The LHCb Silicon Tracker M. Needham University of...

The LHCb Silicon Tracker

M. NeedhamUniversity of Zurich

on behalf of the LHCb Silicon Tracker group:

Heidelberg-Kiev-Lausanne-Santiago-Zurich

6th International Conference on Large Scale Applications and Radiation Hardnessof Semiconductor Detectors

FirenzeSeptember 29th-October 2nd, 2003

The LHCb Silicon Tracker page 1M. Needham

University of Zurich

The LHCb Silicon Tracker

• LHCb dedicated 2nd generation B physics experiment at LHC

• Single forward arm spectrometer covering 2 < η < 5

• Silicon Tracker project:

– Inner part of 3 tracking stations after magnet (IT)

– Large area tracking station in front of the magnet (TT)

– Total Silicon area 12 m2, ∼ 306 k readout channels

– Project moving from R+D to construction phase

��

100��

M1

M3M2

M4 M5

RICH2HCAL

ECALSPD/PS

Magnet

T1T2T3

z5m

y

5m

− 5m

10m 15m 20m

TTVertexLocator

RICH1



Silicon Tracker: Requirements:

Minimize material ⇒ thin detectors• Minimize secondary interactions– Keep detector occupancy low– Particles should traverse entire detector• Minimize multiple scattering– Dominates momentum resolution

Provide high efficiency with fast shaping• bunch spacing 25 ns• Fast shaping ⇒ large noise

Minimize number of readout channels• Hit resolution 70 µm ⇒ pitch 200 µm• Long ladders ⇒ large capacitances (noise)

Goal: optimize noise and charge collectionefficiency

Radiation enviroment ∼4 MRad (max) after 10years



The Inner Tracker

21.8

41.4

52.9

125.6

36.35 36.35

19.8

• 3 stations after magnet (4 m2 Silicon)• 2% area but 20% tracks• Station made of 4 independent boxes• Box provides thermal insula-

tion/electrical shielding• Ladders mounted on cooling plate

and operated at 5◦C– Leakage currents contribute less

than 10% to total noise after 10years

• Each box ⇒ 4 layers (0◦,±5

◦, 0◦)



Inner Tracker

• 320 µm thick p-on-n Silicon strips

• Sensors produced from 6” wafers

• (1 Sensor) 11 and (2 Sensor) 22 cm ladders



TT: The Trigger Tracker

• Integral part of Level-1 trigger• 4 layers of Silicon upstream of mag-

net• Arranged in 2 half stations separated

by 30 cm• Split gives some track direction in-

formation• Ladders 11, 22, 33 cm in length

3 0

3322

11

132

3322

11121

T T a T T b

120.

8

1 5 . 1 5

117.

1

1 4 3 . 7

7.7



Trigger Tracker

• Same geometry sensors as IT• 11 (12) sensor long ladders sup-

ported by Carbon fibre rails• 5 (6) readout sensors per ladder• Box providess electrical/thermal in-

sulation• Detector will be operated at 5◦C• Cooling plates in detector frames

(outside acceptance)

X

Z

77

78

3 3

6.5



Trigger Tracker

• Hybrids located outside acceptance ⇒ minimize material

• Kapton interconnects up to 55 cm in length to take out signals

• First prototypes (no backplane) 0.17 pF/cm ⇒ acceptable pickup noiseperformance in lab

• New prototypes (with Cu mesh backplane) 0.50 pF/cm ⇒ added robustness inLHCb

• Approximately equal total loads for all ladders



Front end: Beetle chip

Beetle 1.2 readout chip:

• Custom developed 0.25 µm CMOS, 40 MHz clock

• Irradiated up to 45 MRad with no significant loss in performance

• Risetime ∼ 14 ns

• Programmable parameter (Vfs) to set signal shaping

– Trade-off betweeen noise and signal remainder afer 25 ns

• Noise 450e− + 47e− × C/pF , for fastest shaping



IT Prototype ladders

• Test of prototype ladders for IT de-scribed in TDR (LHCC 2001-040)

• Show S/N ∼ 12 can be achieved for22 cm long 320 µm ladders

• 320 µm Silicon baseline for IT• What about TT ?



TT Prototype ladders

5 test ladders constructed to study:

• 1,2 Sensor IT ladders ⇒ Performance with Beetle 1.2

• Determine optimal thickness for TT sensors

Sensors available for TT prototypes:

• LHCb multi-geometry sensors

– Used for IT prototyping

– 2 pitches (198 µm, 238 µm)

– 4 different w/p

• CMS-OB2 sensors

• GLAST2000 sensors

Ladder Thickness/µm Strip Length/cm Capacitance/pF Pitch /µm

LHCb3 320 32.4 52.6 198/240

Glast 410 26.3 43.3 228

CMS 520 28.9 39.6 183



Sensor characteristics

Depletion voltage

0

0.05

0.10

0.15

0.20

0 20 40 60 80 100 120bias voltage [V]

1/C

2 [1018

/pF

2 ]

LHCb sensors

Sensor 1Sensor 2Sensor 3Sensor 4Sensor 5

0

0.1

0.2

0.3

0.4

0 20 40 60 80 100 120bias voltage [V]

1/C

2 [1018

/pF

2 ]

GLAST sensors


0

0.1

0.2

0.3

0.4

0 50 100 150 200 250 300bias voltage [V]

1/C

2 [1018

/pF

2 ]

CMS sensors


1

1.2

1.4

1.6

1.8

tota

l spe

cific

cap

acita

nce

[pF

/cm

]

GlastCMSLHCb Reg. ALHCb Reg. BLHCb Reg. CLHCb Reg. DLHCb Reg. E

• Total strip capacitances• Agree well with ANSYS finite el-

ement model



Laser test-stand

• First measurements on ladders madewith a Laser setup

• 1063 nm Nd:YAG Laser• Stepper motor to allow position scans• Micrometer screw for height adjust-

ment (focusing)• ∼ 12 µm spot size achieved• Studies of pulse shape• HV scans• Charge sharing



Laser test-stand II

time/ns0 20 40 60 80 100 120 140 160 180

AD

C C

ount

s

-20

-10

0

10

20

30

40

50 hit stripleft neighbourright neighbour

• Example delay scan for LHCb1• Laser positioned close to Al• Signal on neighbouring strips

reproduced in simulation takingaccount of capacitive coupling

capacitance/pF

Rem

aind

er

LHCb1

LHCb2CMS

GLASTLHCb3

Vfs 0 mV

Vfs 400 mV

Vfs 1000 mV

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

10 20 30 40 50 60

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

800 850 900 950 1000 1050 1100 1150 1200 1250 1300

noise/e-

Rem

aind

er

Vfs 1000 mV

Vfs 400 mV

Vfs 0 mV

LHCb1



Testbeam 2003

• Testbeam at CERN-X7 May/June 2003 with 120 GeV π− beam

• Beam telescope provided by Hera-B vertex group (14 µm resolution)

• Ladders and telescope mounted on rails in common detector box

• Hera-B readout chain

• Analysis so far concentrated on the GLAST, CMS, LHCb3 ladders



Testbeam Results

S/N0 10 20 30 40 50

clus

ters

0

200

400

600

800

1000

1200

1400

1600

1800

2000 LHCb3 ladder (V= 200V)

associated clusters

non associated clusters

S/N0 20 40 60 80

clus

ters

0

2000

4000

6000

8000

10000 GLAST ladder (V= 200V)

associated clusters


S/N0 20 40 60 80

clus

ters

0

1000

2000

3000

4000

5000

6000

7000

8000CMS ladder (V= 450V)

associated clusters


sensor position

S/N

LHCb3 ladder Glast ladder CMS ladder6

8

10

12

14

16

18

20

22

24

Near Middle-Near Middle Far-Middle Far

• Low S/N performance for LHCb3sensor ladder

• Investigate S/N dependence alongladder• Performance independent of position



Testbeam Results II

track position0 0.2 0.4 0.6 0.8 1

S/N

0

5

10

15

20

25 LHCb3 ladder (Vbias = 200V)

track position0 0.2 0.4 0.6 0.8 1

S/N

0

5

10

15

20

25 GLAST ladder (Vbias = 200V)

track position0 0.2 0.4 0.6 0.8 1

S/N

0

5

10

15

20

25 CMS ladder (Vbias = 450V)

track position0 0.2 0.4 0.6 0.8 1

effic

ienc

y

0.90

0.92

0.94

0.96

0.98

1.00

LHCb3 ladder (Vbias = 200V)

track position0 0.2 0.4 0.6 0.8 1

effic

ienc

y

0.90

0.92

0.94

0.96

0.98

1.00

GLAST ladder (Vbias = 200V)

track position0 0.2 0.4 0.6 0.8 1

effic

ienc

y

0.90

0.92

0.94

0.96

0.98

1.00

CMS ladder (Vbias = 450V)



Testbeam Results III

Vfs[mV]

S/N

LHCb3 ladder Glast ladder CMS ladder6

8

10

12

14

16

18

20

22

24

0 200 400 600 800 1000Vfs[mV]

Effi

cien

cy o

n st

rips

LHCb3 ladder Glast ladder CMS ladder0.90

0.92

0.94

0.96

0.98

1.00

0 200 400 600 800 1000Vfs[mV]

Effi

cien

cy b

etw

een

strip

s

LHCb3 ladder Glast ladder CMS ladder0.90

0.92

0.94

0.96

0.98

1.00

0 200 400 600 800 1000

S/N performance for 320 µm Silicon not sufficient for 33 cm long ladders

• Significant loss of clustering efficiency between strips

• 410 µm Silicon sufficient for TT station



Summary

LHCb Silicon tracker

• 12 m2 Silicon

• 306 k readout channels

• Strip pitch 200 µm

• Strips up to 33 cm in length

• Fast readout

Testbeam shows

• 320 µm sufficient for IT (22 cm long ladders)

• 410 µm needed for TT (33 cm long ladders)

R+D phase ending ⇒ detector construction starting



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