Detector for a Linear Collider

8th Topical Seminar on Innovative Particle and Radiation Detectors

Siena, 21 – 24 October 2002

Joachim Mnich

RWTH Aachen

• e+ e– - Linear Collider Projects• Physics at a 1 TeV e+e– - Linear Collider• Implications for Detector Design • Vertex Detector• Tracking Detector• Calorimeter

Detector for a Linear Collider

Outline:

Concepts for an e+ e– - Linear Collider (s = 500 GeV – 1 TeV)

• Cavities: superconductive normal • Frequency: 1.3 GHz X- (11.4 GHz) or C-Band (5.7 GHz )

• Route to higher energies (s = 5 TeV): CLIC: Acceleration by Drive-Beam

A) cms-energy:

TESLA-Project (DESY): Technical Design Report March 2001

• 35 MV/m s = 800 GeV already achieved with improved manufacturing (electropolishing)

Superconductive cavities

Acceleration gradient

23 MV/m s = 500 GeV

10.10.2002

800 GeV

Very recent result from 4 nine-cell modules:

B) Luminosity

pointn interactioat dimensions beamσ2)(factor t enhancemen disruption

frequency repetition pulsebunchper )(positrons electrons ofnumber

pulseper bunches ofnumber

)(

rep

e

b

yx

DHfNn

Strong focussing at the interaction point

Dyx

HfNn

L σσ4rep

2eb

nm5σnm550σ yx

Simulation

• Generation of small bunches: Final-Focus-Test (SLAC/DESY)

• Collision of bunches: Fast feedback system (Bunch separation: 337 ns) • use beam deflection/widening after collision• kicker magnets, Piezo-crystals

TESLA Electron-Positron-Collider Project:

Electron-Positron-Annihilation:Cross sections of SM- and MSSM-processes up to 1 TeV

• e+ e– ff pb• e+ e– HZ 10 fb (mH << s)

LC LEP II /10

Luminosity:

• LEP II L = 1032/cm2/s• LC L 1034/cm2/s

Higgs-factory: 100/fb/year = 1000 HZ/year

Giga-Z (s = mZ) 109 Z-bosons in 1/2 year

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 colliderthen precision tests at LEP & SLC

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

Keep in mind:Linear Collider comes probably after major discoveries at LHC

• Higgs physics• Supersymmetry (SUSY)• Alternative Theories• Top-quark physics• Standard Model (Giga-Z)...

• Detection of Higgs Bosons independent of decay

e+ e– H Z H e+ e– (+ – )

Higgs branching ratios:

• Couplings to fermions: gf = mf /v

• Couplings to gauge bosons:

gHWW = 2 mW2/v

gHZZ = 2 mZ2/v

Determination of Higgs couplings:

Higgs physics:

Higgs-Strahlung

• Spin: Energy scan at threshold (e.g. 3 points, 20 fb-1, 1/2 year)

Determination of the quantum number of the Higgs:

SM: JPC =0++

• Parity: Angular distribution (continuum) Discriminate SM Higgs and 0–+ -boson A

Verification of Higgs potential:

0λ0μλμ)(V 2422

4322 λH4

1HλHλ)H(V vv

vmH 2λ H

H

H

H H

HH

gHHH gHHHH

• Measurement of double Higgs strahlung e+ e– HHZ:

gHHH/ gHHH = 0.22

• Measurement of gHHHH not possible

λμ- n valueexpectatio Vacuum 2v

Comparison of Higgs physics e+ e– linear collider and LHC:

mH = 120 160 GeV

LHC 2300 fb-1

X/X

LC 500 fb-1

X/X

mH 10-3 310-4

H ---- 0.04 0.06 gu-type ---- 0.02 0.04 gd-type ---- 0.01 0.02 gHWW ---- 0.01 0.03 gtop/gHWW 0.070 0.023 gHZZ/gHWW 0.050 0.022 CP Test ---- 0.03 gHHH ---- 0.22

Linear collider will be in Higgs physicswhat LEP was in W- and Z-physics

Supersymmetry:

If mSUSY < 2 TeV discovery at the LHC

Possible particle spectra:

Advantage of Electron-Positron-Collider:• Mass measurements by energy scans at kinematic threshold • Polarisation of electrons (and possibly positrons)

Separation of SUSY partners, e.g.:

• Skalar partners of fermions

• Fermionic partners of bosons

• 2 Higgs doublets

g~,χ~,,χ~,χ~ 04

01

HA,H,h,

SUSY will be new Standard Model

21 t~,t~,,μ~,μ~,e~,e~ LRLR

RRRRLLLL e~e~ee e~e~ee

Detector R&D for an e+ e– - Linear Collider:

• Higher particle energies from GeV to TeV

• More complex final states e+ e– ZHH 6 jets/leptons e+ e– H+H– tb tb 8 jets

• Resolution e+ e– ZH e+ e– (+ – ) + X SUSY (missing energy)

• Accelerator background, luminosity, bunch separation

...we want to build the best apparatus...

Why new & improved e+ e– detector?

More differences to LEP

• Small cross section of signal two-photon background• Large Lorentz boost high particle density in jets, e.g. 1/mm2 in vertex detectorTrigger:(example TESLA)

• bunch trains 1 ms, • 5 Hz repetition rate• bunch separation 337 ns• but 199 ms between two trains

200 ms

1 ms

no hardware trigger

No dead time• Store data of whole train in front end• Software selection within 200 ms

Detector R&D for an e+ e– - Linear Collider:

World wide R&D effort started

Use most modern technology for best suited LC detector

I. Vertex detector III. CalorimeterII. Tracker

Here 3 examples:

I. Vertex detector

• Precise reconstruction of primary and secondary event vertices

• Identification of b- and c-quarks, - leptons in Higgs decays

Multi-layer pixel detectorTESLA SLD

Inner radius 15 mm 28 mm

Single point resolution < 5 m 8 m

Material per layer (X0) 0.06% X00.4% X0

Total material budget < 1% X0

Impact Parameter 300 m for > 3(independent of s)

Goal: reconstruction of primary vertex

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

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

1. Material budget:

• Thin detectors 60 m (= 0.06% X0)• Minimise support stretched silicon

3 m sagitta for 1.5 N tension

Three main issues:

Baseline design with 5 layers:

• Stand alone tracking• Internal calibration

3. 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

CCD design

2. Radiation hardness:

• High background from beam-strahlung and beam halo

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

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: Three technologies under consideration

1. Charge Coupled Device

• Create signal in 20 m active layer etching of bulk to keep total thickness 60 m • 800 million pixels (SLD 300 million pixel)• Coordinate precision 2-5 m • Low power consumption (10 W)

• But very slow!

use column parallel readout

CCD classic CP CCD

2. DEPFET (DEPleted Field Effect Transistor)

Fully depleted sensor with integrated pre-amplifier

• Low power: 1 W/sensor• Low noise: 10 e– at room temperature!• Thinning to 50 m possible

Result from a 64 × 64 pixel matrix:

50 m × 50 m pixel 9 m reolution

To be shown: Column wise readout with 50 MHz

1987 (Kemmer,Lutz)

3. MAPS (CMOS Monolithic Active Pixel Detectors)

Standard CMOS wafer, integrates all functions

1999

• Same unique wafer for sensor and electronics i.e. no connections like bump bonds• Very small pixel size achievable• Radiation hardness proven• Power consumption pulse power?

II. Tracker

• Study of Higgs production independent of Higgs decay lepton momenta

ideally: recoil mass resolution limited by Z width

• SUSY mass measurements

- Pair production of scalar leptons (decay to lepton + neutralino)

- Mass determination from end points of Momentum spectra

Precise measurement of charged particle momenta:

Momentum resolution

(1/pt ) < 5 × 10-5 (GeV/c )-1 (full tracker)

Large Si-Tracker à la LHC experiments?• much lower particle rates at linear collider• keep material budget low

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

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

10 times better performance than at LEP

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

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

• 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

Disadvantage of electron signal:

No signal broadening by induction

• 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• Alternative pad geometries

Strip coupling chevrons

III. Calorimeter

• Hermiticity to exploit missing energy signature of SUSY

No cracks Calorimeter inside magnet coils

• Fast readout & good time resolution to avoid event pile up

• Excellent energy and angular resolution

- Mass reconstruction e.g. e+ e– t t

- Distinguish hadronic W- and Z-decays

e+ e– t t at threshold

Goal for jet energy resolution

EE %30

E%30E%60

Jet energy resolution:

W/Z identification by mass reconstruction in 4 jets: Include Fig 4.3.2 from TDRInclude Fig 4.3.2 from TDRInclude Fig 4.3.2 from TDRInclude Fig 4.3.2 from TDR

To get best jet energy resolution:

measure every particle in the jet

Energy distribution in typical multijet event:

• 60% charged particles Tracker• 30% photons Ecal• 10% neutral hadrons Ecal + Hcal

+ good lepton ID

Fine granularity (in 3 dim.) of electromagnetic and hadron calorimeters

Combine tracks and clustersFrom energy flow to particle reconstruction!

Highly granular calorimeter:

Electromagnetic:• identify particles down to low energies• longitudinal segmentation X0

• X0/ small• transversal segmentation rM

• no cracks, magnet coil outside

Hadron calorimeter:

• cell size close to X0 • good cluster separation• good energy resolution

Si/W natural choice rM= 9 mm

ECAL, HCAL with different absorbers and sampling non compensatingECAL, HCAL with different absorbers and sampling non compensating

But very expensive!

particle

Silicon-tungsten electromagnetic calorimeter:

• 1 cm2 silicon pads• 40 layers• energy resolution

E/E < 0.1/E/GeV 0.01

0.1

ATLAS

CDF

GLAST

CMS

NOMAD

AMS01

CDF LEP

DO

Silicon Area (m²)

100

1000

10

1

2000 m²

Required silicon: 1 – 3 103 m2

Price today: 5 $/cm2

Alternative design for electromagnetic calorimeter:

Tile fibre calorimeter(lead scintillator)

Challenge: • Fibre readout in 4 T field• Optimize light yield of fibres

Hadron calorimeter• Use same design & components• Coarser segmentation• Compensation (lead/scint. 4/1) • Use stainless steel ()

Coarser granularity

e.g. 5 5 cm2

Digital hadron calorimeter

Alternative design for hadron calorimeter:

• Highly segmented 1 cm2 pads• Binary readout per RPC or small wire chambers• Simple frontend electronics

Precision measurements at Linear Collider

high demands on detector performance

LEP/SLC like detector not sufficient

Summary

• Flavour tagging H cc• Momentum resolution - e+ e– H Z H e+ e– (+ – ) from lepton recoil mass

- endpoint mass spectra in SUSY cascade• Jet energy resolution - Higgs self-coupling HZZ

- Multi-jet final states like ttH

...

World wide R&D projects started:

• TPC Europe, US, Canada (TPC Working group alephwww.mppmu.mpg.de/~settles/tpc/welcome3.html)

• Calorimeter Europe, Asia, US (CALICE coll. polyww.in2p3.fr/tesla/calice_offic.html)

Much more R&D effort needed!

International Linear Collider Detector R&D committeehttp://blueox.uoregon.edu/~lc/randd.pdf