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CMS Tracker Upgrade

Thanks to many CMS Tracker collaborators, past and present

Geoff Hall RHUL Nov 2009 2

CMS Compact Muon Solenoid

ECAL

Tracker

HCAL

4T solenoid

Muon chambers

Total weight: 12,500 tOverall diameter: 15 mOverall length 21.6 mMagnetic field 4 T

First pp collisions in 2009.. up to 10 TeV CM energy in 2010

Quick review of CMS status

• CMS was completed and closed in August 2008– Significant prior commissioning with cosmics (~350M triggers)

– Successful start with beam on 10 September

• Several days of operation before 19 Sept incident– Extended cosmic run Oct/Nov with 4T field (CRAFT)

• Shutdown to Spring 2009: attend to (very) few weak points– Tracker cooling plant refurbishment, fraction of FPIX lost now repaired,

few muon chambers, some HCAL HPDs

– Global runs and cosmic data since July 2009

• First 2009 beam, November


9 December 2009 4

BSC Trigger History of Splashes• 12 hour history from 11pm 7‐Nov to 11am 8‐Nov:

• 7pm 8‐Nov to 8am 9‐Nov:

• >1100 shots in total

• Vertical scale is arbitrary

9 December 2009 5

Beam 2

• ECAL energy deposits in red, Preshower in green, HCAL energy deposits in blue (light blue for HF and HOlight blue for HF and HO), RPC muon hits are RPC muon hits are in yellowin yellow, and CSC muon hits are in magenta.

9 December 2009 6

• ECAL energy deposits in red, Preshower in green, HCAL energy deposits in blue(light blue for HF and HOlight blue for HF and HO), RPC muon hits are in yellowRPC muon hits are in yellow, and CSC muon hits are in magenta.

Beam 2

LHC machine upgrade

Cern Injector Complex

Geoff HallRHUL Nov 20098

PSBPSB

SPSSPSSPS+

Linac4

(LP)SPL

PSPS

LHC / SLHCLHC / SLHC DLHC

Out

put e

nerg

yO

utpu

t ene

rgy

160 MeV160 MeV

1.4 GeV1.4 GeV4 GeV4 GeV

26 GeV26 GeV50 GeV50 GeV

450 GeV450 GeV1 TeV1 TeV

7 TeV7 TeV~ 14 TeV~ 14 TeV

Linac2Linac250 MeV50 MeV

(LP)SPL: (Low Power) Superconducting Proton Linac (4-5 GeV)

PS2: High Energy PS(~ 5 to 50 GeV – 0.3 Hz)

SPS+: Superconducting SPS(50 to1000 GeV)

SLHC: “Superluminosity” LHC(up to 1035 cm-2s-1)

DLHC: “Double energy” LHC(1 to ~14 TeV)

Proton flux / Beam power

PS2

R.G.9LHCC – 1 July, 2008Geoff Hall9 RHUL Nov 2009

R. Garoby

R. Garoby

SPS

PS2

SPL

Linac4

PS

ISOLDE

R.G.10LHCC – 1 July, 2008Geoff Hall10 RHUL Nov 2009

Parasitic upgrade of injector complex possible

Parasitic upgrade of injector complex possible


Upgrade to CMS

• CMS was designed for 10 years operation at L = 1034 cm‐2.s‐1

– Max L1 trigger rate 100kHz & decision latency ≈ 3.2µs

• Eventually expected to operate at L ~ 1035 cm‐2.s‐1

– most of CMS will survive & perform well with few changes

• Several “continuous” upgrades possible during CMS lifetime

–now foreseen in two major steps (Phase I & II)

• Notable exception is tracking system– pixels easily replaceable while outer tracker is much larger task

– greater radiation tolerance, especially sensors, eventually required

• ASIC electronic technologies will be adequate but

0.25µm CMOS, pioneered by CMS, will probably not be accessible

– L1 trigger using tracker data is essential

Possible luminosity evolution

sLHCsLHC

LHCLHC

Luminosity Leveling(Same Integrated L)

RHUL Nov 2009 12Geoff Hall

T VirdeeAll CMS meetingOct 2009

Reminder of why this is needed

• We don’t yet know!– but expect eventually to be statistics limited

– time to reduce errors

– it may be that the physics targets will be different than we expect

• However, the environment is very challenging– we are asked for same or better performance!


1035103510341034

Full LHC luminosity~20 interactions/bx

Proposed SLHC luminosity~300-400 interactions/bx

H→ZZ → μμee, MH= 300 GeV vs luminosity


TOBTOB

TIDTIDTIBTIB

TECTEC

PDPD

Current Tracker system

• Two main sub‐systems: Silicon Strip Tracker and Pixels– pixels quickly removable for beam‐pipe bake‐out or replacement

Microstrip tracker Pixels

~210 m2 of silicon, 9.3M channels ~1 m2 of silicon, 66M channels

73k APV25s, 38k optical links, 440 FEDs 16k ROCs, 2k olinks, 40 FEDs

27 module types 8 module types

~34kW ~3.6kW (post‐rad)

Phase 1: L=2‐3x1034cm2s‐1

Pixels Upgrade

(Coordinators R. Horisberger, S. Kwan)

Today’s pixel detector

• 3‐hit detector

00

10

20

10 20 30 40 50 60

r (cm)

z (cm)

BPIX

FPIX

Phase‐1: 4 hit detector

• Add extra layers for a 4 hit detector

– 66M to 120Mpixels

– 16k to 30k readout chips (ROC)

• Also make modifications to ROC– E.g. extend buffers to

reduce inefficiency0

0

10

20

10 20 30 40 50 60

r (cm)

z (cm)

BPIX

FPIX

Aggressive mass reduction

– Ultra‐light mechanics, pipes (CO2), module supports

Aggressive mass reduction

– Ultra‐light mechanics, pipes (CO2), module supports

• Thinner sensor– 285μm to 225μm

• Thinner ROC– 175μm to 75μm

Further material reduction

• Move BPIX optoelectronics further out

Further material reduction

• Move BPIX optoelectronics further out

Ref: B. Meier, TWEPP 08

• Use micro‐twisted wire cables instead of flex‐cables

Radiation Environment

• Foresee replacement of pixels after ~6x1014cm‐2

– replacing should ideally then survive to SLHC

Ref: CMS Tracker TDR

Fluences (1013/cm2) and doses for 500fb‐1

CMS Pixel detector handling

• Flexibility: Pixel system removable/installable in few days

• Removal foreseen for – Bakeout of beam pipe

– Eventual service/upgrade

• FPIX successfully removed, maintained, reinserted this year

Note: Physical envelope, position of beam‐pipe supports and rails all fixed

• Not enough capacity with current services

• Impossible to add more cables, pipes, fibres

• Use DC‐DC converters – Deliver necessary power on same

cables

• Increase output bandwidth – 320Mbit/s binary data on same

fibres

• CO2 cooling with same Cu pipes to bulkhead

Pixel services constraint

Phase 2: L < 1035cm2s‐1

Full Tracker Upgrade


A better tracker for SLHC?

• Present detector looks to be very powerful instrument

• No physics reason to improve spatial and momentum measurement precision– but want to maintain tracking and vertexing performance

• Heavy ion tracking simulations are encouraging:– Track density similar to SLHC

– Extra pixel layer would restore losses

• Must optimise layout of tracker for– CPU‐effective track finding

– Trigger contributions

• Weakest point in present system is amount of material– Electron & photon conversions

– Hadronic interactions


Tracker services

• Major constraint on upgraded system– Complex, congested routes

– Heat load of cables must be removed

– Cable voltage drops exceed ASIC supply voltages

Installation of services was one of the most difficult jobs to complete CMS

It will probably be impossible to replace cables and cooling for SLHC

PFE ≈ 33kW I=15,500A PS = 300kVA

Defining a new layout

• Present design suffered from limited simulations– we did not know how many layers would provide robust tracking

– pixel system was a late addition, which has an important impact

– the material budget estimate was not as accurate as desired

• A new tracker might be “easy” to design based on experience– but provision of trigger information adds a major complication

– and the tools to model CMS at L = 1035 were not in place

– major uncertainties in power delivery, sensor type, readout architecture

• Hence big emphasis on simulation of new detector


New Requirement: Tracker input to Level‐1 trigger

Geoff Hall TWEPP Sep 2009 31

Why tracker input to L1 trigger?

• Single µ, e and jet L1 trigger rates will greatly exceed 100kHz– Tracker data appears to be only extra info capable of improving selectivity

• can increase latency, to 6.4µs, but must maintain 100kHz for compatibility

Single electron trigger rate

<pT> ≈ few GeV/bx/trigger tower

Isolation criteria alone are insufficient to reduce rate at L=1035 cm‐2.s‐1

5kHz @ 1035

L = 2x1033

L = 1034 muon L1 trigger rate

The track‐trigger challenge

• Impossible to transfer all data off‐detector for decision logic– eg ~0.5% occupancy at R ≈ 25cm at 1035cm‐2s‐1 in 2.5mm x 100µm pixels

– => ~20Mpix x 24bits => ~96,000 Gb/s

– on‐detector data reduction (or selective readout) essential

• Large fraction of low pT tracks– not useful for trigger– conceptually simple to measure– hit density means high combinatorials


Track‐trigger approaches – cluster width

• Method 1: Cluster width

• CW decreases with PT– Can eliminate low PT tracks

– Simple on‐chip approach

• But, would like thinner sensors– (radiation, material)

– Maybe limits method to higher radii

• No info for z‐vertex at L1

Track‐trigger approaches – stacked layers

• Method 2: Stacked layer(s)

• Closely stacked layers ~1mm separation

• PT cut set by angle of track in stack• Compare pattern of hits in stack

• (Off detector) Correlate track stubs from multiple stacked layers

• Z‐coordinate from 2mm pixel length

• But, power hungry, heavy and requiring a lot of development

Upper Sensor

Lower Sensor

Pass Fail

~100μm

~1mm

Simulation results

• Sensors untilted (no Lorentz compensation)


R ≈ 25cm10,000 di‐muon events

Row window = 3 pixelsColumn window = 2 pixels @ 0.5mm;

3 pixels @ 1mm‐ 2mm

Row window optimised for each sensor separation setting

ΔR [mm] εmax [%]Fake [%]

Reduction factor

0.5 99.0 0.7 8.0

1.0 99.4 4.1 22

2.0 97.7 17.8 96

3.0 96.0 39.0 210

4.0 92.9 47.2 254

M Pesaresi

Making a trigger

• Stubs provide track trigger primitives

• Not yet proven how these contribute to trigger– and rate reduction achievable

– many simulation studies under way

– expect to match a series of stubs to a calorimeter or muon object• using off‐detector processors

• Questions to answer include– how many layers are needed?

– what is the optimal location, allowing sufficient η coverage?– what is the impact of material? – in trigger layers and elsewhere

– how important is z‐measurement, and resolution?

– what is the impact on tracking performance?

– cost, power and material budget?

– L0 trigger to guide?


Tracking at SLHC

Tracking with Phase 2 detector

• Want to maintain (if not improve) tracking performance

• Current Tracker has a lot of material – modules, power cables,

cooling, support structures

– Particularly between barrel and endcaps

Ref: J. Inst CMS paper, 200

Layout tool

• Positioning of modules in barrel layers and endcap disks

• Material for supports, power cables, cooling etc..

• Outputs:

– number of hits per track

– radiation and interaction lengths

– occupancy

– number of channels

– silicon area Material budget validated against current Tracker Outer Barrel

D Abbaneo et al

Example of layout under investigation

• “Hybrid” layout

• 2x barrel ‘PT layers’• R1~22cm, R2~35cm

• Stacked modules

• 100um x 2mm pixels

• ‘Outer Tracker’– Barrel plus endcap

– Strips 2.5cm, 5cm, ~100μm pitch

Assumptions for powerReadout: 0.5 mW / channelPT: 0.1 mW / channel2 W / GBT optical channel

General concepts

• Strip length reduced to ≈ 5 or 2.5 cm to cope with particle density• Hybrids mounted on sensors. One hybrid serving two rows of strips• Pitch adapter integrated on hybrid (or on sensor) • Power through wires, data through twps, no large PCBs• Optical links (GBT) integrated at the end of the rods (periphery of disks)

– GBTs receive twps from modules– Assume TOB twps, for the time being

• Power converters integrated on small separate PCBs, one per hybrid• Mechanics and cooling contacts adapted from present TOB

– Assume CO2 cooling

• For material modelling take wires, connectors and all other elements from TOB– A priori pessimistic– Should ensure that nothing relevant is forgotten

41

Modelling of Outer Layers (readout only)

42

3D design by Antonio Conde Garcia

Integration studies @CERN

Thermal modelling @ UCSB

Susanne Kyre, Dean WhiteFirst results very encouraging

Outer readout

• Present architecture– analogue, unsparsified, analogue optical links, synchronous

– external digitisation, cluster finding, zero suppression

– 0.25µm CMOS, FP edge‐emitting lasers, single‐mode fibres

• Future– unsparsified binary readout

• 2.5 ‐ 5cm µstrips, 0.5mW/channel

• DC coupled

• 130nm CMOS – submit Spring 2010

– + digital links (CERN GBT + VOL)


pipe. control

FE amp comp. digital pipeline

digitalMUX

vth

vth

vth

vth

256 deep

pipeline+

32 deepbuffer

testpulse

biasgen.

fastcontrol

slow control

CMS Binary Chip

CBC preamp: 35µm x 108µm

44

0.13μm preamp/shaper – 2 supply rails only

IPRE

IPSF

ISHA

ISSF

CSENSOR

Cfp

CC

Cfs

Cload

simulated FE amplifier performance

for short strips (CSENSOR ~ 5 pF) choose preamp andshaper input device currents (and Rfs) to achieve50 and 20 nsec CR-RC pulse shapes

0.96

0.94

0.92

0.90

0.88

0.86

volts

3002001000nsec.

50 ns 20 ns

simulated pulse shapes (CSENSOR = 5 pF)

Rfs

peaking time

50 ns 20 ns

IPRE [uA] 40 90

IPSF [uA] 15 15

ISHA [uA] 10 30

ISSF [uA] 35 15

total [uA] 100 150

power [uW] 120 180

noise [e] 800 890

=> for short (~few cm) strips can get quite goodpreamp/shaper noise performance for > factor 5 less than APV (~1 mW) even with only 2 rails

speed

pipe capacitance

0.13 μm simulation example

M RaymondTWEPP 08

Layout variant

• Large effort in developing SLHC tracking simulations

• Started from tools hard‐wired to current CMS TK geometry

• Now working with similar geometries to layout tool Ambitious, all trigger layer, concept

Layout tool results: Outer Tracker (‘hybrid’ layout)

• 19M strips – (85m2, 12kW, 1700 optolinks)

• Lightweight

• Could be done with very few module geometries

<radiation length> [0<η<2.4]: 12 %

<interaction length> [0<η<2.4]: 3.7 %

Layout tool results: PT layers (‘hybrid’ layout)

• 115M pixels in PT layers – (27m2, 24kW, 6300 optolinks)

• (As expected) PT layers dominate the power and material!

<radiation length> [0<η<2.4]: 52 %

<interaction length> [0<η<2.4]: 15 %

PT module schematic

Geoff Hall HPT7 Sep 2009 48

concentrator

sensor

ROC

assembler

PCB

PCB

~2mmR‐φ section

80mm

data outcontrol in

26mm

φ

z

φ

R

custom part or integrated into PCB

Alternative, vertically integrated, design

Geoff Hall HPT7 Sep 2009 49

250um150 um100 um800 um100um150 um250 um

Substrate

…

…

7.2 mm

TFEA TFEA TFEA

z

R

Read Out16 mm

other service functions

φ

R

Sensor

Sensor

A Marchioro

low profile wire bonds

• Basic module: ROC ASICs bump bonded to sensor

z

Conclusions

• CMS is trying systematically to develop a new Tracker design– using simulations to define new layout

– Aim to match performance of the present detector• would like to reduce the material budget

• The largest challenges are– power delivery and distribution

– provision of triggering data

– but many developments of sensors, readout, cooling,….

• The building of LHC experiments was an amazing achievement– this is even harder

– the objectives may evolve, along with machine and experiment performance


BACKUPS



Calorimeter Algorithms

e/photon

tau jet

• Electron/photon– Large deposition of energy in

small region, well separated from neighbour

• tau jet– Isolated narrow energy

deposition

– simulations identify likely patterns to accept or veto

Jet triggers

• The rates for electromagnetic triggers as a function of threshold for various types of event (left: jet events, middle: H‐>4e, right H‐>γγ) at a luminosity of 2x1033 cm‐2.s‐1[Physics TDR Vol 1]. Scaling to 1035 cm‐2.s‐1, it is clear that typical single isolated electron rates would be far higher than tolerable for practical thresholds.


Electron triggers

• Rejection vs efficiency for electron identification obtained from the HLT pixel matching and low (left) and high (right) luminosity [Physics TDR Vol 1]. The upper curve shows the performance with the existing pixel detector.


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