1. IFR Detector R&D status
Wander Baldini
On behalf of the Ferrara SuperB group
SuperB Workshop, SLAC Oct

2. W. Baldini, INFN sez. di Ferrara
Detection Technique
Scintillator bars + WLS fibers readout on both ends by Geiger mode APDs
Scintillator:
2x4x400 cm3 scintillator bars coated
with TiO2
Light collection through WLS fibers
Fibers housed in a surface grove
or in an embedded hole
WLS fibers:
f = 1.0 or 1.2 mm type Y11(200/300) (Kuraray) or BCF92 (Saint Gobain), Attenuation length l ≈ 3.5m, trapping efficiency ε ≈ 5.5%
Photodetectors:
Multi Pixel Photon Counters (Hamamtsu), Silicon Photo Multiplier (IRST-FBK Trento-Italy):
Gain >105, DE ≈ 40% 500 nm, MPPC) (DE = Q.E x Fill factor x Avalanche probability)
< 1ns risetime
Low bias voltage (35V SiPM, 70V MPPC)
Dark current room temperature, few 1.5 phe, few 100s 2.5 phe, few p.e.
W. Baldini, INFN sez. di Ferrara

3. W. Baldini, INFN sez. di Ferrara
Detector Layout
2 layouts under study: time readout, double coordinate digital readout
Time readout: azimuthal coord f measured from the hit bar, polar coord q from the arrival time of the signal
Double coord binary readout: two layers of orthogonal scintillating bars provide directly the f and q coordinates. Easier from the point of view of electronics but more complicated for the mechanics
W. Baldini, INFN sez. di Ferrara

4. W. Baldini, INFN sez. di Ferrara
Readout
To reduce the radiation effects on SiPM ,we considered the option of bringing the light signal out of the detector through clear fibers, 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) to 3 or 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 long shielded cables
W. Baldini, INFN sez. di Ferrara

5. Update on detector R&D activities in Ferrara
W. Baldini, INFN sez. di Ferrara

6. Measurements after Perugia Workshop
We have measured the efficiency AND time resolution (for the time readout option) for 10mm and 20 mm thick scintillator bars for the following configurations:
2 and 3 WLS fibers directly coupled to SiPM (no clear fibers)
1.0 Bicron and 1.2 mm
1.5, 2.5, 3.5 p.e. thresholds
Good 2x2 mm2 SiPM (FBK) and irradiated (1.25 x 1010 n/cm2)
Scintillator-fibers coupling with/without optical grease
20mm
10mm
Binary readout
Time readout
W. Baldini, INFN sez. di Ferrara

7. W. Baldini, INFN sez. di Ferrara
Cosmic ray test setup S1
SiPM 2x2
WLS fibers
Scintillator S2
SiPM 2x2
Prototype
inputs
Discrim.
out
TDC S2
Trigger = S1 x S2
trigger
inputs S1
DAQ
Fast discriminator
/ trigger board
W. Baldini, INFN sez. di Ferrara

8. W. Baldini, INFN sez. di Ferrara
The setup
Dark Box
two 1.0 cm thick scintillators
“sandwiched” tfor the time readout
Trigger scintillators
WLS fibers on a
2x2 mm2 SiPM
W. Baldini, INFN sez. di Ferrara

9. W. Baldini, INFN sez. di Ferrara
Working conditions
SiPM: Vbias = 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
W. Baldini, INFN sez. di Ferrara

10. Binary readout Time resolution Efficiency 1 fiber 2 fibers 3 fibers *
1.5pe
2.5pe
3.5pe
1 fiber
2.4 m
2.06
2.26
2.48
96.4%
93.0%
83.3%
2 fibers
1.87
2.16
2.14
98.8%
97.4%
91.6%
2.4 m (no grease)
2.30
2.49
2.64
97.2%
94.9%
85.7%
3 fibers
1.60
1.65
1.76
98.7%
99.2%
98.5%
2.4 m (bicron)
1.41
1.58
1.79
96.6%
93.6%
86.0% *
Tests with 3 kuraray fibers and no grease to be done, we expect a few % loss
* All Kuraray ϕ=1.2 mm unless otherwise stated 10

11. Time readout option * * All Bicron ϕ=1.0 mm
Time resolution
Efficiency
1.5 pe
2.5pe
3.5pe
1.5pe
2 Fib.
0.3m
0.91
0.95
---
95.4%
98.6%
2.2 m
1.38
1.44
95.9%
96.5%
3 Fib.
0.89
0.97
94.2%
98.9%
99.4%
2.2m
(no grease)
1.16
(1.32)
1.17
(1.37)
1.26
(96.1%)
99.1%
(97.4%)
(94.4%) *
Dark counts: 2.4MHz-1.5pe, 450kHz-2.5pe, 50kHz-3.5p.e. Vbias=33V
* All Bicron ϕ=1.0 mm

12. Time readout option with irradiated SiPM: 1.25x1010 n/cm2
Time resolution
Efficiency
1.5 pe
2.5pe
3.5pe
1.5pe
2 Fib.
Close End
---
Far End
1.80
1.74
81.4%
84.4%
3 Fib.
0.99
1.10
89.5%
97.8%
1.38
1.41
89.7%
95.5%
Dark counts: 4.2MHz -1.5pe, 1.0MHz - 2.5pe, Vbias=32V

13. W. Baldini, INFN sez. di Ferrara
Some comments...
The 3 fibers option allows us to reach the desired parameters (Tres ~ 1ns, Eff>95%) on both readouts
A dose of 1.25 x neutrons does not spoil too much the performances, but of course devices have to be properly shielded. Precise simulation on expected dose is very important
The devices are rather noisy and gets ~ a factor 2 worse when irradiated, put 3.5 p.e. will reduce it ~ factor 10
The noise affect also the efficiency due to accidentals (e.g. 1.5 p.e. eff is lower than 2.5 p.e.) and time resolution
Putting no optical grease reduce ~ 2-3% eff but would greatly simplify the assembly process
W. Baldini, INFN sez. di Ferrara

14. Proposed baseline configuration
Tested
Baseline
20mm
New Dye
400mm
Aluminum foil
Already existing dye with 2 holes…
10mm
400mm
In the “baseline” version we expect to collect more light than in the tests version
W. Baldini, INFN sez. di Ferrara

15. W. Baldini, INFN sez. di Ferrara
Some comments...(II)
For the 20mm scintillator: we will ask for a new dye since no 20mm x 400mm dye exists at the FNAL-NICADD facility
For the 10mm scintillator: a production of 10mm x 400mm scintillator with 2 embedded holes is forseen by the end of the year
Given the small amount (120 bars, 60cm long) we might have them almost for free…
we can then add a central groove to house the additional fiber, this is OK for the prototype
W. Baldini, INFN sez. di Ferrara

16. Conclusions and next steps
The 3 fibers configuration allows us to reach the desired parameters
Some tests still to be done but the baseline configuration is almost defined
In contact with the FNAL-NICADD (scintillator) and with FBK and Hamamatsu (photosensors) to arrange productions for the prototype
Place orders as soon as possible
W. Baldini, INFN sez. di Ferrara