Cosmic ray test of RPC for the ATLAS experiment Napoli Givi Sekhniaidze VI Workshop on Resistive Plate Chambers and Related Detector Coimbra 26-27 November 2001

The Test Station Atlas RPC

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

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

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

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

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

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

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

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

The Tracker ... we correct it!

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

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