DELPHI Barrel Muon Chambers

Technical description

The DELPHI Barrel Muon chambers (MUB) consist of 1372 drift chambers arranged into 24 sectors on the A end and C end of DELPHI, with 2 additional sectors between the legs of the detector. The layout of these sectors, as viewed from the C end of DELPHI is shown below

Each sector contains three modules of chambers, the inner module is embedded in the HCAL, the outer and peripheral modules lie on the outside of DELPHI, the peripheral modules cover the holes in the coverage of the other modules in adjoining sectors, providing more-or-less hermetic muon chamber coverage in the barrel. The outer and peripheral contain 7 chambers arranged in two layers on layer of 4 chambers the other of 3 staggered with respect to the first layer, allowing a solution in most instances of the left right ambiguity in a single chamber. In the inner module there are three layers, in a 5-4-5 arrangement usually only chambers from the first two layers are read out, the third layer being used only if there is a fault with chambers in the other layers. The layout of the modules and chambers is shown below.

Each chamber can provide up to three signals, one anode signal and two delay line signals (near and far), which can be used to give space points for particles passing through the chambers. The time of the anode signal gives the perpendicular distance of the track from the anode wire, while the time difference of signals from the two ends of the delay line give the position of the track along the length of the chamber. A combination of three signals from one chamber is known as a triplet if one signal is missing then the combination is called a doublet. Single signals are usually the result of noise in the electronics. The internal geometry of a muon single muon chamber is shown below.

Chambers in sectors 1 to 12 are read out on the D side, those in sectors 13-24 are read out on the B side. The readout chain for a signal wire is shown below.

Each signal from the chambers has a time associated to it by an LTD. There are 14 LTD's in total, 7 in counting room B2, and 7 in counting room D2. Each LTD channel has 6 multiplexed inputs, thus it is necessary to store each signal in a separate buffer known as a Hit Latch Buffer (HLB), so that it is possible to work out which chambers were hit in a given event. The anode/near/far signals from a given chambers are distributed to more than one LTD to minimise the risk of loss of a genuine triplet of hits corresponding to the passage of a real particle through the chamber. It sometimes occurs that a signal is registered in an HLB but does not have a corresponding time in the LTD, and vice versa. The logical flow of data into the LTD and HLB is show below.

Quantities measured

Space points for particles passing through the Muon Chambers:

R, Phi and Z