Clean tracks for ATLAS

First cosmic ray tracks in the integrated ATLAS barrel SCT and TRT tracking detectors.


A snap-shot of a cosmic ray event seen in the different layers of both the SCT and TRT detectors.

The ATLAS Inner Detector Integration Team celebrated a major success recently, when clean tracks of cosmic rays were detected in the completed semiconductor tracker (SCT) and transition radiation tracker (TRT) barrels. These tracking tests come just months after the successful insertion of the SCT into the TRT (See Bulletin 09/2006).

The cosmic ray test is important for the experiment because, after 15 years of hard work, it is the last test performed on the fully assembled barrel before lowering it into the ATLAS cavern. The two trackers work together to provide millions of channels so that particles' tracks can be identified and measured with great accuracy. According to the team, the preliminary results were very encouraging.

After first checks of noise levels in the final detectors, a critical goal was to study their response to cosmic rays using a set of scintillators to give the external trigger, thus undertaking the challenge of integrating the full chain of the detectors, the data acquisition system (DAQ), and the reconstruction and monitoring software.

One-eighth of the barrel is instrumented and now operating stably in the SR1 test area, while the DAQ and monitoring systems for the two detectors are currently controlling and reading out the SCT-TRT barrel. One of the first crucial tests was to time-in and synchronize both detectors with the SR1 cosmic trigger and synchronization systems using the ATLAS Local Trigger Processors.

After much preparation, the team was rewarded with the first clean cosmic rays tracked in a completed barrel, while offline software provided prompt reconstruction of the events. The monitoring of histograms and event displays is now continuously done online to ensure good data quality.

The team is now working on readying the two SCT end-caps for insertion into the TRT now that all the parts have arrived at CERN. Recently, the second end-cap arrived from the National Institute for Nuclear Physics and High Energy Physics in Amsterdam, while the end-caps for the TRT are being completed at CERN.

In the coming months, the SCT-TRT barrel will be installed in the cavern and about four months will be spent on cabling it before the final commissioning. The end-caps will follow the same steps and in March 2007 the pixel detector, the last piece of the inner detector, will be inserted into the barrel.