Thoughts About (Silicon) Tracking for the Linear Collider Detector(s) Bruce Schumm SCIPP & UC Santa Cruz SCIPP Seminar May 10, 2005

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! )

“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.” Fall 2001 recommendation of the High Energy Physics Advisory Panel (HEPAP) to the Department of Energy’s Office of Science: 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. More recently (March), a Global Design Effort has been formed, to be led by CalTech’s Barry Barish. Similarly international groups are being assembled to flesh out detector concepts.

E cm up to 1 TeV, de- pending on site chosen Design luminosity of 2x10 34 cm -2 s -1 Beam spot: 550x5.7 nm Crossings every 337 ns for about 1  s; repeats at 5 Hz TESLA NLC

Linear Collider Detectors (approximate) “L” Design: Gaseous Tracking (TPC) R max ~ 170cm 4 Tesla Field Precise (Si/W) EM Calorimeter “S” Design: Solid-State Tracking R max = 125cm 5 Tesla Field Precise (Si/W) Calorimeter

The SD-MAR01 Tracker B=4T B=5T The Trackers Gaseous (LD, LDC, …) Solid-State (SD, SiD, …)

… and Their Performance Error in radius of curvature  is propor- tional to error in 1/p , or  p  /p  2. Code: This is very rough; details and updates in a moment!

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

Reconstructing Higgsstrahlung ++ -- Haijun Yang, Michigan M  for  p  / p  2 = 2x10 -5

Supersymmetry: Slepton Production Slepton production followed by decay into corresponding lepton and “LSP” (neutralino) Endpoints of lepton spectrum determined by slepton, neutralino masses

SDMAR01 NO MATERIAL PERFECT POINT RESOLUTION PERFECT POINT RESOLUTION, NO MATERIAL |cos  | < 0.8 |cos  | < SUSY Point “SPS1a” at E cm =1TeV SELECTRON MASS RESOLUTION (GeV/c 2 )

Choice of Tracking Techonolgy (Si, Gas) Tracker needs excellent pattern recognition capa- bilities, to reconstruct particles in dense jets with high efficiency. But as we’ve 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? Let’s compare. In some cases, conventional wisdom may not be correct…

Some “facts” that one might question upon further reflection 1 Gaseous tracking is natural for lower-field, large-radius tracking In fact, both TPC’s 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.

2 Gaseous tracking provides more information per radiation length than solid-state tracking X X X X X X X X X X X X X X X s R For a given track p  and tracker radius R, error on sagitta s determines p  resolution Figure of merit is  =  point /  N hit. Gaseous detector: Of order 200 hits at  point =100  m   = 7.1  m Solid-state: 8 layers at  point =7  m   = 2.5  m Also, Si information very localized, so can better exploit the full radius R.

For gaseous tracking, you need only about 1% X 0 for those 200 measurements (gas gain!!) For solid-state tracking, you need 8x(0.3mm) = 2.6% X 0 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 (we’ll confirm this soon), but you can only make layers so thin due to amp noise  material still an issue.

3 Calibration is more demanding for solid-state tracking 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.

4 All Other Things Equal, Gaseous Tracking Provides Better Pattern Recognition It’s difficult to challenge this notion. TPC’s 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 don’t know how many layers is “enough” (K 0 S, kinks), but tracking efficiency seems OK evevn with 5 layers (and 5 VTX layers)

Caveat: What can gaseous tracking really do? 55  m 2 MediPix2 Pixel Array (Timmermans, Nikhef) ?

X s R X X 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”. X R X X GAS Si Current gaseous tracking designs recognize this in part (Si tracking to about R/4).

Hybrid Tracker Optimization Let’s try filling the Gaseous Detector volume (R=20cm-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 (R=125cm) Si design with 8 layers

all gas TESLA club sandwich all Si (8 layers) SiD (8 layers) sandwich Higgs Dilpetons SUSY SPS1A 500 GeV SUSY SPS1A 1 TeV

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.

Tim Nelson, SLAC

J. F. Genat Moderate noise (two preamp channels); use to read out ~60cm ladders. Fast channel provides crude z measurement Existing chip

The Longest Ladders of all: The Gossamer Tracker Agilent 0.5  m CMOS process (qualified by GLAST) Min-i for 300  m Si is about 24,000 electrons Shaping (  s) Length (cm)Noise (e - ) Q: Can the entire half-length be read out as a single element?

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!

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

Carrier Diffusion Hole diffusion distribution given by Offest t 0 reflects instantaneous expansion of hole cloud due to space-charge repulsion. Diffusion constant given by Reference: E. Belau et al., NIM 214, p253 (1983)  h = hole mobility

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)

Result: S/N for 167cm Ladder At shaping time of 3  s; 0.5  m process qualified by GLAST

Design in 0.25  m complete; to be submitted May 9

RMS Gaussian Fit RMS Gaussian Fit Readout Threshold (Fraction of min-i) Trigger Threshold 167cm Ladder 132cm Ladder Resolution With and Without Second (Readout) Threshold

Non-normal incidence

Thicker Sensors? Trade-off be- tween efficien- cy and sensor thickness still needs thought

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.

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 1 st -pass design of mechanical structures PERFORMANCE SIMULATIONS Arguing with Marty Breidenbach Help!!!

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