Speaker
Mr
Bjorn (on behalf of the ATLAS Tile
Calorimeter system) Nordkvist
(Stockholm University)
Description
The ATLAS Tile Calorimeter is ready for data taking during the
proton-proton collisions provided by the Large Hadron Collider (LHC). The
Tile Calorimeter is a sampling calorimeter with iron absorbers and
scintillators as active medium. The scintillators are read out by wave
length shifting fibers and PMTs. The LHC provides collisions every 25ns,
putting very stringent requirements on the synchronization of the ATLAS
triggering systems and the read out of the on-detector electronics. More
than 99% of the read out channels of the Tile Calorimeter have been time
calibrated using laser pulses sent directly to the PMTs. Timing constants
can be calculated after corrections for i) propagation of trigger and
clock signals, ii) differences in laser light paths to the different parts
of the calorimeter. The calibration is implemented by i) programming
delays in the on-detector electronics for groups of 6 channels, ii)
residual deviations from perfect synchronization are stored in a database
and used during the offline reconstruction of the Tile Calorimeter data.
From the point of view of triggering and clock signals the Tile
Calorimeter is divided into 4 independent sections. The time calibration
has been used in each of the 4 sections, on the data taken during long
ATLAS cosmic runs and during LHC beam time in September 2008. This has
confirmed a timing uniformity of 2ns in each of the 4 calorimeter
sections. The remaining delays between the 4 calorimeter sections have
been measured i) using the laser pulses interleaved with cosmic trigger
inside a global ATLAS run and ii) using real LHC events, and show
consistent results. The main limitations on the precision of the time
calibration are presented.
Author
Mr
Bjorn (on behalf of the ATLAS Tile
Calorimeter system) Nordkvist
(Stockholm University)
Co-author
Dr
Christophe Clement
(Stockholm University)
