Title: The Hades second level trigger: from the concept to the first results
1The Hades second level trigger from the
concept to the first results
Alberica Toia Jörg Lehnert II Physikalisches
Institut Justus-Liebig-Universität Gießen,
Germany for the HADES Collaboration
- Motivation and Requirements of the 2nd Level
Trigger - Functionality
- Components
- Algorithms
- Performance
- Suppression factor
- Efficiency
- Comparison Online-Offline Analysis
2HADES Physics Program
- Modification of vector meson properties due to
interaction with the medium - Access
- normal nuclear matter p, p beam
- dense nuclear matter heavy ion beam
Electromagnetic form factors of hadrons in time
like region w transition form factorfew
existing data not in agreement with VMD models
SPECTRAL FUNCTION OF r MESON
w TRANSITION FORM FACTOR
ee- -gt p0 w
Model M.Post et al., Nucl.Phys.A 689 (2001)
753 University of Giessen European Graduate School
w -gt p0mm-
need for electromagnetic probes(no strong final
state interaction) r,w -gt ee-(branching
ratio 10-5 10-6 )
Model F.Klingl, et al., Nucl.Phys.A 624 (1997)
527 Data R.Dzhelyadin et al., Phys.Lett.B 102
(1981) 296 V.Druzhinin et al., INP84-93
Novosibirsk
3HADES Detector
- Components
- MOMENTUM RECONSTRUCTION
- Mini Drift Chambers (MDC) in front and behind a
supreconducting toroid magnet - LEPTON IDENTIFICATION
- Hadron-blind Ring Imaging Cherenkov (RICH)
detector - Electromagnetic Shower detector
- Time of Flight (TOF) wall
- Features
- 106 events / s
- 45 geometrical acceptance
- up to 200 charged particles
- 1 mass resolution
TOF
SHOWER
MDC
RICH
MAGNET
4Trigger System
First Level Trigger multiplicity -gt reaction
centrality
1100
- Second Level Trigger I (Image Processing Units -
IPU)Identification of electron candidates - Cherenkov rings
- Electromagnetic showers
- Time-of-flight
- Second Level Trigger II
- (Matching Unit - MU)
- Selection of lepton pairs
- Correlation of electron candidates in front of
(RICH) and behind magnetic field (Shower, TOF) - Invariant mass determination
- 60 VME boards
- FPGA, CPLD, DSP implemented
- decision 10 ms
- process 3 GByte/s raw data
5Ring Recognition Requirements
- Ring Recognition
- constant ring diameter
- small ring size (8 pads diameter, 32 pads on
circumference) - incomplete rings (short radiator length of
36-65cm) - smeared out rings (optical distortions, wire
chamber response) - detector background
- scintillation-/Cherenkov light (radiator/window)
- direct ionization in the detector
- electronic noise
- background electron sources
- low mass dalitz pairs (p0-dalitz)
- conversion pairs
- Technical Boundary Conditions
- 105 decisions / s
- short latency (some 10 ms)
- flexible algorithms
- flexibility in input data order
6The Ring Recognition Hardware
- VMEBus Cards
- system speed 40 MHz
- Pattern Reconstruction Card
- pipelined operation, three units in parallel
- interfaces to readout and matching unit (16/20
MHz) - configuration, status, test
- Ring Recognition Unit
- 12 FPGA
- all 96 columns in parallel,rows sequential_at_12
MHz
- Pattern Reconstruction Card
- Cards for one HADES sector
- Hardware Operation
- Tests with HADES Daq-Trigger System
- with selected subsystems 17 kHz
- Standalone Tests up to 48 kHz
- Operation in CC beamtimes
- approx. 450 Mio events
- rates up to 11 kHz (current system limit)
- Operation in different modi
- ring recognition, pad recognition
7Ring Recognition Algorithm
Task Recognition of asympotic Cherenkov rings on
96x96 pad plane
- The Algorithm
- Based only on hit pattern information
- Fixed ring diameter of 8 pads
- Evaluation of 2 regions on 13x13 pad square
- ring circumference (32 pads)
- inner/outer veto region (48 pads)
- Logical OR in groups of 3-4 pads (at least
one pad) - different grouping of pads
- Number of valid pad groups in both regions
- Threshold conditions
- Local maximum search (Sum in ring region)
8Performance 1- Suppression Factor
Ring Recognition Thresholds
fraction of accepted events for different sets of
thresholds
- suppression factor depends on
- reaction conditions
- detector conditions
Matching Unit Selectivity
- fakes at low pad multiplicity
- efficiency loss for higher thresholds
9Performance 2- Efficiency
Single Lepton Recognition Efficiency
- Efficiency studied with simulations of
-
- pure e-
- e- embedded in CC
p (MeV)
- No momentum dependence
- Increases with polar angle (due to longer
radiator path length)
q (degrees)
- SIMULATIONS
- Uncertainty of event generator
- Uncertainty of hit digitization
- Need for an absolute reference system pp
-gt pph
Efficiency
Fakes/evt pure e- (10 lt ? lt 90
100 lt p lt 1000 MeV 88.7 0.17Noise
1) CC(1.9AGeV) e- 87.6 0.4
10Performance 3 Comparison Online-Offline
Analysis 1
- Good identification of particles
- Good separation between positive and negative
tracks
electrons
p 1/DqMETA - MDC
Low magnetic field better understanding of
background sources (p0 Dalitz, conversion)
positrons
MDC opening angle
11Performance 3 Comparison Online-Offline
Analysis 2
Compatible results at large opening angle
satisfactory reconstruction of open
pairs Discrepancies at small opening angle due to
different screening mechanism close pairs ?
efficiency loss ?
12Beam Time 2002 Trigger Operation
Trigger condition 1 lepton (1
ring matched by TOF / Shower) Event Reduction
8 accepted events
Matching Unit
- no polar cut
- azimuthal match ( correction due to
inhomogeneous field)
13Beam Time 2002 Lepton Enhancement
- Enhancement of correlated rings in triggered
events
Trigger condition
LVL2 Triggered Events
LVL1 Minimum Bias Events
0.2 lept / evt
0.025 lept / evt
--gt lepton candidate enhancement 8.25
14Summary and Outlook
Jörg Lehnert Alberica Toia I.Fröhlich,
A.Gabriel, D.Kirschner, W.Koenig, W.Kühn,
E.Lins, T.Pérez, M. Petri, J.Ritman, D.Schäfer,
M.Traxler II. Physikalisches Institut Justus-Lie
big-Universität Gießen, Germany GSI Darmstadt
- Characterization of second level trigger and its
components - Estimation and methods for
- Suppression factor
- Single lepton efficiency
- Pair ratios online/offline and vice versa
- Low magnetic field
- possibility of resolving close pairs
- better understanding of the ring properties
- Production run background suppressed by a
factor gt 10