with 8x8 pads: detection vs. x
Number of detected signals vs. x
 Small variation over central part

Response similar to 2x2 MCP PMT: charge sharing and long tails
October
18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
due to
photo-electron
back-scattering.
8x8: Timing uniformity for single pads
TDC vs. x correlation of single pads:
same features as for the 2x2 tube
 uniform for central pads
 large variation for pads at the outer
edges of the tube
ch. 4
October 18, 2007ch.
1
RICH07, Trieste
ch. Peter
8 Križan, Ljubljana
Conclusions
Back-scattering range and spread in timing depend on the
d1

photocathode-MCP plate distance g

photocathode-MCP plate voltage
−
e
b
The distance should be as small as possible, ~0.5mm-1mm
(in the tested tube 6mm)
The voltage should be as high as possible, 500V max.
allowed (in the tested tube fixed to 200V)
 Some of the effects will be reduced (or disappear) in high
B field, some will remain (timing)
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
l
Summary
Burle multianode MCP PMTs have been tested in beam and
bench tests  stable operation, very good performance
They have excellent timing properties  a promising photon
detector also for very precise time measurements.
Additional bench tests were carried out: study detailed timing
properties and cross-talk
Next: determine their influence on the position resolution and
time resolution
Still some work to do...
• Read-out electronics (wave-form sampling, G. Varner?)
• Ageing studies
• Cost estimate...
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Back-up slides
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Timing uniformity
1
TDC vs. x for channels 1 and 2
 large deviation at active area edge
 small deviation at pad boundaries
1
2
2
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana
Beam test: Cherenkov angle
resolution and number of photons
NIM A521(2004)367; NIM A553(2005)58
Beam test results with 2cm thick aerogel tiles:
>4s K/p separation
s 0~
15mrad
October 18, 2007
RICH07, Trieste
Npe~6
Peter Križan, Ljubljana
Radiator with multiple
refractive indices
How to increase the number of photons
without degrading the resolution?
normal
 stack two tiles with different refractive
indices: “focusing” configuration
n1= n2
NIM
A548
(2005) 383
October
18, 2007
n1< n2
RICH07, Trieste
 focusing
radiator
Peter Križan, Ljubljana
Focusing configuration – data
4cm aerogel single index
2+2cm aerogel
October 18, 2007
RICH07, Trieste
Peter Križan, Ljubljana