# Presentation: 483153

## SVT Calibration and STI tracking status 

- An update of work since the SVT review
- and the STAR upgrades meeting

- and the STAR upgrades meeting

## SVT Calibration and STI tracking status 

- An update of work since the SVT review
- and the STAR upgrades meeting

## Calibration Tasks

-  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.

## Laser - Hit position reproducibility 

**spot 1**
**σ****=4.4****μ****m**

**spot 2**
**σ****=3.0****μ****m**

**anode**

**Laboratory laser tests:**
**anode direction**: σ=6 μm

**3 laser spots**
-   **2 spots** are at:
-   hybrid=1, layer=6,
-   ladder=15, wafer=7
-   **1 spot** is at:
-   hybrid=2, layer=6,
-   ladder=7, wafer=1

-  SVT proposal

- Similar resolution in STAR
- as on bench

## Time variations of laser spot - cooling

- Temperature oscillations have a period of ~2.5 min
- Temperature oscillation is ~1oc peak-to-peak
- Position peak-to-peak change is ~70 μm

- drift distance of spot 1

## 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 

**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

**Time variations of laser spot – burn-in**

**spot 1**

**spot 4**

**spot 2**

- Detailed study shows that this behavior
- is not common to all runs or SVT
- downtime. Most runs show no strong
- burn-in variation. We have decided to
- not to try to calibrate this effect out

## Drift velocity from hits (single value per wafer)

- 3 cm

-  Mean distortion is a few 100 m

## Polynomial drift representation

- 9th order polynomial

- Difference from fit

- Difference
- from fit

- RMS=17.9 μm

-  Account for
-   focusing region

-  Have bench measurement
- for each hybrid
- now in database

## Anode temperature profile 

-  40 ns/TB = ~270 μm/TB
-  ~150 m max shift

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

-  Have bench measurement for each hybrid now in database

## 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

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

- The Question

## 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 B=0 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 B=0 data (can take longer to get started).

## x, y, corrections

******x, ********y, ********corrections**

- *x =* *-1.9 mm*
- *y = 0.36 mm*
-  *= -0.017 rad*

- Matches well the survey data

-  Looks pretty good after 2nd iteration

## 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 (*x**local*) for each wafer.
-  Now influence of mis-calibration (*t**0* and drift velocity) cannot be neglected.

- 	 *v`* is the correct drift velocity and t0` is the correct time zero.

- 0, if t0 is Ok

- These two equations can be used to fit the “residuals” distribution
- fixing the same geometrical parameters for all wafers.

## Ladder by ladder (One ladder as example)

**Ladder by ladder (One ladder as example)**

- *x =* *-0.81 mm*
- *y = 0.56 mm*

- *x =* *-0.19 mm*
- *y = 0.024 mm*

## Technique works!

- Done with ladder by ladder (36 total) checking of correction numbers and the effect of them on the “residuals”.
- Done with considering the rotation degree of freedom.

- Next step is to fit each wafer separately.

## Alignment progress adding survey data

**Alignment progress adding survey data**

## Alignment progress adding drift velocity

## Track Residual: AuAu Prod 62 GeV

|  | Anode Direction | Drift Direction | Solution |
| --- | --- | --- | --- |
| Average over all Barrel 2 | 180 um | 300 um |  |
| Ladder 03 | 84 um | 140 um | Ladder Alignment  |
| L03/wafer 48  | 60 um | 140 um | Wafer Alignment |
| L03/wafer 48/hybrid-02 | 60 um | 60 um | T0 and drift velocity |

## Status of calibration tasks before production

| Task | Detail | Fully tested | In chain now | In chain by Aug.1st |
| --- | --- | --- | --- | --- |
| Drift velocity calibration | Different constant for each hybrid | yes | yes |  |
|  | Different polynomial for each hybrid | in a week | no | yes |
|  | Temperature variation in drift based on laser | yes | yes |  |
|  | Burn-in correction based on laser | yes | no 
(no plans) | no |
|  | Temperature variation in anode based on bench meas. | yes | yes |  |
| Alignment | Software alignment (ladder) | yes | yes |  |
|  | + survey geometry (wafer) | in a week | no | yes |
| Gain calibration |  | yes | no  | for 2005 |
| Slow simulator |  | yes |  |  |

## STI in dA test production - primaries

**Vtx = +-50 cm**

**Vtx = +-10 cm**

- Still 30% of TPC primaries have no SVT hit, another 30% have only one SVT hit
- STI for SVT not fully tuned yet

## STI performance in central AA simulations

## STI in dA test production - Lambdas

## STI performance in minbias AA simulations

- Matching Eff.: >1 SVT hit common / > 1 SVT hit MC, 15 good TPC hits

- Purity: common hits – reconstructed hits

- STI, small hit error

- STI, large hit error

- EST

## STI performance in central AA simulations

**Com. vs. RC**

**Efficiency:**
**  ****RC vs. MC**

**STI performance in central AA simulations**

**Efficiency:**
**SVT hits vs MC**
** **

- Final tracking numbers
- (from Kai):
- Central HIJING (0-5%)
- TPC tracking efficiency: 86%
- SVT tracking effic. (2 hits): 60%
-  2 or more SVT hit matching: 70%
- 1 or more SVT hit matching: 87%

## STI performance summary

- 1.) The number of SVT hits assigned to the TPC track is low in central AA simulations, and to some extent in the dA production. Need to find the reason. (geometry problem ?)
- 2.) The purity of SVT hits assigned to the TPC tracks is very high.
- 3.) minbias AA simulations show that the STI performance is presently comparable to EST in terms of momentum resolution and efficiency and superior to EST in terms of purity when small hit errors for the SVT are used in the STI tracking.
- 4.) we will continue to tune the STI-SVT tracking parameters until the production starts. Present level of performance is sufficient when compared to EST.

## Are we ready to go ?

- 1.) we need about 2-3 more weeks to finish all necessary calibration and alignment steps.
- 2.) we will use that time also to continue further tuning of the SVT tracking parameters in STI.
- We expect to be ready by August 1st.