Hep'97 #306 the Silicon Tracker in the Delphi Experiment at Lep2 Preliminary Delphi Collaboration

The nal upgrade of the DELPHI Silicon Tracker, to enable DELPHI to meet the physics requirements of LEP2, was completed in 1997. The tracker contains 888 detecting elements having a total active surface of about 1.6 m 2 of silicon, has 1399808 readout channels and covers polar angles between 11 and 169. It consists of: the Silicon Barrel, extending from 21 to 159 and playing the role of vertex detector and the Very Forward Tracker (VFT) in the form of two silicon endcaps, providing standalone pattern recognition and increasing the track reconstruction eeciency between 11 and 25. The complete Silicon Barrel and a large part of the VFT was already in operation during the 1996 data taking at LEP2. The complete Silicon Tracker is now installed and is currently taking data. The Silicon Barrel consists of 640 AC coupled microstrip silicon detectors, arranged in three layers at average radii of 6.3, 8.9 and 10.8 cm. The 149504 electronics channels read signals collected on the strips which give either R measurements (in all three layers, with a readout pitch of 50 m) or Rz measurements (in two and a half layers, with a readout pitch between 42 m and 176 m). The material in the sensitive region is kept to a minimum by the use of double sided detectors, double metal readout and light mechanics. Each of the two VFT endcaps contains two layers of silicon pixel detectors and two layers of ministrip detectors. The pixels (squares of 330 330 m 2 , 1225728 in total) are connected to the readout electronics channels using an industrial bump bonding method. Their readout is performed by a sparse data scan circuit. The AC coupled ministrip detectors (96 in total) have a strip pitch of 100 m, a readout pitch of 200 m and a signal to noise ratio of about 40. DELPHI is one of the rst experiments in which the pixel detectors are used in tracking.