**Instrumentation inside the Inner Field Cage of STAR**

The Solenoidal Tracker At RHIC (STAR) detector is designed to search for
signatures of quark-gluon plasma formation, investigate the properties
of strongly interacting matter at high energy density and to study the
spin dependent parton distributions of the proton. To accomplish these
goals the baseline STAR detector includes a large acceptance Time
Projection Chamber (TPC) with full azimuthal coverage ( = 2, \< 2). A
Silicon Vertex Tracker (SVT) and Silicon Strip Detector (SSD) to detect
secondary vertices from short lived hyperons is located co-axial with
the beam line, inside the inner field cage of the TPC. A barrel
electromagnetic calorimeter (BEMC) and an endcap electromagnetic
calorimeter (EEMC) located outside the TPC are used to measure
transverse energy, and to trigger upon jets. These detectors are located
inside a solenoidal magnet with a 0.5T field. A complete description of
the instrumentation which comprises the STAR set-up may be found in "The
Relativistic Heavy Ion Collider Project: RHIC and its Detectors", NIM
A449 (2003).

**Present Status:**

Beginning in 2000, continuing until summer of 2007, the instrumentation
inside the STAR inner field cage at mid-rapidity consisted primarily of
the STAR Silicon Vertex Tracker (SVT): 3 concentric layers of silicon
drift detectors. An additional layer of double sided silicon strip
detectors (SSD) contributed by the French institutions participating on
STAR was added outside the third layer of the SVT in 2002. Collectively
these two tracking detectors allowed for a resolution of approximately
100-150 microns at the vertex, affording capability for detector
secondary decays of long lived mesons and hyperons (e.g. K^0^~S~, ^0^).

These detectors operated successfully for Cu+Cu data taking in Run 5 and
Au+Au data taking in Run 7, and after an extensive calibration and
alignment effort, have demonstrated that they achieved their design
performance. Physics results on K^0^~S~, ^0^, as well as potentially
limited information on charm production in the reactions studied are
expected in the summer of 2008.

Having achieved their scientific mission and the design limit of their
performance, these detectors were removed from the STAR detector in the
summer of 2007 to free up space for a new low mass, high precision
charm-class microvertex detector (the Heavy Flavor Tracker), and to
reduce the material shadowing the endcap-calorimeter and the STAR TPC
for polarized proton measurements made in Run 8.

At forward pseudo-rapidity ( 2.5 \< \< 3.8 ) on either side of the
interaction point, Forward Time Projection Chambers contributed by MPI
are located. Utilizing a radial drift to maximize resolution in this
high track density environment, these detectors provide tracking in this
forward region which is essential to extend STAR's tracking coverage in
pseudorapidity, and to allow for event-plane determination outside the
acceptance of the TPC at mid-rapidity. This is essential to eliminate
auto-correlations in the determination of elliptic flow.

Both the SVT+SSD and the FTPC's are supported from the STAR detector,
and do not couple to the standard Be beam pipe provided by C-AD which is
located on the longitudinal axis of the STAR detector.

**Future Plan:**

In the future, after the critical point search in Run 10, it is planned
that the FTPC on the west side of the STAR detector will be removed to
make room for the support structure of the Forward GEM Tracker, a
tracking detector based on Gas Electron Multiplication (GEM) technology
which will be crucial to accurately determine the charge sign of
electrons and positrons from W decays which are detected in the STAR
endcap electromagnetic calorimeter. If the Heavy Flavor Tracker project
is sufficiently advanced that its support structure is ready to be
installed at this time (summer of 2010), the east FTPC will be removed
as well. Otherwise, the FGT support structure will be installed first
utilizing a modification of the support for the existing SSD, and the
HFT support structure will be installed during a subsequent shutdown.
The support structure for the FGT and the HFT are being coordinated by
J. Kelsey at MIT who is the integration engineer for both projects. The
two structures are being made modular so that they can be installed at
separate times if necessary, and so that the installations can be
performed during regular summer shutdown periods.

The FGT will consist of six triple-GEM disk, located perpendicular to
the beam line at a longitudinal position on the west side of the
interaction point which allows the detector to fully shadow the
acceptance of the STAR endcap electromagnetic calorimeter.

The STAR HFT will consist of two layers of active pixel sensors,
followed radially outward by a single layer of silicon strips and the
existing double sided SSD.

A new Be beam pipe with a smaller radius and minimal thickness will be
required to minimize multiple scattering. Discussions with the
Collider-Accelerator Department concerning the requirements and design
of this beam pipe are ongoing. The STAR inner tracking detectors will be
supported from the STAR detector, and will not couple to the support for
the new beam pipe.

A new event plane detector, or an upgrade of the existing STAR Beam-Beam
counters will be required to replace the functionality of the Forward
Time Projection Chambers for determining the event plane, particularly
for future low energy runs, once these detectors are removed. A design
based on MRPC technology is being considered in case the first option is
chosen.