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

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 rate @ room temperature, ≈ MHz @ 1.5 phe, few 100s kHz @ 2.5 phe, few 10 KHz @ 3.5 p.e.

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

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

Update on detector R&D activities in Ferrara 

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

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

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

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 (thresholds @ ~ 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

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

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 (@constant gain of ≈ 12mV/p.e.): SiPM1 2.4MHz-1.5pe, 450kHz-2.5pe, 50kHz-3.5pe Vbias=33.0V SiPM2 1.3MHz-1.5pe, 150kHz-2.5pe, 15kHz-3.5pe Vbias=32.3V All fibers: Bicron ϕ=1.0 mm

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

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