Development, Simulation, and Prototype Performance Measurements of - - PowerPoint PPT Presentation

Development, Simulation, and Prototype Performance Measurements of the Mu2e Straw Tracker

Richie Bonventre Fermilab Users Meeting June 20th, 2018

Lawrence Berkeley National Lab

Outline

• 1. Brief overview of Mu2e and physics motivation
• 2. Mu2e straw tracker design
• 3. Tracker Prototype low level measurements
• 4. Simulating the tracker
• 5. Comparing resolution + efficiency from prototype data and

simulation

See upcoming talk by Tomonari Miyashita for more details on the experiment!

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Charged Lepton Flavor Violation

• Mu2e will search for neutrinoless conversion of a muon to an

electron in a nuclear environment: µ−N → e−N

• This would violate charged lepton flavor, something that

has never been seen before

• Any detection of charged lepton flavor violation would be an

unambiguous sign of new physics! (SM contribution is < 10−50)

• Mu2e goal is a 104 improvement!

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The Mu2e Experiment at Fermilab

• Stop 1018 muons on Aluminum
• Conversion produces monoenergetic 105 MeV electrons
• Main background is decay-in-orbit electrons
• Only distinguishable by momentum, want high precision

measurement that can handle high rate

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The Straw Tracker Detector

• Cylindrical straw tracker operating in uniform field
• Tracker is in vacuum
• Measurement is multiple scattering dominated
• Entire detector much less than one radiation length of material

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Tracker Configuration

• 18 stations, each containing 12x 120◦ panels for

stereo measurement

• Blind to DIO electron momentum peak and

beam flash

• Expected resolution better than 200 keV/c

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The Straw Tracker Detector

• ∼21,000 low mass straw tubes in vacuum
• 5mm diameter, 0.5-1.2m long
• 15µm mylar wall, 25µm tungsten wire
• 1 atm of 80/20 Ar:CO2, wire at 1425V

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What are we measuring

• Individual threshold crossings digitized in time (TDC)
• Drift time → radial resolution ∼200 µm
• Straws are instrumented on both sides
• Time division → longitudinal resolution ∼4 cm
• Falling edge digitized for Time over threshold
• Measure of path length / radius independent of t0
• ADC measures pulse waveform for background rejection

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Tracker Electronics

(*) Summing optional

Discrete Coercial Aalog ICs FPGA FPGA

ADC TDC TDC

PCB transmission line

Preamp Preamp

Readout Controller

DAQ

Straw

Output Control & Buffer

∑

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Tracker Electronics

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Tracker FPGAs and Firmware

• Most of functionality in FPGAs - highly configurable
• Have already taken advantage to add new features (Time over

threshold)

• Originally had Altera FPGAs, now using Microsemi SmartFusion2

for radiation tolerance

• 2x Digi FPGAs that digitize 48 channels each
• Separate TDCs for each end of straw
• Continous readout of summed ADC waveform at 50 MHz
• Data buffering, DAQ communication, tracker slow controls in

ROC FPGA

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Firmware TDC Design

• Need ∼4cm resolution longitudinally along straw
• Near speed of light signal → <100ps time resolution
• Achieve resolution in firmware while minimizing resource

usage

• Initial design based on wave-union design by Jinyuan Wu
• Delay chain for sub-clock tick precision
• Average multiple chains to subdivide large delays
• Auto calibration of bin widths

1 delay chain 3 delay chains 8 delay chains

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Firmware Design

FPGA resource usage for 48 channel design

• Have managed to implement design that fits all 48 channels in

a single chip

• Learning process dealing with Microsemi FPGAs
• Architecture changes from Altera version
• Much smaller community, support resources
• Difficulties with timing constraints - manual placement of delay

chains and ADC interface

• Several hour compilation time for full design
• Demonstrated readout chain from digitizing FPGAs through

to DAQ computer over SERDES

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An 8-straw tracker prototype for testing and performance mea- surements

• Portable self-contained setup
• Cross talk → proton beam from 88” cyclotron at Berkeley Lab
• Radiation sensitivity → UC Berkeley High Flux Neutron Source
• Straw and electronics parameters → radioactive sources
• Efficiency/resolution → cosmic rays
• Read out over USB serial using custom DAQ

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Sources used to measure gain, energy resolution, time division, simulation tuned to results

(mm) T + z ∆ ⋅ /2)

eff

(v 400 − 300 − 200 − 100 − 100 200 300 400 0.05 0.1 0.15 0.2 0.25

Mu2e Straw Longitudinal Resolution

0.7 mm ± = 29.9

z

σ z = -175.0 mm, 0.6 mm ± = 30.3

z

σ z = -87.5 mm, 0.5 mm ± = 26.3

z

σ z = 0.0 mm, 0.9 mm ± = 34.7

z

σ z = 87.5 mm, 0.9 mm ± = 35.0

z

σ z = 175.0 mm,

0.5 mm/ns ± = 203.0

eff

gain v

4

10 ⋅ Fe source at 1.33

55

(Tom-Erik Haugen)

• Gas gain by measuring current

with 55Fe

• Energy resolution using 5.9 keV

x-ray peak

ADC peak value (counts) 50 100 150 200 250 300 350 400 450 500 0.01 0.02 0.03 0.04 0.05 0.06 8-Straw Prototype G4 + Straw Simulation Fe Peak

55

5.9 keV

High Voltage [V]

1200 1250 1300 1350 1400 1450 1500 1550 1600 4

10 × Gain

5 10 15 20 25

ax + b

Fit = e Fe Data)

55

Prototype ( Prototype (Fit)

(Andrew Edmonds)

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Simulation of the straw tracker response

• Detailed Geant4 simulation of full detector
• Custom code takes energy deposition in each straw and

models physics and electronics response

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Simulation of the straw tracker response

Simulation of waveform threshold crossing at each end of straw

1000 1050 1100 1150 1200 time (nSec) 5 − 5 10 15 20 Waveform (mVolts) 1000 1050 1100 1150 1200 time (nSec) 5 − 5 10 15 20 Waveform (mVolts)

• Each ion cluster modelled individually, including drift, wire

propagation, and electronics response

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Simulation of the electronics response

Input pulse shape → Apply electronics response

Time (ns) 10 20 30 40 50 60 70 80 90 Signal (mV) 10 20 30 40 50 Fe waveform, 0 cm

55

Fe waveform, 120 cm

55

Fit

(Data from Manolis Kargiantoulakis) (SPICE sim from Vadim Rusu)

• Use unshaped waveforms from source at different distances to

model attenuation, dispersion

• Fit for transfer function describing preamp and integrator

response

• Model includes saturation effects, pulse shape distortion
• Important for accurately determining proton discrimination,

modelling pileup

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Reconstructing track position for performance measurements

• Use PMT trigger and ATLAS FEI4 pixel

detectors to allow precise reconstruction

• f cosmic ray tracks
• MIPs similar to conversion electron signal
• Allow resolution and efficiency

measurements

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Reconstructing track position for performance measurements

STRAW MEASUREMENT Drift time (ns) 10 20 30 40 50 60 70 80 PIXEL MEASUREMENT Track position (mm) 2 4 6 8 10 12 14 16

Straw 2 Straw 3 Straw 4 Straw 5 Straw 6

• ATLAS FEI4 detectors measure track position
• 2.0x1.9cm chips, 250x50µm pixels
• PMT trigger gives t0 for drift time measurement
• ∼600ps time resolution
• Reconstruct relative position and timing of pixels, PMTs,

straws, wires with maximum likelihood fit

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Transverse resolution

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.005 0.01 0.015 0.02 0.025 0.03 0.035

8-Straw Prototype G4 + Straw Simulation 0.0 < DOCA < 0.5

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05

0.5 < DOCA < 1.0

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05

1.0 < DOCA < 1.5

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05 0.06

1.5 < DOCA < 2.0

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05 0.06 0.07

2.0 < DOCA < 2.5

• Agrees with simulation tuned to low level

parameters

• Model and simulation include full DOCA

dependence of resolution

• gaussian smearing × exponential with constant τ
• τ encodes effect of cluster statistics

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Transverse resolution

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.005 0.01 0.015 0.02 0.025 0.03 0.035 8-Straw Prototype 8-Straw Prototype Fit G4 + Straw Simulation G4 + Straw Simulation Fit

0.0 < DOCA < 0.5

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05

0.5 < DOCA < 1.0

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05

1.0 < DOCA < 1.5

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05 0.06

1.5 < DOCA < 2.0

Drift Radius Residual (mm) 0.5 − 0.5 1 1.5 Arbitrary Units 0.01 0.02 0.03 0.04 0.05 0.06 0.07

2.0 < DOCA < 2.5

• Agrees with simulation tuned to low level

parameters

• Model and simulation include full DOCA

dependence of resolution

• gaussian smearing × exponential with constant τ
• τ encodes effect of cluster statistics

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Longitudinal resolution and efficiency

Distance from wire [mm]

0.5 1 1.5 2 2.5 3 3.5 4

Efficiency

0.2 0.4 0.6 0.8 1

8-Straw Prototype 8-Straw Prototype Fit G4 + Straw Simulation G4 + Straw Simulation Fit 0.006 ± = 0.947 ε 0.001 ± = 0.950 ε

Longitudinal Positon Resolution [mm]

• 300
• 200
• 100

100 200 300

Arbitrary Unit

20 40 60 80 100 120

8-Straw Prototype 8-Straw Prototype Fit G4 + Straw Simulation G4 + Straw Simulation Fit

1.422 ± = 43.371 σ 1.277 ± mean = 0.653 1.245 ± = 41.733 σ 1.308 ± mean = 2.232

• Efficiency measured at many voltages/thresholds to determine
• ptimal running conditions

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Time over threshold

• With just hit time measurement, require t0 estimate from

track reconstruction before drift time can be determined

• Time over threshold allows a measure of path length (and thus

radial distance) independent of t0

• Implemented in firmware, being added to reconstruction
• Simulation agrees well with data
• Shows predictive power of detailed model

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Track Resolution

(MeV/c)

true

• p

measured

p 4 − 3 − 2 − 1 − 1 2 3 4 Entries / 0.010 MeV/c 1 10

2

10

3

10

4

10

Core width = 159 keV/c

momentum resolution at start of tracker (simulation)

• Sensitivity studies now include results of simulation tuned to

prototype measurements

• Track resolution depends on hit level resolution and efficiency,

as well as reconstruction techniques

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Conclusion

• Mu2e will search for CLFV with greatly improved sensitivity
• Straw tracker provides a precise momentum measurement,

made possible by timing and waveform measurements from the straws

• 8-straw prototype was used to tune detailed simulation of

straw physics and electronics

• Hit level performance proven with prototype
• Momentum resolution will allow us to reach our sensitivity

goals!

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