CMS Bulletin

MUON DETECTORS: DT

It is three years without access to the chambers and their front-end electronics, and the DT collaboration is preparing for a substantial work of maintenance and upgrade during LS1 in 2013/14.

Even though, thanks to the constant care provided by the on-site operation team, the fraction of good channels is still very high at 98.8% and the downtime caused to CMS as a consequence of DT failures is to-date <1%, the original robustness of the system has deteriorated and many small local interventions are needed to restore it.

The excellent stability and linearity with luminosity of the DT trigger rates has been
exploited and currently DT rates are published as an additional online luminometer in WBM.
The calibration is calculated from the correlation with pixel luminosity for 2011 data while
a preliminary independent calibration for 2012 data based on the analysis of Van der Meer scan data
 (project of CERN summer student Jessica Turner) has to be refined into periods
to take care of changes to the DT trigger system (V_drift, changes in the overlap with CSC).


Thorough measurements of the noise from single-hit rate outside the drift-time box as a function of the LHC luminosity show that the noise rate and distribution are amazingly consistent with expectations from the simulations in the Muon TDR, which have guided the detector design and construction. The MB4 at the top of CMS show the largest rate. Extrapolations to luminosities of 1-2 10³⁴ cm^–2s^–1 expected in 2015–2018 are well within the operation range of the DT chambers.

The upgrade activities planned for LS1 evolve in good accordance to the schedule, both for the theta Trigger Board (TTRB) replacement and for the Sector Collector (SC) relocation from UXC to USC. The TTRB work aims at reconstituting the stock of spare boards for the long-term operation of the chamber Minicrates. With the SC work, data and trigger primitives from each of the 250 DT chambers will be available in USC on optical fibers. Since the project was reviewed in an ECR by a panel of experts from the CMS Electronics and Technical Coordination teams in June, measurements on the signal transmission from the chambers up to the USC electronics have been going on with the prototypes of the new electronics, in order to optimise the design parameters of the optical transmission links. This work is the corner stone for any long-term upgrade plan of the DT system.