The PHENIX Forward Silicon Vertex Detector

A new silicon detector has been developed to provide the PHENIX experiment with precise charged particle tracking at forward and backward rapidity. The Forward Silicon Vertex Tracker (FVTX) was installed in PHENIX prior to the 2012 run period of the Relativistic Heavy Ion Collider (RHIC). The FVTX is composed of two annular endcaps, each with four stations of silicon mini-strip sensors, covering a rapidity range of $1.2<|\eta|<2.2$ that closely matches the two existing PHENIX muon arms. Each station consists of 48 individual silicon sensors, each of which contains two columns of mini-strips with 75 $\mu$m pitch in the radial direction and lengths in the $\phi$ direction varying from 3.4 mm at the inner radius to 11.5 mm at the outer radius. The FVTX has approximately 0.54 million strips in each endcap. These are read out with FPHX chips, developed in collaboration with Fermilab, which are wire bonded directly to the mini-strips. The maximum strip occupancy reached in central Au-Au collisions is approximately 2.8%. The precision tracking provided by this device makes the identification of muons from secondary vertices away from the primary event vertex possible. The expected distance of closest approach (DCA) resolution of 200 $\mu$m or better for particles with a transverse momentum of 5 GeV/$c$ will allow identification of muons from relatively long-lived particles, such as $D$ and $B$ mesons, through their broader DCA distributions.