R&D of Calorimeter using Strip/Block Scintillators with SiPM H. Miyata, E.P. Jacosalem, S. Iba, N. Nakajima, H. Ono, & A.L. Sanchez　 Niigata University For GLD-CAL group Contents 1. Motivation 2. Study on scintillator strips 3. Laser test of SiPM 4. Source test of scinti. strip with SiPM 5. Summary Good afternoon to each and everyone. I am Editha P. Jacosalem from Niigata University and would like to share with you the progress of our current research. Our work is about the R&D of Calorimeter using Strip/Block Scintillator with SiPM. This is a collaborative work of the following persons. E.P. Jacosalem, S. Iba, N. Nakajima, H. Ono, A.L. Sanchez and all are under the supervision and guidance of our energetic and ever physics enthusiastic sensei; Prof. Hitoshi Miyata. Calorimetry and Muons session LCWS05 at Stanford March 19, 2005

1. Motivation Present design of GLD Calorimeter Fine segmentation scintillator read out by SiPM We might need smaller segmentation Striplet: 10x40x2mmt Study of surface covering X,Z-layer strip scinti.: 10x200x2mmt Tile-layer: 40x40x2mmt

2. Scintillator study Setup Source point location 10mm 2.5mm Setup Sensor : Strip type scintillator (10mmx2mmt with length: 4,8,12cm) Surface covering: Black tape, White paint, Teflon wrapped, White+Teflon, Al and Gold evaporation WLS fiber diameter: 1.0mm (length 13cm, 22cm) Source : Sr-90 (beta-ray) PMT (sensor) : 16 Ch MAPMT H6568-10, HV : -950V On the systematic study of scintillator, we used the set up shown. For the meantime we ONLY do ADC measurements for the following small scintillators: for strip-type, we used 10mm width and 2mm thick with lengths of 40, 80, 120 mm; for block type; we use 10x10mm with thickness of 2 and 5mm. We use 10x80x5mm size scintillator which is directly connected to H3164 PMTas trigger. 90Sr is used as beta source and we used WLS fiber with diameter of 1.0mm and with length of 13 cm and 22 cm. The sensor uses 16 Ch MAPMT H6568-10 with HV source of -950V. Later, we will consider using other types and sizes of scintillator such as 16cm strip type and 4mm, 6mm and 8mm thick block type scintillators The right figure shows the location of the source point in the scintillator/sensor when doing the ADC measurement. For the strip type; we placed the source point 1cm at the far end (from the PMT) and 2.5mm from the side. For the block type; we put the source point at 2.5mm from the side and 5mm from the end.

PH vs strip length for different WLS fiber length Signal Pulse Height signal pedestal PH White paint: WLS 13cm White paint: WLS 22cm Black sheet: WLS 13cm Black sheet: WLS 22cm length We compared the Pulse Height in ADC counts attained from every length of strip type scintillator covered with white paint and black tape only and with WLS fiber lengths of 13cm and 22cm.. The graph shows that the pulse height increases with the scintillator length but decreases as the WLS length was increased from 13cm to 22 cm. Strip length PH increases as scintillator strip becomes long for White paint covering due to the larger acceptance of reflection lights.

Pulse height vs surface covering Legend: Al - Aluminum Au - Gold BT - Black Tape T -Teflon WP – White Paint WPT – White Paint with Teflon Al White Gold Black Used Strip type scintillator: 10x40x2mmt, WLS fiber length : 22cm Compared surface covering effect on the scintillator Black tape, White paint, Teflon wrapped, White+Teflon, Al and Au evaporation We plotted and compared the Pulse Height in ADC counts against the different surface covering. We used the 10x40x2mm strip type scintillator and used WLS fiber length of 22cm. The figure shows how the PH varies with each surface coverings. As per data taken, it shows that white paint + teflon had a maximum pulse height. Teflon wrapping maybe makes a smooth surface. White paint +Teflon is the best surface covering

3. SiPM study Wire Bonding A 34x34 =1156 pixels K 2mm Micro Avalanche Photo Diode (APD) with each pixel in Geiger mode 34x34=1156 pixels in small area　(1.2x1.2mm) Pixel Size : 30x30um High Gain : ~106 Operational at low voltage (60~70V) The SiPM study: The SiPm is a compact device and is believed to be cheap compared to the commonly used PMT. This SiPM only needs a low voltage source (around 60-70V) unlike the PMT which needs hundreds or even thousands of volts as source . (Read the specifications of the SiPM on the transparency.) 30um

Setup of laser test Logic YAG Laser & Scan Table System Wave length & Power: 532 nm (10mJ), 1064 nm (20mJ) Pulse width : < 10nsec Filter: down to 10-8 Precision of laser position: ±2um Trigger : from laser system The Set-Up for the SiPM study: The left figure is the output circuit plan of SiPM which was provided by its manufacturer in Russia. The upper right figure is a picture of the Laser system used in the characterization on SiPM, while the lower right figure is the logic circuit of the SiPM characterization measurement whereby laser system is also used as trigger. Filter is used to lower down the laser’s intensity for about 10 -8. Charge was set to 20mJ/cm2 as laser default for 1064nm laser source and lower it to 10mJ/cm2 for 532 nm laser source. Output Circuit

Bias voltage dependence (532nm) PH Whole sensitive area is covered by Laser sigma Pedestal Signal We also measure the sensor bias distribution of 532nm wavelength laser source. As observed from the figure, where we plotted the pulse height against bias voltage, no saturation has been observed and much noise had been produced at bias voltage above 68V, however, below 65.5 V bias voltage, we got a very low ADC signal. Bias Very low gain for < 65V No saturation up to 68.5V

Noise level & S/N (532nm) Noise level S/N Noise level at 532nm: As noticed, similar to 1064nm laser source, the noise level quickly increases as the bias voltage increases. Also, similar to 1064nm, the S/N rate had minimal fluctuations from range 65.5V to 67V; as if “plateau” is formed in this range. In this case, we chose 66.5V as the best operational bias voltage at this time since it is located at the center of the “plateau”. Bias Bias Noise level (Pedestal sigma) increases for higher voltages Best S/N (Pedestal sigma /PH) seems to be achieved around 66.0V ~67.5V

Position dependence of pixel PH Laser hitting area (9 pixels) Laser wave length : 1064nm Sensor bias : 66.5V 49points (7x7points) were measured Laser output fluctuation: ~10% or less Sensor position distribution using 1064nm wavelength laser source. 49 points were being measured as shown in figure at the upper left. Figure at the lower left shows that the laser hits more than 1 pixel. This picture was seen through the microscope. The right figure shows that maximum pulse height were located at the center of the sensor. Areas of the same color in the graph indicate the same pulse height level. It is also observed that corners at the sensor has the lowest pulse height. Laser has an output fluctuation range of about 10%. Central part showed higher PH

Cross sectional view 1 pixel = 5 ADC counts

4. Source test of scinti. strip with SiPM Setup Striplet Sensor scinti. type: 10x40x2mmt striplet Surface covering: White paint & Teflon wrapped

Pedestal Signal 250ns 5mV Trigger Sensor 66.0V PH Comparing ADC counts of laser injection and beta ray signals at same bias voltage (66.5V), the number of photons we observed for beta ray is ~5. Bias

5. Summary Scintillator study White Paint +Teflon is the best surface covering Longer strip-type with shorter WLS fiber has largest PH SiPM study Bias voltage dependence of PH, Noise, S/N were measured. For whole area exposure of 1000 pixels SiPM with 532nm laser light, good operation voltage span was ~1.5V. Central region of SiPM showed higher PH. Need to check more SiPMs. Beta ray signal from scintillator strip with SiPM Signal was observed for 10x40x2mmt striplet Number of photons: ~5 As a summary, for SiPM; laser signal is characterized, had determined the best operation voltage at about 66.6V, and observed that corners of the sensor had the lowest PH and the highest PH is located at its center: For Scintillator study: White Paint + Teflon was found to be the best surface covering; Longer strip-type with shorter WLS fiber has the greatest PH, and the 5mm-thick block type white painted scintillator has greater PH compared to 2mm thick.

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PH vs Block Type Scintillator Thickness This is just a trivial case where we only compare two points however this is just our starting point. We compared the Pulse height of the 10x10mm block type scintillator of 2mm and 5mm thickness. We will do the same measurement on 4, 6, 8 and 10mm thick 10x10mm block type scintillators. The graph shows that 5mm thick scintillator with white paint had greater pulse height compared to 2mm thick, however, 2mm thick black taped scintillator had a little larger pulse height than that of 5mm thick. Compare the PH vs thickness 5mm thick scintillator had greater PH

Photon number of scintillator and SiPM measurements Position distribution(1064nm) Laser insert into 9 pixels Saturation occurred -> 9 photons yielded 66.5V : PH=47 (ADC count) 5.2 (ADC count) / 1 photon Connection scintillator and SiPM 66.5V : PH=31 (ADC count) ~6 photon yielded 5 ADC count