Status of the Development of MPPC for LXe detector Upgrade Daisuke Kaneko International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 0

Reminder 1 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 1 Application to LXe detector Sensitivity to VUV (λ=175nm) 1 p.e. resolve with 12x12 ㎟ Long tail (τ ～ 200ns) Worse S/N Increase pileup How to reduce long tail ? Target is about 50ns ( ～ Scintillation decay) etc. 0 p.e. 1 p.e. 2 p.e.

Reminder 2 2 Reduce quench resistance as low as possible. Reduce input resistance of amplifier Divide and connect in series active sensor area Tail is not be reduced than expected with lower quench Waveform is distorted with long coaxial cable International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam Rs = 33Ω, 10m cable 200ns How to reduce long tail of 12×12 ㎟ MPPC ? Most realistic plan The effect was confirmed at room temperature test.

Serial connection of MPPC 3 Reduce sensor capacitance by subdividing 12mm×12mm of active sensor region. Signal is expected to be sharpened due to smaller capacitance, while there is anxiety that S/N become worse. International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

Serial connection test at room temp. International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 4 LED MPP C mask 4parallel 200ns 4 serial 30ns 2serial,2parallel 50 ns Observed Waveform LED light, averaged Set up for room temp. test

6mm Set up for LXe temp. test 5 We tested 2 types of connection Simple serial and Hybrid connection in LXe. International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam Hybrid connection Simple serial connection bias preamp ○ Less parts ○ Automatically over voltage is adjusted × 4 times higher voltage × Voltage difference between each sector × Extra parts × Gain uniformity is required ○ Same voltage as single MPPC ○ All sectors have common voltage Serial – signal Parallel - bias

Assembly work International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 6 Every time the xenon chamber needed to be open to modify connection of MPPCs. Yuki Nakai from Kyushu univ. LED MPP C

Waveform of 1 photo electron 7 charge → V → Flashing LED and trigger with synchronized pulse. Waveform is as sharp as 3×3 ㎟ MPPCs 1 p.e. signal can be resolved International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam Hybrid 4segments Hybrid 2segments Vov = 3.0V Parallel Vov =1.5V ×10 amp Simple Vov = 3.0V 0 p.e. 1 p.e. 2 p.e. Simple 3.0V t → Baseline RMS have no significant difference, ～ 2mV

How many segments to divide International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 8 We tested 4 & 2 segments. 4 segments (C/16) 2 segments (C/4)

Gain (multiplication factor) 9 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam C = e × Gain / VHybrid1 : 18.7 ±1.9 [fF] Hybrid2 : 32.9 ±0.4 [fF] Gain is 4 ～ 10×10 5 Gain is lower as capacitance is smaller. Amplitude is almost the same. Lower than that of parallel connection, but 1 p.e. is still resolved with proper voltage. 2 segments 4 segments

Decay time and Connection type 10 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam Estimated time constant (τ = RC) from 1.20MΩ quench resistance and previous capacitance C 4 segments : 22.4ns 2 segments : 39.4ns Calculated decay constant by fitting waveform by event. 4 segments 25ns 2 segments 46ns ↕ Parallel 200ns 50ns of target time constant is achieved in both cases. Consistent to observation within about 20% error. 2 segments 4 segments

Leading edge and connection type 11 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam ↓ To use pico sec pulse laser, Hamamatsu PLP nm. Available soon. Leading time constant is also shorter in smaller capacitance. Leading time constant seems to depend on o.v., fitting for small waveform was difficult. 2 segments 4 segments

Effect of long cable 12 Gain does not change, while decay time slightly increases (1ns/m). Constant is 56ns at 11m of 2 segments, but still acceptable. International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam In MEG LXe detector, long coaxial cable of about 10m exists between sensor and read-out electronics. Cable Length [m] 2 segments 4 segments

Summary of serial connection International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 13 Gain 3V) Peak separation Noise rms [mV] Decay const [ns] Rise const [ns] 4 segments4×10 5 ○2.0 – ～ 33 2 – 3 2 segments8×10 5 ◎ 2.0 – ～ 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.

Package design (preliminary) International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 14

PCB based feedthrough International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 15 Charges of 1 p.e. event are compared between usual LEMO-connector and PCB feedthroughs. Slope (Charge/Voltage) = ± 1.2 [fF] LEMO = ± 2.0 [fF] MMCX About for charge, there is no difference. Another properties are being analyzed.

Summary and prospects International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 16 Several types of serial connection were tested in LXe. ・ 30 – 50 ns of decay constant was achieved. ・ Single p.e. can be resolved All basic requirements to MPPC were satisfied Hybrid, 4-segment connection is advantageous for main design Next to do Confirm improvement of PDE in new technology MPPC. MC simulation with concrete MPPC parameters. Detailed assembly design of detector and prototype. Preparation of prototype test. Hamamatsu Comment Low PDE of previous sample was caused by a unwanted layer on surface, and this layer can be removed by some process. New samples arrive soon

Fin.

現 MEG における液体キセノン検出器 18 μ + →e + γ 崩壊で発生する 52.8MeV の γ 線を検出する。 900ℓ の液体キセノン (LXe) 入射面に 216 個 他の面に 630 個の 有効面積の直径が 46mm の 光電子増倍管 (PMT) PMT に近い位置で γ が反応した場合、光 子の収集効率に場所依存性が大きくな る。 ↓ 検出器の浅い位置では分解能が悪い。 Present PMT γ-ray International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

xenon volume γ γ acceptance ← 現在 更新後 → 入射面の幅を広げる → エネルギー漏れが減少 光電面を同平面上に → レスポンスがより均一に 入射前の物質量が減少 → 検出効率が向上 ( 約 10%) 液体キセノン検出器の更新 19 より小型のセンサーを入射面に 配置して uniformity を良くして、 分解能を向上させる 浜松ホトニクス製のピクセル 光検出器 (MPPC) を採用する予定 入射面に約 4000 個の 紫外線に感度があり有感面積 12×12mm 2 を持つ MPPC International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam MPPC PMT γ-ray Upgraded CG image

シャワーの見え方の違い International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 20 現在更新後 MC による、同一の γ 線パイルアップイベント イメージング能力が格段に向上

更新後の性能 エネルギー分解能 21 σ up 2.4% ↓ 1.1% σ up 1.7% ↓ 1.0% depth ＜ 2cm 40 % of events 52.8MeV(MEG で探索する信号 ) に対する応答 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam depth ≧ 2cm 60 % of events Present Upgraded Present Upgraded

Red : Present Blue : Upgraded 更新後の性能 位置分解能 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 22 Depth from inner face [cm] Position resolution in σ [mm]

23 Raw-Waveform 25μ Low Rq 25μ Mid Rq 25μ High Rq 50μ Low Rq 50μ Mid Rq 50μ High Rq International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

pre amplifier International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 24

Result : Waveform and Quench-R 25 ・ The tail time constant do not depend on Rq so much ・ 25µm pitch MPPC is not so different from 50µm. 1 Rising & 1 Trailing component, τ r,τ t Fitting waveforms with a double- exponential function works well. MPPC Type Quench R [kΩ] Trail time constant τ t [ns] Rise time constant τ r [ns] 50 Over voltage [V] R1 Low R2 Mid R3 High Over voltage [V] R1 Low R2 Mid R3 High International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

How to shorten waveform 26 Smaller Rs → Effective, but only in limited situation. Rs = 33Ω long cable Rs = 50Ω short cable Smaller Rp → Not effective Tail is reduced with small Rs, but the waveform is distorted with a long read-out cable because of the impedance mismatch. Rs = 33Ω short cable ↓Data taken with large-area MPPC at room temperature↓ τ t = 192 nsτ t = 138 ns International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

Cause of long waveform 27 … RqRq CdCd CsCs bias voltage VbVb quench resistance diode (sensor) RsRs shunt resistance stray capacitance amplifier Waveform can not be shortened only by reducing the quench resistance and cell capacitance. AMP side MPPC side Rs,Rp×Cs term is dominant against Rq×Cd term under small Rq condition? RpRp protect resistance International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

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6mm Set up for LXe temp. test 29 We tested 2 types of connection Simple serial and Hybrid connection International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam Hybrid I (4 sectors) Hybrid II (2 sectors) Simple serial connection bias preamp ○ Less parts ○ Automatically over voltage is adjusted × 4 times higher voltage × voltage difference between each sector × Extra parts × Gain uniformity is required ○ Same voltage as single MPPC ○ All sectors have common voltage Actual test was done with 3 MPPCs because 1 sample was broken

1 p.e. ピークの広がり 30 International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam

Detailed PDE calculation of G-type MPPC In 2013Feb-1 test UM-R2 voltage PDE +/ Voltage Errors Gain3.1%1.6% Alpha peak0.26%0.21% Correction3.2%1.7% Model syst.14%22% total15.3%22.2% International Seminar on Lepton Flavor Physics with Most Intense DC Muon Beam 31