The LHCb Silicon Tracker ProjectJohan Blouw, for the Silicon Tracker Group

Max Planck Institute for Nuclear Physics

The LHCb Silicon Tracker Project – p. 1/12

Overview• Introduction• LHCb Spectrometer• Trigger Tracker• Inner Tracker• Readout Chip• Testbeam Results• Outlook

The LHCb Silicon Tracker Project – p. 2/12

Introduction• study CP violation and rare B meson decays with

very high precision• provide understanding of quark flavour physics in

Standard Model• reveal signs of physics beyond Standard Model• at LHCb: 1012 bb̄ pairs per year

The LHCb Silicon Tracker Project – p. 3/12

Introduction• At LHC, bb̄ pairs produced at forward and

backward angles

(rad)1θ

0 0.5 1 1.5 2 2.5 3(rad)

2θ

00.5

11.5

22.5

3

• construct a forward-angle spectrometer

The LHCb Silicon Tracker Project – p. 3/12

LHCb Spectrometer

The LHCb Silicon Tracker Project – p. 4/12

Requirements• 40 MHz interaction rate → good event rejection

needed.• measure PT in Trigger Tracker for use in L1

trigger.• match granularity to particle density

(5 × 105 cm−2s−1) around beam-pipe• good (∼ 100%) hit finding efficiency• low (∼ 1%) occupancy for pattern recognition• excellent δp/p ≈ 0.4% resolution for

reconstruction of Bs mass

The LHCb Silicon Tracker Project – p. 5/12

Trigger Tracker• 28.3 and 37.7 cm long modules per ladder

• cover full acceptance with silicon (total of 8.3 m2)

• located in fringe-field in front of dipole magnet

• operated at 5◦ Celcius

The LHCb Silicon Tracker Project – p. 6/12

Trigger Tracker

• two stations with each two planes in an (0, 0′) and(−5◦, 5◦) stereo-angle configuration

• connect inner modules with flexible Kapton cableto read-out frontends

The LHCb Silicon Tracker Project – p. 6/12

Inner Tracker• located in proximity of beampipe behind magnet• 1.3% area, but 20% of tracks• three stations, four boxes of four layers each

around beampipe (0◦, +5◦,−5◦, 0◦)

The LHCb Silicon Tracker Project – p. 7/12

Inner Tracker

• 110 × 78 mm2 sizesensors

• 1- and 2-sensorladders

• 197 µm pitch• operating tempera-

ture 5◦ C

The LHCb Silicon Tracker Project – p. 7/12

Ladder Design• 6′′ wavers, n-bulk, p+-strips• single-sided sensors• dead-area of < 2 mm between sensors on

multi-sensor ladder

The LHCb Silicon Tracker Project – p. 8/12

Front-end

• Beetle chip developed byASIC lab in Heidelberg

• 128 channel chargeintegrator

• sampling at 40 MHz

• 25 ns shaping time• 0.25 µm CMOS technology• complete Beetle read-out in 900ns• three Beetle front-end chips per hybrid

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Test Beam

• study pulse shapes ondifferent loads

• signal remainder• tracking efficiency• study signal-over-

noise behaviour for• different substrate thicknesses• different ladder lengths (capacitive load)

Set-up at CERN’s X7 testbeam facility• use charged π beam• tracking performed by HERA-b beam-telescope

The LHCb Silicon Tracker Project – p. 10/12

Test Beam

track position0 0.2 0.4 0.6 0.8 1

S/N

0

5

10

15

20

25

CMS ladder (Vbias = 450V)

500 um

track position0 0.2 0.4 0.6 0.8 1

S/N

0

5

10

15

20

25

GLAST ladder (Vbias = 200V)

410 um

track position0 0.2 0.4 0.6 0.8 1

S/N

0

5

10

15

20

25

LHCb3 ladder (Vbias = 200V)

320 um

500 µm thick 410 µm thick 320 µm thick180 µm pitch 228 µm pitch 198 µm pitch

The LHCb Silicon Tracker Project – p. 10/12

Test Beam

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)

500 um

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)410 um

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)320 um

• signal drop in between two strips due to chargeloss

• impact on efficiency for S/N < 10

• signal drop largest for thinner substrates

The LHCb Silicon Tracker Project – p. 10/12

Test Beam

delay [ns]

sign

al c

harg

e [A

DC

cou

nts] CMS ladder (V=450V)

central strip

left neighbour

right neighbour

left neighbour - 1

right neighbour + 1

-20

-10

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140 160

• signal remainder after 25 ns < 50% of peaking time

• mirror charges arrive quicker

• Beetle tuned to accomodate various load capacitancesThe LHCb Silicon Tracker Project – p. 10/12

Impact on Physics• thicker substrates → reconstruction efficiency loss

• test the impact of thicker substrate with Monte Carlo

• for instance Bs → DsK and Ds → K+K−π:

IDMeanRMS

48-0.8173E-01

1.468

(prec-ptrue)/σp

Eve

nts/

[0.1

2σ]

0

500

1000

1500

2000

2500

3000

3500

x 10 2

-6 -4 -2 0 2 4 6

DsMassEntries 31326Mean 1.97

RMS 0.01534

]2Mass [GeV1.94 1.95 1.96 1.97 1.98 1.99 2

]2C

nts/

[GeV

0

200

400

600

800

1000

1200

1400

1600

1800

2000

DsMassEntries 31326Mean 1.97

RMS 0.01534

DsMassEntries 31326Mean 1.97

RMS 0.01534

Ds Mass (before mass constrained fit)

µ1 = −0.136, σ1 = 1.15 µ2 = −0.133, σ2 = 1.15

The LHCb Silicon Tracker Project – p. 11/12

Conclusions• minimal substrate thickness: 410 µm for

multisensor ladder• no adverse effect on tracking and physics

performance

• large pitch: 200 µm

• long strips: 10 − 30 cm

• fast read-out: O(25 ns)

• signal remainder < 50%, 25ns after peak• ∼ 300, 000 readout channels

The LHCb Silicon Tracker Project – p. 12/12