The H1 Forward Silicon Tracker

The new H1 Forward Silicon Tracker (FST) extends the central silicon tracker (CST), which was already used in HERA-I, into the forward direction (see fig.54a). The FST consists of five layers of two silicon strip planes each providing $u$-$v$ coordinates and two $r$-planes. It covers a range of polar angles between $8^{\circ}$ and $16^{\circ}$. The additional angular acceptance of the FST leads to an increase of the reach for charm physics in Bjorken-$x$ as illustrated in fig.54.

In the 2004 data, the FST was shown to have a signal hit efficiency of close to 100% and a track efficiency of larger than 95% [236]. The alignment of the device and the optimization of the reconstruction algorithms are not fully completed yet. For the analysis of charm production optimal transverse momentum resolution and impact parameter resolution are required. These are limited by significant multiple scattering effects. At the end of the 2004 running period the FST was damaged by a water leak. It is planned to reimplement a reassembled FST detector, equipped with radition hard electronics, in the shutdown 2005/06.

Figure: a) Side view of the interaction region of the H1 detector. The three silicon strip detectors FST, CST and BST are indicated. b) Acceptance for charm events $(ep\rightarrow D^*X \rightarrow D^0\pi _s X \rightarrow K\pi \pi _s X)$ for $Q^2<100$ GeV$^2$ using the central tracker and the CST (open points) and adding the FST (and the backward silicon tracker BST) with different assumptions on the acceptance range $\eta$ of the $D^*$ (full points).