W. Yan

First results from the first level of the H1 fast track trigger

The H1 experiment at the electron-proton collider HERA has built a new fast track trigger to increase the selectivity for exclusive final states and to cope with the higher background rates after the HERA luminosity upgrade. Hits measured in the central jet chamber of H1 are combined to track segments by performing 5times1012 mask comparisons per second using content addressable memories (CAMs). These segments are collected and transmitted via 5 Gbit/s LVDS links to custom made multi-purpose boards and linked to tracks. The latency of the fully pipelined processing chain implemented in programmable logic (FPGAs) is 0.72 mus. During the summer 2004 running period, the FTT level one system delivered first physics triggers from which performance figures were extracted. A single hit efficiency of more than 95% was achieved, and first studies on the pT resolution of tracks were performed using triggered rho meson candidates.

First Results from the Third Level of the H1 Fast Track Trigger

To make the best possible use of the higher luminosity provided by the upgraded HERA collider, the H1 collaboration has built the Fast Track Trigger (FTT). It is integrated in the first three levels (L1-L3) of the H1 trigger scheme and provides enhanced selectivity for events with charged particles. The FTT allows the reconstruction of tracks in the central drift chambers down to 100 MeV. Within the 2.3 mus latency of the first trigger level coarse two dimensional track information in the plane transverse to the beam is provided. At the second trigger level (20 mus latency), high resolution, three dimensional tracks are reconstructed. Trigger decisions are derived from track momenta, multiplicities and topologies. At the third trigger level a farm of commercial PowerPC boards allows a partial event reconstruction. Within the L3 latency of 100 mus exclusive final states (e.g. D*,J/psi) are identified using track based invariant mass calculations. In addition an on-line particle identification of electrons and muons with additional information from other subdetectors is performed. First results obtained from the third level, which is fully operational since 2006, are presented.