Performance of UVsensitive MPPC for liquid xenon detector

Performance of UV-sensitive MPPC for liquid xenon detector in MEG experiment Daisuke Kaneko, ICEPP, Univ. of Tokyo on behalf of MEG collaboration

MEG experiment 1 μ+→e++γ 2013 Nuclear Science Symposium and Medical Imaging Conference

MEG upgrade 2 2013 Nuclear Science Symposium and Medical Imaging Conference

3 Upgrade of liquid xenon detector Present Upgraded CG image 46 mm PMT γ-ray Resolution was limited by sensor size, especially for shallow events. MPP C m m 12 PMT γ-ray Improved granularity by smaller photo -sensor. 2013 Nuclear Science Symposium and Medical Imaging Conference

4 Performance : Energy resolution depth ≧ 2 cm 60 % of events depth ＜ 2 cm 40 % of events Upgraded Present σup 2. 4% ↓ 1. 1% Upgraded Present σup 1. 7% ↓ 1. 0% Response to 52. 8 Me. V γ (MEG signal) 2013 Nuclear Science Symposium and Medical Imaging Conference

Position resolution in σ [mm] Performance : Position resolution 5 Red : Present Blue : Upgraded Depth from inner face [cm] 2013 Nuclear Science Symposium and Medical Imaging Conference

6 UV sensitive MPPC Development is performed in collaboration with Hamamatsu Photonics. p Requirements • Sensitivity to liquid xenon scintillation (λ = 175 nm) • Large active area (12× 12 mm 2) • Single photon counting capability • Moderate trailing time constant (τ ＜ 50 ns) p In order to improve sensitivity • Remove protection layer • Matched refractive index to liquid xenon • Anti reflection coating Cross-sectional image of MPPC 2013 Nuclear Science Symposium and Medical Imaging Conference

7 Photon Detection Efficiency Achieved performance 25% 0 p. e. 3 x 3 ㎟ (2012 -5) 12 x 12 ㎟ (2012 -12) 20% 12 x 12 ㎟ (2013 -2) 15% 1 p. e. 2 p. e. 10% 5% ↑Charge spectrum with 12× 12㎟ MPPC 0% 0 1 2 Over Voltage [V] ↑ 17% of PDE (crosstalk & after pulse removed) is already achieved. Even higher PDE is expected after new technologies of Hamamatsu will be included. 12× 12㎟ MPPC 3× 3㎟ MPPC 2013 Nuclear Science Symposium and Medical Imaging Conference

Series connection of MPPC 8 p Remaining issue was long tail in waveform (τ ～ 200 ns) due to large capacitance of large-area sensor. p In order to shorten long decay time, reduce sensor capacitance by subdividing active sensor region and connect them in series. 6 mm 12 mm p Signal is expected to be sharpened due to smaller capacitance. However there is anxiety that S/N becomes worse. 2013 Nuclear Science Symposium and Medical Imaging Conference

How many segments to divide 9 We simulated the series connection using four independent small MPPCs (6× 6㎟ each). C is capacitance when all segments are connected in parallel. 4 segments (C/16) 4 × 6 mm 2 segments (C/4) 2 × 12 mm × 6 mm 2013 Nuclear Science Symposium and Medical Imaging Conference

10 2 types of series connection There are two options for series connection of segments; "simple" and "hybrid“. Simple series connection Hybrid connection Serial – signal Parallel - bias amplifier bias ○ Less parts × Extra parts ○ Automatic over voltage adjust × Gain uniformity is required × Higher voltage ○ Same voltage as single MPPC × Different potential between each sector ○ All sectors have common potential Both connection types work in LXe, but hybrid is more advantageous. 2013 Nuclear Science Symposium and Medical Imaging Conference

11 Set up for liquid xenon test 6 mm MPP C LED 10 kΩ 10 n. F 2013 Nuclear Science Symposium and Medical Imaging Conference

12 Waveform of 1 photo electron 2 segments p The tail for 4 segmentation is as short as that for 3× 3㎟ single sensor as expected. V→ 4 segments p Signal tail is successfully reduced down to 30 -50 ns ! Vov = 3. 0 V p 1 p. e. signal can be resolved Vov = 3. 0 V 0 p. e. 1 p. e. Parallel 2 p. e. Vov =1. 5 V × 10 amp t→ charge → Baseline RMS have no significant difference, ～ 2 m. V 2013 Nuclear Science Symposium and Medical Imaging Conference

Decay time and connection type p Calculated decay constant by fitting waveform by event. 4 segments 25 ns 2 segments 46 ns ↕ Parallel 200 ns 13 2 segments 4 segments p 50 ns of target time constant is achieved in both cases. 2013 Nuclear Science Symposium and Medical Imaging Conference

14 Gain (multiplication factor) p Gain is 4～ 10× 105 2 segments p Gain is lower when capacitance is smaller, while pulse amplitude is almost the same. 4 segments p Lower than that of parallel connection, but 1 p. e. peak is resolved with proper voltage. 2013 Nuclear Science Symposium and Medical Imaging Conference

15 Effect of long cable In MEG LXe detector, long coaxial cable of about 10 m exists between sensor and readout electronics. 2 segments 4 segments Cable Length [m] Gain does not change, while decay time slightly increases (1 ns/m). Constant is 56 ns at 11 m of 2 segments, but still acceptable. 2013 Nuclear Science Symposium and Medical Imaging Conference

16 Summary of serial connection Gain (@ 3 V) Peak Noise rms separation [m. V] Decay const [ns] Rise const [ns] 4 segments 4× 105 ○ 2. 0 – 2. 5 25 ～ 33 2– 3 2 segments 8× 105 ◎ 2. 0 – 2. 5 46 ～ 56 4 -5 * 1 segment 1. 2× 106 ○ 3～ 5 ～ 200 ～ 10 * estimation from previous measurement Gain is larger and peak is clearer when number of segment is few. This makes charge calibration easier and relative gain error smaller. On the other hand, signal is sharper with finer segmentation. Timing resolution is expected to be better, and pile-up will be reduced. 4 segments is favorable, because gain error is small enough, and timing resolution should be as good as possible. In addition, if single p. e. can not be resolved, it is easier to switch 2 segments. 2013 Nuclear Science Symposium and Medical Imaging Conference

17 Prototype detector p We are planning to make prototype of MPPC read-out detector p 576 MPPCs on incident face. γ p Beam test will be performed in 2014 CG image of prototype detector 2013 Nuclear Science Symposium and Medical Imaging Conference

18 Summary p We are developing UV-sensitive MPPC for upgrade of liquid xenon detector in collaboration with Hamamatsu Photonics. p >17% PDE was already obtained by 12× 12㎟ and 1 p. e. countable MPPC prototype. p In order to solve problem of long waveform due to the carge capacitance of large-area MPPC, we proposed series connection. p Serial connection was tested in LXe environment. • 30 – 50 ns of decay constant was achieved • Single p. e. can be resolved Prospects p Prototype detector with ～ 600 MPPCs is being prepared. p Detector construction will start in 2014 for next MEG experiment from 2016. 2013 Nuclear Science Symposium and Medical Imaging Conference

Fin. 2013 Nuclear Science Symposium and Medical Imaging Conference 19

20 PCB based feedthrough Slope (Charge/Voltage) Charges of 1 p. e. event are compared between usual LEMO-connector and PCB feedthroughs. = 100. 8 ± 1. 2 [f. F] LEMO = 103. 0 ± 2. 0 [f. F] MMCX About for charge, there is no difference. Another properties are being analyzed. 2013 Nuclear Science Symposium and Medical Imaging Conference

Serial connection test at room temp. Set up for room temp. test 21 Observed Waveform MPP C LED light, averaged 4 serial 30 ns 2 serial, 2 parallel 50 ns 4 parallel 200 ns LED mask 2013 Nuclear Science Symposium and Medical Imaging Conference

22 Reminder 1 Application to LXe detector Sensitivity to VUV (λ=175 nm) 1 p. e. resolve with 12 x 12㎟ 0 p. e. Photon Detection Efficiency 25% 3 x 3 ㎟ (2012 -5) 12 x 12 ㎟ (2012 -12) 20% 12 x 12 ㎟ (2013 -2) 15% 10% 5% 0% 0 1 p. e. 1 2 Over Voltage [V] 2 p. e. Long tail (τ～ 200 ns) How to reduce long tail ? Target is about 50 ns (～Scintillation decay) Worse S/N Increase pileup etc. 2013 Nuclear Science Symposium and Medical Imaging Conference

23 Reminder 2 • Reduce quench resistance as low as possible. • Reduce input resistance of amplifier Tail is not be reduced than expected with lower quench Decay constant [ns] How to reduce long tail of 12× 12㎟ MPPC ? 300 200 100 0 10 • Divide and connect in series active sensor area Waveform is distorted with long coaxial cable Most realistic plan The effect was confirmed at room temperature test. 400 10000 Quench resistance [kΩ] 200 ns Rs = 33Ω, 10 m cable 2013 Nuclear Science Symposium and Medical Imaging Conference

24 Raw-Waveform 25μ Low Rq 50 μ Low Rq 25μ Mid Rq 50 μ Mid Rq 25μ High Rq 50 μ High Rq 2013 Nuclear Science Symposium and Medical Imaging Conference

pre amplifier 25 2013 Nuclear Science Symposium and Medical Imaging Conference

26 Result : Waveform and Quench-R Fitting waveforms with a doubleexponential function works well. ・The tail time constant do not depend on Rq so much ・ 25µm pitch MPPC is not so different from 50µm. MPPC Type 50 25 Quench R [kΩ] Over voltage [V] R 1 Low 349 R 2 Mid 606 R 3 High 8867 Over voltage [V] R 1 Low 719 R 2 Mid 1170 R 3 High 21433 1 Rising & 1 Trailing component, τr , τt Trail time constant τt [ns] 1. 0 246 277 2. 0 - 1. 2 255 288 783 2. 5 214 218 538 1. 5 276 314 3. 0 - Rise time constant τr [ns] 1. 0 19. 6 19 2. 0 - 1. 2 21 19. 4 16. 5 20. 7 20. 1 23. 5 1. 5 24. 3 20. 7 3. 0 - 2013 Nuclear Science Symposium and Medical Imaging Conference

Cause of long waveform Waveform can not be shortened only by reducing the quench resistance and cell capacitance. MPPC side 27 AMP side Vb Rp bias voltage protect resistance amplifier quench resistance Rq Cd diode (sensor) Rs … C s stray capacitance shunt resistance Rs, Rp×Cs term is dominant against Rq×Cd term under small Rq condition? 2013 Nuclear Science Symposium and Medical Imaging Conference

28 How to shorten waveform Smaller Rs → Effective, but only in limited situation. ↓Data taken with large-area MPPC at room temperature↓ τt= 192 ns Rs = 50Ω short cable τt= 138 ns Rs = 33Ω short cable Rs = 33Ω long cable Tail is reduced with small Rs, but the waveform is distorted with a long read-out cable because of the impedance mismatch. Smaller Rp → Not effective 2013 Nuclear Science Symposium and Medical Imaging Conference

29 90% 80% 70% H window 1 60% H window 2 50% H window 3 40% H window 4 30% Total relative charge 80 100% 70 60 50 40 30 20 20% 10 10% 0 0% 269 271 0 273 5 10 15 capacitance [nf] Tail constant 267 20 18 16 14 12 10 8 6 4 2 0 0 5 10 15 capacitance [nf] 2013 Nuclear Science Symposium and Medical Imaging Conference

Width of 1 p. e. peak 30 2013 Nuclear Science Symposium and Medical Imaging Conference

Leading edge and connection type Leading time constant is also shorter in smaller capacitance. 31 4 segments 2 segments Leading time constant seems to depend on o. v. , fitting for small waveform was difficult. ↓ To use pico sec pulse laser, Hamamatsu PLP-10 400 nm. Available soon. 2013 Nuclear Science Symposium and Medical Imaging Conference

32 Detailed PDE calculation of G-type MPPC Voltage In 2013 Feb-1 test 130150 UM-R 2 PDE 1. 7 Errors 25% type-I 3 x 3 ㎟ (12年 5月) 12 x 12 ㎟ (12年 12月) 12 x 12 ㎟ (13年 2月) 20% 1. 4 Gain 3. 1% 1. 6% Alpha peak 0. 26% 0. 21% Correction 3. 2% 1. 7% Model syst. 14% 22% total 22. 2% 15. 3% 15% 10% voltage 1. 4 1. 7 PDE +/- 15. 5 2. 5 16. 9 3. 7 5% 0% 0 0, 5 1 1, 5 2 2, 5 3 Over Voltage [V] 2013 Nuclear Science Symposium and Medical Imaging Conference