the mppc study for the gld calorimeter readout
DESCRIPTION
Introduction Measurement of basic characteristics Gain, Noise Rate, Cross-talk Measurement of uniformity with microscopic laser Summary and plans. 2006/10/31 Takashi Maeda Institute of Physics, University of Tsukuba for KEK-DTP photon sensor group for the GLD Calorimeter group. - PowerPoint PPT PresentationTRANSCRIPT
The MPPC Study for the GLD Calorimeter Readout
• Introduction• Measurement of basic characteristics
– Gain, Noise Rate, Cross-talk
• Measurement of uniformitywith microscopic laser
• Summary and plans
2006/10/31
Takashi Maeda
Institute of Physics, University of Tsukuba
for KEK-DTP photon sensor group
for the GLD Calorimeter group
• Sampling calorimeter with Pb/W - scintillator sandwich structure with WLSF readout
• Particle Flow Algorithm (PFA) needs particle separation in the calorimeter
• Fine granularity with strip/tile scintillators
• Huge number of readout channels– ~10M (ECAL) + 4M (HCAL) !
• Used inside 3 Tesla solenoid
Need a new photon sensorwhich is compact and low-cost,can operate in a strong magnetic field
GLD (Global Large Detector) Calorimeter … a candidate detector for ILC (International Linear Collider)
particles
readout
absorber plate1 cm x 5cm x 2 mm
1 cm x 5cm x 2 mm
EM-scintillator-layer model
~ 1 mm
20~100 m
Depletion region ~ 2 m
~ 8 m
Substrate
1600 pixels
400 pixels
substrate p+
p-
Guard ring n-
Al conductorp+ n+
Si Resistor Bias voltage (~70V)
The Multi-Pixel Photon Counter (MPPC)…novel photon sensor being developed by Hamamatsu Photonics (HPK)
Requirements for the GLD Calorimeter• Gain: ~ at least 105, preferably 106
• Dynamic range: up to ~1000 p.e. (need > 2500 pixels)
– to measure EM shower maximum• Single Photon Detection Efficiency: ~ 30 %
– to identify MIP signals• Noise rate : < 1 MHz (threshold = 0.5 p.e.) • Good uniformity, small cross-talk• Timing Resolution ~ 1 nsec• Sensor area: 1.5 x 1.5 mm2
– to place a larger number of pixels• Should be stable against bias voltage / temperature /
time
Characteristics of the 1600-pixel MPPC• Evaluate performance as a function of bias voltage
– Gain, Noise Rate, Cross-talk probability– Photon Detection Efficiency, Linearity
(measurements still ongoing)• Temperature dependence is also measured
– MPPC performance is known to be sensitive to temperature
Thermostatic Chamber
Green LED MPPC
Gain measurement
)( oBias VVe
CGain
・30℃・25℃・20℃・15℃・10℃・ 0℃・ -20℃
d
eA
dSGain
S : ADC sensitivity = 0.25 pC/ADCcount
A : Amp gain = 63e : electron charge = 1.6 x10-19 C
C : Pixel capacitanceV0: Geiger-mode starting voltage
Pedestal
1 pix. fired
2 pix. fired
70V, 20℃
C, V0 vs. Temperature
V0 = aT +b
• C looks not sensitive to temperature, at least under < 20oC
• V0 is linear to temperature
a = (5.67 ± 0.03) x10-2 V/oCb = 66.2 ± 0.1 V
V0=aT+b
Noise Rate … rate of avalanche signals induced by thermal electrons
Vbias – V0(T) [V]
・30℃・25℃・20℃・15℃・10℃・ 0℃・ -20℃
Lower temperature Lower noise rate
1MHz
Cross-talk
• Cross-talk probability looks stable with temperature in Vbias – V0 < 2.5V.
.).5.0(
.).5.1(
epRate
epRatePcrosstalk
The cross-talk to adjacent pixelsis caused by photons created inan avalanche.
Cross-talk probability ismeasured from dark noise rates :
・30℃・25℃・20℃・15℃・10℃・ 0℃・ -20℃
Vbias – V0(T) [V]
Using
a microscopic laser system
we perform
• scan within a pixel
• pixel-by-pixel scan
to see the variation of
• Gain
• Hit probability
• Cross-talk
1 pixel
1 pixel
Measurement of uniformityin the sensor
Measurement with Microscopic Laser System
1600 pixel MPPC
• Introduced by KEK-DTP
• YAG Laser, = 532 nm (green)
• Pulse width ~ 2 nsec, rate ~ 8 kHz
• Spot size ~ 1 m
• Light yield ~ 0.5 p.e. (not calibrated)
• Can perform precise pinpoint scan with the well-focused laser
~25m
Laser spot
)(
.).5.0(
allN
epNP
ev
evHit
Hit fraction vs. Bias Voltage• Inject laser to center of a pixel.
The hit fraction depends on bias voltage,but is stabilized in Vbias > 70 V.
Pedestal
1 pix. fired
2 pix. fired (cross-talk)
Hit
frac
tion
Uniformity within a Pixel
• Fraction of sensitive region ~ 20%• Variation within a sensitive region
~9.2% (RMS)
1 pixel
• The shape of sensitive region is not changed with bias voltage
Bias voltage・ -71.0V・ -70.0V・ -69.5V・ -69.0V
Hit
prob
abili
ty
Gain Uniformity within a Pixel
•Higher gain in central part•Gain variation in a sensitive region ~ 2.7% (RMS)
Gain (x105)
y-po
int
(1
m p
itch)
x-point (1 m pitch)
Edge of the sensor
Vbias = 70.0 V
Cross-talk Variation within a Pixel
.)2(.)1(
.)2(
pixNpixN
pixNP
evev
evXtalk
• Shape of the cross-talk probability depends on bias voltage• Edge part shows larger cross-talk
Bias voltage
・ -71.0V・ -70.0V・ -69.5V・ -69.0V
Sensitive region in a pixel
Pedestal
1 pix. fired
2 pix. fired (cross-talk)
Pixel-by-pixel Scan - Hit fraction
0.44
0.55
edge of the sensor
Variation ~3.2%
20 x 20 pixels
Sensor
Pixel-by-pixel Scan - Gain
3.2(x105)
3.8 (x105)
edge of the sensor
• Edge pixels have
higher gain• Strange structure is seen, reason unknown• Variation ~2.4%
Summary• We are evaluating the MPPC performance from
viewpoint of the GLD calorimeter readout use– Gain, Noise rate, Cross-talk are acceptable
• The MPPC properties are sensitive to Vbias-V0(T)and temperature
– Lower Noise rate and Cross-talk with lower temperature• The MPPC properties are observed to be uniform
within a sensor.
• Measure photon detection efficiency and Linearity• Perform same measurements for new MPPC samples
and evaluate device-by-device variation(We just have been provided new samples by HPK)
Plans