LHCb Silicon Detectors: The Run 1 to Run 2 transition ......MPV Module Number: 36, R: All-1 = 0.04...

LHCb Silicon Detectors:The Run 1 to Run 2 transition

&First Experience of Run 2

Kurt Rinnert

On behalf of the LHCb VELO & ST Groups

VERTEX 2015Santa Fe, 1 – 5 June 2015

The LHCb Detector

More on tracking in Stefano’s talk (up next)

LHCb VELO & ST — VERTEX 2015 — Santa Fe, 1 – 5 June 2015 1 /28

The Vertex Locator (VELO)

Retractable detector halves21 R/Phi modules per half+4 R-type PU veto2048 strips on each sensorPitch varies from 40 μm to100 μmBest hit resolution 4 μmFirst strip at 8.2 mmOperates in secondaryvacuumBi-phase CO2 cooling,Si at -10 ◦CSeparated from beam vacuumby 300 μm thick Al foil


The Tracker Turicencis (TT)

~30 cm

TTb

TTa

zy

x

132.

4 cm

157.2 cm

132.

4 cm

138.6 cm7.

4 cm

7.74 cm

Silicon microstrip sensors,p-on-n by HPKThickness 500 μmStrip Pitch 183 μmReadout strip lengthup to 37 cm ⇒ up to 60 pF∼144k readout channelsTotal area: 8 m2

Sensors at ∼ 8◦ C99.7% working channels(Run I average)Resolution 53.4 μm


The Inner Tracker (IT)

21.8

cm

41.4

cm

125.6 cm

19.8 cm

Silicon microstrip sensors,p-on-n by HPKTwelve layersThickness 320 μm (1 sensor,11 cm) or 410 μm (2 sensors22 cm)Strip Pitch 198 μm∼130k readout channelsstereo angles ()0◦,−5◦,+5◦,0◦,Total area: 4.2 m2

Sensors ar ∼ 8◦ C98.6% working channels(Run I average)Resolution 54.9 μm


Evaluation of Radiation Damage

Methods with and without beam:

Current vs. temperature (IT)Changes of current vs. voltage (IV)Changes of effective depletion voltageCluster finding efficiency


Leakage Current (VELO)

Two contributions: bulk and surface currentSurface contribution negligible after irradiation

Bulk dominated beforeBulk dominated after

Surface dominated beforeBulk dominated after



Measurement of the effective bandgap energy.(T) ∝ T2ep(−Eg2kT )

Bulk dominated beforeBulk dominated after

Luminosity EgVoltage[fb−1] [eV][V]0.48 1.17 ± 0.07 ± 0.041000.48 1.18 ± 0.05 ± 0.041500.82 1.14 ± 0.06 ± 0.041501.20 1.15 ± 0.04 ± 0.04150

Literature: Eg = 1.21 eVLHCb VELO & ST — VERTEX 2015 — Santa Fe, 1 – 5 June 2015 7 /28


IV-scans performed weekly in data taking periodsBulk currents increase with fluence as expectedOccassional drops due to annealing

Sep2010

Feb2011

Apr2011

Jun2011

Aug2011

Oct2011

Dec2011

Feb2012

Apr2012

Jun2012

Aug2012

Oct2012

Dec2012

Feb2013

Cu

rren

ts [

mA

]

0

0.02

0.04

0.06

0.08 Individual Sensors

Mean - Measured

Mean - Predicted

LHCb VELO

]

-1 [

pb

int

L

2000

4000

6000

Delivered Luminosity

C]

oT

[

-20

0

20 Sensor Temperatures


Leakage Current (TT + IT)

Data normalised to a temperature of 8◦C (Eg = 1.21 eV)


Predicted Fluence (VELO)

Good agreement with predictionParticle fluences well understood

z [mm]0 500

% e

rror

0

0.5

1

1.5

2

2.5

3

3.5

4

z [mm]0 500

21

MeV

neu

tron

s cm

0

10

20

30

40

50

60

701210!

z [mm]0 500

% e

rror

0

0.05

0.1

0.15

0.2

0.25

z [mm]0 500

Cur

rent

[mA

]

0

0.02

0.04

0.06

0.08

0.1A Side PredictionC Side PredictionA Side R sensors

sensors"A Side C Side R sensors

sensors"C side

LHCb VELO!


Charge Collection Efficiency (VELO)

Use reconstructed unbiased tracksExtrapolate to test sensor and record nearby chargeVary voltage between 40 and 250 V

Same concept for ST, scans are simultaneous.


Charge Collection Efficiency (VELO)

Collect data for various bias voltages for each sensorFit the MPV distributionDefine effective depletion voltage (VED) as the voltagewhere MPV is 80% of maximum

ADC Counts-20 0 20 40 60 80

Rel

ativ

e n

um

ber

of

trac

ks

Charge_S36_V10_R_all

Bias voltage:

10V40V

70V

-1 = 0 pbL

LHCb VELO-1 = 0.04 fbL

Rel

ativ

e n

um

ber

of

trac

ks

Bias voltage [ V ]0 20 40 60 80 100 120 140 160

MP

V o

f AD

C C

ou

nt

Dis

trib

uti

on

0

5

10

15

20

25

30

35

40

LHCb VELO

R-type sensor

-type sensorφ

MPV Module Number: 36, R: All

-1 = 0.04 fbL

Same concept for ST, scans are simultaneous.


VED Dependency on Fluence (VELO)

VED decreases with fluence to a minimum of ∼18 V forn-type sensorsInversion point is 10 − 15 × 1012neqcm−2After inversion n-in-n increase at a similar rate as n-in-p


Comparison with Hamburg Model

Good agreement apart from inversion regionNo inversion observed for ST

VELO

fluenceeq1 MeV n1010 1110 1210 1310

Eff

ecti

ve D

eple

tio

n V

olt

age

[ V

]

10

20

30

40

50

60

70

80

Initial EDV:55 - 65 V45 - 55 V25 - 35 VHamburg model

Initial EDV:55 - 65 V45 - 55 V25 - 35 VHamburg model

LHCb VELO preliminary

ST


VELO VED Predictions for Run 2

Sensor VED at 4.4 fb−1 [V] VED at 10 fb−1 [V]

R 172 ± 12 432 ± 30ϕ 164 ± 11 404 ± 26

VED will no longer be uniform across sensorsDifferent voltage steps in CCE scansWell below 500 V in worst case


Second Metal Layer (VELO)

CFE depends on distance to routing linesEffect seems to reduce after type inversionNo effect on track finding efficiency observed

Y [mm]-50 -40 -30 -20 -10 0 10 20 30 40 50

X [m

m]

-10

0

10

20

30

40

50

CF

E [%

]86

88

90

92

94

96

98

100

LHCb VELO preliminary-1 = 3.4 fbL

m ]µRL distance [

Clu

ster

Fin

ding

Effi

cien

cy [

% ]

88

90

92

94

96

98

100

0 4 8 12 16 20 24 28 32 36 40 ~ 2000

d = distance to edge of nearest strip

m) < 0µd(m) < 5µ0 < d(m) < 10µ5 < d(

m) < 15µ10 < d(m) < 20µ15 < d(

LHCb VELO preliminary-1 = 3.4 fbL


Maintenance during LS 1

The detectors have been kept cooled and monitored.Regular scheduled operations to ensure all is well.The VELO LV system has been refurbished.The IT adjusted to nominal position and a new alignmentmonitoring system has been installed.Maintenance of VELO cooling & vacuum system and newcooling plant for ST.Some challenging times with the VELO under Ne and nobeam pipe attached.PVSS is now called WinCC/OA – manychanges/improvements to control infrastructure.

And more. . .


New ST Cooling Plant

Cooling performace degraded over Run1, due to lubricantcontaminating coolant.Manual recirculating necessary ervery 2-3 days.New Cooling plant installed for Run 2; better insulationneeded.


IT Postion

After installation of new beam pipe IT could be moved toits nominal position.New position monitoring system installed (BCAM).


VELO Maintenance Examples

VELO under Ne w/o beampiperequired installing mechanicalsupport.Replaced LV bulk supplieswith A3485 units to mitigateconnector problems.VELO 2 (emergency spare)moved back upstairs.


Preparational Data Taking

TED

Shots on transfer linebeam absorber.Results in muon showersat LHCb in the upstreamdirection.Many parallel tracks,unlike collissions.Special timing settings.

SMOG

Injection of Ne in theprimary LHC vacuum atLHCb.Was done simultaneouslywith injection energy (450GeV) collissions.No stable beams declared,so VELO was open.Allowed to power becausebeams were “quiet”.


TED: IT Track Residuals

IT Top IT A-Side


TED: VELO Alignment

Translation along x

z [m m ]200− 0 200 400 600

m]

µ[x

T

10−

8−

6−

4−

2−

0

2

4

6

8

10TE D 14

2012

xR -sensors T

LHCb preliminary


SMOG: IT CLuster Distributions


SMOG: VELO Beam Monitor


Summary

The LHCb silicon detectors have been maintained &monitored well during LS1.Radiation damage is well understood.Many improvements have been put in place over LS1.The detectors performed well during injection line testsand first collision runs.We will be recording data with stable beams this week!

VELO & ST are in good shape and ready for LHC Run 2


References

PerformanceInt. J. Mod. Phys. A 30 (2015) 1530022J. Instrum. 9 (2014) P09007Radiation DamageJINST 8 (2013) P08002

http://arxiv.org/pdf/1412.6352.pdfhttp://arxiv.org/pdf/1405.7808.pdfhttp://arxiv.org/abs/arXiv:1302.5259

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LHCb Silicon Detectors: The Run 1 to Run 2 transition ......MPV Module Number: 36, R: All-1 = 0.04...

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