APPENDIX: Upgrades to the SVT
a.) Addition of a fourth SDD layer
An SVT extension to a four layer design is being considered. Increased standalone secondary reconstruction capability in the SVT, specifically important for the search for low momentum multistrange baryons and charmed mesons in the central rapidity range can be accomplished. The matching efficiency between SVT and TPC will be further enhanced, providing better tracking capabilities in the event of unexpected high charged particle multiplicities. Both alternatives, an innermost layer as well as an outermost layer, have been considered. An inner layer would be more cost effective, as it requires a small increment in the number of electronics channels whilst yielding an increase in vertexing capabilities. However it presumes a substantial reduction in beam pipe diameter and also requires the design and fabrication of smaller rectangular drift detectors. Thus, the feasibility of an inner layer is still under investigation. Technical difficulties associated with the addition of an outer layer to the present SVT design are minor as it only requires the extension of the present support structure to a radius of about 20 cm. However full azimuthal coverage requires 22 additional ladders, each carrying 8 detectors. 176 additional wafers, identical to the SDDs in layers 1,2, and 3, are needed. By only instrumenting every other anode the number of additional channels is reduced to 42240 without severe compromise in position resolution and track separation. Due to the moderate incremental cost of the FEE, the upgrade cost is estimated not to exceed 250,000 dollars.
b.) Radial SDD array in forward rapidity range.
A high precision tracking device operated in conjunction with a forward
calorimeter would be perfectly suited for the measurement of isospin
fluctuations in the relevant phase space range (
= 3 - 5)
A tracking device positioned at large rapidities will also enhance the
capabilities of higher momentum D meson reconstruction.
We propose to use a four layer device of radial
drift detector disks with a diameter of 8 cm. Such detectors were
designed and developed by the instrumentation group at BNL, and
successfully used in NA45 (CERES) at CERN. Each wafer consists of
about 6000 channels. Four detectors will be located inside the beam pipe,
perpendicular to the beam at distances ranging from 30 cm to 40 cm.
This device has to reside inside the beam pipe and thus relies on RHIC beam
optics to confine the beam to the detector inner radius of 0.25 cm.
The radiation levels inside the beam pipe have to be carefully studied to
determine the feasibility of such a device. The cost of this upgrade is
moderate (around 200,000 dollars) as it does not require the development
of new components. The electronics will be identical to the central SVT
readout chain and thus incremental.
Both upgrades would enhance the physics of STAR and the SVT. At this point we request no money, but rather consider an additional upgrade proposal at a later stage.