Program Listings

N1D3 Trigger Algorithms

Monday, Nov. 2 16:30-18:10 Golden West

Session Chair: Marcello Bindi, University of Göttingen, Germany; Zhen-An Liu, Inst. of High Energy Physics, Chinese Academy of Sciences, China

(16:30) N1D3-1, First results of a detector embedded real-time tracking system with artificial retina

N. Neri, A. Abba, F. Caponio, M. Citterio, S. Coelli, J. Fu, A. Geraci, M. Grizzuti, N. Lusardi, M. Monti, M. Petruzzo

INFN, Sezione di Milano, Universita' di Milano and Politecnico di Milano, Milano, Italy

We present the first results of the prototype of a tracking system based on the artificial retina algorithm for fast track finding. The artificial retina algorithm is based on extensive parallelization and interconnectivity, and allows real-time tracking with offline-like quality with a latency $<1~\mu$s. A tracking system prototype has been built and consists of a telescope with 8 planes of single-sided strip detectors that are readout using custom ASICs providing hit position and pulse height. The artificial retina algorithm has been implemented on a novel custom data acquisition board, based on commercial FPGAs, that we have designed and constructed. The retina architecture is organized in three main blocks: a switch for the parallel distribution of the hits, a pool of processing units for the digital processing of the hits and pattern recognition, and a block for track parameter calculations. In the switch module, memory buffers store hits information according to a hold logic that activates when downstream modules are busy. We will discuss the results obtained on a beam test with few hundreds KHz track rate and when testing the system at track rates larger than 40 MHz with simulated events.

(16:50) N1D3-2, Real-Time Tracking System Using Precise Space and Time Information of the Hit

N. Neri¹, M. Petruzzo²

¹INFN, Sezione di Milano, Milano, Italy
²INFN, Sezione di Milano and Universita' di Milano, Milano, Italy

We report on the design of a real-time tracking system using precise space and time information of the hit. The system is based on a new version of the artificial retina algorithm for fast track finding where the additional precise time information of the hits is included. We demonstrate that a time resolution of 100 ps, that is already achievable in tracking detectors, allows to suppress fake track combinations while improving online track reconstruction. We describe the implementation of the algorithm for a prototype tracking system based on 8 planes of silicon sensors using commercial FPGAs. Also a time-to-digital converter with resolution below 20 ps r.m.s. is implemented in the architecture for fine tracking purposes. According to simulations the system provides offline-like quality tracks with sub-microsecond latency and it is capable to determine the time of the track with 30 ps resolution. The system is modular and can be designed to work at the LHC bunch crossing frequency of 40 MHz with hundreds of tracks.

(17:10) N1D3-3, GPU-Based Low-Level Trigger System for Real-Time Cherenkov Ring Fitting

S. Chiozzi^1,2, A. Cotta Ramusino^1,2, M. Fiorini^1,2, A. Gianoli^1,2, I. Neri^1,2, R. Fantechi³, G. Lamanna^3,4, R. Piandani³, L. Pontisso³, M. Sozzi³, M. Bauce^5,6, A. Biagioni^5,6, O. Frezza^5,6, A. Lonardo^5,6, A. Messina^5,6, P. S. Paolucci^5,6, F. Simula^5,6, P. Vicini^5,6, R. Ammendola⁷, M. Piccini⁸, C. Santoni⁸

¹University of Ferrara, Ferrara, Italy
²INFN, Ferrara, Italy
³INFN, pisa, italy
⁴INFN - Laboratori Nazionali Frascati, Rome, Italy
⁵INFN, Rome, Italy
⁶La Sapienza, University of Rome, Rome, Italy
⁷Tor Vergata, INFN, Rome, Italy
⁸INFN, Perugia, Italy

In rare decays experiments an effective online selection is mandatory for the data acquisition system (DAQ) in order to reduce both the quantity of data written and the bandwidth requirements for the DAQ system. This is the case of the NA62 experiment at CERN SPS, where the high rate of events results in such a high output data rate that it is impossible to save them on disk without some type of filtering.
A multi-level trigger system is therefore being used, which identifies the events to be saved exploiting dedicated hardware and flexible software in standard computers. In particular, the lowest level (L0) trigger is an essential component because it must handle an input event rate of the order of 10 MHz and apply a rejection factor of 10, with a maximum latency of 1 ms.
Here we show the idea of using commercial Graphics Processing Units (GPUs) to build a fast and effective L0 trigger system. In particular, the use of a GPU for the standalone reconstruction of the ring-shaped hit patterns in the RICH Cherenkov detector of the NA62 experiment is presented.
This allows building a L0 trigger based on standard off-the-shelf PCs with CPU and GPU with enhanced computation capabilities.
In our approach, the ring-fitting algorithm is seedless, i.e., it is fed with raw RICH data, with no previous information on the ring position from other detectors. Thus, we can provide the L0 trigger with a more elaborated information than a simple multiplicity number, resulting in a higher efficiency selection.
A GPU-based L0 trigger system is currently integrated in the experimental setup of the RICH detector of the NA62 experiment. This relies on a FPGA-based Network Interface Card (NIC) which receives data from the RICH subdetector via Gigabit Ethernet links and immediately store them, via PCI-express, into the memory of the GPU. The GPU then performs rings reconstruction and forwards the information to the experiment trigger system. Results will be shown.

(17:30) N1D3-4, Development of a Phase-II Track Trigger Based on GPUs for the CMS Experiment

F. Pantaleo^1,2, M. Rovere¹, V. Innocente¹, A. Pfeiffer¹, A. Schmidt², B. Hegner¹, A. B. Meyer³, G. Cappello⁴

¹Physics Department, CERN, Geneva, Switzerland
²Physics Department, University of Hamburg, Hamburg, Germany
³DESY, Hamburg, Germany
⁴Universita di Catania, Catania, Italy

The High Luminosity LHC (HL-LHC) is a project to increase the luminosity of the Large Hadron Collider to 5*10³⁴ cm^-2 s^-1. The CMS experiment is planning a major upgrade in order to cope with an expected average number of overlapping collisions per bunch crossing of 140. A key element of this upgrade will be the introduction of tracker information at the very first stages of the trigger system for which several possible hardware implementations are under study. In particular the adoption of Graphics Processing Units in first level of the trigger systems is currently being investigated in several HEP experiments. Graphics Processing Units (GPUs) are massively parallel architectures that can be programmed using extensions to the standard C and C++ languages. In a synchronous system they have been proven to be highly reliable and to show a deterministic time response even in presence of branch divergences. These two features allow GPUs to be well suited to run pattern recognition algorithms on detector data in a trigger environment. Our discussion of an implementation of a track trigger system based on GPUs will include a description of the framework developed for moving data from and to multiple GPUs using GPUDirect and executing pattern recognition algorithms.

(17:50) N1D3-5, Design and Performance of the New Magic Stereo Topological Trigger

R. Paoletti¹, M. Bitossi², R. Cecchi³, R. Lopez¹, D. Mazin⁴

¹University of Siena and INFN Pisa, Siena, Italy
²European Gravitational Observatory, Cascina, Pisa, Italy
³Institut de Fisica d'Altes Energies, Barcelona, Spain
⁴Institute for Cosmic Ray Reasearch, Tokyo, Tokyo

The MAGIC telescopes is an Imaging atmospheric Cherenkov telescopes that exploits a sensitive trigger system to achieve the lowest possible energy threshold. Rapid increase of accidental triggers caused by the ambient light and the after pulses of the photomultipliers is the main challenge when lowering the trigger threshold. Since these unwanted triggers are of random nature, requiring a simultaneous coincidence in the two telescopes removes a large fraction of them. The coincidence trigger between the telescopes strongly suppresses the accidental rate recorded by the telescope, but at even lower trigger threshold, it is difficult to discriminate at the trigger level between the triggers produced by accidental triggers or real cosmic events. A new concept of topological trigger applied to the simultaneous reconstruction in the two telescopes, called "Topo trigger", has been studied and characterized. The selection algorithm has been tested on real MAGIC data taken with the current trigger configuration and we find that no triggers are lost due to the algorithm proposed. In this contribution a detailed explanation of the topological trigger is given first results of its performance will also be shown.