1. Commissioning of the ALICE-PHOS trigger
LIJIAO LIU
University of Bergen
and
Huazhong Normal University
for the ALICE collaboration
May, 2010

2. Outline Introduction (ALICE and PHOS) PHOS readout and trigger system
Firmware and performance of the PHOS trigger
Conclusion and outlook

3. ALICE experiment PHOS detector Heavy-ion collisions
Study the properties of Quark Gluon Plasma
PHOS detector
Electromagnetic Calorimeter with high resolution
Measuring electromagnetic showers with matrix of PbWO4 crystals
Contribution to the generation of L0 and L1 triggers

4. ALICE hardware trigger
Three level trigger : L0, L1, L2
Purpose: Select the event of interest and reduce the overall dataflow
Latency : L0 (1.2 μs), L1 (6.5 μs), L2 (88μs)
PHOS Trigger Requirement L0
minimum bias trigger for pp collisions
high-pt trigger for pp and PbPb collisions
arrival at CTP in 800 ns
L1 - provides information on neutral particles produced in Pb-Pb collisions
Cluster reconstruction -> energy
Identify three energy ranges: L1Low, L1Middle, L1High
Total transverse energy trigger
Isolated photon trigger (to distinguish direct photon from decay photon)
L1 must be ready in 6.1 μs.

5. PHOS readout and trigger system
Front End Card (FEC)
ALICE TPC Read Out (ALTRO)
Trigger region unit (TRU)
Trigger OR (TOR)
Central Trigger Processor (CTP)
Local Trigger Unit (LTU)
Readout Control Unit (RCU)
Data acquisition (DAQ)
L1 accept (L1a)
L1 rejection (L1r)
ALTRO : mixed analogue-digital custom integrated.
circuit dedicated to the digitisation and processing detector signals.
Add real Altro data and Fake altro data flow here

6. The trigger electronics
TOR
TOR:
40 RJ45 input links for 40 TRUs
Virtex4 FPGA
Hosts DCS-board for remote configuration
and re-programming
L0 is ORed in firmware
DCS
TRU:
112 analogue inputs -> 12 bit ADCs
FPGA -> process raw trigger data and prepare L0 decision
40 bit readout bus – communication with RCU
remote configuration and re-programming by
DCS-board on RCU
TRU
3 modules have been installed
Each module has 8 TRUs
Only 1 TOR for PHOS

7. ( 91 parallel calculations in FPGA )‏
L0 trigger algorithm
Serial digital signal
L0 to CTP
Sliding window
Miss pedestal substraction
4x4 (=2x2 Analog-OR)‏
28 x PWO => N = 14
TRU (PHOS)‏
16 x PWO => M= 8
N-1 x M-1 = 91 combinations
( 91 parallel calculations in FPGA )‏

8. L0 latency (test-bench results)
<800ns

9. Commissioning results
Noise of the trigger channels
ALICE work in progress
1 ADC count  30 MeV

10. Commissioning results
Triggering on cosmic rays – e.m. shower
ALICE work in progress
trigger
channel
matrix

11. Commissioning results
Triggering on cosmic rays – muons (MIPs)
Trigger: PHOS with relatively low trigger threshold ( 180 MeV)
Readout: PHOS and TPC
Trigger purity: (events with muon tracks in TPC) / (number of PHOS triggers)
Preliminary result:
Purity  23 % keep in mind: MIP signal ( 210 MeV) is just above trigger threshold
To do:
Noisy channels not yet excluded
Global threshold so far, set individual threshold
ALICE work in progress

12. Commissioning results
Triggering on cosmic rays – muons (MIPs)
Trigger: PHOS with low trigger threshold
Readout: PHOS
Energy distribution of PHOS clusters (mainly single crystal clusters):
Preliminary result:
MIP peak at around 210 MeV (PHOS is not yet fully calibrated)
ALICE work in progress

13. Commissioning results
Triggering on pp collisions
Trigger latency – within specifications
ALICE work in progress

14. Commissioning results
Performance of PHOS – pp collisions
ALICE min. bias trigger – energy channels
Invariant mass distributions for different transverse momentum bins: clear pi0 signal
ALICE work in progress

15. Commissioning results
Trigger efficiency and fake trigger rate – pp collisions
Data set: 155k events
Full trigger information (trigger channels) has been recorded in addition to energy channels
energy channel matrix
trigger channel matrix
signal
no signal
fake trigger
inefficiency
analysis ongoing

16. L1 firmware in TOR Basic L1 (L1Low, L1Middle, L1High)
Receive the 4X4 sum from TRU (3 μs for data transfer)
Find the cluster with the highest energy
Issue L1 decision
Total energy trigger Et
Isolated photon
Construct list of clusters
Decision of isolated photon

17. Conclusion and outlook
PHOS performs according to specs so far (more details in Zhongbao’s and Renzhuo’s talk)
PHOS L0:
timing fulfills 800 ns requirement
performance study ongoing
expected to take part in physics runs in the near future
PHOS L1:
basic L1 trigger firmware works in the lab
behavioural simulation for finding the isolated photon works, we are now implementing the algorithm in HW (in the FPGA)
Thanks for your attention!