Contents Why waveform Waveform digitizer Domino Ring Sampler

Contents • Why waveform ? • Waveform digitizer : Domino Ring Sampler • CEX Beam test data @PSI autumn’ 04 – Templates and time resolution – Pulse Shape Discrimination – Pile-up rejection • Summary 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 2

In the MEG experiment every PMT will be read by a fast waveform digitizer m enn + g m eg g for the best use of the scintillation image. g m reject pile-up of g-rays m ? e timing and energy measurement without ADC ande. TDC particle identification Crucial for the MEG experiment and very difficult without waveform image Major background • Prompt background • Accidental background 24/Mar/2005 Without waveform separate only spatially if > 2 PMTs apart (15 cm) pulse shape separation 日本物理学会第６０回年次大会　　 ＠東京理科大学 3

Requirements • TDC resolution 40 ps [2. 5 GHz(400 ps) • ADC resolution 12 bits • 3000 channels (Xe calorimeter, Timing counter, Drift chamber) Cheap & fast waveform digitizer 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 4

Domino Ring Sampler (DRS) DRS Developed by Stefan Ritt NIM A 518(2004) 470 Analog sampling chip, switching capacitor circuits • Max sampling speed 4. 5 GHz • Sampling cells 1024 • 8 data ch, 2 calibration ch(voltage and time) / chip Readout Shift • Read out speed 40 MHz, 12 bits Register • Domino wave runs continuously, only stopped by the trigger Domino Circuit 0. 2 -1 ns 10 channels 　　x 1024 bins Inverter “Domino” chain IN Waveform stored • ~10, 000/chn Shift Register 24/Mar/2005 Rotating signal “Time stretcher” GHz MHz 日本物理学会第６０回年次大会　　 ＠東京理科大学 Out 40 MHz 5

Two DRS chips installed and data taken in the beam test last autumn 　　 for the first time • 2. 5 GHz sampling (400 ps bin width) Xe detector (Large Prototype) • 6× 2 ch : Xe detector PMTs center 12 PMTs on Front Face • 2× 2 ch : LYSO anti-counter for timing reference Anti-counter LYSO 24/Mar/2005 a-source Short decay time (48 ns) TDC Time resolution ~64 ps p- p gnp 0 p 0 gg g 日本物理学会第６０回年次大会　　 ＠東京理科大学 DRS 0 DRS 1 6

Waveform [m. V] Xe LYSO [msec] spike noise related to the reference clock 24/Mar/2005 [msec] Can be fixed Redesign mezzanine board 日本物理学会第６０回年次大会　　 ＠東京理科大学 7

How to analyze these waveforms ? Fitting takes so much CPU-time Need some kind of devised way or different fast method Averaged waveform Assuming constant pulse shape Now, able to use this template for fitting, for testing algorithm 24/Mar/2005 8 and日本物理学会第６０回年次大会　　 for ＠東京理科大学 simulating pile-up

Fitting by the Template Well fitted Constant Pulse shape 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 9

Time resolution • LYSO time resolution obtained by waveform fitting No time-walk correction is needed TDC • LYSO time resolution is comparable to TDC analysis 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 10

Pulse Shape Discrimination Decay time of scintillation light depend on the incident particle because of the difference in interaction way g a Pulse shape of alpha is much sharper Decay time 45 ns Decay time 4. 2 ns, 22 ns Adopt Pulse Width method for PSD – simply measure time width at the half maximum of the pulse height. 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 11

Pulse Width Noise reduced Take sum over all Xe channels a-run p 0 -run Pulse Width : Pulse Height Noise infection for small signal Possible to use for Trigger(100 MHz) 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 12

Pile-up rejection For [m. V] Previous study by MC example. . 2 g, >2. 5 Me. V, >10 nsec Now, real data are available • Fitting by superposition of two templates • Able to separate two g DT=33 ns 28% To what time difference and energy 2 g’s can be reconstructed ? [sec] Studying by simulation using template and real baseline 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 13

Summary • In the MEG experiment, all PMTs will be read out by waveform digitizer • Waveform data were successfully taken with DRS in p- beam test @ PSI autumn ’ 04 • Analyses have been made in several way – Make template – Comparable time resolution to TDC – Succeed in fast powerful PSD – Study for pile-up rejection now started 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 14

Apply Pulse Width Method for Trigger • Thinned data point 10 ns apart (one point every 25 points). “Virtual” FADC Data (100 MHz) Look still separated enough. 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 16

Xe time resolution measured by waveform fitting No cut and no correction Waveform TDC R 1 420 psec - (L 1+R 1 -L 2 R 2)/4 190 psec 193 psec (L 1+R 2 -L 2 R 1)/4 180 psec 140 psec (L 1+R 2)/2 -(L 2+R 1)/2 Comparable to TDC analysis 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 L 1 R 1 L 2 R 2 17

Raw data Xe LYSO • Random start point • Non-flat response • Spike noise Need Calibration • Global calibration • Gain calibration on each cell • Time calibration 24/Mar/2005 Voltage reference 日本物理学会第６０回年次大会　　 ＠東京理科大学 Time reference 40 MHz clock 18

Simple fitting • Fitting – Powerful and almighty way Simple double exponential function seem to good But fitting takes so much CPU-time ! Need some kind of devised way or different fast method 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 19

Noise Reduction • Still noisy after calibrated. • We have to reduce noise by means of some kind. Moving Average spike removal Each 50 cells ( correspond to 20 ns ) taken average 24/Mar/2005 日本物理学会第６０回年次大会　　 ＠東京理科大学 20