1. Cosmic ray test of RPC for the ATLAS experiment
Napoli
Givi Sekhniaidze
VI Workshop on Resistive Plate Chambers and Related Detector
Coimbra November 2001

2. The Test Station
Atlas RPC

3. The Test Station II Tracking system Drift chambers
TOP & BOTTOM layer 1 m2
2 x and 2 y plane per layer
Resolution in track reconstruction s < 400 mm
Trigger
TOP & BOTTOM layer
1 m2 plastic scintillators per layer
The 2 module housing scintillators & tracking chamber are moved by 2 step motors automatically during data taking

4. The Trigger system A time resolution of ~ 1 ns is achieved
The trigger signal is delayed and then used by DAQ to generate the COMMON STOP for the TDC
A time resolution
of ~ 1 ns is achieved

5. The Drift chambers Each chambers has 2 X layers and 2 Y layers
To disentangle the left-right ambiguity, each layer is staggered respect to the other one on the same view

6. Anyway we need a better estimate
The Drift velocity
Drift velocity has to be determined to have the time to space relation. At good level of approximation it can be considered costant over the cell.
A very rough estimate can be given by geometrical consideration
All events
N hit = 8
N hit > 8
d = cell width
N hit < 8
Anyway we need a better estimate

7. Drift Velocity
The distribution of residuals change according to the drift velocity used.
Two peaks appear unless the correct drift velocity is found

8. Drift Velocity
The plot of the distance between peaks versus
the drift velocity approaches a minimum for the correct drift velocity
This autocalibration is included in the reconstruction program

9. The Tracker
One of the four layers showed a resolution lower than the other

10. The tracker
Using the other 3 layer we check the worst one and we disantangled a misalignement of the wires and ...

11. The Tracker
... we correct it!

12. Impact points distribution of reconstructed tracks on RPC plane.
What we are going to do
The station aims at testing up to eight ATLAS RPC modules simultaneously in completly automatic way. We can scan the all RPC surface in order to check its uniform behaviour.
Impact points distribution of reconstructed tracks on RPC plane.
X Projection
Y Projection
RPC border

13. What we have already done
The L3 RPC were tested in the station
Working point
HV = 7200
On plateau
e  100 %
Spacers clearly visible