1. IFR Detector R&D status
Wander Baldini
On behalf of the Ferrara SuperB group
SuperB Workshop, LNF Dic. 1-st 2009

2. Detection Technique
Scintillator bars + WLS fibers readout by Geiger mode APDs
Scintillator:
2x4x400 cm3 and 1x4x400 cm3
scintillator bars coated with TiO2
Light collection through WLS fibers
Fibers housed in embedded holes
WLS fibers:
f = 1.2 mm type Y11(300) (Kuraray) and f =1.0mm type BCF92 (Saint Gobain), Attenuation length l ≈ 3.5m, trapping efficiency ε ≈ 5.5%
Photodetectors:
Silicon Photo Multiplier (Fondazione Bruno Kessler- FBK Trento-Italy):
Gain >105
< 1ns risetime
Low bias voltage (≈35V)
Dark current room temperature, ≈ 1.5 phe, few 100s 2.5 phe, few p.e.

3. Detector Baseline Layout
2 baseline layouts: time readout (barrel), double coordinate Binary readout (endcaps)
Time Readout: azimuthal coord f measured from the hit bar, polar coord q from the arrival time of the signal
BInary ReadOut: two layers of orthogonal scintillating bars (half thickness) provide directly the f and q coordinates. Easier from the point of view of electronics, a little more complicated for the mechanics
20mm
40mm
10mm
40mm

4. Readout
To reduce the radiation effects on SiPM ,we considered the option of bringing the light signal out of the detector but the light loss in the needed 10m of clear fibers is too high (factor 3)
Increasing the number of WLS fibers (for scintillating bar) up to 4 allows us to recover only a factor < 2, when coupled to clear fibers
So the SiPM have to be coupled directly to WLS fibers and put on the detector (and properly shielded).
The signal from SiPM will be brought to the FE electronics (kept out of the detector) through ~ 8-10m of shielded cables

5. Update on detector R&D activities in Ferrara

6. Measurements after SLAC Workshop
Putting no grease would simplify the production process…
So we have continued the studies on the effect of optical grease on efficiency and time resolution for the two balseline configurations:
3 fibers per scintillator, directly coupled to SiPM (no clear fibers)
ϕ=1.0mm – Saint-Gobain for 20mm scintillator (sandwich)
ϕ=1.2 mm – Kuraray for 10mm scintillator
SiPM area: 2x2 mm2
20mm
10mm
Binary readout
Time readout

7. Cosmic ray test setup DAQ TDC S2 Trigger = S1 x S2 S1 S1 SiPM 2x2
WLS fibers
Scintillator S2
SiPM 2x2
inputs
Discrim.
out
TDC S2
Trigger = S1 x S2
trigger
inputs S1
DAQ
Fast discriminator
/ trigger board

8. The setup Dark Box two 1.0 cm thick scintillators
“sandwiched” for the time readout
Trigger scintillators
WLS fibers on a
2x2 mm2 SiPM

9. Working conditions SiPM: Vbias = 32.2-33.0 V
Thresholds: 1.5, 2.5, 3.5 p.e.
Fiber length:
2.4m, ϕ=1.2mm kuraray, for 10 mm scintillator
2.2m, ϕ=1.0mm Bicron, for 20 mm scintillator
Trigger: 5cm scintillator, readout with 2 MPPC modules ~ 4 p.e.)
Time reference given by a fast PMT
FE electronics: Amplifier Bias Comparator board (ABC) developed in Ferrara by A. Cotta and R. Malaguti, based on MMIC fast amplifiers
data samples ~ 1000 events (tipically 1 night)
Efficiency calculated using only TDC

10. In the binary readout the time resolution is not so important
Efficiency
1.5pe
2.5pe
3.5pe
2 fibers
2.4m grease
1.87
2.16
2.14
98.8%
97.4%
91.6%
2.4m NO grease
2.30
2.49
2.64
97.2%
94.9%
85.7%
3 fibers
2.4 m grease
1.41
1.51
1.85
99.0%
99.4%
97.7%
1.73
1.88
2.15
97.8%
89.2%
In the binary readout the time resolution is not so important
Fibers: Kuraray ϕ=1.2 mm 10

11. Time readout All fibers: Bicron ϕ=1.0 mm
Time resolution
Efficiency
1.5 pe
2.5pe
3.5pe
1.5pe
3 Fib.
2.2m with grease
1.16
1.17
1.26
95.9
99.1
2.2m (no grease)
SiPM1
1.32
1.37
96.1%
97.4%
94.4%
2.2m (no grease) SiPM2
1.19
1.36
1.45
95.8%
90.8%
Dark counts gain of ≈ 12mV/p.e.):
SiPM MHz-1.5pe, 450kHz-2.5pe, 50kHz-3.5pe Vbias=33.0V
SiPM MHz-1.5pe, 150kHz-2.5pe, 15kHz-3.5pe Vbias=32.3V
All fibers: Bicron ϕ=1.0 mm

12. Some comments...
Difference in efficiencies of the order of 2-3% for 1.5p.e. and 2.5p.e., up to 8% for 3.5p.e.
Difference in time resolution of about 0.2ns (for time readout)
But the conditions are not exactly the same:
Different SiPM (the one used so far got broken..), characteristics rather different…
Last measurements taken with a different PMT
More studies ongoing using different SiPMs to better understand (and quantify) the effect
We will make also some tests using optical GLUE (like Bicron BC600) instead of grease

13. Other ongoing activities
Fibers/SiPM couplers have
been designed and first
prototypes will be build soon
As soon as they are available
quality tests will be performed
Fiber polishing quality is critical for optimal light transmission to SiPM. Single/multiple fiber polishing is under evaluation.
Scintillator-fibers-SiPM holder (“pizza box”) is being designed
Orders for Fibers, SiPM, PCBs placed (see tomorrow’s presentation for more datails).
Fibers
SiPM