A. Schöning

A fast high resolution track trigger for the H1 experiment

After 2001 the upgraded ep collider HERA will provide an about five times higher luminosity for the two experiments H1 and ZEUS. In order to cope with the expected higher event rates the H1 collaboration is building a track based trigger system, the Fast Track Trigger (FTT). It will be integrated in the first three levels (L1–L3) of the H1 trigger scheme to provide higher selectivity for events with charged particles. The FTT will allow to reconstruct 3-dimensional tracks in the central drift chamber down to 100 MeV/c within the L2 latency of ∼23 μs. To reach the necessary momentum resolution of ∼5% (at 1 GeV/c) sophisticated reconstruction algorithms have to be implemented using high density Field Programmable Gate Arrays (FPGA) and their embedded Content Addressable Memories (CAM). The final track parameter optimization will be done using non-iterative fits implemented in DSPs. While at the first trigger level rough track information will be provided, at L2 tracks with high resolution are available to form trigger decisions on topological and other track based criteria like multiplicities and momenta. At the third trigger level a farm of commercial processor boards will be used to compute physics quantities such as invariant masses. Keywords— Trigger, Fast Track Trigger, Track Trigger, FPGA, Content Addressable Memory, CAM, DSP, H1 Collaboration, HERA ColliderAfter 2001, the upgraded ep collider HERA will provide an about five times higher luminosity for the two experiments H1 and ZEUS. To cope with the expected higher event rates, the H1 collaboration is building a track-based trigger system, the Fast Track Trigger (FTT). It will be integrated in the first three levels (L1-L3) of the H1 trigger scheme to provide higher selectivity for events with charged particles. The FTT will allow reconstruction of three-dimensional tracks in the central drift chamber down to 100 MeV/c within the L2 latency of /spl sim/23 /spl mu/s. To reach the necessary momentum resolution of /spl sim/5% (at 1 GeV/c), sophisticated reconstruction algorithms have to be implemented using high-density field-programmable gate arrays and their embedded content addressable memories. The final track parameter optimization will be done using noniterative fits implemented in digital signal processors. While at the first trigger level rough track information will be provided, at L2 tracks with high resolution are available to form trigger decisions on topological and other track-based criteria like multiplicities and momenta. At the third trigger level, a farm of commercial processor boards will be used to compute physics quantities such as invariant masses.

A multifunctional processing board for the fast track trigger of the H1 experiment

The electron-proton collider HERA is being upgraded to provide higher luminosity from the end of the year 2001. In order to enhance the selectivity on exclusive processes a fast track trigger (FTT) with high momentum resolution is being built for the H1 collaboration. The FTT will perform a three-dimensional (3-D) reconstruction of curved tracks in a magnetic field of 1.1 Tesla down to 100 MeV in transverse momentum. It is able to reconstruct up to 48 tracks within 23 /spl mu/s in a high track multiplicity environment. The FIT consists of two hardware levels L1, L2 and a third software level. Analog signals of 450 wires are digitized at the first-level stage followed by a quick lookup of valid track segment patterns. For the main processing tasks at the second level such as linking, fitting, and deciding, a multifunctional processing board has been developed by the ETH Zu/spl uml/rich, Switzerland, in collaboration with Supercomputing Systems, Zu/spl uml/rich. It integrates a high-density field programmable gate array (FPGA) and four floating point digital signal processors (DSPs). This presentation will mainly concentrate on second trigger level hardware aspects and on the implementation of the algorithms used for linking and fitting. Emphasis is especially put on the integrated content addressable memory (CAM) functionality of the FPGA, which is ideally suited for implementing fast search tasks like track segment linking.

Performance of the H1 fast track trigger - operation and commissioning results

The H1 experiment at the electron-proton collider HERA has built a new fast track trigger to increase the selectivity for exclusive final states, especially those with heavy quarks, 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 5 middot 1012 mask comparisons per second using content addressable memories (CAMs). These segments are collected and transmitted via 5 Gbit/s LVDS links to custom made multipurpose processing boards, where they get linked and reconstructed to three dimensional tracks within 20 mus. On the third level resonances are identified in 100 mus by a farm of PowerPC boards. Since 2005 the FTT level one has replaced the existing drift chamber trigger and is the major track trigger of the H1 experiment. In order to further increase the selectivity the second level has started to operate. First analyses of the data show that also the second level fulfills the design specifications

60 GHz wireless data transfer for tracker readout systems—first studies and results

To allow highly granular trackers to contribute to first level trigger decisions or event filtering, a fast readout system with very high bandwidth is required. Space, power and material constraints, however, pose severe limitations on the maximum available bandwidth of electrical or optical data transfers. A new approach for the implementation of a fast readout system is the application of a wireless data transfer at a carrier frequency of 60 GHz. The available bandwidth of several GHz allows for data rates of multiple Gbps per link. 60 GHz transceiver chips can be produced with a small form factor and a high integration level. A prototype transceiver currently under development at the University of Heidelberg is briefly described in this paper. To allow easy and fast future testing of the chips functionality, a bit error rate test has been developed with a commercially available transceiver. Crosstalk might be a big issue for a wireless readout system with many links in a tracking detector. Direct crosstalk can be avoided by using directive antennas, linearly polarized waves and frequency channeling. Reflections from tracking modules can be reduced by applying an absorbing material like graphite foam. Properties of different materials typically used in tracking detectors and graphite foam in the 60 GHz frequency range are presented. For data transmission tests, links using commercially available 60 GHz transmitters and receivers are used. Studies regarding crosstalk and the applicability of graphite foam, Kapton horn antennas and polarized waves are shown.

A new track reconstruction algorithm for the Mu3e experiment based on a fast multiple scattering fit

A new fast track reconstruction algorithm developed for the high track multiplicity environment of the Mu3e experiment where track uncertainties are dominated by multiple scattering is presented. The goal of the Mu3e experiment is to search for the LFV decay μ+ → e+e−e+. To reach the sensitivity of 10-16 the experiment will be performed at a future high intensity beam line (HiMB) at the Paul-Scherrer Institute (Switzerland) providing more than 109 muons per second. Muons with a momentum of about 28 MeV/c are stopped on a target. Their decay at rest, in which mainly low momentum electrons with energies below 53 MeV are produced, is measured by the Mu3e tracking detector consisting of four cylindrical layers of thin silicon pixel sensors. The high granularity of the pixel detector with a pixel size of 80 × 80 μm2 allows for precise track reconstruction in the high occupancy environment of the Mu3e experiment reaching up to 100 tracks per readout frame of 50 ns. These tracks will be reconstructed online using a trigger-less readout scheme. The implementation of a fast 3-dimensional multiple scattering fit based on hit triplets, where spatial uncertainties are ignored, is described and performance results in the context of Mu3e experiment are presented. Also the implementation on Graphics Processor Units (GPUs) for fast online reconstruction is discussed.

General analysis of HERA II data

A model-independent search for deviations from the Standard Model prediction is performed in e±p collisions. Data collected in the years 2003-2007 corresponding to an integrated luminosity of about 340 pb-1 are analyzed. All event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is applied to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. No significant deviation is observed in the phase-space and in the event topologies covered by this analysis.

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.