Sep 20 – 24, 2010
Aachen, Germany
Europe/Zurich timezone

Detailed Performance Study of ATLAS Endcap Muon Trigger with Beam Collision Data

Sep 23, 2010, 4:00 PM



Mr Takashi Hayakawa (Department of Physics-Kobe University-Unknown)


In 2009 the first beam collision was occurred at LHC and the ATLAS detector has started data taking with beam collision at 7TeV since May 2010. Thanks to the eagerest commissioning works with test pulses, cosmic rays and single beams, the Level-1 endcap muon trigger system can successfully provide trigger signals on proper timing for the ATLAS detector. The phase adjustment of the gate timing, optimization of the gate width and others have been done using real muons from the beam collision in the commissioning phase. Insufficient immunity of the system against the frequency change during LHC ramping-up and beam chromaticity was found. After the detailed investigation into such unexpected feature, we could optimized data taking procedure eventually by minimizing error occurrence. We report results of detailed studies on the performance of Level-1 endcap muon trigger with beam collision data.


The Level-1 endcap muon trigger system is a part of the first stage among the
three level of ATLAS trigger system. It selects events containing muons with
transverse momentum (pT) greater than 6 GeV/c.
The coverage of the Level-1 endcap muon trigger system is from η = 1.05 to 2.4.
The Thin Gap Chambers (TGCs) are installed in three stations with seven layers in
each ATLAS endcap region. A muon is identified with three station coincidence and
course pT with six level thresholds is measured in r-φ space.

We have been taking the data using cosmic rays and single beams since 2008. And
we have developed the system to keep the best trigger performance as much as
possible through precise timing adjustment, fixing of cable connection bugs,
recovery of noisy or dead channels, and measurements on chamber efficiencies.

The Level-1 endcap muon trigger has so far provided on good timing in beam
collision. However, some TGCs have the time jitter over than 25 ns (repletion time
of bunch crossing). We need finer adjustments on the gate timing and gate width in
order to give more reliable trigger signals.
In commissioning with beam, we have also found that our electronics system is
sensitive to clock phase shifts. Frequency and phase of LHC clock are slightly
changed during the beam ramp up, and some optical links lose the synchronization
and it causes problems on data read out. In addition when the system clock source is
changed, our system fails to find bunch identification for events. We will introduce
new features on our timing and trigger control system to recover synchronization.
In this report we will discuss various problems encountered and overcome in the
system development stage and report the first results of systematic study of the
performance of Level-1 endcap muon trigger with beam collision data.

Primary author

Mr Takashi Hayakawa (Department of Physics-Kobe University-Unknown)

Presentation materials