Development of a tracking detector for physics

at

the Large Hadron Collider

Geoff Hall

October 2002G Hall 2

CMS = Compact Muon Solenoid detector• missing element in current theoretical framework - mass

Total weight 12,500 tonsDiameter 15mLength 21.6mMagnetic field 4T

Total weight 12,500 tonsDiameter 15mLength 21.6mMagnetic field 4T

Tracking system

10 million microstripsDiameter 2.6mLength 7mPower ~50kW

Tracking system

10 million microstripsDiameter 2.6mLength 7mPower ~50kW

October 2002G Hall 3

LHC parameters (CMS)

•Consequences

High speed signal processingSignal pile-up

High (low) radiation exposure High (low) B field operation

Very large data volumes

New technologies

p p P b - P b

L u m i n o s i t y1 0

3 4

c m

- 2

. s

- 1

1 0

2 7

c m

- 2

. s

- 1

A n n u a l i n t e g r a t e d L5 x 1 0

4 0

c m

- 2

?

C M e n e r g y 1 4 T e V 5 . 5 T e V / N

σ

i n e l a s t i c

~ 7 0 m b ~ 6 . 5 b

i n t e r a c t i o n s / b u n c h ~ 2 0 0 . 0 0 1

t r a c k s / u n i t r a p i d i t y ~ 1 4 0 3 0 0 0 - 8 0 0 0

b e a m d i a m e t e r 2 0 µ m 2 0 µ m

b u n c h l e n g t h 7 5 m m 7 5 m m

b e a m c r o s s i n g r a t e 4 0 M H z 8 M H z

L e v e l 1 t r i g g e r d e l a y ≈ 3 . 2 µ s e c ≈ 3 . 2 µ s e c

L 1 ( a v e r a g e ) t r i g g e r r a t e ≤ 1 0 0 k H z < 8 k H z

October 2002G Hall 4

Design philosophy• Large solenoidal (4T) magnet

iron yoke - returns B field, absorbs particlestechnically challenging but

smaller detector, p resolution, trigger, cost• Muon detection

high pT lepton signatures for new physics• Electromagnetic calorimeter

high (E) resolution, for H => (low mass mode)• Tracking system

momentum measurements of charged particlespattern recognition & efficiency

complex, multi-particle eventscomplement muon & ECAL measurements

improved p measurement (high p)E/p for e/ identification

October 2002G Hall 5

Parameters for hadronic collider physics• E, p, cos, prefer variables which easily Lorentz transform

e.g E, pT, pL,

• pT divergences from simple behaviour could imply new physics

eg heavy particle decay => high pT lepton (or hadron)

• rapidity

Lorentz boost

• pseudorapidity

y=12

ln(E +pL

E −pL

) dy=dpL

E

y→ ′ y =y+12

ln(1+β

1−β)

dNdy

invariant=>

d2Ncharged

dη.dpT≈H.f(pT ) H~ 6 || < 2.5

LHC

y=12

ln(cos2(θ 2)+

m2

4p2 +...

sin2(θ 2)+m2

4p2 +...) ≈−lntan(θ 2)≡η

October 2002G Hall 6

Physics requirements (I)• Mass peak - one means of discovery

=> small σ(pT)

eg H => ZZ or ZZ* => 4l±

typical pT(µ) ~ 5-50GeV/c

• Background suppressionmeasure lepton chargesgood geometrical acceptance - 4 leptonsbackground channel t => b => l

require m(l+l-) = mZ Z ~ 2.5GeVprecise vertex measurement identify b decays, or reduce fraction

in data

m2 = Ei2

i∑ −pi

2

tt

October 2002G Hall 7

Physics requirements (II)

ΔpT

pT

≈0.15pT (TeV)⊕ 0.5%

• p resolution

large B and L

• high precision space pointsdetector with small intrinsic σmeas

• well separated particlesgood time resolutionlow occupancy => many channelsgood pattern recognition

• minimise multiple scattering• minimal bremsstrahlung, photon conversions

material in tracker most precise points close to beam

σ(pT )pT

~pT

σmeas

B.L2 Npts

October 2002G Hall 8

Silicon diodes as position detectors

Q(x)

Microstrip detectorsBeamTarget

• Spatial measurement precision defined by strip dimensions

ultimately limited by charge diffusionσ ~ 5-10µm

October 2002G Hall 9

Vertex detector ~1990

October 2002G Hall 10

Interactions in CMS

7 TeV p

7 TeV p

October 2002G Hall 11

2.4m

~ 6m

Microstrip tracker system

~10Mdetectorchannels

October 2002G Hall 12

Event in the tracker

October 2002G Hall 13

• Constraints on trackerminimal material high spatial precisionsensitive detectors requiring low noise readoutpower dissipation ~50kW in 4T magnetic fieldradiation hardBudget

• Requirementslarge number of channelslimited energy resolutionlimited dynamic range

Silicon detector modules

October 2002G Hall 14

Radiation environment• Particle fluxes

Charged and neutral particles from interactions ~ 1/r2

Neutrons from calorimeternuclear backsplash + thermalisation ≈ more uniform gasonly E > 100keV damaging

• Dose energy deposit per unit volume Gray = 1Joule/kg = 100rad

mostly due to charged particles

October 2002G Hall 15

Imperial College contributions to Tracker

FED

APV25APVMUX/PLL

• Hardware development• Hardware construction• Beam tests & studies• Preparation for physics

October 2002G Hall 16

programmable gain

APV25 0.25µm CMOS

Low noisecharge

preamplifier

50 ns CR-RC

shaper

192-cell

analogue

pipeline

1 of the 128 channels

SF

SF

Analogue unity

gain inverter

S/H

APSP

128:1 MUX

Differential current

O/P

APV25-S0 (Oct 1999)APV25-S0 (Oct 1999)

APV25-S1 (Aug 2000)

Chip Size 7.1 x 8.1 mm

Final

APV25-S1 (Aug 2000)

Chip Size 7.1 x 8.1 mm

Final

amplifierspipelinememory

signal processing

& MUX

control logic

October 2002G Hall 17

Chip testing

• Automated on-wafer testing~1min/site~100,000 to test

October 2002G Hall 18

0.001

2

3

4

5

6789

0.01

Noise [

μ/V Hz

1/2

]

104

2 4 6

105

2 4 6

106

2 4 6

107

Frequency [Hz]

pre-rad 10 Mrad 20 Mrad 30 Mrad 50 Mrad anneal

0.001

2

3

4

5

6789

0.01

Noise [

μ/V Hz

1/2

]

104

2 4 6

105

2 4 6

106

2 4 6

107

Frequency [Hz]

pre-rad 10 Mrad 20 Mrad 30 Mrad 50 Mrad anneal

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Id [A]

-0.6 -0.4 -0.2 0.0 0.2Vg [V]

Pre-rad 50 Mrad Anneal

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Id [A]

-0.6 -0.4 -0.2 0.0 0.2Vg [V]

Pre-rad 50 Mrad Anneal

Irradiations of 0.25µm technology

• Extensive studies CMS tracker data from IC, Padova, CERN

ALL POSITIVE and well beyond LHC range

• CMOS hard against bulk damageQualify chips from wafers with ionising sources

• Typical irradiation conditions50kV X-ray source Dose rate ~ 0.5Mrad/Hour

to 10, 20, 30 & 50Mrad

PMOS

PMOS2000/0.36

400µA

October 2002G Hall 19

APV25 irradiations (IC & Padova)• IC x-ray source

Normal operational bias during irradiation clocked & triggered

also 10 MeV linac electrons(80Mrad) and 2.1x1014 reactor n.cm-2

Post irradiation noise change insignificantPost irradiation noise change insignificant

500400300200100

0250200150100500

10 Mrad

500400300200100

0250200150100500

pre-rad APV25-S1APV25-S1

October 2002G Hall 20

Silicon as a detector material

• Detectors operated as reverse biased diodedark current = noise sourcesignals small

typical H.E. particle ~ 25000 e 300µm Si10keV x-ray photon ~ 2800e

• Deplete entire wafer thicknessVbias ~ NDd2

ND ~ 1012 cm-3

=> Vbias ~ 50V for 300µm

ND : NSi ~ 1 : 1013

ultra high purity

• Further refining requiredFloat Zone: local crystal melting with RF heating coil

October 2002G Hall 21

Radiation effects in (bulk) silicon• Silicon atoms dislodged from lattice sites…

causing more damage as they come to rest...

increased dark currentsaltered substrate doping

primary defects = V & Idiffuse and become trapped

influenced by O & C impurity levels

increased dark currentsaltered substrate doping

primary defects = V & Idiffuse and become trapped

influenced by O & C impurity levels

after irradiation

October 2002G Hall 22

CMS Silicon Strip Tracker Front End Driver

VME-FPGA

TTCrx

BE-FPGAEvent Builder

Buffers

FPGAConfiguration

PowerDC-DC

DAQInterface

12

12

12

12

12

12

12

12

Front-End Modules x 8Double-sided board

CERNOpto-

Rx Analogue/Digital

96 TrackerOpto Fibres

VMEInterface

XilinxVirtex-IIFPGA

Data Rates

9U VME64x Form Factor

Modularity matched Opto Links

Analogue: 96 ADC channels (10-bit @ 40 MHz )

@ L1 Trigger : processes 25K MUXed silicon strips / FED

Raw Input: 3 Gbytes/sec*

after Zero Suppression...

DAQ Output: ~ 200 MBytes/sec

~440 FEDs required for entire SST Readout System

*(@ L1 max rate = 100 kHz)

FE-FPGAClusterFinder

TTC

TCS

TempMonitor

JTAG

TCS : Trigger Control System

9U VME64x

October 2002G Hall 23

CMS Silicon Strip Tracker FED Front-End FPGA Logic

ADC 1 10 10s

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hit DP

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averages8header status

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nc

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emulator in

mu

x

Serial I/O

Se

ria

l In

t

B’Scan

Lo

ca

lIO

Config

Cluster Finding FPGA VERILOG Firmware

Full flags

data

Global reset

Co

ntr

ol

Sub resets

10

10

Ph

as

eR

eg

iste

rsP

ha

se

Re

gis

ters

2 x 256 cycles 256 cycles nx256x16

trig1Synch error

4x

Temp Sensor

Delay Line

Opto Rx

Clock 40 MHzD

LL

1x2x4x

per adc channel phase compensation required to bring

data into step

+ Raw Data mode, Scope mode, Test modes...

160 MHz

October 2002G Hall 24

The CMS Tracking Strategy

Radius ~ 110cm, Length/2 ~ 270cm

3 disks TID

6 layersTOB

4 layersTIB

9 disks TEC

Number of hits by tracks:Total number of hitsDouble-side hitsDouble-side hits in thin detectorsDouble-side hits in thick detectors

• Rely on “few” measurement layers,each able to provide robust (clean) and precise coordinate determination

2-3 Silicon Pixel 2-3 Silicon Pixel 10 - 14 Silicon Strip Layers10 - 14 Silicon Strip Layers

October 2002G Hall 25

Vertex Reconstruction

At high luminosity, the trigger primary vertex is found in >95% of the events

Primary vertices: use pixels!

October 2002G Hall 26

High Level Trigger & Tracker

In High Level trigger reconstruction only 0.1%

of the events should survive.

“How can I kill these events using the least

CPU time?”

This can be interpreted as:o The fastest (most approx.) reconstructiono The minimal amount of precise reconstructiono A mixture of the two

DAQ

40 MHZ40 MHZ

100 KHz100 KHz

100 Hz

Same SW would be use in HLT and off-line :

algorithms should be high quality

algorithms should be fast enough

Events rejected at HLT are irrecoverably lost!

HLT Track HLT Track findingfinding

October 2002G Hall 27

References• A. Litke & A. Schwarz Scientific American May 1995

• T. Liss & P. Tipton Scientific American September 1997

• N. Ellis & T. Virdee. Experimental Challenges in High Luminosity Collider Physics. Ann. Rev. Nucl.

Part. Sci 44 (1994) 609-653.

• G.Hall Modern charged particle detectors Contemporary Physics 33 (1992) 1-14 & refs therein

• G.Hall Semiconductor particle tracking detectors Reports on Progress in Physics.57 (1994) 481-531

• A. Schwarz 1993 Heavy Flavour Physics at Colliders with silicon strip vertex detectors. Physics

Reports 238 (1994) 1-133.

• C. Damerell Vertex detectors: The state of the art and future prospects. Rutherford Appleton

Laboratory report RAL-P-95-008 A pdf version is available on the CERN library Web site.(Search

preprints)

• CMS Web pages http://cmsdoc.cern.ch/cmsnice.html

• http://cmsinfo.cern.ch/Welcome.html Letter of Intent (most readable) and and Technical proposal

• http://cmsdoc.cern.ch/cms/TDR/TRACKER/tracker.html CMS Tracker Technical Design Report (even

more detail on many aspects) of the tracker.