A modified magnetic calorimeter

The modification and the practical use of a magnetic calorimeter detector (MAC) for the TRISTAN experiment are discussed. As for the central drift chamber, the radius of 50 cm is kept, the identification of ''wrong sign'' μ+μ- or e+e- is scarcely required, and the solenoidal field is increased to the design limit, 10 kG. The spatial resolution will be about 100 μm, and a factor of 5 or 10 in the spatial resolution will be obtained by using additional field wires. The entire central drift chamber can be replaced by a TPC which has the additional advantage of dE/dx and particle identification capabilities. For the electromagnetic calorimeter, about 104 crystals of bismuth germanate (Bi4Ge3012 = BGO), of which the energy resolution was proven to attain a few MeV, are used. A preamplifier, a shaping amplifier and a logarithmic amplifier are attached to each crystal. The BGO shell is about 30 cm thick. The new solenoid coil made of copper or aluminum has an 80 cm inside radius. The hadron calorimeter is used with minor repair and some electronics upgrade. As for the muon drift system, the momentum resolution is estimated to be 0.3 at 30 GeV. A number of physics objectives for e+e- annihilation at TRISTAN energy with the practical use of the proposed detector are summarized: i) the calorimetry experiments including R measurement near the Z0 pole, jet studies, μ+- charge asymmetry, e+- charge asymmetry, μ+- and e+- inclusive spectra, and quark flavor tagging, ii) the precise γ or e+- energy measurement including e+e- → γ anti-ν near the Z0 pole, γ (t anti-t) + H, and toponium studies, iii) the lifetime measurement of a 15 GeV tau, and the hadron identification and inclusive spectra. (Ito, K.)