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

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

Welcome to BNL- RHIC!

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

SVT Installation Installed for the first time 2001-2 RHIC run

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

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

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

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

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

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.

SVT Temperature Control Au-Au

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?

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

Using SVT for TPC Calibration Track dip angle < 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

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

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

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

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

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

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

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!

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