The SVT Physics and Future Lifetime

1
The SVT Physics and Future Lifetime
As impressive as the.. other.. editions are, they
seem a little tame compared to the SVT. In fact,
this little honey should be able to run with some
pretty tall dogs with pretty fancy pedigrees
......for the truly young and restless, the SVT
is something special.
(New Car Test Drive.com ( Ford SVT Contour))
2
Performance in run IV
Down Feb. 7th, 8th, and 9th Problems with TCD
Position Missed 2.51 M evts.
87.6 Lost MinBias were in Jan. 48 those
from 25th -31st
3
Detector Status

• Averaged Over the Run 85 of the SVT is good
• Three Half-Ladders (1.5 each) L07B3, L11B3,
  L12B2
• L07B3 no HV above -350 V
• L11B3 lost ¼ during '02, rest during shutdown
• L12B2 exhibiting abnormally high noise
• RDOE7 (4.2) Lost due to electronics failure,
  March 6th
• RDOW3 RDOW4 down, rectifier failure in PS,
  March 29th
• Recovered April 2nd
• Typical fluctuation 3

4
Bad channels history
Bad dead or noisy

• 36 Ladders built Ended Jan 2001 lt 1
• Ladders mounted on end-rings installed cone
• Ended March 2001
• Run II Au-Au Aug 2001 - Nov 2001
• Run II p-p Dec 2001 - Jan 2002 3.7
• Shut down (leak repair) Feb 2002 - Sept 2002
• Run III commissioning Oct 2002 - Dec
  2002 10.5
• Run III d-Au and p-p Jan 2003 - May 2003
  12.7
• Start Run IV Jan 2004 13.6
• End Run IV May 2004 15.9

Note doesnt show those used in various run
but those intrinsically damaged. i.e. Read Out
Boxes failed but were repaired during the run.
Therefore a slightly lower operational used
than shown here.
Seems that when SVT left alone number of bad
channels stays stable
5
Detector lifetime

• Future difficult to predict
• This year a maximum of 3 bad channels added
• Extrapolating 5 years ? 70 alive BUT
• Most failures seem to be grouped
• one sca out of 5 fails
• one analog driver is bad
• bad/broken connector from detector to rdo
• bad adc in rdo
• Not much trend of single channel failures

With minimal handling and disconnecting from
RDOs things may not be that bad
6

• The rest is MERE calibrations!!

7
Calibration Techniques

• Gain
• Hybrid to hybrid and within hybrid.
• Look at hits placed on tracks with given mtm and
  average charge should be the same. Scale gain
  to force them to be.
• Drift Velocity
• Hybrid to Hybrid and within hybrid.
• Look at start and stop of hits Know drift
  3cm, calc Vdhybrid
• Use laser spots to monitor temp. variation event
  by event..
• Use bench measurements to account of
  non-linearity of drift.
• Use bench measurements to account for temp.
  profile across anodes.
• Alignment
• Global, Barrel, Ladder, Wafer.
• Project TPC tracks to SVT hits, calc. residuals.
• Refit TPC tracks with SVT hits, calc. residuals.
• Refit matched SVT hits and primary vertex, calc.
  residuals.
• Deviations from means of zero give shifts.
• Try shifts and rotations to minimize offsets.
• Some offsets due to TPC distortions not ONLY SVT.

8
Drift velocity from hits
3 cm
Mean distortion is a few 100 mm
9
Polynomial drift representatopm
Difference from fit
9th order polynomial
Difference from fit
RMS17.9 µm
Account for focusing region
10
Hit position reproducibility
anode

• 3 laser spots
• 2 spots are at
• hybrid1, layer6,
• ladder15, wafer7
• 1 spot is at
• hybrid2, layer6,
• ladder7, wafer1

spot 1 s4.4µm
spot 2 s3.0µm
Laboratory laser tests anode direction s6 µm
Similar resolution in STAR as on bench

• SVT proposal

11
Time variations of laser spot positions
drift distance of spot 1
Temperature oscillations have a period of 2.5
min Temperature oscillation is 1oc
peak-to-peak Position peak-to-peak change is 70
µm
12
Time variations of laser spot

• water cooling ? time variations of laser
  spot positions
• spot positions change in phase
• BUT
• spots behave differently after SVT is switched on
  and gets stabilized
• ( 1 hour !)
• spot 1 80 microns
• spot 2 stable
• spot 4 300 microns

spot 1
spot 2
Can we calibrate out the burn in?
spot 4
13
Drift velocity calibration

• Use 2 spots on one wafer

d1 d2 d12 v(t1-t2)

• Distance is in fact the same so apparent change
  is due to Dv

• Using ltt1-t2gt and ltvdgt can calc. Dv
  event-by-event

Time difference of spot 1 and 2
Time variations of drift velocity
14
Corrected laser spot positions
black before, red after the drift velocity
calibration
before s(22.10.2)µm
after s(10.00.1)µm

• Get delta function for spots used in calc phew!

Laser spot on other wafer improves by factor 2
time direction s (5 23) µm (depending on the
position) (NIM A439, 2000 SVT proposal)
15
Anode temperature profile

• 40 ns/TB 270 µm/TB
• 150 mm max shift

• Temperature gradient across wafers must be taken
  into account
• Due to resistor chains at edges

Have bench measurement for each hybrid needs to
be used
16
Alignment

• We seek for 6 parameters that must be adjusted in
  order to have the SVT aligned to the TPC
• x shift
• y shift
• z shift
• xy rotation
• xz rotation
• yz rotation
• Have to calculate for each wafer 216 in total

The Question

• How to disentangle and extract them without
  ambiguity from the data?
• Many approaches are possible. We are using two
  of them...

17
The two approaches

• First approach
• Calculate the residuals between the projections
  of TPC tracks and the closest SVT hit in a
  particular wafer.
• Advantage
• can be done immediately TPC calibration is OK
  (not final), even without B0 data.
• Disadvantage
• highly dependent on TPC calibration.
• the width of these residuals distributions and
  therefore the precision of the procedure is
  determined by the projection resolution.

• Second approach
• Use only SVT hits in order to perform a
  self-alignment of the detector.
• Advantage
• a better precision can be achieved.
• does not depend on TPC calibration.
• Disadvantage
• it is harder to disentangle the various degrees
  of freedom of the detector (need to use primary
  vertex as an external reference).
• depends on B0 data (can take longer to get
  started).

18
First approach TPC track projection

• Try to disentangle the 6 correction parameters in
  2 classes
• x shift, y shift and xy rotation.
• z shift, xz rotation and yz rotation.
• Look at residuals from the SVT anode direction
  (global z direction)
• Choose tracks with dip angle close to zero (
  tracks parallel to the xy plane)
• Study as function of z
• deviations from a flat distribution centered
  at zero show mis-alignment
• They are not completely disentangled, but it
  works as a first approximation..

• Make the alignment in steps
• global alignment, i.e., one set of parameters for
  the whole detector
• ladder by ladder alignment, i.e., a set of
  parameters per ladder
• wafer by wafer alignment, i.e., a set of
  parameters per wafer.

19
Dx, Dy, Dj corrections
?x -1.9 mm ?y 0.36 mm ?? -0.017 rad
Matches well the survey data
Looks pretty good after 2nd iteration
20
First look z shifts, no corrections

• Only ladders at xz plane

• Only ladders at yz plane

No sizable correction needed
21
Next step ladder by ladder

• Look at residuals from the SVT drift direction
  (global x-y plane).
• Study them as a function of drift distance
  (xlocal) for each wafer.
• Now influence of mis-calibration (t0 and drift
  velocity) cannot be neglected.

0, if t0 is Ok
v is the correct drift velocity and t0 is the
correct time zero.
These two equations can be used to fit the
residuals distribution fixing the same
geometrical parameters for all wafers.
22
One ladder as example
?x -0.81 mm ?y 0.56 mm
?x -0.19 mm ?y 0.024 mm
23
Technique works!

• Need to go ladder by ladder (36 total) checking
  the correction numbers and the effect of them on
  the residuals.
• Still need to consider the rotation degree of
  freedom.

Next step is to fit each wafer separately.
24
Near future perspectives

• Finalize first approach
• calculate ?x, ?y, and ?? ladder by ladder. (Just
  finished for inner barrel)
• extend it to wafer by wafer making small
  corrections if necessary
• calculate z shift, xz rotation and yz rotation
  (global, ladder by ladder and wafer by wafer -
  they should be small)
• use B0 data. ( Work being done now)

• It is a lot of work, but it depends mostly on
  man power.
• Software is ready
• The whole procedure does not depend on many
  iterations of the reconstruction chain. Can be
  applied and tested without full reconstruction

25
Track matching efficiency
Note Get similar tracking results with Sti
SVT is most efficient between PV - 10 cm!!!
26
Track matching efficiency II
Number of EST tracks does not increase with
multiplicity, an indication that there is no
increase of ghost tracks.
27
Identifying primary tracks

• Data

• Hijing

Significant improvement in impact parameter for
primary tracks
28
Track residuals simulated data

• Dependency on the attributed hit error
  simulation had 20 mm smearing

p-p
29
Track Residuals

• HIJING AuAu simulated data, with SVT hits
  position smeared by 80 mm.

Resolution of SQRT(11072) 90 mm
30
Track Residuals AuAu 62 GeV
31
Track Residuals AuAu 62 GeV
32

• OK but what are you going to DO with it?

33
Physics interests

• Measurement of low pT (60-200 MeV/c) particles
• Improved reconstruction of strange baryons
• Reconstruction of heavy quark mesons
• (not going to discuss)
• Improvement of high pT primaries
  reconstruction/resolution
• (already shown dca improvement)

34
Low-pT yields compared to models

• Event generators unable to consistently describe
  low pT yields.
• HIJING overpredicts yields at low pT.
• Ratio of measured to HIJING yields averaged over
  low pT range
• (Strangeness Production in PHOBOS, C. Henderson,
  MIT, RHIC/AGS Users Meeting, May 2004, BNL)

35
Low pT physics particle yields

• p-p dN/dy
• X
• Exponential
• 0.00268 /- 0.0005
• Power Law
• 0.00181 /- 0.0004
• ?X
• Exponential
• 0.00270 /- 0.0005
• Power Law
• 0.00178 /- 0.0004

Distinguishing between fit models is critical to
determine yields!
36
Sti - efficiency and purity

• Clean up via normal tracking first
• Start with SVT and move outwards

• Efficiency is low but that
• would be OK as long as pure

• By removing obviously bad hits
• purity good

Work just starting but looks promising!
37
K0s in Au-Au 62 GeV
K0s raw yield vs PT
PT lt 400 Mev/c
SVT/TPC yield
120 improvement in lowest pT bin similar
result seen in p-p
3 improvement for K0s
38
L in Au-Au 62 GeV
PT lt 800 Mev/c
40 improvement in lowest pT bin 100 seen in p-p
for pT lt 0.5 GeV
15 improvement for L
39
MSB from AuAu-Simulation

• W enhanced Hijing events

W
SVTTPC Tracks 3210 Os
TPC only Tracks 2020 Os
Increase of signal by 60
40
Slow simulator close to tuned
41
Embedding Works
anode
embedded data
time
anode
42
Correcting data seems OK
requiring 2 SVT hits on EST track
Preliminary test on 200 GeV dAu data
Black TPC only Red TPC SVT
43
SVT lifetime expectations

• We do not see evidence for aging or continuous
  channel loss therefore the limitation of the
  usefulness of the detector is due to the RDO.
• The detector can run up to a maximum DAQ rate of
  around 200 Hz without serious performance
  limitations
• Between 200 to 300 Hz the required SCA settling
  time will lead to increased noise levels and the
  detector requires hardware changes to the RDO.
• The detector can not operate above 300 Hz.
• The detector electronics can not be upgraded as
  was done in the case of the TPC.

44
SVT future plans

• We do not anticipate to remove the detector for
  repair or electronics upgrades.
• We would like to run the detector until STAR
  decides to remove it due to readout speed
  limitations.
• We like to be in STAR at least until 2009 beam
  time.
• The detector is designed such that the inner
  layer can be removed to generate space for the
  APS upgrade.