High Level Triggerapplications fortheALICE experiment

FortheALICEexperiment attheLHC,a High LevelTrigger Systemforon-line eventselection anddatacom- pression hasbeendeveloped andacomputing cluster ofseveral hundreddual-processor nodesisbeinginstalled. A majorsystemintegration testwascarried outduring the commissioning oftheTimeProjection Chamber(TPC), wherethe HLT alsoprovides amonitoring system. Allmajorpartslike a small computing cluster, hardware input devices, theon-line data transportation framework, andtheHLT analysis couldbetested successfully. A commoninterface forHLTprocessing components hasbeendesigned torunthecomponents fromeither theon-line oroff-line analysis framework without changes. Theinterface adapts thecomponenttotheneedsoftheon-line processing andallows thedeveloper atthesametimetousetheoff-line framework foreasydevelopment, debugging, andbenchmarking. Results canbecompared directly. Fortheupcoming commissioning ofthewholedetector, the HLT iscurrently prepared torunon-line dataanalysis forthe maindetectors, e.g. theInnerTracking System (ITS), theTPC, andtheTransition Radiation Detector (TRD).TheHLT pro- cessing capability isindispensable forthePhotonSpectrometer (PHOS), wheretheon-line pulse shapeanalysis reduces thedata volumebyafactor 20.A commonmonitoring framework isin placeanddetector calibration algorithms havebeenported to theHLT. Thearticle describes briefly thearchitecture oftheHLT system. Itfocuses on typical applications andcomponentde- velopment.