Critical Questions for SiD

1
Critical Questions for SiD

• A Configuration has been proposed
• for the Silicon Detector.
• This serves as a starting point, and
• suggests the Critical Questions.
• Effort must now systematically explore
• optimization.
• Based on Critical Questions for SiD,
• J. Brau, M. Breidenbach, J. Jaros, H. Weerts,
  Aug 23, 2003
• (It is assumed this list is incomplete)

2
LC Detector Requirements

• Any design must be guided by these goals
• a) Two-jet mass resolution comparable to the
  natural widths of W and Z for an unambiguous
  identification of the final states.
• b) Excellent flavor-tagging efficiency and purity
  (for both b- and c-quarks, and hopefully also for
  s-quarks).
• c) Momentum resolution capable of reconstructing
  the recoil-mass to di-muons in Higgs-strahlung
  with resolution better than beam-energy spread.
• d) Hermeticity (both crack-less and coverage to
  very forward angles) to precisely determine the
  missing momentum.
• e) Timing resolution capable of separating
  bunch-crossings to suppress overlapping of events.

3
SiD Nominal Configuration

Scale of EMCal Vertex Detector
4
Architecture arguments

• Silicon is expensive, so limit area by limiting
  radius
• Get back BR2 by pushing B (5T)
• This argument may be weak, considering
  quantitative cost trade-offs. (see plots)
• Maintain tracking resolution by using silicon
  strips
• Buy safety margin for VXD with the 5T B-field.
• Keep (?) track finding by using 5 VXD space
  points to determine track
• tracker measures sagitta.

5
Cost Trade-offs
D vs R_Trkr1.7M/cm
Delta , Fixed BR25x1.252
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Assumptions

• Energy flow calorimetry is essential for good jet
  resolution
• We need to demonstrate this, and to determine
  rational major detector parameters that optimize
  it.
• Detector cost is constrained.
• This assumption will not be buttressed by
  simulation, but is considered reasonable by most.
  
• The energy flow demonstration is a simulation and
  reconstruction strategy issue, as are most of
  these questions.
• However, there are a few specific hardware
  developments that are crucial to determining
  rational major detector parameters.

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Tracking

• Tracking for any modern experiment should be
  conceived as an integrated system, combined
  optimization of
• the inner tracking (vertex detection)
• the central tracking
• the forward tracking
• the integration of the high granularity EM
  Calorimeter
• Pixelated vertex detectors are capable of track
  reconstruction on their own, as was demonstrated
  by the 307 Mpixel CCD vertex detector of SLD, and
  are being developed for the linear collider
• Track reconstruction in the vertex detector
  impacts the role of the central and forward
  tracking system

8
Silicon Tracking

• Superb spacepoint precision allows linear
  collider tracking measurement goals to be
  achieved in a compact tracking volume
• Compact tracker makes the calorimeter smaller and
  therefore cheaper, permitting more aggressive
  technical choices (assuming cost constraint)
• Robust to spurious, intermittent backgrounds
  (esp. beam loss) extrapolated from SLC experience
  
• linear collider is not storage ring

9
Calorimetry

• Current paradigm Particle/Energy Flow (unproven)
• Jet resolution goal is 30/?E
• In jet measurements, use the excellent resolution
  of tracker, which measures bulk of the energy in
  a jet

Headroom for confusion
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Energy/Particle Flow Calorimetry
Follow charged tracks into calorimeter and
associate hadronic showers
Identify EM clusters not associated with charged
tracks (gammas)
Remaining showers will be the neutral hadrons
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Calorimeter Questions

• For a fixed detector technology, bigger appears
  to be better.
• There is general agreement that the numerator of
  an energy flow figure of merit is BR2.
• R is the outer radius of the tracker or the inner
  radius of the EMCal, probably different by about
  a cm.
• If the cost of the calorimeter can be reduced
  without affecting performance, then BR2 can be
  increased.
• Therefore, primary questions are
• 1. Can the number of layers of Si in the EMCal
  (currently 30) be reduced?
• 2. Do we need 30 radiation lengths? Is 25 or 20
  enough?
• 3. Would a tungsten based HCal with 2X0 thick W
  ease the EMCal
• requirements?

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EM Calorimetry

• Physics with isolated electron and gamma
• energy measurements require 10-15 / ?E ? 1
• Particle/Energy Flow requires fine grained EM
• calorimeter to separate neutral EM clusters
• from charged tracks entering the calorimeter
• Small Moliere radius
• Tungsten
• Small sampling gaps so not to spoil RM
• Separation of charged tracks from jet core helps
• Maximize BR2
• Natural technology choice Si/W calorimeters
• Good success using Si/W for Luminosity monitors
  at SLD, OPAL, ALEPH
• Oregon/SLAC/BNL
• CALICE
• Alternatives Tile-Fiber (challenge to achieve
  required granularity)
• Scintillator/Silicon Hybrid
• Shaslik
• Scintillator Strip

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Energy Flow Issues

• Using the latest version of the parametric
  detector calculator, increasing the tracker
  radius (from 1.25 m) at fixed B5T costs about
  2.1M/cm.
• If BR2 is held fixed at 7.8 Tm2 , then increasing
  the tracker radius (from 1.25 m) costs about
  0.6M/cm.
• Note that the baseline design of R 1.25 m and
  B5T is a cost minimum if B5T is considered a
  maximal field.
• So assuming an EMCal with gaps of 1 mm and pixels
  small compared to the Moliere radius, and
  sampling often in depth, then
• 4. Are the EMCal assumptions above realizable
  (Physical prototype required)?
• 5. Is BR2 7.8 sufficient for the physics
  benchmark processes?
• 6. Is the improvement expected from increasing
  R at fixed BR2 justified by the improvement in
  physics benchmark performance? Why would this
  improve things ?
• 7. Can a reasonable energy flow figure of merit
  beyond BR2 be demonstrated by simulation and
  reconstruction by early 2005? This should be
  analogous to understanding the performance
  variation with B, R, and the calorimeter
  properties. It is likely that calorimeter means
  both EMCal and HCal. Are there issues for the z
  position of the forward calorimeters.

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Silicon/Tungsten EM Calorimeter

• SLAC/Oregon/BNL
• Conceptual design for a dense, fine grained
  silicon tungsten calorimeter well underway
• First silicon detector prototypes are in hand
• Testing and electronics design well underway
• Test bump bonding electronics to detectors by end
  of 04/early 05
• Test Beam in 05/06

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Silicon/Tungsten EM Calorimeter (2)

• Pads 5 mm to match Moliere radius
• Each six inch wafer read out by one chip
• lt 1 crosstalk
• Electronics design
• Single MIP tagging (S/N 7)
• Timing lt 5 nsec/layer
• Dynamically switchable feedback capacitor scheme
  (D. Freytag) achieves required dynamic range
  0.1-2500 MIPs
• Passive cooling conduction in W to edge

Angle subtended by RM
GAP
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Hadron Calorimeter

• The baseline assumption is that the HCal is
  inside the coil, and that it is 4 l thick
  (nominally 34 layers of stainless 20 mm thick
  with 10 mm gaps).
• 8. Is this HCal configuration sufficient for
  the benchmark physics processes?
• a. Is this the right radiator? How about
  tungsten?
• b. How about more sampling, and is 4 l
  sufficient?
• c. The gaps are expensive because they drive
  out the coil radius. Could they be reduced?
• d. 1 to 2 cm square pixels have been
  assumed. Is this right, particularly if the
  HCal density is increased?
• e. Can thin, cheap, reliable, good
  resolution detectors be made?
• (Physical Prototype required)
• (Note that Si is out of the question!!)

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Digital Hadron Calorimetry

• 1 m3 prototype planned to test concept
• Lateral readout segmentation 1 cm2
• Longitudinal readout segmentation layer-by-layer
• Gas Electron Multipliers (GEMs) and Resistive
  Plate Chambers (RPCs) being evaluated
• Objectives
• Validate RPC approach (technique and physics)
• Validate concept of the electronic readout
• Measure hadronic showers with unprecedented
  resolution
• Validate MC simulation of hadronic showers
• Compare with results from Analog HCAL

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Superconducting Solenoid

• The superconducting solenoid is large, with more
  than a GJ of stored energy.
• There are concerns that the hoop stress in a 5T,
  Rcoil2.6 m might be excessive.
• In addition, the coil is a major cost driver, and
  it thus affects directly what BR2 might be within
  the cost constraints.
• 9. Are there serious technical problems with a
  (thick) solenoid of these nominal parameters?
  Does the addition of serpentine correction
  coils for a crossing angle introduce horrible
  problems?
• 10. What is a rational cost parameterization
  for coils of this scale?

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Silicon Tracking

• The barrel tracking and momentum measurement are
  baselined as 5 layers of pixellated vertex
  detector followed by 5 layers of Si strip
  detectors (in 10 cm segments) going to 1.25 m.
  The momentum resolution for found tracks seems
  excellent.
• 11. Does it need to become more complicated?
• 12. Develop a baseline for the Forward
  direction.
• 13. Does this system find tracks well? What
  about machine and physics backgrounds?
• 14. Are there issues regarding K0s and ?s
  i.e. can they be detected efficiently ?
• 15. Demonstrate (if true) the need to minimize
  tracker material to minimize multiple
  scattering.

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Silicon Tracking

• With superb position resolution, compact tracker
  is possible which achieves the linear collider
  tracking resolution goals
• Compact tracker makes the calorimeter smaller and
  therefore cheaper, permitting more aggressive
  technical choices (assuming cost constraint)
• Linear Collider backgrounds (esp. beam loss)
  extrapolated from SLC experience also motivate
  the study of silicon tracking detector, SiD
• Silicon tracking layer thickness
• determines low momentum
• performance
• 3rd dimension may be achieved
• with segmented silicon strips,
• or silicon drift detectors

(1.5 / layer)
(TPC)
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Central Tracking (Silicon)

• Optimizing the Configuration

support
Cooper, Demarteau, Hrycyk
R. Partridge
H. Park
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Silicon Tracking w/ Calorimeter Assist
Primary tracks started with VXD reconstr.
V0 tracks reconstructed from ECAL stubs
E. von Toerne
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Other Important Questions

• There are many other important questions that
  must be studied, but still do not seem to drive
  the basic design or challenge the fundamental
  strategy of SiD. For illustration, some of these
  questions are
• 1. What is a rational technology and a more
  detailed design for the VXD?
• 2. What is the technology for the muon
  trackings? Should it be the same as the HCal?
• 3. What is a design for the very forward
  calorimetry?

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Very Forward Instrumentation

• Hermiticity depends on excellent coverage in the
  forward region, and forward system plays several
  roles
• maximum hermiticity
• precision luminosity
• shield tracking volume
• monitor beamstrahlung
• High radiation levels must be handled
• 10 MGy/year in very forward detectors

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Machine Detector Interface

• A critical area of detector RD which must be
  optimized is where the detector meets the
  collider
• Preserve optimal hermiticity
• Preserve good measurements
• Control backgrounds
• Quad stabilization

20 mr crossing angle, silicon detector
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Summary

• A systematic investigation of the Silicon
  Detector is needed soon.
• An initial list of Critical Questions has been
  constructed.
• What are the additional Critical Questions which
  should be added to the high priority list?

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Collider Constraints

• Linear Collider Detector RD has had to consider
  two different sets of collider constraints
  X-Band RF and Superconducting RF designs
• With the linear collider technology selection,
  the detector efforts can concentrate on one set
  of parameters
• The ILC creates requirements similar to those of
  the TESLA design

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Inner Tracking/Vertex Detection

• Detector Requirements
• Excellent spacepoint precision ( lt 4 microns )
• Superb impact parameter resolution ( 5µm ?
  10µm/(p sin3/2?) )
• Transparency ( 0.1 X0 per layer )
• Track reconstruction ( find tracks in VXD alone )
• Concepts under Development for Linear Collider
• Charge-Coupled Devices (CCDs)
• demonstrated in large system at SLD
• Monolithic Active Pixels CMOS (MAPs)
• DEpleted P-channel Field Effect Transistor
  (DEPFET)
• Silicon on Insulator (SoI)
• Image Sensor with In-Situ Storage (ISIS)
• HAPS (Hybrid Pixel Sensors)

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Inner Tracking/Vertex Detection (CCDs)

• Issues
• Readout speed and timing
• Material budget
• Power consumption
• Radiation hardness

• RD
• Column Parallel Readout
• ISIS
• Radiation Damage Studies

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Column Parallel CCD

• SLD Vertex Detector designed to read out
  800 kpixels/channel at 10 MHz, operated at 5 MHz
  gt readout time 200 msec/ch
• Linear Collider demands 250 nsec readout for
  Superconducting RF time structure
• Solution Column Parallel Readout
• LCFI (Bristol, Glasgow, Lancaster, Liverpool,
  Oxford, RAL)

(Whereas SLD used one readout channel for each
400 columns)
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Column Parallel CCD (2)

• Next Steps for LCFI RD
• Bump bonded assemblies
• Radiation effects on fast CCDs
• High frequency clocking
• Detector scale CCDs w/ASIC cluster finding
  logic design underway production this year

• In-situ Storage Devices
• Resistant to RF interference
• Reduced clocking requirements

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Image Sensor with In-situ Storage (ISIS)

• EMI is a concern (based on SLC experience) which
  motivates delayed operation of detector for long
  bunch trains, and consideration of ISIS
• Robust storage of charge in a buried channel
  during and just following beam passage (required
  for long bunch trains)
• Pioneered by W F Kosonocky et al IEEE SSCC 1996,
  Digest of Technical Papers, 182
• T Goji Etoh et al, IEEE ED 50 (2003) 144 runs up
  to 1 Mfps.

• charge collection to photogate from 20-30 mm
  silicon, as in a conventional CCD
• signal charge shifted into stor. register every
  50ms, providing required time slicing
• string of signal charges is stored during bunch
  train in a buried channel, avoiding
  charge-voltage conversion
• totally noise-free charge storage, ready for
  readout in 200 ms of calm conditions between
  trains for COLD LC design
• particles which hit the storage register (30
  area) leave a small direct signal (5 MIP)
  negligible or easily corrected

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Radiation Effects in CCDs
N. Sinev et al.

• Drift of charge over long distance in CCD makes
  detector very susceptible to effects of
  radiation
• Transfer inefficiency
• Surface defects

Traps can be filled

• neutrons induce damage clusters
• low energy electrons create point defects but
  high energy electrons create clusters Y.
  Sugimoto et al.
• number of effective damage clusters depends on
  occupation time some have very long trapping
  time constants modelled by K. Stefanov

Hot pixels

• Expect 1.5x1011/cm2/yr of 20 MeV electrons at
  layer-1
• Expect 109/cm2/yr 1 MeV-equivalent dose from
  extracted beamline