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The LHCb Vertex detector

15/9/2003

• Physics– Goals– Properties and consequences

• LHCb– Overview of the detector

• Vertex– Specifications– Silicon stations– Overview– Details– Radiation hardness– Read-out chip developments

• Conclusions & ProspectsVertex2003, Sander Klous (on behalf of the LHCb

collaboration)

2

PhysicsGoals

Current status

• Investigate difference between Matter and Antimatter

• CP violation in standard model– Rotation between mass

eigenstates and weak eigenstates (CKM matrix)

– Expressed with Wolfenstein parameterization

• One of the 6 Unitary Triangles– Order or 2 for all sides

nWolfensteielementsCKM

AiA

A

iA

VVV

VVV

VVV

tbtstd

cbcscd

ubusud

1)1(

21

)(2

1

23

22

32

Accessible by LHCb

cdcb

tdtb

VV

VV*

*

0 1

Bs DsK

cdcb

udub

VV

VV*

*

Bs Ds

3

PhysicsProperties and consequences• You want B decays!

– B’s are heavy– Results from B – factories– LHCb offers

• Bs production• Higher yield

– Over constrained triangle

• LHC Production channel– Gluon fusion~ 1012 bb pairs a year– Boosted system (decay

length)

P

P

b

b

P

P b

b

Angular coverage• 15–300 mrad in bending plane• 15-250 mrad in non-bending plane

4

LHCbOverview of the experiment

Luminosity: 2 . 1032 cm-2s-1

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Vertex detectorSpecifications

• Forward detector– Detectors only 8 mm from beam– 360º coverage in

• overlapping detectors• Low number of pp interactions per event

– In level-0 trigger (40 MHz)– Pile – Up detector

• Trigger on high pt displaced tracks– In level-1 trigger (1 MHz)– Standalone track reconstruction– Use stray field to select high pt

• Identify Bs oscillations– Vertex resolution:

17 m + 32m/pt 44 fs (Ds– 5 sensitivity to Bs oscillations with:

ms = 68 ps-1

• Tight material budget

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y

x

y

x

z

R

Vertex has standalone track and vertex reconstruction (Projection in

R-z plane)

Vertex detectorSilicon stations

45º segments

Second metallayer

42 mm8 mm

pitch from 40 to 103

m

Highest x-y resolution naturally

closest to interaction region

Stereo -20° and 10°

A

A

21 + 2

Thickness 220 mTemperature -5 ºCCO2 Cooling system

1meter

Pile - Upstations 250 mrad

15 mradAA

Interaction region = 5.3cm

Trigger:Talk on

Wednesday,Thomas

Schietinger

7

Vertex detectorOverview

Silicon stations in vacuum

Retractable detector halves

for beam injection

Thin exit foil

R detector

Phi detector

Beam

Detector onX-Y tables

8

Vertex detectorDetails

Bellows to accommodate

retractable detector halves

• 250 m thick• Complex shape (overlapping detectors)• Super plastic, hot gas formation

Thin separation between silicon

stations and beam

• Secondary vacuum• RF shield• Wakefield guide• Controlled pressure

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Middle station

Far station

Vertex detectorRadiation hardness

Radiation hardness• Replace detectors every 4 years

– Maximum irradiation per station5 x 1012 to 1.3 x 1014 neq/cm2/year

• Detector could have undepleted layer after irradiation– Resolution of p on n detector degrades fast

• Undepleted layer insulates strips from bulk– n on n ~100% efficient for only 60% depletion depth

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Beetle was selected in January 2003• Used in Vertex Detector and Silicon

Trackers• 0.25 m CMOS technology

– Intrinsically radiation hard– Single Event Upsets

– Triple redundant logic

• Analogue and digital output• Digital output used in level-0• Analogue output used in level-1

Read-out (Beetle)Introduction

x 186

x 128

Vpre

Ipre

Vsha

Isha IbufMux

to comparator (digital out)

In Out

Pipelinecells

Front-endsFront-end

Readout

Pipeline

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Read-out (Beetle)Analogue specifications

• 40 MHz clock frequency• 1 MHz read-out• Signal / Noise > 14• Rise time < 25 ns• Spill over < 30 %

Beetle1.1• Tested in SPS beam• 16 chips on 1 hybrid• PR02-R p-on-n detector

90%

10%

Rise time

Spill over

25 ns

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noise BaselineSignal

3 ns

3 ns

• Goal– Optimize performance– Check chip behavior

• 16 chips on 1 hybrid• Test beam environment

• Mimic LHCb operation– Sampling mode– Sampling rate

• Took 10 million events

Read-out (Beetle) Analysis

Peak

Spill over point

Convolution ofLandau and Gaussian

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enc

(e- )

Detector bias =70 V Isha ( A) Ipre ( A) Vfs (mV) Events (M)1 Pulse shape scan, various settings and chips various 350 various 32 High statistics run on chips 0, 1, 2, 3, 4, 7 32 350 400 1

Detector bias =150 V3 Pulse shape scan, chips 8, 9, 10, 13, 14, 15 32 350 various 1,44 High statistics run, chips 8, 9, 10, 13, 14, 15 32 350 700 15 Confirmation runs, all chips 32 350 various 1,66 Single time sample run 32 350 700 17 High trigger rate run 32 350 700 1

Total 10

Read-out (Beetle)Results

Threshold = 14

Efficiency

Hits from previous

bunch crossing

Average capacitance: 10 pFSignal/Noise = 17.4 0.2Spill over = 36.1 % 1Rise time = 23.5 ns 0.5ENC = 500 + 50 e-/pF

Detector capacitance : 6 - 14 pFResulting S/N range: 14.5 -

21.5

14

Time1 2 3 4 5 6 70

Time sample

Continuous beam

Read-out (Beetle)Mimic sampling

mode/rateMimic sampling rate1. Occupy read-out circuit

• Send test pulses at high rate2. Mix with physics triggers3. Let ADC only read physics triggers

No deteriorating effects were found• Test beam mode: 19.7 0.2• Single time sample: 19.6 0.2

• Test beam mode: 18.7 0.2• High trigger rate: 18.7 0.2

Note: comparison with other settings

Time1 2 3 4 5 6 70

Time sample

Test beam mode

1

LHCb sampling mode

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Silicon and Read-outTo do

Beam test with irradiatedCzochralski silicon

To do:• Analysis of beam tests

– Irradiated Czochralski silicon– Single Beetle1.2 chip

• Beam test with new hybrid– 16 Beetle1.2 or 1.3 chips on

hybrid• Thinner detectors• 3D detectors ???

High resistance High oxygen content

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Conclusions

• LHCb is a next generation experiment for CP violation measurements• The vertex detector for LHCb is a mechanically challenging project

– Production has started• The silicon and hybrid developments are in their final phase

– Results from the beam test with irradiated Czochralski silicon are coming– The new hybrid will be tested in the test beam with 16 Beetle1.2 chips

• The Beetle read-out chip developments are in their final phase as well– Version 1.1 is extensively tested and complies almost with specifications– Version 1.2: a single chip is just tested in the test beam– Version 1.3 is the final version and is submitted on a MPW run in June

• Next year, system tests will start• The construction of the LHCb vertex detector is on track

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• Level-0 trigger combines– High pt info from calorimeters and muon

detectors– Pile - Up information from Pile – Up detector

• Counts number of primary vertices per event• 2 dedicated stations in the vertex detector• Digital read-out at 40 MHz• Outside acceptance

• Level-1 trigger– Identify displaced tracks at 1 MHz

• Low occupancy• High efficiency• R/Phi configuration

• Match with high pt tracks

Trigger:Talk on Thursday,

Thomas Schietinger

Vertex

Station: A B

ZA ZB

RARB

RA/RB = ZA/ZB = k

LHCbVertex and Trigger

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PhysicsProperties and consequences

• You want B decays!– B’s are heavy– Results from B – factories– LHCb offers

• Bs production• Higher yield

– Over constrained triangle

• LHC Production channel– Gluon fusion~ 1012 bb pairs a year– Boosted system

P

P

b

b

P

P b

b

20

LHCbSpecifications

• Angular coverage– 15–300 mrad in bending plane– 15-250 mrad in non-bending

plane• Trigger on displaced vertices• Excellent vertex resolution• Single pp interactions• Particle identification

– K/ separation– Flavor tagging– 1 – 150 GeV

For Bs decay is in the order of a few mm