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) J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

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. J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

3. 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. J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

4. Cost Trade-offs D $ vs R_Trkr~1.7M$/cm Delta $, Fixed BR2=5x1.252 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

5. 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”. J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

6. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

7. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

8. Neutral Hadrons EM Charged Hadrons ~ 20% / E 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

9. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

10. 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? J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

11. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

12. Energy Flow Issues • Using the latest version of the parametric detector calculator, increasing the tracker radius (from 1.25 m) at fixed B=5T 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 B=5T is a cost minimum if B=5T 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. J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

13. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

14. Silicon/Tungsten EM Calorimeter (2) • Pads ~5 mm to match Moliere radius • Each six inch wafer read out by one chip • < 1% crosstalk • Electronics design • Single MIP tagging (S/N ~ 7) • Timing < 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

15. 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!!) J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

16. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

17. 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, Rcoil=2.6 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? J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

18. 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 K0’s and Λ’s i.e. can they be detected efficiently ? 15. Demonstrate (if true) the need to minimize tracker material to minimize multiple scattering. J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

19. 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) J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

20. Central Tracking (Silicon) • Optimizing the Configuration support Cooper, Demarteau, Hrycyk R. Partridge H. Park J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

21. Silicon Tracking w/ Calorimeter Assist Primary tracks started with VXD reconstr. V0 tracks reconstructed from ECAL stubs E. von Toerne J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

22. 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? J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

23. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

24. Machine Detector Interface • A critical area of detector R&D 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

25. 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? J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

26. J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

27. Collider Constraints Linear Collider Detector R&D 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

28. Inner Tracking/Vertex Detection Detector Requirements • Excellent spacepoint precision ( < 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) J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

29. SLD VXD3 307 Mpixels 5 MHz  96 channels 0.4% X0 / layer ~15 watts @ 190 K 3.9 m point res. av. - 2 yrs and 307 Mpxl Inner Tracking/Vertex Detection (CCDs) Issues • Readout speed and timing • Material budget • Power consumption • Radiation hardness R&D • Column Parallel Readout • ISIS • Radiation Damage Studies J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

30. Column Parallel CCD SLD Vertex Detector designed to read out 800 kpixels/channel at 10 MHz, operated at 5 MHz => 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) J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

31. Column Parallel CCD (2) Next Steps for LCFI R&D • 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

32. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004

33. 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 J. Brau - ACFA Workshop, Taipei - Critical Questions November 9, 2004