1. LENA Detector development
ANT2010, Santa Fe
2010/09/18
Marc Tippmann
Technische Universität München

2. Most relevant topics at the moment
Detector construction
Cavern construction
Tank design
Liquid handling
Scintillator purification
Liquid scintillator
Attenuation length vs. wavelength
Decay time constants
Emission spectra
Photo sensors
Photo sensor requirements
PMT characterization
Winston Cones
Pressure encapsulations
Electronics
PMT arrays
Software
Geant4 simulation of optical model of detector
Tracking with Liquid Scintillator Detectors

3. LENA (Low Energy Neutrino Astronomy)
Physics objectives:
Low energy:
Neutrinos from galactic Supernova
Diffuse Supernova neutrinos
Solar neutrinos
Geoneutrinos
Reactor neutrinos
Indirect dark matter search
Higher energy:
Proton decay
Long-baseline neutrino / beta beams
Atmospheric neutrinos
Detector layout:
Liquid scintillator
ca. 50kt LAB
Inner vessel (nylon)
Radius (r) = 13m
Buffer (inactive liquid scint.)
Δr =2m
Cylindrical steel tank, k PMTs (8“) with Winston Cones (2x area)
r = 15m, height = 100m,
optical coverage: 30%
Water cherenkov muon veto
5000 PMTs, Δr > 2m to shield fast neutrons
Cavern egg-shaped for increased stability
Rock overburden: 4000 mwe

4. Detector construction

5. Detector construction
LAGUNA:
European site + design study for a next generation neutrino and p-decay detector
7 preselected sites
Proposed experiments: GLACIER, LENA, MEMPHYS
Includes cavern design study

6. Detector construction: Cavern construction
New: Rockplan tank + excavation study for Pyhäsalmi
Based on Technodyne study → substantial improvements
Worked out excavation process and extra structures to fulfill safety requirements:
2 access tunnels, spherical work tunnel, 1 or 2 new shafts
Long term rock stability simulations → elliptical horizontal cross-section and kink in vertical cross-section
→ Higher volume for Water Cherenkov detector

7. Detector construction Tank design
Conventional Steel Tank + well known, straightforward to build, robust - expensive, single passive layer defense, a lot of elements and connections Sandwich Steel Tank + cost effective, room for cooling, fast install, high QA/QC, laser welds - a lot of welding, little used solution, mechanically challenging
Sandwich Concrete Tank
+ well known, straightforward to build, robust, improved physics
- steel plates and rebar prevent continuous casting, slow to build
Hollow Core Concrete Tank
+ room for cooling, mechanically strongest, improved physics, quick build
- little used solution, active leak prevention may lead to sustained pumping

8. Liquid Scintillator properties
Extensively covered last year on ANT09 by Michael Wurm → only new results
Liquid Scintillator properties are essentially understood + known
Only particular measurements remain to be done
Started to repeat measurements with higher precision

9. Liquid scintillator properties Attenuation length vs. wavelength
Michael Wurm
Wavelength (nm)
Attenuation length (m)
10m
Martin Hofmann
Already measured with a 1m scintillator tube (10nm accuracy) + 10cm cell (1nm) → transparency considerably increases with wavelength → need longer tube
→ New experiment with ≈10m tube length
Is being set up at new Munich underground lab (≈ 10mwe rock overburden)
All parts ordered, most have arrived
Should be able to start measurements within the next months 1m

10. Liquid Scintillator properties Decay time constants
Paolo Lombardi, LENA Meeting
Paolo Lombardi has set up a new experiment in Milan
Measured time behavior of different scintillators (PC, LAB, DIN) with varying PPO concentration
→ Cross-check with Munich experiment possible
Measurements on LAB in both experiments in good agreement in some variables, deviation in others → maybe due to different manufacturers / batches →will study this further
preliminary

11. Liquid Scintillator properties Emission spectra
Paolo Lombardi, LENA Meeting
Measurements done in Perugia by Fausto Ortica and Aldo Romani
→ Cross-check with Munich experiment possible
Very good agreement of results for LAB with 1.5 resp. 2g/l PPO
Teresa Marrodan, PhD thesis

12. Photo sensors

13. Photo sensors: Photo sensor requirements PMT timing behavior
Normal
Pulses
Early
Pre-Pulses
Late Pulses
Transit Time Spread
(FWHM, spe)
Dark Noise

14. Photo sensors: Photosensor requirements
Area Inner Detector: m²
Targeted optical coverage: 30%
→ 3130 m² effective photosensitive area
PMTs probably the only photosensor type
Meeting the physical requirements
Having a low enough cost /(area*photon detection efficiency)
Durable for at least 30 years AND
Utilizable until start of construction
Important properties:
Transit time spread, afterpulsing, gain, dynamic range, area, quantum efficiency, dark noise, peak-to-valley-ratio, early + pre-pulsing, late pulsing, pressure resistance, long term stability, low radioactivity, price

15. Photo sensors: Photosensor requirements Necessary parameters for PMTs
Diameter
Transit Time Spread (FWHM)
Ion Afterpulses,
Brems-strahlung AP
Dark Noise
Dynamic Range (pe)
Gain
Number PMTs in Inner Detector (using 2x Winston cones ) 3“
<3ns
<1%
(if not less!)
<0.75 kHz
1 to > 10
some 106
343,000 5“ “
<2kHz
1 to > 40
124,000 8“
<5kHz
1 to >100
48,000
10“
<8kHz
1 to >150
31,000

16. Photo sensors: PMT characterization Selection of feasible PMT models for LENA
Manufacturers available for 100k+ PMTs:
Hamamatsu Photonics
Electron Tubes Enterprises Ltd.
Study most promising PMTs with diameters from 3“-10“
Measured until now:
Hamamatsu: R6091(3“), R6594(5“), R5912(8“) and R7081(10“)
ETEL: 9351(8“)

17. Photo sensors: PMT characterization
Borexino PMT testing
Excellent time resolution: 410nm laser diode light source, pulse FWHM <30ps, trigger output jitter <100ps; electronics jitter ≈45-90ps
→ total time resolution <140ps
Can measure up to 32 PMTs simultaneously
Repaired + reactivated setup
Further improved setup:
Use second channel to measure fast AP up to ≈25-30 ns after primary pulse, triggered by pulse in first channel
Low noise preamp near PMT → increased p/V by a factor of 2

18. Photo sensors: PMT characterization Results: Comparison R6594(+) vs
Photo sensors: PMT characterization Results: Comparison R6594(+) vs. R7081(+) 5“
R6594 (5“)
R7081 (10“)
Voltage
+1670V
+1520V
Gain
1.0∙107
1.3∙107
pe/trigger (npe)
5.53%
2.91%
TTS(FWHM) (acc. to HP)
1.91ns (1.5ns)
3.05ns (3.5ns)
EP (all non-gaussian)
2.95%
0.57%
LP (all non-gaussian)
34.16%
42.90%
LP (after NP peak)
3.13%
3.09%
10“

19. Photo sensors: PMT characterization - Comparison PMTs
R6091 (3“) with 1.8“ aperture
R6594 (5“)
R5912 (8“)
R7081 (10“)
ETL9351 (8“) no. 1732
ETL9351 (8“) average
Voltage
+1760V
+1670V
+1425V
+1520V
+1500V
≈+1450V
Gain
1.0∙107
1.3∙107
pe/trigger (npe)
2.21%
5.53%
1.83%
2.91%
4.78%
5.19%
TTS (FWHM)
(manufacturer)
1.89ns
(2.0ns)
1.91ns (1.5ns)
2.04ns
(2.4ns)
3.05ns (3.5ns)
2.16ns
2.76ns
EP (all non-gaussian)
0.14%
2.95%
1.93%
0.57%
1.23%
0.75%(3σ)
LP (all non-gaussian)
27.29%
34.16%
55.01%
42.90%
8.70% -
LP (after NP peak)
6.26%
3.13%
2.88%
3.09%
4.08%
7.90%(3σ) DN
0.192kHz
(5.23kHz)
1.62kHz
2.64kHz
1.72kHz
2.48kHz
DN/m²
120.9 kHz/m²(eff.)
(462.6 kHz/m²)
50.5 kHz/m²
52.6 kHz/m²
53,0 kHz/m²
76,5 kHz/m²
Ion AP
0.94%
6.62%
5.12%
2.57%
4.9%
p/V
2.04
3.88
2.99
3.09
2.25
2.10

20. Photo sensors: PMT characterization Improve + extend Munich PMT testing setup
PMT test setup at TUM, Garching (currently)
FlashADC (10bit, up to 8 Gigasample/s = 125ps time resolution, 4 channels)
→ excellent
Currently using LED (430nm peak-wavelength) with moderate relaxation time (≈5-10ns) driven by 5ns FWHM voltage pulse → bad
→ Build in fast light pulser developed by George Korga: fast LED driven by Avalanche Diode -> total time jitter FWHM ≈1ns or lower
Medium term: build in ps laser diode → time jitter ≈30ps
→ Confirm results from Italy
→ Can measure in addition pulseshape + fast afterpulses (Δt<30ns) + prepulses
Status: coincidence running; working with two students on improving readout + evaluation software

21. Photo sensors: PMT characterization HQE measurements
Paolo Lombardi, LENA Meeting
(Another) experimental setup of Paolo Lombardi in Milan to characterize PMTs:
Picosecond laser (405nm)
8bit 1GS/s FADC
Measured Hamamatsu super-bialkali PMTs (~34% peak-QE): R6594-SEL, R5912-SEL, R7081-SEL
→ Direct comparison with standard photocathode PMTs Borexino PMT testing facility possible

22. Photo sensors Winston Cones
Attach Compound Parabolic Concentrators („Winston Cones“) to increase effective area of PMTs by a factor of 2-8(!) → increases number of detected photons / MeV deposited → increased resolution
Limits field of view by introducing an acceptance angle (conservation of etendue) → can be used to limit field of view to fiducial volume
…coming soon: study influence on detector performance with the Geant4 Monte Carlo simulation of LENA (software development finished + working)
Borexino Winston Cone
CTF Winston Cone

23. Photo sensors Pressure encapsulations
Pressure at tank bottom might be too high for PMT glass envelopes →
a) Try if thicker glass envelope (4mm) fulfills pressure tests
b) Develop pressure encapsulations →
Can use standard PMTs
Integrate Winston Cones + µ metal shielding into design
Starting points for development e.g. Borexino encapsulation with pressure-withstanding window instead of thin PET window with pressure-resistant window in front
Development will commence soon

24. Electronics

25. Electronics: PMT arrays
Employ PMT arrays with central on-site front-end electronics on chip
→ Reduce number of channels (only 1 cable for data + voltage); however voltage not adjustable for individual PMTs after installation + can read out pulse shape only for sum of PMT channels
Currently under development in PMm² project
PICS collaboration between LENA + MEMPHYS
→ can use existing R&D of PMm² (3 years) for LENA!
PMm²: 16 PMs(12“) + frontend electronics (PARISROC)
PMm² has studied this concept for the past 2 years, however mainly for MEMPHYS (partially in general for large experiments with PMs), scheduled end of R&D mid > much experience, great part of R&Dalready done,
PMm² PMA, collaboration of LENA/MeMPhys??
Concept: array of PMs with pre-evaluation electronics instead of single PMs and centralized electronics (chip)
Schema(PMm²) + explanation (as short as possible)
For LENA: Pros (main reason: lower costs) + Cons, pros>cons (how can cons be compensated)
J.E. Campagne, LENA - PMm² meeting 07/04/2009

26. Electronics: PMT arrays PMm² frontend electronics: PARISROC
Triggerless
Individual channels
Charge + time measurement
Variable gain of preamplifier
Common HV for PMs
1/3pe 100% efficiency
1ns time resolution
16 trigger channels or 1 OR-trigger-output
2 gains per channel (not showed here):
0-10pe & 0-300pe
Scaleability

27. Electronics: PMT arrays
Advantages:
Data transfer digital → less attenuation
Lower cost (less cables, voltage in cables smaller, bundled frontend electronics reduces data processing cost/channel)
Disadvantages:
Same HV for each PMT within module → counter measures: partial compensation via individual gain adjustment, combine similar PMTs for a module
Different physical requirements for PMT Arrays
→ adopt R&D of PMm² as far as possible
+ adapt setup where neccessary
Can‘t adapt voltage of each PM to achieve same gain, can‘t compensate aging effects
Similar PMs -> need all more or less same voltage for same gain
Basically a lot of great advantages and only one disadvantage which can be mostly compensated -> interesting concept
Different Physical requirements(which pr are there??) from original purpose of PMm² => adopt concept and development of PMm² as far as possible + adapt setup where neccessary: PMs and electronics
One especially important aspect: After pulses (what other aspects are important for apllication of PMAs to Lena??)

28. Software

29. Software Tracking in Liquid Scintillator Detectors
Light front generated by GeV particles resembles a Cherenkov cone → directionality → can use arrival time of first photons on PMTs and total photon count for tracking
→ Can be used for p decay, neutrino beams and atmospheric neutrinos
Have developed two event reconstruction programs for tracking:
„Scinderella“ by Juha Peltoniemi
Tracking script for the Geant4 LENA optical detector model by Dominikus Hellgartner
J. Learned, arXiv/ , J. Peltoniemi, arXiv/

30. Software: Tracking in Liquid Scintillator Detectors: „Scinderella“
Single-Particle Tracks (leptons, CC QES): excellent reconstruction
Multi-Particle Vertices (deep inelastic neutrino scattering creates pions, 1-5GeV): new reconstruction algorithm fits a superposition of the light fronts generated by MC sample tracks to the overall PMT signal
→ for ≤ 3 pions good track reconstruction at ≤ 5% E resolution possible
→ LSD is good tracking detector at E > 1GeV: excellent flavour recognition, E resolution typically < 5%, very good for neutrino beams: sin²(2ϑ) > 10-2 – 10-3 if not lower
If pulse-shape of PMT signals available even better
Detector simulation software based on Java developed by Juha Peltoniemi
Can do both event simulation and event reconstruction
Event simulation → record observation time of photons in PMTs
Track reconstruction by comparing light pattern produced by test track with that of track from simulation → minimalization of deviation
Reco of 4GeV  deep-inelastic sample event
J. Peltoniemi

31. Software: Tracking in Liquid Scintillator Detectors Tracking script for Geant4 optical model
Developed by Dominikus Hellgartner based on work done by Michael Wurm on tracking in Borexino
Procedure: minimize log-likelihood value of photon pattern depending on all track parameters
→ Look at even lower energies than 1GeV:
First preliminary results:
a) MeV single-track muons: very good track reconstruction with <≈1+/-2cm position uncertainty and 0.1+/-0.1ns time uncertainty for the starting point and 2.5° direction deviation
b) MeV single-track electrons: all uncertainties comparable to muon events, however one problem occurring: for some events, the direction is reconstructed with wrong sign → starting point at end of track → outliers; are working on this right now
Dominikus Hellgartner

32. Software: Tracking in Liquid Scintillator Detectors Proof of principle: Borexino
Borexino is actually a low E calorimetry detector; not optimized for tracking at all
LENA will be designed for tracking capability
Reconstructed tracks from CNGS beam in Borexino
No simulation:
real data!
Michael Wurm

33. Summary
Pyhäsalmi site study finished → elliptical cavern, steel or concrete tank
Liquid scintillator properties mostly known, setting up attenuation length precision measurement at the moment
Photo sensor: 5“-10“ PMTs (which type will be decided shortly) with Winston Cones and pressure encapsulations
Bundle PMTs to arrays to save channels
Geant4 detector simulation is running, have to measure last missing properties for optical model
Liquid Scintillator Detectors are actually quite good at tracking

34. Backup slides

35. Detector construction Excavation

36. Scattering Length Results
no hints for Mie-scat.
anisotropic scattering in good agreement with Rayleigh expectation
correct wavelength- dependence found
literature values for PC, cyclohexane correctly reproduced
Results for l=430nm
LS = 22±3 m
after purification in Al2O3-column
Michael Wurm

37. Liquid Scintillator properties Quenching factors
Gamma Quenching light output of low-energetic electrons (E<200keV) by small-angle Compton scattering
…in progress q
Timo Lewke, Jürgen Winter
Proton Quenching
using neutron recoils (AmBe-source, n-generator)
…coming soon
scintillator
sample

38. Proton decay
Large impact on proton decay (into K+n) detection efficiency:
Signal of kaon (t=13ns) and of its decay products (mostly muons) must be separated by rise time analysis
Background Source: Atmospheric Muon-Neutrinos
Kaon
Muon
Efficiency ranges from 56% to 69%
for typical rise times of 7 to 10 ns

39. Proton decay

41. Software: Tracking in Liquid Scintillator Detectors: „Scinderella“
Single-Particle Tracks
excellent flavour recognition
Positional accuracy: a few cm
Angular accuracy: a few degrees
initial neutrino energy + momentum can be determined at 1%(?) accuracy from lepton track (CC QES)
Multi-Particle Vertices
- deep-inelastic scattering of neutrinos creates pions (1-5 GeV)
- new reconstruction algorithm fits a superposition of the light fronts generated by MC sample tracks to the overall PMT signal
- resolution of vertices featuring ≤ 3 ‘s is possible at % accuracy
- recoil protons/neutrons quenched, not invisible, allowing a calorimetric measurement of the event energy deposited.
- time-resolved response of individual PMTs needed for optimum result

42. Software: Tracking in Liquid Scintillator Detectors Tracking script for Geant4 optical model
Developed by Dominikus Hellgartner based on work done by Michael Wurm on tracking in Borexino
Procedure:
For muon: separate track signal + decay signal: look for second peak in detected photons vs. time -> time cut
Determine start values for fits:
Energy → from number of photons of track; barycenter fit → position on track; first PMT hit → crude direction: vertical or horizontal
Vertical: Fit point-like source from first hit times for PMT-ring containing minimum hit time PMT → starting point → with barycenter fit direction → with energy track length → track
Horizontal: TOF-correction to barycenter → direction from most negative first hit times; table of position of charge barycenter vs track E (input from other simulations) → with energy track
Main fit: minimize log-likelihood value depending on all track parameters
→ Look at even lower energies than 1GeV:
First preliminary results:
a) MeV single-track muons: very good track reconstruction with <≈1+/-2cm position uncertainty and 0.1+/-0.1ns time uncertainty for the starting point and 2.5° direction deviation
b) MeV single-track electrons: all uncertainties comparable to muon events, however one problem occurring: for some events, the direction is reconstructed with wrong sign → starting point at end of track → outliers; are working on this right now
Dominikus Hellgartner

43. Requirements on PMTs in LENA

44. Other types of photosensors
Avalanche Photodiode (APD): solid state equivalent to PMTs; price/area too high; Dark Noise very high, if not cooled; low amplification
SiPM: array of small APDs; excellent tts (FWHM < 0.5ns), excellent energy resolution, high QE(?), immense cost/area; huge dark count (some 100kHz up to several MHz)
Cupid/ Hybrid Photo-Detector: Photocathode just like in PMTs, e- however focussed on APD in center instead of dynode chain; problems with huge DN? Still working on fixing that
Microchannel Plate (MCP): Photocathode, e- accelerated along very thin etched channels perpendicular to cathode, coated with metal on inside, thickness of coating varies along axis -> increasing voltage along flight path, e- crashes on walls + knocks out more e- -> amplification

45. Other types of photosensors
Quasar: Photocathode, solid scintillator block in center with a small PMT looking at it; apply very high voltages (typ.25-30kV) -> e- creates scintillation light in crystal -> light signal on PMT
advantages: small jitter even for large photocathode area, excellent energy resolution, …, price=? Already used in BAIKAL, however needs further development
Hybrid-Gas Photomultiplier: photocathode in vacuum, e- accelerated through mebrane into Thick Gas Electron Multiplier (THGEM) -> accelerated through holes in metal-covered plate, different voltage on upper+ lower side -> very high field inside holes -> e- scatters off gas atoms -> produces further e- -> amplification; use several THGEMs in series for higher amplification
still under development, needs several more years to be ready for production

46. Photomultiplier Tubes (PMTs) Principle of operation
Extremely sensitive light detectors capable of detecting single photons
Photon → photo electron(pe) → amplified by ≈10^7 in dynode chain
Gain = amplification factor

47. PMTs Ocurring effects + basic parameters
Ion Afterpulses
Dark Noise
Primary Pulses
(Next laser pulse)
Afterpulse: delayed additional pulse caused by the primary pulse
Ion Afterpulses: typically µs later
Bremsstrahlung Afterpulses:typ ns later
Dark Noise: electrons emitted from cathode without incident photon; mostly thermionic emission

48. PMTs Ocurring effects + basic parameters
Single photo electron (spe) spectrum: components: normal pulses, underamplified pulses + noise
Peak-to-valley-ratio (p/V): ratio between value of maximum and valley
noise
under-
amplified
pulses
spe (normal pulses)
Peak
2 pe
Valley

49. PMTs Voltage behavior Two different modes of applying voltage:
a) Photocathode at ground potential → positive voltage on anode
→ need capacitor to separate DC voltage from electronics
b) Negative voltage applied to photocathode → anode at ground potential → signal can be sent directly to electronics
Advantage: faster
Disadvantage: DN higher
Dynamic Range: number of photons incident at the same time on the cathode, which can be detected
Raise voltage → gain rises, transit time decreases, jitter decreases, however: AP rise, DN rises if voltage is very high (field emission), dynamic range decreases
→ find optimum working point

50. PMTs in LENA Transit time spread must be low → tracking
Bremsstrahlung Afterpulses (fast AP) can blur out proton decay coincidence
Ion Afterpulses (slow AP) can prevent position reconstruction of neutrons → decreases detection rate of cosmogenics (C11): C11 is main background for CNO-ν-flux
Michael Wurm, TUM, LENA - PMm² meeting 07/04/2009

51. PMTs in LENA
High Dark Noise: random coincidences of DN pulses + bad for tracking; DN approx. Q cathode area
Gain must be high enough or part of pulses overlaps with noise in spe spectrum → less pulses usable
Dynamic range: Detector must be able to detect single photons as well as HE events (muon, proton decay)
Assuming 1GeV event, 500pe/MeV, illuminating only 10% of PMTs →
1pe pe/(m² effective photosensitive area)
= 1pe – 100pe for 8“ PMT with 2x Winston Cone
upper boundary x10 if only 1% illuminated
p/V: the bigger it is, the better spe events can be distinguished from noise

52. PMTs in LENA
EP + PreP + maybe LP bad for tracking (uses first pulses = first photons)
Area per sensor:
Smaller → better tracking, dynamic range of detector increases, transit time spread smaller
Bigger → less sensors + channels → cost/area lower (if not too big)
→ generally sensor area as small as affordable
Quantum efficiency: higher → less PMTs needed for same energy resolution + threshold
Pressure resistance: At least 10 (100m head of liquid scintillator) +1 (vacuum in tube) + 3 (safety margin for implosions) = 14bar
at the moment no PMTs meet the pressure requirements → maybe use encapsulations for lower PMTs

53. Measurements at the Borexino PMT testing facility @LNGS (INFN), Italy

54. Measurements @LNGS Setup + Measurements
Setup can measure:
Transit time (TDC) → TTS, EP, PreP, LP
AP/Primary Pulse (PP) transit time (MTDC) → slow AP (+some fast AP), DN, pe/laser trigger (npe)
In second channel: transit time of first AP (TDC) → fast AP
For both channels: charge spectrum (ChargeADC) -> p/V
Measurements:
Measured all PMTs with positive + negative HV at a gain of 1·107
Find new operating point for LENA
→ Sampled over complete reasonable voltage range for pos. voltages
→ scanned PMT properties over complete feasible range of gain for single photon electrons

55. Measurements @LNGS Measurements
Also:
Developed fast LED light source with emission time spread (fwhm) <≈ 1ns
Measured R SEL: 3“ UBA photocathode, max. QE ≈43%(!)
Measured several ETL9351 PMTs for comparison
→ gave one to Paolo Lombardi to calibrate new flash ADC setup in Milano → planned to exchange data of measured PMTs; e.g. R7081 ↔ R SEL (UBA)
Evaluated up to now: Runs with ≈107 gain + positive voltage

56. Borexino PMT testing facility Block diagram - original configuration

57. Measurements @LNGS Results: Comparison R6594(+) vs. R7081(+)
Voltage
+1670V
+1520V
Gain
1.0∙107
1.3∙107
npe
5.53%
2.91% DN
(5.23kHz)
2.64kHz
DN/m²
( kHz/m²)
52.59 kHz/m²
Ion AP
0.94%
5.12%

58. Measurements @LNGS Results: Comparison R6594(+) vs. R7081(+)
Voltage
+1670V
+1520V
Gain
1.0∙107
1.3∙107
npe
5.53%
2.91% DN
(5.23kHz)
2.64kHz
DN/m²
( kHz/m²)
52.59 kHz/m²
Ion AP
0.94%
5.12%

59. Measurements @LNGS Results: Comparison R6594(+) vs. R7081(+)
Voltage
+1670V
+1520V
Gain
1.0∙107
1.3∙107
npe
5.53%
2.91%
p/V
3.88
3.09

60. Measurements @LNGS Preliminary Results
Most promising candidate – judging from only one sample each:
Hamamatsu R6594 (5“ diameter) using positive HV (dark noise rate much higher for negative HV):
transit time spread 1.9ns, total afterpulse rate 0.9%, peak-to-valley ratio 3.9
→ Need more samples to be able to determine mean parameters