Precision Tracking

COLLID04

Novosibirsk

May 2004

Joachim Mnich

Precision Trackingat future colliders

LHC: Large Silicon Tracker LC: A Novel Time Projection Chamber

ATLASCMS

Detector for TESLA

The Large Hadron Collider (LHC) at CERN(Geneva)

protons

protonsAtlas

CMS

ATLAS

pp-collisions at very high energy (2 7 TeV) and luminosity 1033-1034/cm2/s

Tracking at the LHCLHC physics programme Higgs SUSY and New Physics searches Test of the Standard Model + heavy ion

Challenges for tracker LHC 25 ns bunch crossing rate fast detector response 20 pp interactions 1000 tracks/bx high granularity Resistance to high radiation

Tracking with silicon detectors Vertex: layers of pixel detectors Main tracker: large area silicon strip detectors + transition radiation detector (ATLAS) straw tubes & radiator

Examples: H ZZ 4 H 4 jets tt bb + 2 jets + l l l

Atlas: bb + 22 min. bias events

5.4 m

Outer Barrel –TOB-

Inner Barrel –TIB-

Endcap –TEC-

Pixel

2,4

mInner Disks

–TID-

ATLAS:• Hybrid pixel detectors 3 layers• Silicon strip detector (SCT) 4 layers in barrel 9 layers in endcap all layers 2 stereo detectors • Transisiton Radiation Tracker straw tubes + radiator (36 points)

• All in a 2 Tesla solenoid

Design Comparison

CMS:• All silicon tracker • Hybrid pixel detectors 3 layers• Silicon strip detectors 10 layers in barrel 9 layers in endcap• All in a 4 Tesla solenoid

Radiation HardnessExpected radiation doses• Pixel vertex detectors per year 31014 n/cm2 (1 MeV equiv.) 150 kGy charged particles• Strip detectors in 10 years 1.51014 n/cm2

60 kGy

Effects on silicon sensors• Creation of impurities• Change of depletion voltage type inversion• Increase of dark current• Increase of oxide charges strip/pixel capacitance

Effects on readout chips• Change of MOS structures• Change of amplification• Single event upset (bit flip)

Radiation Hardness

Radiation hard sensors:

• Operate at low temperature ( –

10°C) increases time constant of reverse annealing to many years reduces dark current & avoids thermal runaway

• Use <100> crystal orientation reduces charge trapping at Si/SiO2

boundariesRadiation hard chips:• Deep sub-micron technology 0.25 m structures

Small oxide structres intrinsically radiation hard Industrial standard cheap

DMILL technology relies on high quality oxide

1 10 100 1000 10000

annealing time at 60oC [min]

0

2

4

6

8

10

N

eff [

1011

cm-3

]

NY, = gY eq

NC

NC0

gC eqgC eq

NA = ga eqNA = ga eq

annealing

reverseannealing

Vertex Detectors

Hybrid pixel detectors• Active silicon sensor• Bump-bonded to readout chip

parallel readout & processing required for 40 MHz bunch crossing

CMS

General detector layout:

Pixel detectors: ATLAS CMS

# layer barrel

endcap

3

4

3

2

radii [cm] 5/10/12 4/7/10

pixel size [m2] 50 300/400 100 150

# channels 8107 7107

sensitive area [m2] 2 1.1

Vertex Detectors

Comparison of parameters:

area of LEP vertex detectors

CMS readout chip

Status of Pixel Detectors• R&D finished

• Prototyping:

• Testbeam:

ATLAS

CMS sensor in 25 ns beam at

LHC hit rates of 80 MHz/cm2

Silicon Strip Detectors

At larger radius no pixel detector possible (# of readout channels)

pixel 0.1 0.1 mm2

strip 0.1 100 mm2

0.1

ATLAS

CDF

GLAST

CMS

NOMAD

AMS01

CDF LEP

DO

Silicon Area (m²)

100

1000

10

1

Silicon strip det.: ATLAS CMS

# layer barrel

endcap

4 stereo

9 stereo

10 (4 stereo)

9 (33% stereo)

# modules 2 4088 15200

# channels 6106 10106

silicon area [m2] 61 206

Largest silicon detectors ever build!

CMSATLAS

Example of modules:

CMS outer barrel

ATLAS endcap

Silicon Strip Detectors

• Mass production of modules has started

• Use robots to assemble thousands of modules to O(20 m) precision

Production of Silicon Strip Detectors

CMS

Part of the CMS barrel carbon fiber support structure

Integration of Modules & Construction of Tracker

Support structure for the ATLASbarrel tracker

Expected Performance of LHC Trackers

pT resolution transverse impact parameter

(IPT) 10 m

Example CMS:

For high momentum tracks:

(pT)/pT 1.5 10-4 pT/GeV

(=0)

Example: expected b-jet tagging with CMS

Physics Performance of LHC Trackers

ATLAS Transition Radiation TrackerBonus: electron/pion separation

Two threshold analysis

5.5 keV

0.2 keV

Bd0J/ψ Ks

0 ~1 TR hit

~7 TR hits

• Large scale silicon tracker à la CMS have large material budget• Support, cooling, electronics, cables etc.• Active silicon contributes only marginally

Degradation of calorimeter performance Disadvantage compared to a gaseous trackers (TPC, jet chamber, ...)

Active silicon

CMS

The back side of the medal:Example: CMS full silicon tracker

LHC Tracker

Summary LHC Tracker (ATLAS & CMS)

• LHC enviroment requires fast, radiation hard detectors

Choice of large silicon (pixel & detectors) (+ straw tubes at larger radii)

Largest silicon detectors ever build

• Detectors under construction are adequate for the LHC physics programm

- High resolution on momentum and secondary vertices- Can cope with hostile conditions at the LHC

high muliplicity and extreme radiation doses

e+e– - Linear Collider

A Linear Collider with• Energy in the TeV range• High luminosity (> 1034/cm2/s)

is the next large international HEP project

Concepts:• Superconducting cavities: TESLA (Europe, DESY et al.)• Warm cavities: NLC (America) and GLC (Asia)• Drive beams: CLIC (CERN) route to multi-TeV energies

Comparison of physics at LC and LHC• LHC discovery machine for Higgs & SUSY• LC precison measurements

cf. discovery of W- and Z-bosons at hadron colliderfollowed by precision tests at LEP & SLC

Physics at a 1 TeV e+e– - Linear Collider

Example: Study of Higgs properties

e+ e– H Z H e+ e– (+ – )

Tag Higgs through leptonic Z decay (recoil mass) Study Higgs production independent of Higgs decay

1000 events/year

Momentum resolution (full tracker)

(1/pt ) < 510-5 GeV-1

Higgs Physics at the Linear Collider

Couplings to fermions: gf = mf /v

Couplings to gauge bosons:

gHWW = 2 mW2/v gHZZ = 2 mZ

2/v

Best possible vertex detector to distinguish b- and c-quarks

Determine Higgs branching ratios:

ideally: recoil mass resolution only limited by Z width

Main difference for detector design between cold and warm machines timing of bunches

TESLA GLC/NLC

bunch intervall 337 ns 1.4 ns

# bunches/train 2820 192

bunch length 950 s 0.27 s

repetition rate 5 Hz 100 – 150 Hz

• TESLA: higher readout speed to limit occupancy (several readout cycles per bunch train) • GLC/NLC: bunch separation is more difficult

2820 bunchest = 337 ns

199 ms

time

TESLA192 bunchest = 1.4 ns

7-10 ms

time

GLC/NLC

Tracking at the Linear Collider

Vertex Detector

Goal (TESLA TDR)reconstruction of primary vertex to

(PV) < 5 m 10 m / (p sin3/2 )

cf: SLD 8 m 33 m / (p sin3/2 )

Multi-layer pixel detector

• Stand alone tracking• Internal calibration • Small pixel (20 m 20 m)

• 800 million channel

TESLA SLD

Inner radius 15 mm 28 mm

Single point resolution < 5 m 8 m

Material per layer (X0) 0.06% 0.4%

Total material budget < 1% X0

Three main issues:

I. Material budget

• Very thin detectors 60 m (= 0.06% X0) of silicon• No electronics in central part, i.e. no hybrid design• Minimise support

II. Radiation hardness

• High background from beam-strahlung and beam halo

• Much less critical than LHC• But much more important than at LEP/SLC

TESLA

(ri = 1.5 cm)

CMS

(ri = 4.3 cm)

Dose (,e–,h) 10 kGy 1000 kGy

Neutron flux 1010/cm2 1015/cm2

Vertex Detector

III. Readout speed Integration of background during long bunch train

• Small pixel size (20 m 20 m) to keep occupancy low

• Read 10 times per train 50 MHz clock (TESLA)

CCD design

Use column parallel readout

CCD classic CP CCD

Vertex Detector

Vertex Detector Technology Several technologies under studyExamples: Charge Coupled Device:• Classical technology• Create signal in 20 m active layer etching of bulk total thickness 60 m • Coordinate precision 2-5 m • Low power consumption

DEPFET (DEPleted Field Effect Transistor)• Fully depleted sensor with integrated pre-amplifier• Low noise 10 e– at room temperature!

Prototype (Bonn):50 m × 50 m pixel 9 m resolution

• Standard CMOS wafer integrating all functions i.e. no connections like bump bonds• Very small pixel size achievable• Radiation hardness proven• Power consumption is an issue Pulse power?

MAPS (CMOS Monolithic Active Pixel Detectors)

Vertex Detector Technology

Large Si-Tracker à la LHC experiments?• Much lower particle rates at Linear Collider• Keep material budget low

Large Time Projection Chamber

• 1.7 m radius• 3% X0 barrel (30% X0 endcap) • High magnetic field (4 Tesla)

Goals • (1/pt ) < 510-5 GeV-1

• 200 points (3-dim.) per track• 100 m single point resolution• dE/dx 5% resolution

10 times better single point resolution than at LEP

Main TrackerSimulation of one TESLA bunch trainbackground (beam strahlung) + 1 Higgs

New concept for gas amplification at the end flanges:

Replace proportional wires with Micro Pattern Gas Detectors

- Finer dimensions- Two-dimensional symmetry

(no E×B effects)

- Only fast electron signal

- Intrinsic ion feedback suppression

GEM or Micromegas

Wires

GEM

Time Projection Chamber

Gas Electron Multiplier (GEM) (F. Sauli 1996)

140 m Ø 75 m• 50 m capton foil, double sided copper coated

• 75 m holes, 140 m pitch

• GEM voltages up to 500 V yield 104 gas amplification

For TPC use GEM towers for safe operation, e.g. COMPASS

Micromegas (Y. Giomataris 1996)

• Asymmetric parallel plate chamber with micromesh

• Saturation of Townsend coefficient mild dependence of amplification on gap variations

• Ion feedback suppression

50 m pitch

Detection of electron signal from MPGD: no signal broadening by induction

short & narrow signals

If signal collected on one pad No centre-of-gravity

Possible Solutions• Smaller pads• Replace pads by bump bonds of pixel readout chips• Capacitive or resistive coupling of adjacent pads

Micro Pattern Gas Detectors

Carlton/Victoria

DESY/Hamburg

Karlsruhe

Orsay/Saclay

R&D Work on TPC

Aachen

Triple GEM structure

Examples

DESY

• Short & narrow pulses

Examples of first results from triple GEM structures in high magnetic field

• Low ion feedback 2 10-3 • Single point resolution O(100 m)

R&D Work on TPC

Summary & Conclusions

Tracking at the LHC:• Large & precise tracking detectors mainly based on silicon technology under construction• Hybrid pixel vertex detectors • Start of data taking in 2007

Electron-Positron Linear Collider:• Vertexing with ultrafine & fast silicon pixel detectors• Tracking with high precision TPC exploiting micropattern gas detectors• Worldwide R&D programs ongoing