Muon Barrel (MB)

The muon barrel [26] consists of 110 drift chambers arranged so that there are 44 chambers on either side of the OPAL detector, twelve chambers below and ten above. The side chambers are 10 m long, the top 6 m long and the bottom chambers 8.4 m long. All the chambers are 1.2 m wide and 900 mm deep. Four layers of chambers give polar angle coverage of $\vert\cos\theta\vert < 0.68$, but due to structural support, only one layer gives coverage up to $\vert\cos\theta\vert < 0.72$. The cells consist of two chambers containing 90% argon and 10% ethane. They have a $z$-position resolution of 2 mm and a $\phi$-position resolution of 1.5 mm.