Speaker
Description
Summary
A key point of CMS (Compact Muon Solenoid) is its ability to trigger on and reconstruct muon tracks at high luminosities. This task is performed by various CMS subdetectors, among them, the DT (Drift Tube) chambers.
The 250 DT chambers are hosted in the five wheels of the CMS barrel, with a total of 172,200 drift cells. A DT chamber is made of three (or two in the outer layer) superlayers, each made by four layers of rectangular drift cells staggered by half a cell, which provide track measurement in the magnetic bending plane (r,) and in the Z position along the beam line.
DT read-out electronics is designed to perform time digitization of the signals generated by charged particle tracks and further data merging to achieve a read-out of the full detector at a Level-1 trigger rate of 100 kHz.
The purpose of the DT trigger system is to provide muon identification and precise momentum measurement, as well as bunch crossing identification. It provides an independent Level-1 muon trigger to the experiment, selecting the four best muon candidates on each event.
From May 2008 DT has participated in several long periods of data-taking with the 100% of the detector operational, such as CRUZET (Cosmics Run at Zero Tesla) and CRAFT (Cosmic Run At Four Tesla). Participation in these Global Runs has proven the DT system to be well integrated inside the CMS framework, with good reliability and stability. Operation during more than one year showed that failure rates are very low.
About 320 and 370 million events of cosmic muons were collected at CRUZET and CRAFT respectively and no significant effect on the performance of the electronics was observed due to the magnetic field.
Continuos operation over more than 3 weeks showed good stability of the power distribution systems, low voltage and high voltage, as well as of the reliability of the trigger and read-out links. Some issues with the cooling system are now being solved.
Furthermore, running periods at simulated high rate have shown no problems on the performance on the system when operated at full speed.
The efficiency to reconstruct high quality local track segments has been measured to be of the order of 99% in all chambers. Also, very good stability in the calibration constants has been found.
Moreover, fine tunning of the trigger system timing, which was optimized for cosmic tagging, shows a very good synchronization with the rest of the subsytems.
Noise levels were monitored and the number of death and noisy cells is very low and it is stable in time. Sensitivity to some sporadic noise, usually related with activities in the cavern, is being studied at present.
Experience during these exercises has allowed improving significantly control and monitoring systems, which at present allow configuring all parts in an easy and flexible way and obtaining comprehensible synthetic information of the complete status of the detector.
Summarizing, the behaviour of the system is very satisfactory, being ready for operation at LHC running.
