Jrg LehnertDPG Spring Meeting 04 Cologne

1
Performance of the HADES Trigger System in CC
reactions at 1-2 AGeV

• J. Lehnert, A. Toia, R. Djeridi, I. Fröhlich, W.
  Koenig, W. Kühn, E. Lins ?, T. Perez, M.
  Petri?, J. Ritman, M. Traxler for the HADES
  Collaboration
• II. Physikalisches Institut Univ.
  GießenGesellschaft für Schwerionenforschung
  Darmstadt ? Current Address Beck IPC, Wetzlar
  ?Current Address Robert Bosch GmbH,
  Schwieberdingen
• The HADES Dilepton Trigger
• Trigger Analysis Strategy
• Characterisation of Single Trigger Components
• Performance in CC Experiments (Nov01/02) Event
  Sample, Efficiency, Reduction
• Status Outlook

Trigger Analysis part ofPhD thesis of A. Toia
2
The HADES Dilepton Trigger
MDC

• First Level Trigger
• TOF multiplicity reaction centrality
• Second Level Trigger I (Image Processing Units)
• Cherenkov rings
• Electromagnetic showers
• Time of flight
• Second Level Trigger II (Matching Unit)
• Correlation of electron candidates in front of
  (RICH) and behind (Shower, TOF) magnetic field
• Invariant mass determination
• Third Level Trigger
• Matching with MDC tracklets (offline)

MAGNET
ElectronSignatures
SHOWER
RICH
TOF
3
Trigger Analysis Strategy
Second Level Trigger
Hardware orHardware Emulation
Source
LeptonSignature
IPU Lepton Candidate
Lepton
MU Matched Lepton
Combination into pairs
CorrelatedHits
In Addition Investigation of a reaction with
known dilepton cross section pp ? pph
4
Online Ring Recognition
? Most significant differences between online and
offline algorithm
? Highest selectivity in electron identification
Lepton Efficiency from Simulations

• Lepton Efficiency Compared to Analysis Leptons
• 80 of leptons found
• 92 of leptons in positively triggered
  events lepton efficiency lt event efficiency

Pair Efficiency Closed pairs ? dependent
(48-66) Open Pairs (w) pair efficiency 45
Efficiency
Fakes/evtpure e- 85.6 0.17CC(1.9AGeV)
e- 85.6 0.40
Leptons 0.03/evt ?Misidentified
leptons dominant
5
Full Lepton Algorithm
Shower Condition
Matching Unit Window
? No q (momentum) cut
? Symmetric f-dependent f cut
Charge Ratio Layer2/Layer1
Df vs f
6
Triggered Event Samples in CC
Dileptons
LVL1 Downscaled Event Sample (Minimum
bias) LVL2 Online Lepton Trigger LVL3 Offline
Match with MDC
Leptons
Opening AngleDistribution
Scaled to same number of leptons !!
7
Trigger Performance in CC
Event Reduction
Lepton Efficiency

• Nov01/02 CC at 1/2 AGeV
• Lepton Efficiency 57
• Event efficiency 62
• Event efficiency with modified
• ring recognition parameters 83
• algorithm 89
• Dilepton (4) 84
• Dilepton (8) 92

Hardware Single Lepton Trigger
Lepton Enhancement

• Event Reduction
• LVL2 12
• LVL3 5
• Enhancement LVL2-LVL1 LVL3-LVL1
• Lepton 7.5 13
• Dilepton (4) 10 15.6
• Dilepton (8) 11 17.3

8
Status and Outlook

• HADES Second Level Trigger actively used since
  Nov02 CC beamtime
• Achieved event reduction sufficient for DAQ
  purposes
• lepton trigger
• Good understanding of trigger behaviour
• Unbiased lepton sample (Lvl2)
• Reasonable efficiencies
• Useful for offline analysis (e.g. Lvl3)
• Dilepton trigger
• Heavier systems
• Analysis of data from pp beam time (Jan04)
  pp ? pph

HADES Trigger Distribution Talk T. Perez now
HADES Analysis Results Plenary Talk J. Stroth
Thu. 900
European Graduate School