Thoughts About Silicon Tracking for the Linear Collider Detectors

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Thoughts About (Silicon) Tracking for the Linear
Collider Detector(s)

• Bruce Schumm
• SCIPP UC Santa Cruz
• SCIPP Seminar
• May 10, 2005

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OUTLINE

• What are the Linear Colliderand the Linear
  Collider Detector?
• Physics drivers for tracking
• Gaseous vs. solid-state tracking
• Approaches to solid-state tracking
• Tiled trackers
• Long Ladders
• Some issues for long ladder / long shaping-time
  approach (help!)

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Fall 2001 recommendation of the High Energy
Physics Advisory Panel (HEPAP) to the Department
of Energys Office of Science
We recommend that the highest priority of the
U.S. program be a high-energy, high-luminosity
electron-positron collider, wherever it is built
in the world. This facility is the next major
step in the field, and should be designed, built,
and operated as a fully international effort.
More recently (March), a Global Design Effort has
been formed, to be led by CalTechs Barry Barish.
Similarly international groups are being
assembled to flesh out detector concepts.
The LC group at SCIPP has been re-energized by
these developments, and has continued to bolster
its efforts with both public outreach and
international cooperation.
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Ecm up to 1 TeV, de-pending on site
chosen Design luminosity of 2x1034 cm-2
s-1 Beam spot 550x5.7 nm Crossings every 337
ns for about 1 ?s repeats at 5 Hz
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Linear Collider Detectors (approximate)
L Design Gaseous Tracking (TPC) Rmax
170cm 4 Tesla Field Precise (Si/W) EM
Calorimeter
S Design Solid-State Tracking Rmax 125cm
5 Tesla Field Precise (Si/W) Calorimeter
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The Trackers
Solid-State (SD, SiD, )
Gaseous (LD, LDC, )
The SD-MAR01 Tracker
B4T
B5T
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and Their Performance
Error in radius of curvature ? is propor-tional
to error in 1/p?, or ?p? /p?2.
This is very rough details and updates in a
moment!
Code http//www.slac.stanford.edu/schumm/lcdtrk.
tar.gz
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Linear Collider Physics

• At leading order, the LC is a machine geared
  toward the elucidation of Electroweak symmetry
  breaking. Need to concentrate on
• Precision Higgs Physics
• Strong WW Scattering
• SUSY

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Reconstructing Higgsstrahlung
Haijun Yang, Michigan
M?? for ?p?/ p?2 2x10-5
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Supersymmetry Slepton Production
Slepton production followed by decay into
corresponding lepton and LSP (neutralino)
Endpoints of lepton spectrum determined by
slepton, neutralino masses
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SUSY Point SPS1a at Ecm1TeV
cos? lt 0.8
cos? lt 0.994
SDMAR01
NO MATERIAL
PERFECT POINT RESOLUTION
SELECTRON MASS RESOLUTION (GeV/c2)
PERFECT POINT RESOLUTION, NO MATERIAL
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Choice of Tracking Techonolgy (Si, Gas)
Tracker needs excellent pattern recognition
capa-bilities, to reconstruct particles in dense
jets with high efficiency. But as weve seen,
recent physics studies (low beam-energy spread)
also suggest need to push momentum resolution to
its limits. Gaseous (TPC) tracking, with its
wealth of 3-d hits, should provide spectacular
pattern recognition but what about momentum
resolution? Lets compare. In some cases,
conventional wisdom may not be correct
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Some facts that one might question upon further
reflection
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Gaseous tracking is natural for lower-field,
large-radius tracking
In fact, both TPCs and microstrip trackers can
be built as large or small as you please. The
calorimeter appears to be the cost driver.
High-field/Low-field is a trade-off between
vertex reconstruction (higher field channels
backgrounds and allows you to get closer in) and
energy-flow into the calorimeter (limitations in
magnet technology restricts volume for higher
field). The assignment of gaseous vs solid state
tracking to either is arbitrary.
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Gaseous tracking provides more information per
radiation length than solid-state tracking

• For a given track p? and tracker radius R, error
  on sagitta s determines p? resolution
• Figure of merit is ? ?point/?Nhit.
• Gaseous detector Of order 200 hits at
  ?point100??m ? ? 7.1 ??m
• Solid-state 8 layers at ?point7?m
• ? 2.5?m
• Also, Si information very localized, so can
  better exploit the full radius R.

X
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s
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For gaseous tracking, you need only about 1 X0
for those 200 measurements (gas gain!!) For
solid-state tracking, you need 8x(0.3mm) 2.6
X0 of silicon (signal-to-noise), so 2.5 times the
multiple scattering burden. BUT to get to
similar accuracy with gas, would need (7.1/2.5)2
8 times more hits, and so substantially more
gas. Might be able to increase density of hits
somewhat, but would need a factor of 3 to match
solid-state tracking. Solid-state tracking
intrinsically more efficient (well confirm this
soon), but you can only make layers so thin due
to amp noise ? material still an issue.
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Calibration is more demanding for solid-state
tracking
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The figure-of-merit ? sets the scale for
calibration systematics, and is certainly more
demanding for Si tracker (2.5 vs. 7.1 ?m). But,
? is also the figure-of-merit for p?
resolution. For equal-performing trackers of
similar radius, calibration scale is independent
of tracking technology. Calibrating a gaseous
detector to similar accuracy of a solid-state
detector could prove challenging.
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All Other Things Equal, Gaseous Tracking Provides
Better Pattern Recognition
Its difficult to challenge this notion. TPCs
provide a surfeit of relative precise 3d
space-points for pattern recognition. They do
suffer a bit in terms of track separation
resolution 2mm is typical, vs 150 ?m for
solid-state tracking. Impact of this not yet
explored (vertexing, energy flow into
calorimeter). For solid-state tracking, still
dont know how many layers is enough (K0S,
kinks), but tracking efficiency seems OK evevn
with 5 layers (and 5 VTX layers)
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Caveat What can gaseous tracking really do?
?
55?m2 MediPix2 Pixel Array (Timmermans, Nikhef)
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Hybrid Trackers the Best of Both Worlds?
In an ideal world, momenta would be determ-ined
from three arbitrarily precise r/?
points. Optimally, you would have Si tracking at
these points, with massless gaseous tracking
in-between for robust pattern recognition ?
Si/TPC/Si/TPC/Si Club Sandwich.
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Hybrid Tracker Optimization
Lets try filling the Gaseous Detector volume
(R20cm-170cm) with various things

• All gas No Si tracking (vertexer only)
• TESLA Si out to 33cm, then gas
• Sandwich Si out to 80cm, and then just inside
  170cm
• Club Sand Si/TPC/Si/TPC/Si with central Si at
  80cm
• All Si Eight evenly-spaced Si layers
• SD Smaller (R125cm) Si design with 8 layers

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all gas
TESLA
sandwich
SiD (8 layers)
club sandwich
all Si (8 layers)
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So, one way or another, it appears that
solid-state tracking will play a role in the
Linear Collider Detector(s) (e.g. all-Si SiD
design)
Bill Cooper, FNAL
Different groups (SLAC, Paris, UCSC) are
explor-ing different approaches, somewhat
collabora-tively.
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Tim Nelson, SLAC
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Tim Nelson, SLAC
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Tim Nelson, SLAC
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(No Transcript)
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Existing chip
Moderate noise (two preamp channels) use to read
out 60cm ladders. Fast channel provides crude z
measurement
J. F. Genat
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The Longest Ladders of all The Gossamer Tracker
Q Can the entire half-length be read out as a
single element?
Agilent 0.5 mm CMOS process (qualified by GLAST)
Min-i for 300mm Si is about 24,000 electrons
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Potential Advantages of the Gossamer Tracker
Such a tracker may prove mechanically simpler,
and offers the greatest possibility of competing
with gaseous tracking at low p?.
Substantial work needed in fleshing out design
we will expand our discus-sion at SCIPP soon can
use much help!
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Pulse Development Simulation
Long Shaping-Time Limit strip sees signal if and
only if hole is col- lected onto strip (no
electrostatic coupling to neighboring strips)
Charge Deposition Landau distribution
(SSSimSide Gerry Lynch LBNL) in 20 independent
layers through thickness of device
Geometry Variable strip pitch, sensor thickness,
orientation (2 dimen- sions) and track impact
parameter
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Carrier Diffusion
Hole diffusion distribution given by
Offest t0 reflects instantaneous expansion of
hole cloud due to space-charge repulsion.
Diffusion constant given by
mh hole mobility
Reference E. Belau et al., NIM 214, p253 (1983)
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Other Considerations
Lorentz Angle 18 mrad per Tesla (holes)
Detector Noise From SPICE simulation,
normalized to bench tests with GLAST electronics

• Can Detector Operate with 167cm, 300 ?m thick
  Ladders?
• Pushing signal-to-noise limits
• Large B-field spreads charge between strips
• But no ballistic deficit (infinite shaping time)

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Result S/N for 167cm Ladder
At shaping time of 3ms 0.5 mm process qualified
by GLAST
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Design in 0.25 ?m complete to be submitted May 9
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Resolution With and Without Second (Readout)
Threshold
Trigger Threshold
167cm Ladder
132cm Ladder
Readout Threshold (Fraction of min-i)
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Non-normal incidence
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Thicker Sensors?
Trade-off be-tween efficien-cy and sensor
thickness still needs thought
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Timing Resolution Another Aspect of Optimization
Temporal resolution of amplifier with response
time ?shape signal-to-noise ratio SNR, and
comparator threshold ? is approximated by
For ?shape 3?s, this is of order 400 ns, as
compared to the 337 ns beam crossing time ?
identify source of hit to within a few beam
crossings.
Can optimize timing resolution (shaping time)
against sensor thickness and resolution for inner
layers.
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And so

• Silicon-strip based central tracking is a
  compelling solution for the LCD, whether in a
  stand-alone SiD application or a hybrid Si/Gas
  application.
• The long-ladder approach is an interesting
  concept, but needs a lot of fleshing out
• Test run (planning and infrastructure)
• Back-end architecture
• Data transmission
• 1st-pass design of mechanical structures
• PERFORMANCE SIMULATIONS
• Arguing with Marty Breidenbach
• Help!!!

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Thoughts About (Silicon) Tracking for the Linear
Collider Detector(s)

• Bruce Schumm
• SCIPP UC Santa Cruz
• UC Davis Experimental Particle Physics Seminar
• April 26, 2005