1. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 1/18 ALICE HLT in the TPC Commissioning IRTG Seminar Heidelberg – January 2008 Jochen Thäder Kirchhoff Institute of Physics

2. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 2/18 ALICE - Overview heavy-ion mode –5.5 ATeV pb-pb –10 MHz interaction rate Aim : Creation of the Quark-Gluon Plasma a state of matter predicted to exist during the first few microseconds after the big bang TPC

3. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 3/18 ALICE – High-Level Trigger (HLT) Large off-the-shelf PC cluster farm Several hundred nodes. Tasks: –Incoming data reduction ~ 22 GB/s (HI mode)  1.25 GB/s (to permanent storage) –Trigger decisions Event rejection Online data reconstruction

4. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 4/18 ALICE Time Projection Chamber (TPC) Drift chamber Inside the L3 solenoid (homogeneous B-field) Main tracking device Largest data producer 36 sectors (on 2 sides) 216 readout partions (patch) ~ 26 rows per patch ~ 90 pads per row = 557,568 pads OROC IROCrow pad

5. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 5/18 Reconstruction Steps Raw Data (Ordering, Zero Suppression) Cluster Finding (in readout partition) Tracking (Conformal-Mapping / Track Follower) - Data amount + Computing amount

6. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 6/18 HLT - TPC Online Monitoring (AliHLTGUI) Reconstructed event visualisation in real time Supports HLT developers to finalize online reconstruction algorithms Supports detectors specialists to understand detector Connects to every data source in HLT online analysis chain Displays: –Raw data –Cluster data –Track data

7. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 7/18 General Features AliHLTGUI Selection of single sectors, range of sectors, pair of sectors, all Event loop / single events Show track parameters Cuts on track parameters (nHits, p t, charge,...) Used / unused cluster (in respect to tracking process) 3D display / histograms Option of saving histograms Easy extendible for special needs

8. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 8/18 Features AliHLTGUI (1) Pad Display –Signal histograms for raw ADC data with neighbouring pad Padrow Display –Padrow histogram for raw ADC data Front Display –Endcap view TPC histogram

9. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 9/18 Features AliHLTGUI (2) 3D Display –Geometry, raw ADC data, cluster, tracks –Selection of single sectors, range of sectors, pair of sectors, all sectors Charge Display –Charge distribution of found Clusters

10. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 10/18 Features AliHLTGUI (3) Residuals Display –Residual distribution of all tracks –Residuals of single tracks –Track parameter of single tracks

11. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 11/18 AliHLTGUI - Class Layout 3 Layers –Graphical User Interface (GUI) Layer Qt based –Interface Layer Handles Qt ROOT, data input from HLT chain –Worker Layer ROOT based AliHLTTPCDisplay Worker Worker Layer Interface Layer GUI Layer ROOT Containter AliHLTTPCDisplayMain Control panel action ROOT action response ROOT response Data AliHLTGUI AliHLTTPCDisplayXXX

12. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 12/18 HLT Cluster for the TPC Commissiong 7 Opteron PCs in CR2 connected to TPC via DDLs 1 Opteron PC in TPC Cleanroom running test setup for TPC – DAQ – HLT interfaces All equipped with : –HLT Data framework –AliRoot offline framework –modified TPC analysis components –HLT TPC Online Display

13. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 13/18 TPC Commissioning - Setup TPC sector TR TDS Front-End Processors second sector HLT - cluster FEP CFRPH-RORC BDW RPH-RORC BDW FEP H-RORC BDW H-RORC BDW FEP H-RORC BDW CFRPH-RORC BDW CF RP CFRP CFRP DAQ HLT Online Display reconstrcution data flow display data flow Components RP :RORCPublisher CF: ClusterFinder TR: Tracker TDS: TCPDumpSubscriber BDW: BinaryDataWriter

14. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 14/18 General Experiences for HLT Several issues not related to analysis components –Hardware –Infrastructure –Hardware / Software Interface  Typical startup problems  All solved  Not so much time for reconstruction tests

15. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 15/18 Issues related to Raw Data Raw data from TPC not zero suppressed  Lots of noise  Clusterfinding / Tracking impossible Solution:  Noise Reduction –Zero-Suppression added –Occupancy limit for single pads added

16. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 16/18 Laser Event with Central Membrane

17. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 17/18 Issues related to Tracking TPC not designed for tracks parallel (or small angle) to rows Existing tracker not designed for tracks parallel (or small angle) to padrows cosmic particle  New tracking approach Based on cellular automaton of Ivan Kisel First version finished and tested in last week of data taking Further tests necessary

18. > IRTG – Heidelberg 2007 < Jochen Thäder – University of Heidelberg 18/18 Further working fields Implementation of combined TPC-TRD Jet trigger for the HLT (Not yet started) –Improvement of the TPC tracking algorithms –TRD tracks as seeds for jets –Continued with TPC tracks Search for –High pT jets in hadron-hadron collisions –Di-jets in pb-pb collisions  Prepare the HLT for first year ALICE