The CMS Drift Tube Chambers

The Drift Tube (DT) chambers are a fundamental component of the CMS detector, further information of the DTs can be found here. Their aim is to identify, measure and trigger on muons from LHC collisions in the central part of the detector. Each chamber is a gaseous detector composed by hundreds of individual measurement units called "cells", capable of reconstructing muon tracks on a large detection surface. Many interesting physics signals from CMS contain high momentum muons, therefore a highly performant muon system is fundamental.

Our group has been a member of the DT group since the first stages of the experiment. We have participated in the design and assembly of the system, having built in our workshop almost 30% of the detector, and most of its readout electronics. Further information about the CIEMAT DT electronics can be found here. Since more than 15 years the construction, tests, commissioning, operation, maintenance and upgrade of the detector are one of the main activities of our group. 

  • DT description
  • Operation
  • DT Electronics
  • HL-LHC and CMS upgrade

The basic element of the DT chamber is the drift tube, which has cross section dimensions of 13 mm x 42 mm. The total number of sensitive cells is around 172,000. Any charged particle going through the cell volume will generate a signal (hit) in its anodic wire that will be amplified and discriminated by the front-end electronics for further time digitization. The position of the charged particle can be related to the time measurement since the drift velocity in the cell volume is approximately constant. The maximum drift time in each tube is around 400 ns and the spatial resolution that can be achieved at the cell level is in the order of 250 µm.

Image of a DT chamber during assembly.

A DT chamber is made of three (or two in MB4) Superlayers (SL), each consisting of four layers of rectangular drift cells staggered by half a tube width. The wires in the two inner and outer SLs are parallel to the beam line and provide the track measurement in the magnetic bending plane (r,  Ф). In the central SL, the wires are orthogonal to the beam line and measure the position along the beam. This inner q Superlayer is not present in the MB4 chambers, which therefore measure only the Ф coordinate.

The DT chambers are installed in the five wheels of the return yoke of the CMS magnet (named YB-2, YB-1, YB0, YB+1 and YB+2). Each wheel is divided in 12 sectors each covering ~30º around the interaction point and each sector is organized in four stations of DT chambers named MB1, MB2, MB3 and MB4 going from inside to outside, where MB stands for Muon Barrel. There are a total of 250 DT chambers in CMS.

Transverse view of the CMS detector.


Image of a quadrant of the CMS detector with the view of all the muon systems.