1. PMG Meeting February 2000 A Split Central Silicon Tracker W. E. Cooper on Behalf of the D0 Silicon Group 3 February 2000

2. PMG Meeting February 2000 Motivation  The baseline D0 silicon tracker uses a 66” long carbon-fiber / epoxy cylinder to support and align the barrel and F-disk modules.  Each end calorimeter can normally be opened 39” from its closed position.  That limited motion prohibits installation and removal of a 66” support cylinder in the collision hall and requires installation of the central silicon from the south in the assembly hall.  To eliminate those restrictions, we have begun investigating the possibility of splitting the central silicon into two halves about z = 0.

3. PMG Meeting February 2000 Potential Benefits  The ability to install or remove silicon with the detector in the collision hall  The ability to install and begin testing one half of the silicon while the second half is being completed  Better internal alignment of silicon within one cylinder half  Added flexibility during upgrade installation

4. PMG Meeting February 2000 Tracker Region

5. PMG Meeting February 2000 Central Silicon Installation in the Baseline Design  ECS is off the platform; ECN is open 39”

6. PMG Meeting February 2000 Proposal under Investigation  Split the support cylinder into two pieces, each ~33” long u We believe that the present support cylinder can be completed and then divided into two halves.  Support each piece at its outer end from CFT barrel 1 as before u A ring is used to connect the end of the support cylinder to the end ring of CFT barrel 1.  Support each piece at its inner end, near z=0, from the inner surface of CFT barrel 1 u Carbon-fiber reinforcement would be added to the inner surface of CFT barrel 1 to control out-of-round distortions. u Beam-like transverse deflections should be acceptable (<1 mil).

7. PMG Meeting February 2000 Installation Space u Both EC’s are shown withdrawn 39”. u The beryllium beam pipe has been moved 39” to the left of its normal position u Sections of beam pipe outside the EC’s have been removed to allow the pipes through the EC’s to be withdrawn 39”.

8. PMG Meeting February 2000 Installation Space u One possible cable arrangement during installation

9. PMG Meeting February 2000 Positioning and Alignment  Near z=0, radial support from CFT barrel 1 is proposed at ±45 o from 6 o’clock. A limiting or spring loaded radial support may be provided at 12 o’clock.  The half-length support cylinders will be installed and positioned within CFT barrel 1 at Lab 3. u Reference spheres on each half-length cylinder will be measured. u The z=0 measurements will require care. Either the Hamar laser alignment system or the Lab 3 LK could be used. u Absolute precision is expected to be ±20  m near z=0. u Precision from one half to the other is expected to be ±10  m near z=0.  The support cylinders will be moved to SiDet for silicon installation.

10. PMG Meeting February 2000 Support at z=0

11. PMG Meeting February 2000 Issues  This would be a major undertaking. We will need to be sure that it works and that backup plans are in place should there be complications.  Alignment at z=0 is critical and would need to be done well.  Handling u Each silicon half, including support structures, cooling manifolds, and the portion of cables in that region weighs about 20 LB. u The cables extending from the support cylinder along the CC face weigh another 30 LB per silicon half. u Proper support and means of guiding the cables will be needed.

12. PMG Meeting February 2000 Issues  Beam pipe u Temporary fixturing will be needed to position the beam pipe while allowing it to be moved longitudinally. u Protection will be needed to ensure that the beam pipe will not contact silicon.  Cooling u Presently, two lines supply coolant from one tracker end and two lines return coolant from the other. Coolant manifolds run the full length of the silicon tracker. u We will need two supply and two return lines at each end. Separate manifolds will be needed for each tracker half.  Engineering u Additional engineering effort will be needed.

13. PMG Meeting February 2000 Acknowledgements  Many of the ideas proposed for positioning and alignment came from Hans Jöstlein.  Many considerations in the design came from discussions among members of the D0 silicon group and the D0 upgrade.