The STAR Heavy Flavor Tracker

A Brief Introduction to the STAR Heavy Flavor Tracker

(with additional links at the bottom of the page)

The STAR Heavy Flavor Tracker is a high resolution Si pixel detector that will surround the interaction point at STAR and provide high resolution space points for forming tracks. The detector will be mounted at the center of the STAR Time Projection Chamber.

The STAR TPC is approximately 4 meters long and 4 meters in diameter. The Heavy Flavor Tracker is much smaller. A conceptual design for the HFT is shown, below. The HFT is built with approximately 2 cm x 2 cm Si chips, and 10 chips in a row form a ladder. The ladders are arranged to cover two cylindrical layers; one layer at approximately 2.5 cm radius and the other at approximately 7 cm radius. A ladder is approximately 20 cm long.

The figure on the right shows forty five Si chips; they have not yet been cut or sliced from the 6 inch wafer on which they were fabricated. The sensor chip design and fabrication is done by Marc Winter’s group in Strasbourg, France, with additional R&D done in Berkeley. The readout electronics are being developed in Berkeley and are based on components and designs for ALICE at CERN.

The mechanical engineering challenge is to deploy ladders full of these chips around the STAR beampipe, and to know and hold their position to 10 microns precision (and stability).

The STAR beampipe is not a simple object and it, too, is a significant engineering challenge.

The design of the beam-pipe has changed since the figure, above, was printed. However, the essential point is that the beam-pipe is very thin and requires an exo-skeleton over the thinnest part of the beam-pipe in order to make is sufficiently stiff and robust so that it can be handled in the RHIC collider environment. The HFT detector must fit inside the exoskeleton. Another significant feature of the beam-pipe is that it tapers down from a diameter of 10 cm far from the interaction point to a diameter of 4 cm near the interaction point. The HFT must be able to expand and collapse as it slips over the beampipe, from one end, and finally locks in place at the interaction point.

The HFT is designed so that it can be removed from the STAR detector in a matter of a few hours. It is unique in this respect; no other STAR detector is removable without taking STAR offline for several months. Our goal is to be able to remove and replace the HFT during a 1 day shutdown of the collider.

The proposed funding profile for building the HFT is shown below. This is not the technically driven schedule, but rather it is the potentially available schedule of funds based on the BNL mid-term plan for RHIC detector upgrades. The technically driven schedule is faster than what is shown, below.

Probable HFT Funding Profile

06 07 08 09 10

4% 14% 11% + 4% 35% 35%

R&D R&D R&D+Const Const Const

There are several R&D challenges that need to be addressed during the development of the HFT. They include:

– The Silicon Chips

– Further refinement of on-chip electronics

– Readout Electronics

– Speed, heat dissipation, compatibility with STAR DAQ

– The Mechanical Arms to insert the detector

– Alignment and stability

– Calibration, Tracking & Software

– New levels of precision

– The beam pipe

– Smaller than ever before … Operation and robustness

We propose to go through these developmental steps by building a sequence of prototype detectors. These R&D steps are summarized in the following high-level diagram.

The RHIC collider usually runs from late November until early May. Thus the ‘x’ marks the date on the timeline when the detector component must be installed in STAR in preparation for the next years run.

A preliminary cost and schedule estimate is available in Microsoft Project format. A high level roll-up is shown, below.