Performance of the ALICE TRD with first LHC collisions

In December 2009 a milestone of the ALICE Transition Radiation Detector (TRD) [1] was marked when the detector was turned on to record tracks of particles produced by first stable beams in collision at the Large Hadron Collider. We report here the performance of the detector during the ensuing data taking period of 2 weeks. Of the 18 TRD supermodules, 7 are currently installed in the ALICE setup. Assembly and testing is ongoing for the rest, envisioned to be installed during the next LHC shutdown period end of 2010. The LHC provided beams at the injection energy of 450 GeV per beam, with bunch intensities of up to 10 protons. Triggering with the Silicon Pixel Detector and the V0 detector, ALICE acquired about 2.5·105 events with a good collision vertex. About 90% of the 210 individual chambers in the TRD recorded data at their nominal settings. Chamber calibration [2] was performed both online and based on a dedicated reconstruction pass performed at GSI.