# Presentation: 511263

## Year 2 Tracking Strategies

**Year 2 Tracking Strategies**
**For STAR**

- STAR/ALICE Meeting
- April 2000

- Helen Caines

## STAR in Year 2

**SVT**

- Near 4acceptance
- multi-signature Event-by-Event analysis

- RICH

**TPC Inner radius    = 50cm**
**Outer radius   = 200cm**
****
** ****SSD        layer radius     = 25cm**
****** ****=  ********1**
**SVT **
**	****1****st**** layer radius= 6cm**
**	****2****nd**** layer radius=10cm**
**	****3****rd**** layer radius= 15cm**
****** ****=  ********1**

## SVT - Details

**   ****A wafer is 6.2 cm x 6.2 cm area,  300 micron thick  - 0.3%X****0**
**Average radiation length seen by a particle if 4.5%X****0****  incl. fee cards etc.**
**Consists of  216 wafers**
**  ****3 barrels:  Inner barrel has 8 ladders     –  4 wafers/ladder**
**                  ****Middle barrel has 12 ladders   – 6 wafers/ladder**
**	****  ****Outer barrel has 16 ladders     –  7 wafers/ladder**
**Resolution: ~ 20 microns**

** ****Outer radius – 15cm**
**Middle Radius – 10cm**
**Inner radius - 6cm**
**Length - ********21cm **

## SSD Details

**The SSD:**
**Double sided silicon strip detectors 16 wafers per ladder**
**Stereo angle 35 mrad**** ****pitch 95 microns.**
**Detector size is 7.5cm x 4.2xm**
** ****300 microns thick. Resolution is: **
**15 microns in r **
**700 microns in z**
**radiation length of 1 ladder is 0.7%X****0**

## Integrated Tracking Methods with the Year 2 detectors

- Two methods:
- Track-Track matching between TPC and vertex detectors
-  Form tracks independently  in the SVT+SSD and the TPC.
- Then project all tracks to a given radius and match vectors
- Track-Space point matching between TPC and vertex detectors
-       Project the TPC to individual barrels and match the closest space-point within given constraints.

## SVT-SSD Stand-Alone Tracking Algorithms

- Grouping Technique (finder only):
- If one assumes straight lines for the tracks instead of helices a trivial mapping in from the primary vertex  places all hits on a track into the same location.
- For a particle with pt =100MeV/c in a 0.5T field
- (R=15cm)–(R=5cm) = 5.10
- So we need bins of close to  50 so most tracks have all their space points within a  bin
- If you iterate increasing the binning for hits you move
-  to lower and lower pt (or larger radii of curvature).
- Advantage:this method is fast.

## Tracking via grouping

- For primaries this technique has been shown to be over 94% efficient, and for pt >200MeV/c the efficiency 97% when using the SVT alone.

## Tracking with the Year 2 Method 1

- Disadvantage of the grouping technique is you can only find primaries, or tracks appearing to originate from the primary vertex.
- So we have a standard “follow your nose” tracker which tries to identify secondary tracks and those tracks with too low a pt to be successfully identified by the grouping technique.
- It starts at the primary vertex.
- Takes a point on the first barrel
- Using straight line projections it projects to the second barrel, finds closest hit within a search cones
- Projects to next barrel, finds closest hit etc to 4th barrel
- All 3 hit candidates for that hit are identified. A helix fit is done for each “track”. Best fit is selected as the track
- Hits are removed from pool and iteration starts with next hit

## Tracking with the Year 2 detectors

- Primaries

- Secondaries

- 0

- 1 GeV

- 1GeV

- 0

## Tracking Matching between Vertex detectors and TPC

- We then take all tracks from SVT+SSD and tracks from TPC.
- Project tracks to a common radius. Form a footprint of each track at that radius, size of footprint dependant on errors from track fit and a gross estimate of the material the track as passed through.
- Match best pairs of tracks.
- We take advantage of the this step and have VERY loose cuts in the SVT+SSD tracking. This means we pass many fake tracks to the matcher. The matcher then weeds these bad tracks out. i.e the SVT tracking tries to get a high efficiency at the expense of purity.

## Tracking with the Year 2 Method 1

- Track-Track matching
- SVT+SSD+TPC:
- Primary
- Findable 1743
- Correct   1366    - 78%
- Ghost      158     - 10%

- Secondary
- Findable 252
- Correct   71      - 28%
- Ghost     31      - 30%

## Slide 12

## Space Point – Track Matching

- Takes 5 passes:
- At least 1 hit in each layer
- At least one hit in each layer with larger search cone
- At least one is in 3 different layers
- At least one hit in 2 different layers
- At least one hit in the SSD
- In each pass there are 7 iterations over pt thresholds (high pt        		first)
-   Project to SSD, find hit, refit track, mover to next barrel

## Track-Hit Matching Efficiency

- 0

- 1.5

- -1

- 1

## Tracking with the Year 2 detectors Method 2

- Track-Space point matching
- Note there are now more findable hits as allow as few as 1 hit per track
- Primary
- Findable   1778 (1743)
- Correct     1399 (1366)  - 78%
- Ghost 	     263   (158)    - 16%

- Secondary
- Findable  333 (252)
- Correct   202  (71)   - 61%
- Ghost    90     (31)   - 31%

- Secondary
- Findable 252
- Correct 71        - 28%
- Ghost 31          - 30%

##  Upgrades/ Future work

-  Upgrades/ Future work

- Speed!!!!
-  Integrate space point to track matching with grouper technique
-  Take out the easy to find high mtm tracks using a fast method then apply track-hit matching
- The improvement of the secondary reconstruction is counterbalanced by the increase in ghost contamination
- Integrate dE/dx into the hit matching from SVT and SSD
- Take into account the material passed through by the track.
- Take advantage of  kalman /propagation (Geane/other?) work being done for year 1.