# Presentation: 378901

## FIRST RESULTS OF THE 

**FIRST RESULTS OF THE **
**S****ILICON ****S****TRIP ****D****ETECTOR at  STAR**
** **
**Jörg Reinnarth, Jonathan Bouchet, **
**Lilian Martin, Jerome Baudot**
**and the SSD teams in Nantes and Strasbourg (France) and the STAR collaboration**

-  1. The new detector
-  The SSD has been recently installed in the central part of the STAR
-    experiment to enhance the tracking capabilities in this region
-  It provides information on the positions of hits and on the
-    ionization energy loss of charged particles
-  The SSD improves the extrapolation of tracks in the Time
-    Projection Chamber to the hits found in the Silicon Vertex Tracker
-  The improvement of the extrapolation will help to better
-    characterize the tracks especially for secondary particles
-  Thus the reconstruction efficiency for short-lived particles such as
-    K0, Λ and Ω improve accordingly

- 2. Technical Information
-  The SSD consists of 20 ladders x 16 wafers = 320 wafers
-  Each wafer is made up of double sided silicon sensor; 768 strips per side
-  The resolution is 20m in r and 700m in z
-  The SSD covers 2 in r, and -1<<+1; the surface is 1 m2, 500 k channels
-  The A128 front-end chips shows an extended input range of ±13MIPs
-    and extra-low power consumption <350μW per channel
-  Connections between the strips on the wafer and the A128    input channels are done via the Tape Automated Bonding
-  The produced heat on the ladder is removed via an air cooling system
-  On board control chips (COSTAR) monitor temperature, leakage current, etc.

-  3. SSD performance in Run 2005
-  In August 2004 the last 10 (of 20) ladders were installed at STAR
-  Since January the SSD is included in the new beamtime
-  The left picture shows the mean module occupancy for all wafers
-  In Run  ́05 _**74 million**_ CuCu200 events with the TPC were taken
** ****91%** of all TPC events (for CuCu200) include the SSD
** ****93%** of all CuCu62 events include the SSD
-  The picture in the middle shows the events for the different runs

-  4. Hit reconstruction
-  Each module consists of a p(ositive) and n(egative) side with each 768 strips
-  Charged particles deposit charge on one or more strips, depending on charge, angle and
-    momentum of the particle
-  A cluster finding algorithm is used to build clusters from the strips and to merge p-
-   side and n-side clusters to form hits. In case of closed hits, charge matching is used to solve
-   cluster ambiguities (left picture). The usual cluster size is 1.5 strips (middle)
-  The right picture shows the distribution of the total cluster charge

-  5. Upcoming tasks
-  For cluster charge matching p- and n-side will be calibrated (left pictures)
-  Calibration database will be created for fast offline processing
-  Improvement of cluster building due to the calibration will be determined
-  The SSD will be aligned by software to determine the exact wafer positions (right pictures)
-  After alignment the tracking parameters (errors, resolution) have to be tuned
-  The data have to be reprocessed for tracking with the SSD
-  Monte Carlo data with new geometry will be used in the embedding
-  Improvement of reconstruction efficiency for real data will be determined
-  Upgrade of some SSD parts (e.g. cooling system, noise improvement) for upcoming runs
-    will be installed this year

-   6. Summary and outlook
-  The SSD has made a very nice job so far
-  ~90% of all TPC data include the SSD
-  The offline software development is finished and Monte Carlo data exists
-  The detector has to be calibrated and aligned
-  Than the tracking can be done
-  The SSD will definitely enhance the tracking capabilities (left picture)
-  The fine tuning of the tracking in the SSD will be started shortly
-    and then the precise impact of the SSD on the STAR capabilities will be determined

***STAR***

**SSD**

**SVT**

**TPC**

- Email: joerg.reinnarth@subatech.in2p3.fr

- Cu+Cu 200GeV     Cu+Cu 62GeV           pp