Abstract
The CMS silicon tracker consists of two tracking devices utilizing semiconductor technology: the inner pixel and the outer strip detectors. They operate in a high-occupancy and high-radiation environment presented by particle collisions in the LHC. The tracker detectors occupy the region around the center of CMS, where the LHC beams collide, between 4 cm and 110 cm in radius and up to 280 cm along the beam axis. The pixel detector consists of 66 million pixels, covering about 1 m2 total area. It is surrounded by the strip tracker with 10 million read-out channels covering about 200 m2 total area.The proceedings describe the operational experience collected during the first three years of LHC running. Results include operational challenges encountered during data taking that influence the active fraction and read-out efficiency of the detectors. Details are given about the performance of the tracker at high occupancy with respect to local observables such as signal to noise ratio and hit reconstruction efficiency. Studies of radiation effects are presented with respect to the evolution of sensor bias, read-out thresholds in the inner pixels, and leakage current.
Highlights
Layers or disks and n-type back side
The efficiency is measured as the fraction of the number of particles that are expected to pass through the fiducial regions of the sensors in a given layer for which corresponding hits are found
In the case of the pixel detector, a more stringent selection is required in order to address the higher particle occupancy: a hit must be found within a 500 μm radius of the expected intersection point
Summary
In the years of operation between 2010 and 2013, the LHC [2] has delivered about 6.1 fb−1 integrated luminosity of proton-proton collision data at 7 TeV and about 23.3 fb−1 at 8 TeV (figure 2). High instantaneous luminosity causes multiple proton-proton interactions in the detector, known as pile-up. By the time of the shutdown in 2013, about 2.3% of the barrel and 7.2% of the endcap modules of the pixel detector were inactive; mostly due to faulty wire-bonds or poor connections. Over the same period of data-taking, about 2.5% of the strip detector became inactive due to short-circuits in the control rings and HV lines,. Repair of the damaged modules was part of the maintenance performed during 2013; up to 1.5% of the pixel barrel, up to 0.5% of the pixel endcap, and up to 1% of the strip detectors were deemed recoverable
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