Tradeoffs in Drift Cramber

For the physics of the future, at or above 100 GeV center of mass energy, tracking devices will need: 1) Good segmentation, since particle densities are large. 2) Many samples along each track for pattern recognition, momentum resolution, and possibly dE/dx measurement. As an example, to do a good job separating two high momentum tracks from hadronic decay of the Z", angular segmentation 10 mrad is required; typical nearest neighbor tracks of average momentum are separated by . 100 mrad.' If we multiply 10 mrad by 1 meter we get a track separation of 1 cm. Although small this is still large enough that the solutions to the tracking problem developed over the past 5 years are applicable. Thus the central detectors presented in the LEP Letters of Intent are typically outgrowths of existing devices. One solution to the tracking problem is to make a chamber with many small cells; cell full-widths 1 to 2 cm would be needed.' This requires many wires and electronics channels, however each channel is relatively simple in design. An alternative design, still of the axial type, is to make a chamber with large cells containing several sense wires per ce11.3 These chambers have many fewer wires than in the case of small cells, however multihit electronics is needed. The electronics must not only allow recording of several hits, but also suppress the long l/t tail of a drift chamber pulse so that later hit information is not degraded by earlier pulses." This type of chamber has the advantage that most of the very good precision of the drift chamber is available at the pattern recognition stage of track finding since the uniform field over most of the drift path makes a simple linear space-time relation quite accurate. For this reason a local solution of the left-right ambiguity is possible if the wires are slightly (position resolution) staggered, and an accurate local tangent vector to the track can be found by using the times measured by two nearby wires. For tracks coming from the origin this allows a local calculation of the transverse momentum since the radius of curvature is given by: