Pixel Trigger documentation and operation

Links:

Pit FED's server prelimirary manual (pdf)

PIT FED server doxygen documentation (html)

PIT Database configuration library doxygen documentation (html)

PIT configuration database schema

 

The SPD and the Fast-OR 

The ALICE Silicon Pixel Detector (SPD) comprises the two innermost layers of the ALICE Inner Tracker System (ITS). The SPD includes 120 detector modules each consisting of 10 pixel chips, each one of these is capable of generating a Fast-OR signal indicating the presence of at least one pixel hit in the corresponding 8192 pixel matrix. The ALICE Level 0 Pixel Trigger System extracts them, processes them and delivers an input signal to the Central Trigger Processor for the first level trigger decision within a latency of 800 ns.

The PIT Control system

 pixel_trigger_dcs

 

The pixel trigger control system is a distributed system composed by 2 machines, one running PVSS acting as the supervision layer and another one running the PIT FED server acting as the driver layer of the system:

The PIT supervision layer

Based in CERN standard CERN’s standard SCADA (Supervisory Control and Data Acquisition) PVSS . It controls the overall  trigger status taking appropriate corrective actions to maintain the system stability and ensuring the trigger quality.

The PIT driver layer

The PIT FED (Front End Device)  Server  acts as the driver layer of the system. Its communicates with the hardware through the ALICE standard Digital Data Link (DDL), publishes status and receives commands from other computers in the network using CERN standard Distributed Information Management System (DIM).

The PIT Control System Interconnections

The Pixel Trigger Control system was integrated as part of the ALICE Detector Control System (DCS). It the has to interface with several other ALICE sub-systems:

  • the SPD DCS with which exchanges data during calibration scans,
  • the CTP from which it receives configuration commands
  • the Alice Experimental Control System (ECS) to whom it sends status information.

PIT_DCS_InterConnections

 

Pixel Trigger outputs and algorithms

Two versions of PIT processing firmwares are available since Jan 2013. See Firmware 1  and Firmware 2 below.

 

Pixel Trigger Firmware 1

PIT output number
Trigger label
Description
Trigger logic
0 0SMB Minimum bias trigger  Ntot >= total threshold  AND  Nin >= inner threshold  AND  Nout >= outer threshold
1 0SH1 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
2 0SH2 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
3 0SH3 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
4 0SH4 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
5 0SPF Past future protection  Ntot >= total threshold  AND  Nin >= inner threshold  AND  Nout >= outer threshold
6 0SX1 Spare background  Nin >= Nout + background offset inner layer
7 0SX2 Spare background  Nout >= Nin + background offset outer layer
8 0SBK Background  Ntot >= background threshold both layers
9 0SCO Programmable cosmic algorithm  PROGRAMMABLE
 
Algorithm selection
Parameter number
PIT output it applies
Parameter name
Default value
Minimum value
Maximum value
0 0 0 Total threshold 1 0 1200
0 1 0 Inner threshold 1 0 400
0 2 0 Outer threshold 1 0 800
1 1 1 Inner threshold 1 0 400
1 2 1 Outer threshold 1 0 800
2 1 2 Inner threshold 1 0 400
2 2 2 Outer threshold 1 0 800
3 1 3 Inner threshold 1 0 400
3 2 3 Outer threshold 1 0 800
4 1 4 Inner threshold 1 0 400
4 2 4 Outer threshold 1 0 800
5 0 5 Total threshold 1 0 1200
5 1 5 Inner threshold 1 0 400
5 2 5 Outer threshold 1 0 800
6 0 8 Background threshold both 1 0 1200
6 1 6 Background offset inner 1 0 400
6 2 7 Background offset outer 1 0 800
9 0 9 Cosmic algorithm selector 0 0 5
Output number 9 corresponds to a cosmic algorithm selector.  For the selection of the cosmic algorithm see the table below
Algorithm selector
Algorithm logic
0 Coincidence top outer && bottom outer
1 Coincidence inner layer && outer layer
2 >= 2 Fast-Or in the inner layer && >= 2 Fast-Or in the outer layer
3 Coincidence top outer && top inner && bottom outer && bottom inner
4 Coincidence top outer && bottom outer && inner layer
5 Global OR

 

 

 

 

Pixel Trigger Firmware 2

PIT output number
Trigger label
Description
Trigger logic
0 0SMB Minimum bias trigger  Ntot >= total threshold  AND  Nin >= inner threshold  AND  Nout >= outer threshold
1 0SH1 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
2 0SH2 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
3 0SH3 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
4 0SH4 High multiplicity  Nin >= inner threshold  AND  Nout >= outer threshold
5 0STP

Topological trigger for ultra peripheral collisions

Presence of at least two back-to-back pairs of hits in the phi plane (z projection), each pari with one hit in the inner and one in the outer layer
6 0SLT Multiplicity threshold, less than logic Nin <= inner threshold AND Nout <= outer threshold
7 0SX2 Spare background  Nout >= Nin + background offset outer layer
8 0SBK Background  Ntot >= background threshold both layers
9 0SCO Programmable cosmic algorithm  PROGRAMMABLE
 
Algorithm selection
Parameter number
PIT output it applies
Parameter name
Default value
Minimum value
Maximum value
0 0 0 Total threshold 1 0 1200
0 1 0 Inner threshold 1 0 400
0 2 0 Outer threshold 1 0 800
1 1 1 Inner threshold 1 0 400
1 2 1 Outer threshold 1 0 800
2 1 2 Inner threshold 1 0 400
2 2 2 Outer threshold 1 0 800
3 1 3 Inner threshold 1 0 400
3 2 3 Outer threshold 1 0 800
4 1 4 Inner threshold 1 0 400
4 2 4 Outer threshold 1 0 800
5 1 6 Inner threshold 1 0 400
5 2 6 Outer threshold 1 0 800
6 0 8 Background threshold both 1 0 1200
6 2 7 Background offset outer 1 0 800
9 0 9 Cosmic algorithm selector 0 0 5
Output number 9 corresponds to a cosmic algorithm selector.  For the selection of the cosmic algorithm see the table below
Algorithm selector
Algorithm logic
0 Coincidence top outer && bottom outer
1 Coincidence inner layer && outer layer
2 >= 2 Fast-Or in the inner layer && >= 2 Fast-Or in the outer layer
3 Coincidence top outer && top inner && bottom outer && bottom inner
4 Coincidence top outer && bottom outer && inner layer
5 Global OR