1. 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 ( )
Helen Caines -
Yale University

3. Presentation Overview
SVT Introduction
SVT Performance
Track-to-Hit Matching
Vertex Reconstruction
Energy Loss
Strange Particle Decays
Summary & Conclusions

4. Welcome to BNL- RHIC!

5. The STAR Detector
Magnet
Time Projection Chamber
Coils
Silicon Vertex Tracker *
TPC Endcap & MWPC
FTPCs (1 + 1)
ZCal
ZCal
Vertex Position Detectors
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

6. SVT Installation
Installed for the first time
RHIC run

7. 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

8. SVT Design Each wafer is 6.3 cm x 6.3 cm area 300 mm 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
Inner barrel has 8 ladders – 4 wafers/ladder
Middle barrel has 12 ladders – 6 wafers/ladder
Outer barrel has 16 ladders – 7 wafers/ladder

9. 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

10. Calibrations - Pedestals
First Time bucket
Pedestal Subtraction done
online
Other 127 Time buckets
Anode
You can see the edges of the 15 PASA’s 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

11. SVT Performance 7 mV for pp 4 mV design (<7 mV aim) counts Noise:
12 mV for Au+Au (due to a grounding problem now fixed)
4 mV design (<7 mV aim) cm
30 mm resolution reproducibility

12. 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.

13. SVT Temperature Control
Au-Au

14. Hit to Track Matching TPC inner radius = 50cm SVT outer radius = 15cm
Au-Au
Mixed events
Closest hit
TPC inner radius = 50cm
SVT outer radius = 15cm
Project tracks from TPC to SVT
Au-Au
Closest hit
Real events
Yes!
Are we matching correctly?

15. Drift Residuals vs Wafer
Before Alignment
Shifted center of SVT
Relative to TPC by
x=-0.276cm
y=-0.82cm
After Alignment
Magnitudes agree with survey results 1 2 3

16. Using SVT for TPC Calibration
Track dip angle
< 0.1
mean D(Z) = cm
vdrift = 5.56 cm/msec
TPC T0 shift = /5.56
= 9.46 x 10-3 msec
After Corrections
Shift in Z + TPC T0/Vdrift wrong

17. Vertex Finding - Resolution
p-p
STAR Preliminary
Z offset of 0.005cm – Aligned in Z

18. Anode Residuals vs pt
STAR Preliminary
Pt resolution worse at low pt where energy loss and scattering not yet taken into account
Au-Au

19. 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

20. Impact Parameter Improvement
3D impact parameters of track associated
to primary vertex  should be close to zero
pp:
Mean 0.7->0.51 cm
RMS 0.59->0.48 cm
TPC
TPC+SVT cm

21. 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

22. Strange Particle Decays+ -
V0 Reconstruction
Black is TPC only
Red is TPC+SVT
~35-40% greater yield in K0s region
Preliminary
Preliminary
Blue is TPC only
Red is TPC+SVT
Mostly low pT

23. 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!

24. 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
Kent State University
Michigan State University
City College of New York
Ohio State University
Penn. State University
Purdue University
Rice University
Texas A&M
UT Austin
Washington University
Wayne State University
Yale 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