STAR Silicon Vertex Tracker Detector (SVT) Update

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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
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(No Transcript)
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Presentation Overview

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

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Welcome to BNL- RHIC!
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The STAR Detector
Magnet
Coils
Silicon Vertex Tracker
TPC Endcap MWPC
ZCal
ZCal
Endcap Calorimeter
Barrel EM Calorimeter
Central Trigger Barrel TOF patch
RICH
yr.1 SVT ladder

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

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SVT Installation
Installed for the first time 2001-2 RHIC run
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p-p vs Au-Au at vsNN200 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
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SVT Design
Each wafer is 6.3 cm x 6.3 cm area 300 mm thick
- 0.3X0 Average radiation length seen by a
particle 4.5X0 incl. fee cards etc. Consists
of 216 wafers
3 Barrels Outer radius 15cm Middle Radius
10cm Inner radius - 6cm Length - ?21cm
Inner barrel has 8 ladders 4
wafers/ladder Middle barrel has 12 ladders 6
wafers/ladder Outer barrel has 16 ladders
7 wafers/ladder
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Silicon Drift Detector - Principle
Ionizing particle
Z - position from readout anode number
Drift time 5 msec 240 Anodes/wafer 100
samples/anode
SDD
R - position from drift time
X
Electron cloud
Gain 1 e- 7.2mV 4 mV 1
ADC
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Calibrations - Pedestals
First Time bucket
Pedestal Subtraction done online
Other 127 Time buckets
Anode
You can see the edges of the 15 PASAs and more
obviously the 3 analogue buffers where the
multiplexing occurs
96.5 of 103,680 channels operational 91.2 of
103,680 channels used in analysis
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SVT Performance
counts

• Noise
• 7 mV for pp
• 12 mV for AuAu (due to a grounding problem
  now fixed)
• 4 mV design (lt7 mV aim)

cm

• 30 mm resolution reproducibility

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Drift Velocity Calibration
SDDs 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.
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SVT Temperature Control
Au-Au
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Hit to Track Matching
TPC inner radius 50cm SVT outer radius
15cm Project tracks from TPC to SVT
Are we matching correctly?
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Drift Residuals vs Wafer
Before Alignment
Shifted center of SVT Relative to TPC by
x-0.276cm y-0.82cm
2
3
1
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Using SVT for TPC Calibration
Track dip angle lt 0.1
mean D(Z) 0.0526cm vdrift 5.56
cm/msec ?TPC T0 shift 0.0526/5.56
9.46 x 10-3 msec
After Corrections
Shift in Z TPC T0/Vdrift wrong
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Vertex Finding - Resolution
p-p
STAR Preliminary
Z offset of 0.005cm Aligned in Z
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Anode Residuals vs pt
STAR Preliminary
Pt resolution worse at low pt where energy loss
and scattering not yet taken into account
Au-Au
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Primary Matching efficiency
Efficiency is defined as the number of tracks
with SVT hits added (2 or more)
p-p
If you go to 30cm average effic is 45
Flat in pt
Expect 85 from simulation of perfect detector
p-p
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Impact Parameter Improvement
3D impact parameters of track associated to
primary vertex ? should be close to zero
pp Mean 0.7-gt0.51 cm RMS 0.59-gt0.48 cm
TPC
TPCSVT
cm
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Energy Loss in the SVT Layers

• 3 sample maximum
• Higher energy resolution
• Good for low momentum

Preliminary
Preliminary
p

• Independent measure of dE/dx
• Allows 2D cut

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Strange Particle Decays

• Black is TPC only
• Red is TPCSVT

35-40 greater yield in K0s region
Preliminary
Preliminary

• Blue is TPC only
• Red is TPCSVT

Mostly low pT
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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!

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The STAR Collaboration

• Russia
• MEPHI - Moscow
• LPP/LHE JINR - Dubna
• IHEP - Protvino
• U.S. Labs
• Argonne
• Berkeley
• Brookhaven
• U.S. Universities
• Arkansas University
• UC Berkeley
• UC Davis
• UC Los Angeles
• Carnegie Mellon University
• Creighton University
• Indiana University

Brazil Universidade de Sao Paolo China IHEP
Beijing, IMP - Lanzou IPP Wuhan USTC SINR
Shanghai Tsinghua University England University
of Birmingham France IReS Strasbourg SUBATECH -
Nantes Germany MPI Munich University of
Frankfurt India IOP - Bhubaneswar VECC -
Calcutta Panjab University University of
Rajasthan Jammu University IIT - Bombay VECC
Kolcata Poland Warsaw University of Technology