Vertex Trigger Research Articles

B lifetimes and flavour tagging at CDF Run II

Data samples of ~140pb–1 gathered with CDF Run II’s displaced vertex trigger and J/Ψ trigger have led to measurements of B hadron lifetimes in exclusive and semileptonic modes which are presented here. Also discussed are evaluations of flavour tagging techniques in Run II data. PACS: 13.30.-a – 14.40.Nd.

CDF — secondary vertex trigger

At the beginning of 2002 a new data taking with an upgraded trigger system started for the CDF collaboration. One of the major improvements is the track trigger. A fast processor reconstructs tracks in the central drift chamber and the Silicon Vertex Tracker combines these tracks with the silicon vertex detector information to have track parameters with a precision as good as the offline reconstruction. This system allows CDF to trigger on tracks significantly displaced from the primary vertex with high efficiency for signal events like charm and beauty and to keep low background rates. The performances, in terms of resolution and efficiency, of both the processors are illustrated and the firsts physics results are discussed.

First CDF II heavy flavor physics results with the silicon vertex trigger

The renewed CDF II experiment recently re-started data taking. The data collected lately already provides insight in the heavy flavor capabilities of this p p experiment. As a benchmark of these possibilities we present two preliminary results: the measurement of the branching fractions BR ( D° → π + π −) and BR( D° → K + K −) relative to BR ( D° → K ± π ±) and the measurement of the invariant mass difference between D s ± → φπ ±, φ → K + K − and D ± → φπ ±, φ → K + K − The preliminary results are BR(D 0 → π +π −) BR(D 0 → π ±pi; ∓ = 3.37 ± 0.20 (stat) ± 0.16 (sys)%, BR(D 0 → K +K −) BR(D 0 → K ±pi; ∓ = 11.17 ± 0.48 (stat) ± 0.98 (sys)% and Δm ( D s − D +) = 99.28 ± 0.43 ( stat) ± 0.27 ( sys) MeV/ c 2. All results are consistent with PDG expectations.

The BTeV experiment

BTeV is an experiment being constructed at the Fermilab p p collider, designed to study mixing, CP violation, and rare decays of beauty and charm hadrons. The detector covers the forward region (10–300 mrad) and includes a state of the art silicon pixel detector providing real time information to the first level detached vertex trigger, a Ring Imaging Cherenkov detector, providing excellent charge particle identification, a PbWO 4 electromagnetic calorimeter, and a muon system.

BTeV Level 1 vertex trigger

BTeV is a $B$-physics experiment that expects to begin collecting data at the C0 interaction region of the Fermilab Tevatron in the year 2006. Its primary goal is to achieve unprecedented levels of sensitivity in the study of CP violation, mixing, and rare decays in $b$ and $c$ quark systems. In order to realize this, it will employ a state-of-the-art first-level vertex trigger (Level 1) that will look at every beam crossing to identify detached secondary vertices that provide evidence for heavy quark decays. This talk will briefly describe the BTeV detector and trigger, focus on the software and hardware aspects of the Level 1 vertex trigger, and describe work currently being done in these areas.

The LHCb vertex trigger

The second level trigger in LHCb (level 1) is based on the ability to reconstruct high impact parameter tracks in the vertex detector. The feasibility to reconstruct tracks using only the vertex detector in a time window of less than 1.7 ms is shown. Several algorithms under study to improve the performance of the vertex trigger are briefly described.

Evaluation of SCI as a fabric for a computer-based pattern recognition trigger running at 1.17 MHz

The future CERN experiment, LHCb, has the need for a high-speed first-level vertex trigger. The silicon vertex trigger of LHCb processes events at a rate of 1.17 MHz for a total of 3 GB/s of data. To handle this amount of data at the given rate, the plan is to build a cluster of approximately 250 nodes connected by a low-latency network. We have evaluated SCI as a possible candidate for this network. It is especially appropriate due to its low latency and overhead. The memory-mapped character of the connection makes it well-suited for applications relying on device-to-device copy mechanisms. We will present the results obtained with the Dolphin 66/64 PCI cards built around the PSB66 and LC3 chips. The behavior of two different topologies, two-dimensional (2-D) torus and ring, have been studied in detail. Results of DAQ/realtime relevant scenarios have been obtained using transport methods as programmed I/O, DMA, and device-to-device copy mechanism. Analysis of both hardware and software has been used to obtain a detailed picture of the traffic patterns on the buses involved.

Array of Cherenkov radiators for PHOBOS at RHIC

An array of Cherenkov radiators (“the Cherenkov counters”) for the measurement of the vertex position of heavy-ion gold–gold collisions for the PHOBOS experiment at relativistic heavy ion collider is described. These simple, versatile, and highly efficient detectors provide a low bias and easily understood hardware (on-line) vertex trigger. This trigger is ready for the data-acquisition system in about 650 ns . The position resolution of the vertex distribution found by the Cherenkov counters is approx. 4 cm and is very stable as function of the centrality of the collisions. The general characteristics of the Cherenkov counters, their design parameters, and performance are presented, along with the implementation of the hardware vertex trigger used for PHOBOS during the 2001 run.

The LHCb vertex locator and displaced vertex trigger

The vertex locator of the LHCb experiment must provide precise information on the production and decay vertices of b-hadrons both off-line and for the second level trigger. This article reviews the design of the vertex detector and vertex trigger algorithm. Recent test beam results are provided and the future development programme is outlined.

BTeV, a dedicated B experiment at Fermilab

BTeV is a proposed second generation detector designed to do in-depth studies of CP violation and rare B and charm decays. This forward collider detector is designed to operate at the Fermilab Tevatron. Among the unique features of the experiment are a central dipole magnet and a Level I vertex trigger.

Investigation of a VLSI neural network chip as part of a secondary vertex trigger

An analog VLSI neural network chip (ETANN) has been trained to detect secondary vertices in simulated data for a fixed target heavy flavour production experiment. The detector response and associative memory track finding were modelled by a simulation, but the vertex detection was performed in hardware by the neural network chip and requires only a few microseconds per event. The chip correctly tags 30% of the heavy flavour events while rejecting 99% of the background, and is thus well adapted for secondary vertex triggering applications. A general purpose VME module for interfacing the ETANN to experiments, equipped with ADC/DAC circuits and a 68070 CPU, is also presented.

WA92: A fixed target experiment to study beauty in hadronic interactions

The essential feature of the described experimental techniques is the use of two specially designed pieces of hardware: a high precision “decay detector” and a fast secondary vertex trigger processor. Experiment WA92 should be able to obtain a sufficient data sample to measure lifetimes of B ± and B 0 and the B hadroproduction cross section.

Construction and performance of a thin cylindrical multiwire proportional chamber with cathode pad readout for the H1-experiment

We discuss the construction of a thin (0.14% radiation length) cylindrical multiwire proportional chamber with cathode pad readout used in the first level vertex trigger of the H1-experiment at HERA (DESY). The chamber has an active length of 2190 mm, and anode plane radii of 157 and 166 mm with a 3 mm gap. The cathode consists of a graphite layer on a Kapton foil with a resistivity of 400 kΩ/⦜. In order to have a two-dimensional readout the Al-layer on the back of the outer cathode of each chamber is segmented in 36 mm wide pads covering 45° in azimuth. The performance of the chamber with various gas mixtures was studied. Typically a length of the high voltage plateau of 200 V and a time resolution of 75 ns base width has been achieved, sufficient to separate individual HERA bunch crossings. The behavior of the chamber at pad boundaries has been measured and the performance for particles crossing at angles down ϑ = 16° is described.

QUARK FLAVOR SENSITIVITY OF THE MAMMALIAN CORTEX

Most applications of Neural Networks in High Energy Physics have involved the use of simple backpropagation or learning vector quantization networks on offline data sets with relatively low dimensionality. In the present work we raise the question of whether ideas drawn from the current understanding of animal nervous systems can be used to build trigger systems for use on raw high energy physics data of high dimensionality. The problem of a secondary vertex trigger is chosen as an illustrative example.

Bounds on reliability of a noncoherent system using its length & width : Klaus D. Heidtmann. IEEE Trans. Reliab.R-31 (5), 424 (1982)

The Collider Detector at Fermilab (CDF) experiment's Silicon Vertex Trigger (SVT) is a system of 150 custom 9U VME boards that reconstructs axial tracks in the CDF silicon strip detector in a 15μs pipeline. SVT's 35μm impact parameter resolution enables CDF's Level 2 trigger to distinguish primary and secondary particles, and hence to collect large samples of hadronic bottom and charm decays. We review some of SVT's key design features. Speed is achieved with custom VLSI pattern recognition, linearized track fitting, pipelining, and parallel processing. Testing and reliability are aided by built-in logic state analysis and test-data sourcing at each board's input and output, a common interboard data link, and a universal “Merger” board for data fan-in/fan-out. Speed and adaptability are enhanced by use of modern FPGAs.