Commissioning and performance of the LHCb outer tracker

The LHCb experiment is a single arm spectrometer, designed to study CP violation in B-decays at the Large Hadron Collider (LHC). It is crucial to accurately and efficiently detect the charged decay particles, in the high-density particle environment of the LHC. For this, the Outer Tracker was constructed, consisting of ∼55,000∼55,000 straw tubes, covering in total an area of 360 m2 of double layers. The detector is foreseen to operate under large particle rates, up to 100 kHz/cm in the region closest to the beam. The front-end electronics is expected to provide the precise (0.5 ns) drift-time measurement, at an average occupancy of 5% and at 1 MHz trigger rate. At the time of the conference, the detector has been commissioned with cosmic-ray events and with the first LHC beam collision data. After dedicated studies to establish timing and spatial alignment, the first results on the detector performance (efficiency, resolutions, etc.) have been obtained.