# Presentation: 502982

## Tracking at the ILC:Why Silicon Tracking is Best, and How it Might Be Optimized

- Tracking at the ILC:Why Silicon Tracking is Best, and How it Might Be Optimized

- Bruce Schumm
- SCIPP & UC Santa Cruz
- STD6 “AbeFest”
- September 11, 2006

**Notes:**
Motivation, scope, ladder development, pulse simulation, timeline

## ILC Basics

- ILC

- Pulse every ~350 ns for ~1 ms; repeated
- 5 times/s
- (0.5% Duty Cycle)

- Online ~10 yrs after
- LHC  Precision is key

## Reconstructing Higgsstrahlung

**The SD-MAR01 Tracker**

- B=4T

- B=5T

- The Trackers

- Gaseous (GLD, LDC, ...)

- Solid-State (SD, SiD, ...)

## ... and Their Performance

- ... and Their Performance

- Error in radius of curvature  is propor-tional to error in 1/p, or p /p2.

- Code: http://www.slac.stanford.edu/~schumm/lcdtrk.tar.gz

- This is very generic; details and updates in a moment!

## How would Abe think about this problem?

## Some “facts” that one might question upon further reflection

**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

**2**

- Gaseous tracking provides more information per radiation length than solid-state tracking

**X**

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- s

- R

- 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 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% X0 for those 200 measurements (gas gain!!)

- 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 (we’ll confirm this soon), but you can only make layers so thin due to amp noise  material still an issue.

## 3

**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

**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” (K0S, kinks), but tracking efficiency seems OK evevn with 5 layers (and 5 VTX layers)

## 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”.

## 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 (100 m resolution)
-  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
-  SiD:		Smaller (R=125cm) Si design with 8 layers

## all gas

- TESLA

- club sandwich

- all Si (8 layers)

- SiD (8 layers)

- sandwich

## Precision  low mass, low noise

- How might you design ILC Silicon strip ladders?

**Precision**  low mass, low noise
-  Long modules: less servicing but 	worse signal-to-noise
-  Short modules: Excellent signal-	to-noise but more servicing
- Either way: **cycle power** to avoid cooling tubes (~1msec switch-on)

**Notes:**
Motivation, scope, ladder development, pulse simulation, timeline

## Tim Nelson, SLAC

**Notes:**
Motivation, scope, ladder development, pulse simulation, timeline

## KPIX CHIP 

**KPIX CHIP**** **
**(Breidenbach & Co.)**

- Control Logic

- Track and Hold (x4)

- A to D Conversion

- Event Timing

- Dynamic Range Control

## Alternatively, step back...

- Landau fluctuations large...
-  How accurately do you really need to know pulse-heights?
-  How much does electronic noise really hurt you?
-  Simulate!

**Notes:**
Motivation, scope, ladder development, pulse simulation, timeline

##  Time-over-Thresh Analog Readout

- 1/4 mip

- 1 mip

- 128 mip

- Operating point threshold

- Readout threshold

** ****Time-over-Thresh Analog Readout**
** ****Large gain ******** limit vagaries of     ****	****process variation**

## 1.5 s shaping time; analog readout it Time-Over-Thres-hold with 400 nsec clock

- 1.5 s shaping time; analog readout it Time-Over-Thres-hold with 400 nsec clock

## SIMULATED PERFORMANCE FOR 167cm LADDER

- Efficiency and Occupancy as a function of high threshold

- Resolution as a function of low threshold

**SIMULATED PERFORMANCE FOR 167cm LADDER**

## Change from digitized TOT to perfect analog measurement

- 	 no change in resolution
- Eliminate electronic noise
- 	 resolution improves to 5 m
- Change pitch (had assumed 50 m)
- 	 resolution largely unchanged
**Prototype and test!**

- Some simulation results

**Notes:**
Motivation, scope, ladder development, pulse simulation, timeline

## And so...

**And so...**

- Surprisingly (?), solid-state tracking is best bang for the “buck” (in the radiation-length economy)
******strip tracking a must for the ILC**
- Some conventional wisdom about the relative advantages and disadvantages of gaseous/solid-state tracking are probably not correct.
- If ILC settles for one detector, “intentional” **hybrid tracking **may be the way to go.
- Simulation of pulse development and amplification for ILC Si sensors points to economies that can be exploited, as well as some surprising generalities

## Supersymmetry: Slepton Production

- Slepton production followed by decay into corresponding lepton and “LSP” (neutralino)

- Endpoints of lepton spectrum determined by slepton, neutralino masses

## SUSY Point “SPS1a” at Ecm=1TeV

- SDMAR01

- NO MATERIAL

- PERFECT POINT RESOLUTION

- PERFECT POINT RESOLUTION, NO MATERIAL

- |cos| < 0.8

- |cos| < 0.994

- SUSY Point “SPS1a” at Ecm=1TeV

- SELECTRON MASS RESOLUTION (GeV/c2)

## 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...

## Linear Collider Detectors (very approximate) 

- Linear Collider Detectors (very 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