STAR Silicon Vertex Tracker Detector (SVT) Update

Vertex 2002 - Nov

STAR Silicon Vertex Tracker Detector (SVT)

Update

Nothing tends so much to the advancement of knowledge as the application of a new instrument - Sir Humphrey Davy (1778-1829)

Helen Caines -Yale University

Helen Caines

Vertex 2002 – Nov 2002

Helen Caines


Presentation Overview

● SVT Introduction● SVT Performance● Track-to-Hit Matching ● Vertex Reconstruction● Energy Loss● Strange Particle Decays● Summary & Conclusions

Helen Caines


Welcome to BNL- RHIC!

Helen Caines


The STAR Detector

• 1st year, 2nd year, year-by-year until 2003, installation in 2003

ZCal

Silicon Vertex Tracker *

Central Trigger Barrel+ TOF patch

FTPCs (1 + 1)

Time Projection Chamber

Barrel EM Calorimeter

Vertex Position Detectors

Magnet

Coils

TPC Endcap & MWPC

RICH * yr.1 SVT ladder

Endcap Calorimeter

ZCal

Helen Caines


SVT Installation

Installed for the first time2001-2 RHIC run

Helen Caines


p-p vs Au-Au at √sNN=200 GeV

Two very different environments:

p-p - Few tracks, primary vertex not well known

high luminosity

Au-Au – Few 1000 tracks

Vertex well located

Track/hit merging

Helen Caines


Each wafer is 6.3 cm x 6.3 cm area

300 m thick - 0.3%X0

Average radiation length seen by a particle 4.5%X0 incl. fee cards etc.

Consists of 216 wafers

3 Barrels

Outer radius – 15cm

Middle Radius – 10cm

Inner radius - 6cm

Length - 21cm

SVT Design

Inner barrel has 8 ladders – 4 wafers/ladderMiddle barrel has 12 ladders – 6 wafers/ladderOuter barrel has 16 ladders – 7 wafers/ladder

Helen Caines


Silicon Drift Detector - Principle

Ionizing particle

R - position from drift time

Electron cloud

X

SDD

Z - position from readout anode number

Drift time ~ 5 sec240 Anodes/wafer100 samples/anode

Gain : 1 e- = 7.2V 4 mV = 1 ADC

Helen Caines


Calibrations - Pedestals

You can see the edges of the 15 PASA’s and more obviously the

3 analogue buffers where the multiplexing occurs

Anode

First Time bucket

Other 127 Time buckets

Pedestal Subtraction done online

96.5% of 103,680 channels operational91.2% of 103,680 channels used in analysis

Helen Caines


SVT Performance

Noise: 7 mV for pp 12 mV for Au+Au (due to a

grounding problem now fixed)

4 mV design (<7 mV aim)

cm

cou

nts

•30 m resolution reproducibility

Helen Caines


Drift Velocity Calibration

SDD’s modeled using 2 drift velocities. One in the drift region and one in the focusing region

There is a temperature dependence across the wafer which must be accounted for.

Helen Caines


SVT Temperature Control

Au-Au

60

62

64

66

68

70

72

74

76

1/19/200212:28

1/19/200212:57

1/19/200213:26

1/19/200213:55

1/19/200214:24

1/19/200214:52

1/19/200215:21

1/19/200215:50

1/19/200216:19

1/19/200216:48

1/19/200217:16

Time

Tem

per

atu

re (

Far

enh

eit)

72

72.5

73

73.5

74

74.5

75

9:57 10:04 10:12 10:19 10:26 10:33

Time

Tem

per

atu

re (

Far

enh

eit)

Helen Caines


Hit to Track Matching

Au-AuMixed eventsClosest hit

Are we matching correctly?

Au-AuClosest hitReal events

Yes!

TPC inner radius = 50cmSVT outer radius = 15cm

Project tracks from TPC to SVT

Helen Caines


Drift Residuals vs Wafer

Before Alignment

After Alignment

Magnitudes agree with survey results

Shifted center of SVTRelative to TPC by x=-0.276cm y=-0.82cm

1 2 3

Helen Caines


Using SVT for TPC Calibration

Track dip angle < 0.1

Shift in Z + TPC T0/Vdrift wrong

mean (Z) = 0.0526cm vdrift = 5.56 cm/secTPC T0 shift = 0.0526/5.56 = 9.46 x 10-3 sec

After Corrections

Helen Caines


Vertex Finding - Resolution

p-p

Z offset of 0.005cm – Aligned in Z

STAR Preliminary

Helen Caines


Anode Residuals vs pt

Au-Au

Pt resolution worse at low pt where energy loss and scattering not yet taken into account

STAR Preliminary

Helen Caines


Primary Matching “efficiency”

Efficiency is defined as thenumber of tracks with SVT hits added (2 or more)p-p

p-p

Flat in pt

If you go to ±30cm average effic is 45%

Expect ~85% from simulation of perfect detector

Helen Caines


Impact Parameter Improvement

pp:

Mean 0.7->0.51 cmRMS 0.59->0.48 cm

TPCTPC+SVT

cm

3D impact parameters of track associated to primary vertex should be close to zero

Helen Caines


Energy Loss in the SVT Layers

● 3 sample maximum

● Higher energy resolution

● Good for low momentum

● Independent measure of dE/dx

● Allows 2D cut

Preliminary

Preliminary

Helen Caines


Strange Particle Decays

● Black is TPC only● Red is TPC+SVT

● Blue is TPC only● Red is TPC+SVT

Preliminary

Preliminary

~35-40% greater yield in K0s region

Mostly low pT

+

-

V0 Reconstruction

Helen Caines


Summary & Conclusions

✔ Sharpens the primary vertex reconstruction

✔ Improved PID

✔ More precise low pT tracking

✔ Enhanced analyses (already ~40% more K0)

➔ To Do:

●Improve noise reduction

●Understand track to hit matching

●Take more data!

Helen Caines


The STAR CollaborationRussia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - Protvino

U.S. Labs:ArgonneBerkeleyBrookhaven

U.S. Universities: Arkansas UniversityUC BerkeleyUC DavisUC Los AngelesCarnegie Mellon UniversityCreighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinWashington UniversityWayne State UniversityYale University

Brazil: Universidade de Sao Paolo

China: IHEP – Beijing,IMP - LanzouIPP – WuhanUSTCSINR – ShanghaiTsinghua UniversityEngland: University of Birmingham

France:IReS StrasbourgSUBATECH - Nantes

Germany: MPI – MunichUniversity of Frankfurt

India:IOP - BhubaneswarVECC - CalcuttaPanjab UniversityUniversity of RajasthanJammu UniversityIIT - BombayVECC – Kolcata

Poland:Warsaw University of Technology

Helen Caines


Track Matching

Helen Caines


Simulating Radial Mis-Alignments

Drift residual- No shift

Drift residual-With shift(x=2mm, y=0.8mm)

Barrel 1 Barrel 2 Barrel 3

Helen Caines


Next Year – SSD

The SSD:

Double sided silicon strip detectors 16 wafers per ladder

Stereo angle 35 mrad pitch 95 microns.

Detector size is 7.5cm x 4.2xm

300 microns thick. Resolution is:

15 microns in r

700 microns in z

radiation length of 1 ladder is 0.7%X0

Helen Caines


Simulation vs Data (2)

Black contours SvtSlowSim

Colour contours real data

Simulation under predicts the width

Helen Caines


Simulation vs Data (1)

Black contours SvtSlowSim

Colour contours real data

Noise in systemobvious as no change in peakADC as function of drift

Removed with cut

Helen Caines


Noise

Operational values close to bench measurements

Helen Caines


Anode by Anode Calibration

• Better dE/dx and better position resolution

• Can see edges of PASA (not sure why)• Performed by recoding mean charge

on Anode• Of many events assume min-ionising

and force• Each to a common mean

Helen Caines


Pedestal Subtraction

You can see the first time bucket noise and the first capacitor glitch

Have noise at 1st capacitor and in 1st time bucket

1st capacitor is more of a“problem” because it is in a random position each event.

1st time bucket doesn’t contain data

M. Munhoz

Helen Caines


Welcome to BNL- RHIC!

Helen Caines


Location and Identification of Noise

Noise defined as hits with r > 1cm from track

Clear ladders/wafers that are noisy and are eliminated offline

96.5% of 103,680 channels operational91.2% of 103,680 channels used in analysis

Helen Caines


Drift Velocity Calibration

SDD’s modeled using 2 drift velocities. One in the drift region and one in the focusing region

There is a temperature dependence across the wafer which must be accounted for.

Residuals as a function of drift distance from E896 data

Haven’t quite got focusing region correct

Helen Caines


Charge vs Drift

cmCenter of wafer

Drift Drift

Some evidence of“charge loss”~20%

Probably trouble in cluster analysis.

Also at long drift the hits are beginning to merge with the background which pulls down the total charge found

Helen Caines


Average Drift Residuals

Au-AuMixed eventsClosest hit

Au-AuAll hits

Are we matching correctly?

Au-AuClosest hitReal events

Yes!

Helen Caines


Drift Residuals – T0

T0 wrong by~3 timebins

Helen Caines


Occupancy vs Pile-up

High Luminosity

Low Luminosity

Pri

mary

Glo

bal

Pri

mary

Glo

bal

Good hits Good hits

Good hits Good hits

Helen Caines


-2

2

Match Track To CTB To Reject Pileup

Lower Luminosity (Early in Run) Higher Luminosity (Late in Run)

Track Matches CTB Hit

Track Projects To CTBCTB Match Eff. =

Good Measure Of PileupLower Matching Efficiency => Higher Pileup

Azimuth

1

0.5

00 180 360

Z P

osi

tio

n

Azimuth1800 360

Constant matching effic. during whole run.SVT only matches tracks from primary event

Documents

STAR Silicon Vertex Tracker Detector (SVT) Update