Commissioning of the ALICE-PHOS trigger LIJIAO LIU Email:Lijiao.Liu@ift.uib.no University of Bergen and Huazhong Normal University for the ALICE collaboration May, 2010

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

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

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.

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

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

( 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 )‏

L0 latency (test-bench results) <800ns

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

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

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

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

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

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

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

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

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!