H1 Central Trigger
The H1 Trigger System is divided into four levels. The first and second level systems (L1 and L2) are phase-locked to the HERA accelerator clock of 10.4 MHz. The L1 system provides a trigger decision for each bunch crossing after 2.3 sec. without causing dead time. A subset of the subdetector system data is used by most systems to generate fast informations concerning the general properties of the event. This is encoded in Boolean decisions (Trigger Elements). The L2 system decision is presently derived from a combination of two independent hardware systems within 20 s of the preceding L1 Keep signal, allowing sufficient time for transmission of trigger information and computation of the L2 trigger response.
L1 : 2.3 sec. L2: 20 sec. L3: < 800 sec.  ca. 100 ms
Level 1

(synchronous to HERA clock)

Level 2

(synchronous to HERA clock)

Level 3

(not yet implemented)

Level 4

(asynchronous to HERA clock)

Subdetector Triggers

Rate: 1 kHz

FrontEnd Hardware
Neuronal Network/
topological Analysis
Rate: 100 - 200 Hz

single RISC processor

Rate: 50 Hz

power PC farm

Rate: 5 Hz

Stops the Pipelines Starts the Readout Starts Event building

Data Logging

L1 Internal Page L2 Internal Page
Neuronal Network Trigger
Topological Trigger


L4 Home-page

Published Papers concerning the Central trigger

Internal Notes concerning Central Trigger (L1/L2/L3/L4) and subsystem Trigger (H1 internal)

Subsystem Triggers building the Central Trigger Decision Logic for the H1 Detector :
Trigger Subsystem
General Detector Links to the Detector used
Internal Trigger Links
Central Trigger (Subsystem Triggers)    CT internal page
DC-R/Phi Trigger CJC1/CJC2 Drift Chambers  
z-Vertex Trigger CIP / COP / FPC Prop Chambers     zVtx internal page
MWPC-NIM Trigger CIP Prop Chamber  
DC-R/Z Trigger CIZ / COZ Drift chambers  
Forward Ray Trigger CIP / FPC Prop chambers  
Time of Flight Trigger BToF / FToF / FIT / VLQ -ToF  
Liquid Argon Trigger LAr_el/LAR_had main Calo    LAr Trigger internal page   Jet Trigger Page
Forward Muon Trigger fwd_muon drift chamber  
SpaCal Trigger  Spcl_el/Spcl_had   backw. Calo    SpaCal Trigger internal page
Digital (central) Muon Trigger Instrument. Iron (FC/FB/BB/BC)    Digi_mu internal page
Very low Q^2 Trigger VLQ Si-Tracker/Calo    VLQ Calo Trigger
Backward DC Trigger BDC   
Luminosity Trigger etag_8/33/44/108; gamma_tagger  
Forward Proton/Neutron Trigger FPS / FNC  

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Last modified: Tue Jun 6 17:31:14 MST 2000by Martin zur Nedden (nedden@mail.desy.de)