COMET
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COMET Comments
--Readout for the COMET e Tracker
With special THANKS to
my sponsors of this talk
Satoshi Mihara
Manobu Tanaka
Masaharu Aoki
6/9/1010
Ed Hungerford
University of Houston
(for the COMET Collaboration)
Ed Hungerford
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COMET
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Introduction
to
COMET
• COMET (Phase I) is a search for coherent, neutrino-less
conversion of muons to electron (μ-e conversion) at a single
event sensitivity of 0.5x10-16
• The experiment offers a powerful probe for new physics
beyond the Standard Model.
• COMET will be undertaken at J-PARC. Phase I (COMET)
uses a slow-extracted, bunched 8 GeV proton beam from the
J-PARC main ring.
• A proposal was submit to J-PARC Dec. 2007, and a
Conceptual Design Report submitted June 2009. COMET
now has Stage-1 approval from the J-PARC PAC (July 2009),
and is completing R&D for the TDR.
6/9/1010
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Design Considerations for COMET
(and generally all high precision
COMET
measurements of zero)
•
Electron Resolution
Minimal Detector Material – Thin, Low Z
Vacuum Environment
REDUNDENT measurements of the electron track
• Rates
Up to 500 kHZ single rates
Large channel count
R/O timing (~1 ns) and analog information
• Dynamic Range
Protons 30-40 times Eloss for MIP
Pileup and saturation
Maintain MIP track efficiency
• Low-Power, Low-foot print electronics
Heat
Signal Transmission through the vacuum walls
Noise
• Robust measurements
• REDUNDANCY (Redundancy, Redundancy, Redundancy)
Ambiguous hits, dead channels, accidentals
Ed Hungerford
Reconstruction of ghost
05-30-09
for thetracks
COMET collaboration
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COMET
μ→eγ and μ-e Conversion
COMET
• 
eg
• μ-e
conversion
Background
Challenge
Beam Intensity
accidentals
gamma resolution
limited
beam
e resolution
reconstruction
Less limited
• μ→eγ : Accidental background is given by (rate)2. To push
sensitivity the detector resolutions and timing must be
improved. However, (in particular photon detection) it
would be hard to do better than MEG. The ultimate
sensitivity of MEG is about 10-14 (with a run of 108/sec).
• μe conversion : Improvement of a muon beam is possible,
both in purity (no pions) and in intensity (muon collider
R&D). Higher beam intensity can be used with present
timing technology because no coincidence is required.
6/9/1010
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COMET
COMET
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COMET at J-PARC
Pulsed Proton
Beam
p Source
B( + Al)  e + Al <10-16
 Transport
5m
6/9/1010
 target
electron
Transport
Detection
•Modification of MECO/MELC
•Requires slow extracted, pulsed beam ~8 GeV
Ed Hungerford
•Mu2e at FNAL is another
MECO resurrection
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COMET
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Target and Detector
Solenoids
COMET
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COMET
Comparison to MECO
COMET
• Proton Target
- tungsten (MECO)
- graphite (J-PARC)
• Muon Transport
MECO
- Magnetic fields and
solenoids are different.
- Efficiency of the muon
transport is equivalent
• Spectrometer
- 1011 stopping muons/sec
-Straight Solenoid (MECO)
>500 kHz/wire
- Curved (COMET)
~1kHz /wire
• Planer Tracker
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COMET
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COMET Tracker and Calorimeter
Background
COMET
Total Tracker Rates/plane
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Ed Hungerford
600 kHz
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Muon-to-Electron (μ-e) Conversion
Lepton Flavor Violation
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COMET
μ Decay in Orbit (DIO)
Lepton Flavor Changes
by one unit
μ- → e- ν ν
nucleus
Coherent Conversion
μ- + A → e-+ A
-
Nuclear Capture
μ- + A →ν+ [N +(A-1)]
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COMET
COMET
Background Rejection (~107 s)
(preliminary)
Backgrounds
Events
Comments
Muon decay in orbit
Radiative muon capture
(1)
Muon capture with neutron emission
Muon capture with charged particle emission
0.05 230 keV resolution
<0.001
<0.001
<0.001
Radiative pion capture*
Radiative pion capture
Muon decay in flight*
(2) Pion decay in flight*
Beam electrons*
Neutron induced*
Antiproton induced
0.12
0.002
<0.02
<0.001
0.08
0.024
0.007
Cosmic-ray induced
(3)
Pattern recognition errors
0.10 10-4 veto efficiency
<0.001
Total
•6/9/1010
prompt
late arriving pions
for high energy neutrons
for 8 GeV protons
0.4
•Ed Hungerford
•10
COMET
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Tracking Array
5 Planes – 4 Arrays per plane
Each plane arranged in an
x,x’,y,y’ geometry of arrays
Each array composed of 13 straw
units of 16, 5mm diameter
straws
COMET
Mounted double-array
Unit
•16 straws/unit
•208 straws/array
•832 straws/plane
•4160 straws/detector
1.2 m
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COMET
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Manifold
COMET
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COMET
COMET
Flex Ribbon Cable through
Manifold to FEB
Fused HV
15 ns LRC
Filter/channel
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COMET
Readout Architecture
COMET
•On-Detector amplification and digitizing – events passed
by optical fiber in serial to an external DAQ (Parallel
transfer is also possible)
• Electronics based on CMOS to conserve space and
power (<65 Mw/ch) – radiation damage is not a problem
• Mounted on the detector frame
• A (MECO) system has been previously prototyped and
demonstrated
• COMET Data rates are reasonable
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COMET Tracker FE Organization
Straw Tubes
Number of
Straws
Readout
(TDC)
Readout
(ADC)
Per Array (13 x 16)
208
208
208
Per Plane (4 Array)
832
832
832
Per Detector
5 Planes (MECO 18)
4160
4160
4160
COMET
Manifold
(unit)
Array
Plane
Detector
PA(16)
1
13
52
260
Digitizer(16)
1
13
52
260
1/4
1
5
1/5
1
ROC
Module
Controller
Assuming:
60-125MHz clock and 10-20 clock ticks for an event (160 ns)
(10-20+ 11) x 4x5x1.5 words for an event and 16 bits for a word
1k/s event rate
The total data rate is ~10-15 Mb/sEdwith
zero suppression
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COMET
An Example
The MECO Readout Architecture
COMET
From Anode Wire
Separated PA
And Digitizer
Sequencer
Plane ID for readout
To External DAQ
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COMET
MECO Prototype
COMET
FEATURES
•The number of data transfer lines is 24 (16 data + 6 control)
•A system clock is regenerated by the local buss sequencer
•A trigger input is associated with readout units
•A trigger reset counter determines the data time stamp
•A system reset to return to standard operating conditions
•A slow control buss for control and monitoring
•Low voltage power of +3.3V(300A) and -3.3V (100A)
•Total Power < 1.8 kW (PA and Digitizer only)
•6/9/1010
•05-30-09
• Ed Hungerford
•Ed Hungerford
for the COMET
collaboration
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COMET
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Drift Simulation
Position Along Y (cm)
COMET
Trajectory
Trajectory
Wire
Wire
6/9/1010
Gas – 80 %CF4/20% C6H10
Velocity - 8.5 cm/μs
Drift Time
- 45 ns
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COMET
Measurements and Simulations
COMET
Simulated Anode
signal
Simulated Charge
15 ns Filter
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COMET
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The MECO Prototyped System
• COMET
A front-end board was developed to
• The Digitizing Board layout is
test the ASD-4 and a driver board is
completed, tested, and the
used to adapt the LVDS output to our
digitizing ASIC designed.
lab CAMAC TDC.
Digitizing Boards
FEB Board
Connected by flex cable
Mother Board with FPGA
Memory and PCI controller
6/9/1010
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Elefant Chips (2 x 8 channels)
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COMET
32 Channel MECO Prototype
COMET
6/9/1010
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COMET
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Specifications for COMET
ASIC preamp
COMET
Parameter Name
Value
Note
Polarity
Bipolar
Positive input for
Colorimeter
Channel number
16
Cover 8 cm with 5-mm
straws
Linear range
<60 fC
Input capacitance
20 pF
Equivalent Noise
Charge
0.5 fC
Peaking time
100 ns
Coupling
AC
Timing resolution
<2 ns
Power consumption
<5 mW/ch
Test input
6/9/1010
Amplitude
measurement
(250-ns signal width)
Yes
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COMET
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ASIC Digitizer
• Digitizer ASIC Design
 based on the ELEFANT ASIC used in BABAR (8 channels/ASIC)
 Work in collaboration with design engineers at LBL
 Rescale ASIC to 0.25 m technology and 3.2 V interfaces
 Solves identified problems with the ELEFANT design
 Change clock frequency (20-60 Mhz)
 Change from waveform sampling to time-slice integration
 Increase ADC bits to 10
COMET
• ~5 s Latency, self or external trigger
• Power Consumption 65 mW/channel (Total Power 1,650 W)
Design (LBL Engineer) $518K; Fabrication (2prototypes) 2 x $45k;
Preproduction samples $50k; Production and packaging $231k, Testing $42k
=> $931k + 37% contingency
Several more modern Waveform (ADC Sampling) ASICS designs
e.g.
Belle, PSI designs, ATLAS, etc
6/9/1010are Possible for COMET --Ed
Hungerford
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Digital chip Redesign
COMET
• Benefits:
reduce noise, simplify the system design, better technology, lower
power consumption, lower system cost.
Prediction of the production cost is ~$8-15 per channel.
8ADC
RAM event
buffer
8TDC
Latency
buffer
MUX and
Output FIFO
Local Bus
Logic
control
Clock
Trigger
Time stamp
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MECO Digitizer chip
specs
COMET
Items
Upgraded Digitizer
Channel per Chip
8
System Input Clock
PLL System Clock Divider
System Frequency
7.5~15MHz sine wave differential
4
2
1
30~60MHz
15~30MHz
7.5~15MHz
ADC sampling Clock
ADC Resolution
System Clock
8 bits
9 bits
ADC Implementation
Pipeline ADC
TDC DLL (PLL) Clock
30~60MHz (PLL divided Clock)
TDC resolution
TDC Width (combine with PLL)
0.26 to 0.52ns LSB
6 bits
TDC Implementation
Noise performance
6/9/1010
10 bits
7 bits
8 bits
DLL (PLL)
Digital feed back to the analog channel less than 0.5 LSB
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Elefant II ASIC
COMET
Time and amplitude
samples stored together
in a latency pipeline
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A More Modern Design
CDC – Belle Central Drift Chamber
COMET
6/9/1010
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Other Examples
Readout of ATLAS TRT
• Based on two ASICs: front-end + digitization
• ASDBLR
– Front-end, 8-ch
– Separate preamps
• Track detection
• TR photon detection
– Ternary outputs
• DTMROC
– Digitization, 16-ch
– TDC + FIFO + Serialization
– Each beam bunch has one
slice in FIFO
– Control and thresholds to
ASDBLR
• Power consumption:
40 mW/ch
COMET
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ROC Board Design
To FE Board
COMET
•
•
•
Each ROC has a
FPGA to control the
readout sequence from
the Elefant II chips.
Data are stored on the
board temporarily in
the dual-port RAM.
Configurations, like
the number of
channels connected to
this board, readout
mode (sparse mode,
zero-suppression
mode, etc.), are
configured through the
I2C bus.
6/9/1010
CONN.
CONN.
CONN.
CONN.
CONN.
CONN.
High Speed
Serial Bus
I2 C
Dual Port
FPGA
CPLD
I2 C
RJ-11
Virtex-II pro
Clock
Trigger
Reset
Distribution
RJ-45
Ed Hungerford
RAM
PROM
V3.3 REG
Transmitter
RJ-45
V2.5 REG
Pwr Conn.
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Fast Control Signal
COMET
• Reset, Trigger, and Reference clock are provided by DAQ system
(Trigger and Fast Control Fan-out ).
• These are transmitted as differential signals (LVDS).
• Reference clock is 10MHz with reasonable jitter. On the module
controller or ROC, this clock frequency will be divided by PLL to
the sampling frequency (40-60MHz) with much smaller jitter
(~200ps) to satisfy ADC requirement.
• Event numbers are embedded in the trigger signal (real time
trigger signal followed with the number) .
• The Control module feeds the fast control signal to each ROC Box
through 4 pairs low skew differential, shielded cable. No matter
how far the ROC is from the module controller, all these Fast
Control lines must have the same length to reduce the time skew.
This will also ensure the timing accuracy for the whole system.
6/9/1010
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Data Transfer
• Data transfer from ROC to the module controller uses shielded
twisted pair cable (low skew <150ps /10m).
• From the module controller, data passes feedthrough to the Event
Builder of DAQ: differential copper wire or optic fiber.
• Differential copper wire:
•
Easy to install from the vacuum wall.
•
Can be 100Mb/s (CAT-5e) or 200Mb/s (CAT-6). Up to 100m
•
Full bandwidth is not used due to protocols (handshaking).
•
Cheaper.
• Optic fiber:
•
Penetrations through the vacuum wall? Hermetic feed through
exits. No engineering experience.
•
Fast. Can be ~Gb/s. ~km long.
•
Radiation hardness of the transceiver should be considered.
•
Costs more.
COMET
6/9/1010
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Data Package to the Event Builder
31 28 27 25 24 23 22 20 19
12 11
0
COMET Squencer Header
0000
ROC Header
0010
ROC ID
Event ID
FE Header
0100
FE ID
Event ID
Channel Header
0110
Channel ID
Event ID
Event ID
Sequencer ID
Data
0111
Data 0
Data 1
Data
0111
Data ...
Data ...
Data
0111
Data n-2
Data n-1
1110
Channel ID
FE Trailer 1
1100
FE ID
Event ID
FE Trailer 2
1101
FE ID
DWord Length
ROC Trailer 1
1010
ROC ID
Event ID
ROC Trailer 1
1011
ROC ID
DWord Length
Channel Trailer
DWord Length
Event ID
Repeat Channels
Repeat FEs
Repeat ROCs
Sequencer Trailer 1
1000
Sequencer ID
Sequencer Trailer 2
1001
Sequencer ID
Ed Hungerford
6/9/1010
Event ID
DWord Length
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2nd Coordinate Readout
COMET
Tracking with multiple hits in the detector planes can produce ghost
trajectories. A 2nd readout might reduce ambiguities.
Possible Methods of 2nd Coordinate Measurements in Wire Detectors
1) Induction on the cathode
a) Strips (pads)
b) Delay lines parallel to the anode wires
2) Anode readout
a) Charge division on a resistive anode (NIM A479(02)591) or
Cathode
b) Signal timing between the straw ends
c) Signal rise time
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Charge Division Readout
(IEEE 42(95)1430)
COMET
L/L ~0.6%
Signal Division
Charge Division Issues
COMET
Charge division might provide a 2nd coordinate readout with
resolution on the order of L/L  1%;
BUT
1) The resolution deteriorates with background rate
2) Reducing the integration gate, implementing base
line restoration reduces the collected charge (resolution)
3) Maintaining calibration requires special data runs
and pulser inputs (automated)
4) Careful design of all electronics to reduce noise and
termination of lines (frequency dependence)
5) Precision wire resistance and analog preamp
6) Shaping amp is a compromise between noise
reduction (very sensitive) and rate handling
5) Both ADC and TDC readout
7) Charge integration within a time gate
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Delay Line Readout
COMET
NIM A479(02)591
L = 6.5mm
1.7 m long drift-cell
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Straw Delay Line
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COMET
~1m straw delay line is presently
under construction
Strip width is 1mm spaced by 1mm
Expected time delay for 1m is
45 ns one-way.
Differential readout to remove
common mode propagation
Delay Line Issues
COMET
Delay Line Timing might provide a 2nd coordinate
readout with resolution on the order of L ~ 5 mm. The
time sum equals propagation delay + drift time, better
signal stability, and anode wire hit ID’ed.
BUT
1) Requires additional material
2) More difficult to construct
3) More electronics to build and install in a limited space
4) Capacitive and inductive coupling between channels
5) Careful electronic design
6) Calibration
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COMET
Summary
COMET
• COMET is a Phase I search for coherent, neutrino-less conversion of
muons to electron (μ-e conversion) at a single event sensitivity of 10-16
• The experiment offers a powerful probe for new physics beyond the
Standard Model.
• The experiment will be undertaken at the J-PARC NP Hall using a
slowly-extracted, bunched proton beam from the J-PARC main ring.
• The Experiment is developing a TDR and refining design details. The
experiment has completed a CDR and has Stage-1 approval of the JPARC PAC.
• The electronic readout of the tracker (and calorimeter) is challenging,
requiring new ASIC development that have low power, excellent timing,
reasonable resolution, and rate handling, and are robust.
• The system design requires on detector digitization, storage, buffering,
and latency.
• The event builder must reconstruct events from asynchronous buffer
reads
• We need expert engineering experience with the technical designs
6/9/1010
Ed Hungerford
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