Installation and commissioning of a high-efficiency and high-resolution straw tube tracker for the LHCb experiment

Abstract

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 (OT) was constructed, consisting of ∼55,000 straw tubes, covering in total an area of 360m2 of double layers. The detector is foreseen to operate under large particle rates, up to 100kHz/cm per straw in the region closest to the beam. The front-end electronics is expected to provide the precise (0.5ns) drift-time measurement, at an average occupancy of 5% and at 1MHz trigger rate. The tracking procedure requires high-efficiency (low thresholds), while at the same time putting stringent limits on the noise level. The modular detector structure reflects on the FE electronics: 128 channels are read out by one FE Box. During installation, the dark current, the response to radioactive sources, and the gas-tightness of all detector units was checked and only a handful of bad channels were found. Special hardware and dedicated procedures, integrated within the experimental control system, have been designed for the detector calibration during data taking. At the time of the conference, the detector has been installed and commissioned with the help of cosmic rays events producing tracks through OT. During the first days of the LHC commissioning, the detector was operated on nominal voltage and large-multiplicity events originating at the circulating beam were recorded and studied.