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
Vertex 2002 – Nov 2002
Presentation Overview
● SVT Introduction● SVT Performance● Track-to-Hit Matching ● Vertex Reconstruction● Energy Loss● Strange Particle Decays● Summary & Conclusions
Helen Caines
Vertex 2002 – Nov 2002
Welcome to BNL- RHIC!
Helen Caines
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
SVT Installation
Installed for the first time2001-2 RHIC run
Helen Caines
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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 2002 – Nov 2002
Vertex Finding - Resolution
p-p
Z offset of 0.005cm – Aligned in Z
STAR Preliminary
Helen Caines
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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
Vertex 2002 – Nov 2002
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