The Gossamer Tracker: A Novel Concept for a LC

Central Tracker

Bruce SchummSCIPP & UC Santa Cruz

UC Davis Experimental Particle Physics Seminar

June 3, 2002

“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 this endorsement, and has continued to bolster its efforts with both public outreach and international cooperation.

TESLA

NLC

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= 3x10-5

Strong WW Scattering

Absent Higgs Sector, something else must act to renormalize W couplings

Diagrams: Wolfgang Killian, Karlsruhe

This physics will be produced via the t-channel will tend to be forward

W/Z Separation

Henri Videau; Ecole Polytechnique

Jet energy resolution requires energy-flow technique: excellent track/cluster matching to allow charged track energies to come from tracker

jetjet EE 60.0 jetjet EE 30.0

Precise Reconstruction of SUSYHaijun Yang; Michigan

Precise recon-struction of sparticle masses relies on precise determination of endpoint

p/ p2= 2x10-5

But does not establish as tight a requirement as Higgs physics

The North American Detectors

L Design: Gaseous Tracking (TPC) Rmax = 190cm 3 T Field Conventional (Pb/Sci) Calorimeter

S Design: Solid-State Tracking Rmax = 120cm 5 T Field Precise (Si/W) Calorimeter

The Trackers

The SD-MAR01 Tracker

Tracker Performance

SD Detector burdened by material in five tracking layers (1.5% X0 per layer) at low and intermediate mo-mentum

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

Idea: Noise vs. Shaping Time

Min-i for 300m Si is about 24,000 electrons

Shaping (s) Length (cm) Noise (e-)

1 100 2200

1 200 3950

3 100 1250

3 200 2200

10 100 1000

10 200 1850

Agilent 0.5 m CMOS process (qualified by GLAST)

The Gossamer TrackerIdeas:• Long ladders substantially limit electronics readout and associated support• Thin inner detector layers• Exploit duty cycle eliminate need for active cooling Competitive with gaseous

track-ing over full range of momentaAlso: forward region…

TPC Material Burden

Pursuing the Long-Shaping Idea

LOCAL GROUPSCIPP/UCSC• Optimization of readout & sensors• Design & production of prototype ASIC• Development of prototype ladder; testing

Supported by 2-year, $95K grant from DOE Advanced Detector R&D ProgramSLAC• System performance studies (backgrounds, pattern recognition, vees, etc.)• Mechanical considerations

PRC MeetingDESY, Hamburg, May 7 and 8,

2003

SilC: an International R&D Collaboration to develop Si-

tracking technologies for the LC

Aurore Savoy-Navarro, LPNHE-Universités de Paris 6&7/IN2P3-CNRS, France

on behalf of the SiLC Collaboration

The SiLC CollaborationThe SiLC Collaboration

Brookhaven

Ann Arbor Wayne

Santa Cruz

Helsinki

Obninsk Karlsruhe

Paris

Prague Wien Geneve

Torino

Pisa

RomeBarcelonaValencia

Korean Universities

Seoul&Taegu

Tokyo

EuropeUSA

ASIASo far: 18 Institutes gathering over 90 people from Asia, Europe & USAMost of these teams are and/or have been collaborating.

Roles in the Larger Community

Discussions with Aurore Savoy-Navarro (LPNHE Paris)• Finite element (thermal, mechanical) modelling• Development of mechanical systems• Collaboration on ASIC development

University of Michigan• Interferometric alignment systems

The SCIPP/UCSC Effort

Faculty/Senior

Alex GrilloHartmut Sadrozinski

Bruce SchummAbe Seiden

Post-Doc

Gavin Nesom

(half-time LC postdoc from

1999 program)

Student

Christian Flacco

(will do BaBar thesis)

Engineer: Ned Spencer (on SCIPP base program)

SCIPP/UCSC Development Work

Characterize GLAST `cut-out’ detectors (8 channels with pitch of ~200 m) for prototype ladder

Detailed simulation of pulse development, electronics, and readout chain for optimization and to guide ASIC development (most of work so far)…

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 deviceGeometry: Variable strip pitch, sensor thickness, orientation (2 dimen-sions) and track impact parameter

Uncorrelated Sampling Check

Carrier Diffusion

)(21

exp),(0

2

ttDr

trPq

Hole diffusion distribution given by

Offest t0 reflects instantaneous expansion of hole clouddue to space-charge repulsion. Diffusion constant given by

hq qkT

D

Reference: E. Belau et al., NIM 214, p253 (1983)

sec65.00 nt

h = hole mobility

Other ConsiderationsLorentz 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 3s; 0.5 m process qualified by GLAST

Result: S/N for 132cm Ladder

At shaping time of 3s; 0.5 m process qualified by GLAST

132cm Ladder 300m Thick

Not Yet Considered

• Inter-Strip Capacitance (under study; typically ~5% pulse sharing between neighboring channels)

• Leakage Current (small for low-radiation environment)

• Threshold Variation (typically want some headroom for this!) But overall, 3 s operating point seems quite feasible proceed to ASIC design!

Analog Readout Scheme: Time-Over Threshold

(TOT)

i-min

thresh

e

e

nn

i-min

pulse

e

e

nn

r

TO

T/

/r

/te

etr

TOT given by differencebetween two solutions to

(RC-CR shaper)

Digitize with granularity /ndig

Why Time-Over-Threshold?

4

2

6

10

8

TO

T/

101 1000100

Signal/Threshold = (/r)-1

100 x min-i

With TOT analog readout:

Live-time for 100x dynamic range is about 9

With = 3 s, this leads to a live-time of about 30 s, and a duty cycle of about 1/250

Sufficient for power-cycling!

Single-Hit Resolution

Design performance assumes 7m single-hit resolution. What can we really expect?

• Implement nearest-neighbor clustering algorithm

• Digitize time-over-threshold response (0.1* more than adequate to avoid degradation)

• Explore use of second `readout threshold’ that is set lower than `triggering threshold’; major design implication

RMS

Gaussian Fit

RMS

Gaussian Fit

Readout Threshold (Fraction of min-i)

Trigger Threshold167cm Ladder

132cm Ladder

Resolution With and Without Second (Readout)

Threshold

Lifestyle Choices

Based on simulation results, ASIC design will incorporate:

• 3 s shaping-time for preamplifier

• Time-over-threshold analog treatment

• Dual-discriminator architecture

The design of this ASIC is now underway.

But Can It Track Charged Particles?

1 100.1

Energy (MeV)

z (cm)

Photon Distributions at R = 25 cm

Photon Interactions in Silicon

(Thanks to Takashi Maruyama, SLAC)

Converted electrons can come out of Si B = 5

Tesla E < 0.1 MeV

0.1 < E < 0.5 MeV

0.5 < E < 1 MeV 1 < E < 10 MeV

(Thanks to Takashi Maruyama, SLAC)

Photon Conversion Probability

0.1 1 10 0.1 1 10

Energy (MeV) Energy (MeV)

Edep > 50 keV

60°

75.5°

82.8°

86.4°

(Thanks to Takashi Maruyama, SLAC)

No. of Hits

0.1 1 10Energy (MeV)

Edep > 50 keV

Normal incident

(Thanks to Takashi Maruyama, SLAC)

No. of hits: 68 strips/train 69 strips/train 106 strips/train

Occupancy: 0.27% 0.28% 0.42%25k channels

Tracker Layer 1 Simulation Photon flux: 241 photons/4 bunches 5784 photons/train Use 241 photons 1000 times to

increase statistics.

(Thanks to Takashi Maruyama, SLAC)

Seem tractable at this level.

Where Next?

We’ve just begun the process of fleshing out the design of this `Gossamer Tracker’

In the 3-year R&D window, we need to:

• Demonstrate ability to read out long ladders• Demonstrate resolution and dynamic range • Demonstrate passive cooling (data transmission is an issue!)• Develop ultra-light, rigid mechanical systems• Demonstrate need for low-mass tracker (central, forward)• Prove that such a tracker will perform well in integrated tracking system

Some (Very Preliminary) Roles

Santa Cruz

Develop prototype front-end ASICTest bench results with `makeshift’ ladderTest-beam studies (S/N and resolution as a function of whatever

SLAC

Explore occupancy, pattern recognition issuesExplore mechanical designs

Paris

Mechanical/thermal finite element analysisASIC `Back-end’ architectureExplore mechanical designs

Roles (continued)Michigan

Interferometric alignment systems

New Group? Could begin with simulation…

Calorimeter-assisted tracking (Vees, kinks)Track/cluster matchingPhysics signals

Or not…

Procurement/construction of more appropriate ladder Test beam preparation and executionThermal and mechanical systems

Summary

An ultra-light silicon-strip tracker may well be feasible at a high-energy electron-positron Linear ColliderLooks reasonable on paper, but much work must be done over next 3 years to prove the principle, show needAn international collaboration (SiLC) is forming to explore this and other silicon-tracking option for the LCWork on `Gossamer’ Tracker currently focussed at SCIPP and SLAC, but we expect this to expand