Improvements to Readout Electronics for the Compact Muon

Selenoid Hadron Calorimeter

Robert Schurz, IMSA;Jacob Anderson, Fermilab

Measures the energy of a particle shower caused by the collision of hadrons, which are particles made of quarks and gluons such as pions, kaons, protons, and neutrons

Provides indirect measurement of the presence of uncharged particles such as neutrinos 2

CMS Hadron Calorimeter at CERNIs a sampling calorimeter: finds the position,

energy, and arrival time of a particleUses alternating layers of brass absorbers and

fluorescent scintillators to calculate a particle’s total energy

It attempts to capture every particle in the particle shower caused by a proton collision

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When a particle hits a brass absorber plate, an interaction produces secondary particles

Particles pass through scintillators, producing a light signal

Optical fibers carry light signal to hybrid photodiodes (HPDs)

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HPDs collect the light signals and convert them into electronic signals by the photoelectric effect that are amplified through high voltage

The electrical signal is then digitized by a charge integrating and encoding chip

CMS wants to replace the old HPDs with silicon multipliers

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Have low operating voltage, high gain, large dynamic range, insensitivity to magnetic fields, and good radiation tolerance (Mans et al., 2012)

Large gain provides robust electrical signals that reduce the importance of electrical noise (Buzhan et al., 2002)

The noise of the SiPM is negligible due to a high gain of 6*104 compared to HPD gain of 2000 (Anderson, 2012)

Increased effective quantum efficiency and ability to detect single photoelectrons improves the ability to calibrate and monitor the calorimeter (Crushman et al., 1997)

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Absorption of a photon can excite an avalanche that causes the struck pixel to discharge

Firing of a pixel causes its capacitor to discharge, resulting in a quantized charge output from the SiPM depending on the number of pixels discharged

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Want to measure the charge distribution of each SiPM

Used a simulation to measure the SiPM gain by two methods: Light impulse from an LED

A photon causes a pixel to dischargeMeasure gain by using sigma and the mean of

a Gaussian distribution for the charge distribution assuming Poisson statistics for the number of photons

Electronic pedestal (PED) dataThermal noise causes a pixel to dischargeMeasure gain by subtracting the mean of the

0th photoelectric peak from the mean of the 1st pedestal peak by using Gaussian distributions

How can we best measure the gain of a SiPM: LED amplitude or electronic

PED?

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Tested 158 mounting boards each with 18 different SiPM positions for each event lasting 50 ns

Compared PED to LED method by looking at PED gains, LED gains, difference in LED and PED gains, and the LED signal amplitude

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Plot the charge distribution for the LED amplitude and PED for a specific individual SiPMs

PED method shows a photoelectron peak and a pedestal peak

LED method had an amplitude that allowed us to calculate the gain for each method

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Figure 1. Charge Distribution for LED Amplitude (left) and PED (right) for Mounting Board 58, Run Number 273, and SiPM Position 14.

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Found the root mean square of gains to be 0.3539 fC for the PED distribution and 0.9334 fC for the LED distribution

Indicates that the PED method is a better measurement technique for determining the gain

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Figure 2. Event vs. Gain for LED Amplitude (left) and PED (right). Using the data from the charge distribution for each SiPM we were able to calculate the gain. We obtained a RMS of 0.9334 fC for the LED and 0.3539 fC for PED. 13

Figure 3. Events vs. Number of Photons for LED (left) and Difference in LED and PED Gain (right). Using the Poisson distribution we were able to calculate a mean of 586 photons for the LED. Since the mean for the difference in LED and PED gain was not centered at zero (systematic bias), we concluded that the LED method had some error due to two photons hitting the same pixel.14

PED method is a more robust measurement technique because it causes less error

The LED method had some saturation Quantified the electrical signal we get every

time a pixel fires which can then be converted back into the energy that the particle deposited

Future studies could measure: Noise Hamamatsu value + board offset Break-down voltage Dark current of the SiPM’s Other readout electronics such as QIE chip 15

The study was made possible by the collaboration of IMSA and Fermilab efforts. The author would like to thank all SIR staffmembers, including Dr. Scheppler , and Jake Anderson at Fermilab who made this investigation possible.

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Anderson, J. (2012). Upgrade of the CMS Hadron Calorimeter for an Upgraded LHC.

The Compact Muon Solenoid Experiment Conference Report, 1 (1), 234-240.

Buzhan, P., Dolgoshein, B., Ilyin, A., Kantserov, V. , Kaplin, V., Karakash,

A., ...Kayumov, F. (2002). An Advanced Study of Silicon Photomultiplier.

Advanced Technology & Particle Physics, 23 (2), 717-728.

Crushman, P., Heering, A., Nelson, J., Timmermans, C., Dugad, S. R., Katta, S., &

Tonwar, S. (1997). Multi-pixel Hybrid Photodiode Tubes for the CMS Hadron

Calorimeter. Nuclear Instruments and Methods in Physics Research, 27 (1),

107-112.

Mans, J., & CMS Collaboration (2012). CMS Technical Design Report for the Phase 1

Upgrade of the Hadron Calorimeter. The CMS Collaboration, 26 (3), 84-103.17