Sessions - DPG-Tagungen

Nuclear Physics Tuesday
HK 18 Instrumentation and Applications II
Time: Tuesday 15:30–18:30 Room: C
HK 18.1 Tue 15:30 C
Particle identification in the HADES experiment ∗ — •T.
Christ 1 , M. Golubeva 2 , R. Holzmann 3 , M. Jaskula 4 , J.
Mousa 5 , P. Salabura 4 , P. Tlusty 6 , T. Wojcik 4 , and D.
Zovinec 3 for the HADES collaboration — 1 TU München, Garching —
2 INR, Moscow, Russia — 3 GSI, Darmstadt — 4 Jagiell. Univ. Cracow,
Poland — 5 Univ. of Cyprus, Nicosia, Cyprus — 6 CAS, Rez, Czech
Republic
The HADES experiment at GSI is designed to reconstruct lepton pairs
from decays of vector mesons produced in hadron and heavy ion induced
nuclear reactions at energies of 1-2 AGeV. For a quantitative
understanding of the measured data it is necessary to extract the absolute
abundancies of particle species emitted from the collision zone and
to perform event-by-event track identification. In the HADES analysis
package HYDRA the particle identification (PID) software assigns particle
species to tracks reconstructed from various detector signals. The
HADES PID ansatz is based on Probability Density Functions (PDFs)
and Bayes’ theorem. This ansatz requires measurements and simulations
of particle properties and detector response and a statistical analysis of
correlations among particle signatures. The method and first results from
the PID analysis of data taken in C+C collisions are presented.
∗ supported by BMBF (06MT190) and GSI (TM-FR1, TM-KR1).
HK 18.2 Tue 15:45 C
Prototype of a Dedicated Multi-Node Data Processing
System for Realtime Trigger and Analysis Applications —
•Daniel Kirschner, Marco Destefanis, Roukaia Djeridi,
Ingo Fröhlich, Wolfgang Kühn, Jörg Lehnert, Tiago Perez,
and Alberica Toia for the HADES collaboration — II. Phys. Inst.
Giessen, Heinrich-Buff-Ring 16, 35392 Giessen
Modern experiments in hadron physics like the HADES detector at
GSI-Darmstadt produce a large amount of data that has to be distributed,
stored and analyzed. Analysis of this data is very time consuming
due to the large amount of data and the complex algorithms needed.
This problem can be addressed by a dedicated multi-node and multi-CPU
computing architecture interconnected by Gigabit-Ethernet. Dedicated
hardware has the advantages over “Grid-Computers” in skaleability, price
per computational unit, predictability of time behavior (possibility of real
time applications) and ease of administration. Gigabit-Ethernet provides
an efficient and standardized infrastructure for data distribution. This
infrastructure can be used to distribute data in an experiment as well
as to distribute data in a multi-node computing environment. The prototype
VME-Bus card has of two major units: a network unit featuring
two Gigabit Ethernet over Copper connections and a computational part
featuring a TigerSHARC Digital Signal Processor. The discussion will
concentrate the real-life performance of Gigabit Ethernet as the main
topic. Supported by bmbf and GSI.
HK 18.3 Tue 16:00 C
Performance of the Trigger System of the HADES Detector
in C+C reactions at 1-2 AGeV — •Jörg Lehnert 1 , Alberica
Toia 1 , Roukaia Djeridi 1 , Ingo Fröhlich 1 , Wolfgang Koenig 2 ,
Wolfgang Kühn 1 , Tiago Perez 1 , James Ritman 1 , Daniel
Schäfer 1 , and Michael Traxler 2 for the HADES collaboration
— 1 II. Physikalisches Institut Univ. Gießen — 2 Gesellschaft für
Schwerionenforschung Darmstadt
The HADES detector at GSI Darmstadt investigates the dilepton production
in hadron and heavy ion induced reactions up to 2 AGeV. The
second level trigger system (LVL2) is designed to reduce the event rate
by selecting lepton pairs within a given invariant mass window. The
hardware-based LVL2 consists of Image Processing Units (IPU) which
perform pattern recognition to detect lepton signatures in different subdetectors
and a Matching Unit (MU) which combines the position and
momentum information of these signatures into tracks to select events
with lepton pairs of given invariant mass.
Since the recognition of Cherenkov rings is the most selective algorithm
of the trigger, its behavior has been studied with the help of simulations
and by comparing it to the offline analysis algorithm. This allowed to
study and optimize the performance of the second level trigger and to
improve the analysis of the dilepton content of the analyzed C+C reaction
at 1-2 AGeV in terms of efficiency and purity of the signal. Results
collected during the experiment runs in November 2001 and November
2002 are presented.
HK 18.4 Tue 16:15 C
New VHDL design for the HADES TOF Trigger Unit — •T.
Pérez for the HADES collaboration — II. Physikalisches Institut, Universität
Gießen
The HADES spectrometer is intended to investigate the dilepton production
especially from vector meson decays. The low branching ratios
of vector mesons into dileptons, in the order of 10 −5 . To reach the necesary
amount of statistics it is necessary the use high reaction rates up to
10 5 central heavy ion reactions per second. In order to reduce such an
amount of data a very sofisticated online trigger system is used. With a
combination of trigger several modules for distribution (CTU and DTU)
and detector specific processing (IPUs), maximun speed the goal. That
lead us to upgrade our Detector specific Trigger Units to newer, more
flexible and faster design. And, finaly to adopt VHDL,the standard high
level description language in electronics, as a tool to reach that goal.
HK 18.5 Tue 16:30 C
High Level Trigger Identification of High Energy Jets in ALICE
— •Constantin Loizides for the ALICE collaboration — August-
Euler-Str. 6, 60487 Frankfurt
One interesting observable at ALICE will be the measurement of the
inclusive jet cross section at 100 to 200 GeV transversal jet energy and
its fragmentation function; both to be compared to pp. The window
of about 100 to 200 GeV transversal jet energy is compatible with the
expected pt resolution of the inner tracking complex (ITS+TPC+TRD)
and the energy of the leading parton, but requires an HLT online processing
of TPC data at a rate of 200 Hz central PbPb in order to collect
sufficient statistics. The online trigger algorithm running on the HLT
system is based on charged tracking and jet recognition using a cone jet
finder algorithm,which might be improved by the additional online evaluation
of the EM calorimeter towers. The dependence of the efficiency
versus the selectivity of the trigger has been studied by simulations of pp
and PbPb interactions using PYTHIA and HIJING events. For a chosen
parameter set of the trigger algorithm the triggered events are the relevant
sample of events to be further analyzed by offline. Their resulting
jet Et distribution and the corresponding fragmentation functions might
be sensitive to different jet attenuation scenarios.
HK 18.6 Tue 16:45 C
A Fault Tolerant Data Flow Framework for Clusters
— •Timm M. Steinbeck for the Alice High Level Trigger
collaboration — Kirchhoff Institute of Physics, Ruprecht-Karls-
University Heidelberg, Im Neuenheimer Feld 227, D-69120 Heidelberg,
http://www.ti.uni-hd.de/HLT/
The ALICE experiment’s High Level Trigger (HLT) has to reduce the
data rate of up to 25 GB/s to at most 1.25 GB/s before permanent
storage. To cope with these rates a PC cluster system of several 100
nodes connected by a fast network is being designed. For the system’s
software an efficient, flexible, and fault tolerant data transport software
framework is being developed. It consists of components, connected via
a common interface, allowing to construct different configurations that
are even changeable at runtime. To ensure a fault-tolerant operation, the
framework includes fail-over mechanisms to replace whole nodes as well
as to restart and reconnect components during runtime of the system.
The last functionality utilizes the runtime reconnection feature of the
component interface. To connect components on different cluster nodes
a communication class library is used to abstract from the network used
to retain flexibility in the hardware choice. It contains two working prototype
versions for TCP and the SCI SAN. Extensions can be added
to this library without modifications to other parts of the framework.
Performance tests show very promising results, indicating that ALICE’s
requirements concerning the data transport can be fulfilled. In a test
with simulated proton-proton data for a part of the TPC an event rate
of more than 430 Hz was achieved with full tracking being performed.