Characterization of the Characterization of the Hamamatsu R8900-M16 Hamamatsu R8900-M16

Multianode Photomultiplier Tube Multianode Photomultiplier Tube (PMT)(PMT)

Paul MekhedjianDepartment of Physics

University of California, Santa CruzDepartment of Energy – INFN Summer 2007 Studentship

Why do we care?Why do we care?High granularity Pb-Sci Fibers High granularity Pb-Sci Fibers

calorimetercalorimeterKLOE readout

4.4 x 4.4 cm2 read by photomultipliers

1 module 52x25 cm2 read by 60 photomultipliers.

Increasing granularity by a factor 16 using HAMAMATSU photomultipliers.

Better particle identification Less merging probability for pair of clusters Useful for neutron detection.

Device AspectDevice Aspect

Hamamatsu R8900-M16Window material: Borosilicate glass

Arrangement and Type: 4 x 4 grid Number of channels: 16 (each 5.7x5.7mm2)Effective Window Area: 23.5x23.5mm2

Photocathode material: BialkaliSpectral response range: 300 to 650 nm

Compact form and design practical for assembly and use in calorimeters!

Device scheme:Device scheme:

16 anodes signal

12 (last dynode signal output)

Signal formation process:

1. Photons strike photocathode2. Electrons are produced via photoelectric

effect and directed to the first dynode past the focusing mesh

3. The dynodes are made of materials with very low bandgap energies, which produce additional electrons upon collision

4. Electrons are directed and oriented from the photocathode to the multianode by a simple electric field generated by the dynodes

5. The signal is finally collected at the anode and its gain is dependent on the total number of dynodes and the applied voltage.

Connector Socket

Analog Circuit AmplificationAnalog Circuit Amplification

Connector socket

Each anode/DY12 output can be connected by a LEMO cable to the oscilloscope

Amplifier Circuit:

Summary of TalkSummary of Talk

Quality of Lunch?!Quality of Lunch?! Linearity of responseLinearity of response Signal shape(Rise Time, Fall Time, Full Signal shape(Rise Time, Fall Time, Full

Width at Half Maximum “FWHM”)Width at Half Maximum “FWHM”) Transit Time & Transit Time SpreadTransit Time & Transit Time Spread Relative Gain vs. High VoltageRelative Gain vs. High Voltage Response in Channel HomogeneityResponse in Channel Homogeneity Channel-Channel Crosstalk Channel-Channel Crosstalk

Apparatus & Setup Apparatus & Setup

High Voltage Power Supply Laser Control Unit

Laser Pulse

Low Voltage Power Supply for Analog Amplifiers

Laser / Photon Source

Oscilloscope

2D Micrometer Slide

50Ω Terminator

PMT Input Socket

Apparatus Continued…Apparatus Continued…

• This is what a typical signal would look like on the oscilloscope once the high voltage power was turned on.

A Typical Signal

Signal on the oscilloscopeSignal on the oscilloscopeFrom a single anode…

Rise time: Time from 10% to 90% of the signal amplitudeFall time: Time from 90% to 10% of the signal amplitudeArea (integral) of the signal is proportional to the collected charge at a particular anode

What does this dial do?What does this dial do?

Prior to crosstalk measurements, we discovered that varying the dial amplitude gives interesting results…

Amplitude ResponseAmplitude Response

The signal response of the photomultiplier tube is linear for a certain range of the laser’s dial amplitude. It then enters a breakdown region (past ~900) where

the trend follows an exponential or asymptotic behaviour.

Charge ResponseCharge Response

The response for the channel’s charge on the anode follows a nearly identical trend!

Linearity of Both Linearity of Both Amplitude and ChargeAmplitude and Charge

a = 2.73 +/- 0.01mV

b = -13 +/- 8mV

a = 0.0093 +/- 0.0001 nV*s

b = 0.751 +/- 0.075 nV*s

• After investigating only the dial range of 500 to 850, we have found the linear response region.

Charge OffsetCharge Offset

It should be noted that the It should be noted that the parameters of the linear fit parameters of the linear fit produce a constant which produce a constant which has physical meaning.has physical meaning.

a = 0.0093 +/- 0.0001 nV*s

b = 0.751 +/- 0.075 nV*s

y = 0.0093*x + 0.751

(i.e. Charge = 0.0093*Amplitude + 0.751)

• We know that if a light source has no amplitude, the photomultiplier tube cannot produce a value of

charge.•Thus, based on the fit, there is a charge offset

(given by the parameter b. This parameter will be useful in future slides…

Signal shape vs amplitudeSignal shape vs amplitude

It is important for the uniformity of the calorimeter response with respect to particles of different energy that the signal shape is independent (more or less)

from the signal amplitude.

Slope: 0.003ns/mV

Slope: 0.008ns/mV

Slope: 0.026ns/mV

It should be noted that some signal properties vary more than others

with an increase in amplitude.

Transit Time ShiftTransit Time ShiftSo honestly… How long does it take from a photon to leave the laser, hit the photocathode, photomultiply, and then leave the PMT from the anode?

The time transit is what this quantity is known as and we wished to see how much this quantity differed from channel to channel…

This plot illustrates how other channels deviate from a reference channel (shown as a white box without a number).

This is crucial because it affects the time resolution of a potential KLOE calorimeter upgrade with multianode PMTs.

Charge CharacteristicsCharge Characteristics

• Since charge is collected at the anode, it is interesting to see how this charge fluctuates.

• We can also use this information to study a quantity known as TTS (time transit spread) as a function of the number of photoelectrons (Q/Q). This is where one may use the charge offset previously mentioned to further analyze raw values of photoelectrons which hit the photocathode in the first place.

Relative Gain of PMT Relative Gain of PMT ChannelsChannels

• Hamamatsu documentation suggests gain might not be completely homogenous from channel to channel

• We wished to verify this premise experimentally with our apparatus.• Here, relative gain means that we are normalizing to the data

obtained at 500V for each channel and does not represent an absolute quantity.

Total Channel Relative GainTotal Channel Relative Gain• In this measurement, we had the laser incident on a particular channel and took the

charge collected by the total channel (DY12).• This process was repeated for each channel and its gain represented by a slope in a

linear model, the same process shown in the previous slide.

Channel Homogeneity for Channel Homogeneity for SocratesSocrates

• We also wanted to test how homogeneous channels were.• Below are plots of Socrates, the first PMT we tested this summer.

Amplitude Homogeneity: Charge Homoegeneity :

Channel Homogeneity for Channel Homogeneity for NietzscheNietzsche

• Below are plots of Nietzsche, the eighth PMT we tested this summer.

Amplitude Homogeneity: Charge Homoegeneity :

Making Sense of ChaosMaking Sense of Chaos Fact: After many days without Fact: After many days without

food and water, you can be food and water, you can be convinced that 2+2=5. convinced that 2+2=5. Similarly, we can do the same Similarly, we can do the same things with these plots.things with these plots.

What we need in our data is a What we need in our data is a definitive pattern so we can definitive pattern so we can say that say that “Yes, this happens “Yes, this happens due to this or that. “due to this or that. “

Then we made the FWHM Then we made the FWHM histogram for Socrates and histogram for Socrates and discovered some order…discovered some order…

We hope that we can discover We hope that we can discover additional photomultiplier additional photomultiplier characteristics to make similar characteristics to make similar conclusions.conclusions.

FWHM*10-7 s

Crosstalk MeasurementsCrosstalk Measurements• The crosstalk is the response of a given channel when a different channel is fired

upon by the laser beam.• In the ideal case the channels are completely decoupled but in reality a small

correlation is observed. High crosstalk could potentially spoil the resolution power of the device.

Charge Crosstalk:Amplitude Crosstalk:

Alternate representation…Alternate representation…

Charge Crosstalk: Amplitude Crosstalk:

• Three dimensions help to illustrate how much more profound an effect amplitude has in interchannel communication.

• Charge collection is a more important quantity for the KLOE calorimeter because as an integral quantity, it has the ability to cancel out positive and negative noise to leave only real information, whereas amplitude includes

background noise.

Results and ConclusionsResults and Conclusions

Crosstalk measurements verify that only Crosstalk measurements verify that only channels juxtaposed with the incident channels juxtaposed with the incident channel express crosstalk that could be channel express crosstalk that could be dangerous in experimental settings.dangerous in experimental settings.

Presented in the former slide are the results Presented in the former slide are the results for only one PMT. We measured for only one PMT. We measured eleveneleven in in total, but would need a full day to show them total, but would need a full day to show them all in depth.all in depth.

The data we have collected will be very useful The data we have collected will be very useful in preparation for the initialization of the in preparation for the initialization of the experiment in Frascati.experiment in Frascati.

E poiE poi?? Adesso…We hope to see how well the KLOE Adesso…We hope to see how well the KLOE

calorimeter will work with its array of PMTs. calorimeter will work with its array of PMTs. The granularity of the multi-anode PMTs The granularity of the multi-anode PMTs

should invaluably assist in more precise should invaluably assist in more precise results with respect to determining position results with respect to determining position of photons incident on the tubes.of photons incident on the tubes.

More investigation on definite correlation More investigation on definite correlation and studying of FWHM, the most and studying of FWHM, the most predictable reading we have seen so far.predictable reading we have seen so far.

Thanks!Thanks!

Gratitude goes to INFN, Universita di Gratitude goes to INFN, Universita di Roma III and also to everyone who Roma III and also to everyone who has welcomed me here!has welcomed me here!

Special thanks to Filippo Ceradini, Special thanks to Filippo Ceradini, Paolo Branchini, and Biagio Di Micco Paolo Branchini, and Biagio Di Micco for assisting me with my work.for assisting me with my work.

Grazie milioni!