The CMS collaboration has for the first time operated a whole sector of drift-tube chambers (DTCs) and detected cosmic muons. This is the first stage in commissioning the CMS Muon Barrel detector prior to installation below ground later in 2006.
Since the summer of 2004, the team building the DTCs – from Aachen, Bologna, Madrid (CIEMAT), Padova and Torino – has been engaged in the delicate and complex operation of installing the chambers in the CMS experiment’s iron yoke. The chambers have 12 layers of drift tubes, arranged in three groups of four, two measuring the R-φ coordinate and one measuring the z-coordinate. Each layer has up to 60 tubes. Unlike conventional drift-tube systems, consecutive layers are staggered by half a tube-width, enabling the DTCs to generate trigger signals for CMS, using a “mean timer” method.
Chambers constructed in the collaborating institutes are first assembled on the main site at CERN together with their on-chamber cables, pipes and mini-crates. These “dressed” chambers require very few external components to become operational, and so undergo thorough pre-installation tests before being transported to the CMS site at Cessy. There they are inserted into the CMS iron yoke in the surface building. The chambers are then ready for final commissioning tests, which include long data-taking runs that exploit the chamber’s self-triggering capability with cosmic muons. By February two of the five wheels in the CMS barrel yoke had been instrumented, and 82 DTCs commissioned.
This first sector test marked the beginning of a long series of tests that will culminate this spring with the CMS Cosmic Challenge. At this point the five barrel wheels and the two endcaps will be pushed together in the surface building and the superconducting solenoid operated for the first time. Segments of all sub-detectors will be present and cosmic muons will be detected and measured. The lowering of the CMS sections into the underground cavern is due to begin in the summer.
