photodetector timing resolution burle micro-channel plate photo multiplier tubes (mcp-pmts)
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Photodetector Timing Resolution
Burle Micro-Channel Plate Photo
Multiplier Tubes (MCP-PMTs)
H. Wells Wulsin
SLAC Group B
Winter 2005
31 March 2005 H.W. Wulsin 2
Photo Multiplier Tube Specifications
DIRC PMT 2x2 MCP-PMT
Pixel Size ~2.8 cm ~24 mm
Timing resolution (σ)
1.6 ns [single photo-electrons]
•80-100 ps [single photoelectrons]•30-50 ps [test beam: ~60 photoelectrons]
31 March 2005 H.W. Wulsin 3
End Station A Setup
PiLas laser, 635 nm (int. trigger)
Myl
ar
atte
nuat
ors
Electronics:•ADC•Single threshold discriminator •TDC (25 ps/cnt)
Quartz barsPad 0
Pad 2
Pad 1
Pad 3
Burle MCP-PMT
Path of test beam
31 March 2005 H.W. Wulsin 4
Limits to MCP Timing Resolution
Cross-talk between channels Charge-sharing between pads Electronics noise Avalanche fluctuations [focus of this analysis]
31 March 2005 H.W. Wulsin 5
Timing resolution varies with ADC
• TDC measures hit time when pulse exceeds level set by single threshold discriminator.• Size of pulse (# photoelectrons) affects the measured hit time. • More photoelectrons reduce the variability of measured hit time (avalanche fluctuations have a smaller effect).
Single photoelectron pulses (2 mV/div) ~300 photoelectrons / pulse (200 mV/div)
Threshold Threshold
1 ns
1 ns
31 March 2005 H.W. Wulsin 6
ADC Distribution of Runs 1-8, taken 11-22-04, 11-24-04
Ent
ries
ADC (counts)
31 March 2005 H.W. Wulsin 7
TDC v. ADC, Runs 1-8
ADC (counts)
ADC
TD
C (
coun
ts)
TD
C
31 March 2005 H.W. Wulsin 8
TDC Histogram, Runs 1-8en
trie
s
TDC (counts)
31 March 2005 H.W. Wulsin 9
Linear fit to Run 8
TDC = -0.0209(ADC) + 640.1
ADC (counts)
TD
C (
coun
ts)
31 March 2005 H.W. Wulsin 10
Linear correction to Run 8
ADC ADC
TDCTDC
entr
ies
TD
C
TD
C
entr
ies
σraw = 31.0 ps
σcorr = 30.0 ps
31 March 2005 H.W. Wulsin 11
Linear fit to Run 7
TDC = -0.098(ADC) + 671.5
ADC (counts)
TD
C (
coun
ts)
31 March 2005 H.W. Wulsin 12
Linear correction to Run 7
σraw = 53.5 ps
σcorr = 48.5 ps
ADC ADC
TDC TDC
TD
C
TD
Ce
ntr
ies
en
trie
s
31 March 2005 H.W. Wulsin 13
Hyperbolic fit to Runs 1-6T
DC
(co
unts
)
ADC (counts)
TDC = 632.6 + 509.8 / (ADC – 258.6)
31 March 2005 H.W. Wulsin 14
Hyperbolic correction to Runs 1-6
ADC ADC
TDC TDC
TD
Ce
ntr
ies
en
trie
sT
DC
σraw = 470 ps σcorr = 320 ps
31 March 2005 H.W. Wulsin 15
Independent fits to three data sets
590.0
610.0
630.0
650.0
670.0
690.0
710.0
25
9
28
0
30
1
32
2
34
3
36
4
38
5
40
6
42
7
44
8
46
9
49
0
51
1
53
2
55
3
57
4
59
5
ADC (counts)
TD
C (
co
un
ts)
Linear: Run 8
Linear: Run 7
Hyperbolic: Runs 1-6
31 March 2005 H.W. Wulsin 16
Optimized total fit
By Hand:TDC = 619 + 165/√(ADC – 262)
By Recursion:TDC = 619.2 + 160.7/√(ADC – 262.2)
590.0
610.0
630.0
650.0
670.0
690.0
710.0
259
278
297
316
335
354
373
392
411
430
449
468
487
506
525
544
563
582
ADC (counts)
TD
C (
cou
nts
)
Linear: Run 8
Linear: Run 7
Hyperbolic: Runs 1-6
Total Fit
ADC (counts)
TD
C (
cou
nts
)
31 March 2005 H.W. Wulsin 17
Total correction for Runs 1-8
ADC
ADC ADC
ADC
TD
CT
DC
TD
CT
DC
31 March 2005 H.W. Wulsin 18
Timing Resolution Correction: All Runs
FWHM ~ 50 counts ADC FWHM ~ 15 counts ADC
TDC (counts)TDC (counts)
en
trie
s
en
trie
s
31 March 2005 H.W. Wulsin 19
Use Run 1 (maximum attenuation): ADC counts photoelectrons
Pedestal value: 265.4 counts ADC Single photoelectron mean ADC: 2.1 counts
ADC (counts)
en
trie
s
en
trie
s
No TDC Signal TDC Signal Recordedentries
ADC - Pedestal (counts)
entries
ADC (counts)
entries No TDC Signal TDC Signal Recorded
1 photoelectron = 2.1 counts ADC
31 March 2005 H.W. Wulsin 20
Timing Resolution vs. Photoelectrons
Npe
σ (
ps)
σ (
ps)
σ = 9.08 + 214.61 / √(Npe – 0.45)
Npe
31 March 2005 H.W. Wulsin 21
Comparison to Previous Analysis
photoelectronsphotoelectrons
Time resolution vs (ADC signal)Quartz bar pad 0
10
100
1000
0 50 100 150 200 250
ADC signal [photoelectrons]S
igm
a [p
s]
Sigma 1 rawSigma 1 corrected1/sqr(ADC signal) corrected1/sqr(ADC signal) rawSigma 1 power corrected1/sqr(ADC signal) power corrected
10
100
1000
0 50 100 150 200 250
Photoelectrons
Sig
ma
(ps) σTDC raw
σTDC corr
Fit Corr
Similar resolution spectrum
Wells Josef (different data runs)
31 March 2005 H.W. Wulsin 22
Conclusions Achieved timing resolution of 30 – 50 ps for
~100 photoelectrons (Run 8) down to ~30 photoelectrons (Run 7).
Correction for timing – photon correlation most helpful in comparing disparate runs. For constant number of photoelectrons,
correction less useful. Further study:
Confirm # photoelectrons per ADC count. Examine charge-sharing between pads.
31 March 2005 H.W. Wulsin 23
Thank you to all of Group B for your help all quarter!Thanks to all Group B for lots of help this quarter!
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