MPPC Measurementsat LSU

Brandon Hartfiel

LSU Hardware GroupThomas Kutter, Jessica Brinson,

Jason Goon, Jinmeng Liu, Jaroslaw Nowak Sam Reid

January 2009 Collaboration Meeting

TFB Darkrate

We measure darkrate using the TFB. We integrate randomly triggered 250ns gates, fit the pedestal and 1pe to determine the .5 pe level and then count the number of events below .5 pe. We then calculate the darkrate by

pedestal fraction= exp(-darkrate * gate width)

This calculation assumes that the pulses are randomly distributed in time. Afterpulses are not. Assuming the time distribution of afterpulses isdistributed as an exponential, we can calculate the expected difference between our darkrate method and the threshold crossing rate

• ALTERNATE METHOD We also measure the darkrate using the fit values of the pedestal and 1 pe (with 2pe background) instead of using a cut at .5 pe

TFB Darkrate

Comparing 20C to 25C

Relative change per degree C

4.2 +/- .4 %per degree

bias voltage - nominal

dark

rate

(k

Hz)

cut methodfit method

at 25 C and nominal bias

Hamamatsu rate

our T

FB

rate

slope = .86

purple limits match

our rate / threshold crossing rate

afterpulse creation probability

tau

Simple Simulation at 700kHz Thermal rate. No deadtime.No recharge Time

8.9%per 100mV

all profile plots have RMS errorbars

Temperaturechanges aredefined as

C

CC

25

2025

Scalar Darkrate• A threshold crossing rate is taken for 40 sensors at .5pe with

26ns deadtime (determined by the width of our preamp output)

Hamamatsu rate

Our

Sca

lar

Rat

e

Now the slope is .94The ratio of slopes for the2 LSU measurements is .915

LSU

TF

B rate/ LS

U scalar

rate

ta u

afterpulse creation probability

LSU data ratio in purple

black lines are the resultsfrom page 12

Gain

• The TFB gain is calibrated using the internal calibration systemwith the sensors biased at 60V. We appear to have made a mistakeas our gains are consistently 25% high.

• Gain is measured between the pedestal and 1pe in LED runs with and average of 2.5 pe per event

• ALTERNATE METHOD We also measure the gain from dark spectra

Gain

Comparing 20C to 25C

Relative change per degree C

-3.7 +/- .2 %per degree

bias voltage - nominal

gai

n

LED runDark run

at 25C and nominal bias

gain

7.7%per 100mV

sigma2.9%

Crosstalk + Afterpulses Random trigger dark ADC spectra – Pedestal, 1pe and 2pe are fit with Gaussians. Pedestal fraction is used to predict the 1pe fraction. A deficit implies an excess of > 1pe events which could be either afterpulses or crosstalk ALTERNATE METHOD The LED run ADC spectra are fit using a poisson function modified to include a probability that each original pulse create one crosstalk or afterpulse.

Crosstalk +

Afterpulses

Comparing 20C to 25C

Relative change per degree C

-6.9 +/- .5 %relativeper degree

bias voltage - nominal

CT +

AP

crea

tion

prob

abili

ty

dark runsLED runs

25 C and nominal bias

probability of creating a new pulse

14.9% relativeper 100 mV

sigma6.5%relative

Relative PDE

• Three reference sensors are included with every run and always kept at their nominal bias voltage

• The LED ADC spectra are fit using the poisson + AP+ CT function.

• The average number of pe is divided by the average for the 3 reference sensors.

Relative PDE

Comparing 20C to 25C

Relative change per degree C

-1.3 +/- .4 %per degree

at 25C and nominal bias

pe / pe of reference sensors

rela

tive

pd

e

bias-nominal

6.0% per100mV

sigma3.3%

Afterpulses Only (example TA8088 25C)

.5 pe threshold crossing rate is measured with different deadtimesafter the pulses. This is compared to the expected rate if the pulseswere not correlated in time.

red – fit to expectation if pulses are random in timeseen rate=real rate/(1+deadtime*real rate)

black - data

deadtime (ns)

rate

kH

z

derivativeof thedifference

kHz/

ns

time since original pulse (ns)

afterpulse rate 138kHztau = 80 ns

Afterpulses Only

sensor number

ap c

reati

on

prob

abili

ty

tau

COMPARE WITH PAGE 4

sensor number

The “afterpulse probability” is theintegral of the fit on the right of theprevious page, starting at 0 ns, divided bythe intersection of the red line with they-axis on the left plot. It does not consider the possibility of afterpulsesof afterpulses and so is an overestimation of the actual probability.

afterpulse vs temperature

sensor number

rela

tive

chan

ge p

er d

egre

e

Afterpulses vs Bias Voltage for 3 MPPCs

4.5% absoluteper 100mV

afte

rpul

se

prob

abili

ty

Bias-NominalT

au

Bias-Nominal

Conversion factors LSU/INR

Sensor gainx10^6

Darkrate PDEcompared to our reference

TA9307 .0376 .883 .0826

TA9309 .0390 .865 .0882

TA9310 .0375 .865 .0846

TA9314 .0408 .936 .0847

Average .0387 .887 .0851

% standarddeviation

4.0% 3.8% 2.7%

note: these correction are large because different units were used e.g. number of electrons vs number of ADC bins

EXTRA SLIDES

Our Reference Sensors21.5C and Hamamatsu nominal

bias Sensor gain

x10^6DarkratekHz

PDEcompared to our reference

CT+APcreation probability%

TA7881 1.181 630 1.05 25.3

TA7893 1.170 492 1.06 30.0

TA7930 1.110 645 1.06 26.4

TA7976 1.177 627 1.05 27.6

TA8097 1.088 606 .96 56.0 ?

TA8120 1.125 504 1.02 23.5

TA8160 1.157 510 1.01 23.8

Sensors we received from INR25C and Hamamatsu nominal bias

Sensor gainx10^6

DarkratekHz

PDEcompared to our reference

CT+APcreation probability%

TA9307 .958 931 1.00 18.4

TA9309 .990 909 1.05 19.1

TA9310 .970 877 .99 20.0

TA9314 1.007 820 1.00 20.1

1.5 pe and 2.5 pe scalar rates Sensor 1.5 pe

ratekHz

2.5 peratekHz

TA9307 126 14

TA9309 124 14

TA9310 119 14

TA9314 117 14

TA8097 81 9

TA8120 64 7

TA8160 71 8

results vs

position

dark/hamamatsu dark gain

CT+AP

relative pde

TA8097 vs

day

between dec 13 and dec 20 a bad channel was dropping all voltages by .08this has been corrected for on all other plots

TA8160 vs

day

between dec 13 and dec 20 a bad channel was dropping all voltages by .08this has been corrected for on all other plots

TA8120 vs

day

between dec 13 and dec 20 a bad channel was dropping all voltages by .08this has been corrected for on all other plots

Bad Sensors

Sensor TE5020 was dropped into an unaccessible place

11 sensors failed to meet our cuts at least twice.Some fraction of these failures are probably due tohuman error, but we decided to put these aside just to be safe

• one had the wrong bias voltage• two had very bad fits• two have PDE ~35% too high• 6 were only 15% different from normal