hlt kalman filter implementation of a kalman filter in the alice high level trigger. thomas vik, uio
DESCRIPTION
Data rates ● Event rates -Central Pb-Pb: < 200 Hz -Min. bias pp: < 1000 Hz ● Event size (zero suppressed) -PbPb: ~75Mbyte -pp: ~2.5Mbyte ● Data rates -PbPb: < 15 Gbyte/sec -pp: ~2.5 Gbyte/sec ● Forseen DAQ bandwidth ~1.2 GByte/secTRANSCRIPT
HLT Kalman Filter
Implementation of a Kalman Filter in the ALICE High Level Trigger.
Thomas Vik, UiO
The ALICE detector
Data rates● Event rates
-Central Pb-Pb: < 200 Hz -Min. bias pp: < 1000 Hz
● Event size (zero suppressed) -PbPb: ~75Mbyte -pp: ~2.5Mbyte
● Data rates -PbPb: < 15 Gbyte/sec -pp: ~2.5 Gbyte/sec
● Forseen DAQ bandwidth ~1.2 GByte/sec
What is the Kalman Filter● Iterative data processing algorithm.● Advantages as a tracker:
-Track finding and fitting simultanously -No large matrices needs to be inverted. Number of computations increases linearly with the number of measurements. Therefore fast in situations with multiple scattering and many measurements. -Estimated track parameters follow closely the physical track.
Why do HLT need Kalman Filter
● Merge tracks from the different ALICE sub-detectors.
● Get good estimates of track parameters.● Reduce amount of fake tracks from the HLT
tracker.
Kalman in the TPC● Track parameters:
(y, z, D , tan , C)● Three steps:
-Make seeds: initialize track parameters. -Propagate to next padrow. Look for clusters in window around predicted position. -Update with hit which gives minimum 2.
Track following
Kalman in the HLT
● Calculate seeds from track parameters of the HLT fast tracker.
● Use clusters already assigned to tracks.● Only needs to propagate tracks according to track
model, and update parameters with already found clusters.
● Gives a fast global tracker.
Status● Timing: -
HLT tracker: setup ~50 ms/sector tracking ~70 ms/sector -HLT Kalman Filter: load tracks ~1000 ms tracking ~1000 ms
Example: heavy charm decay
● TRD triggers on possible dielectron candidates.● Large background
pions misidentified as electrons electron from conversions.
● Merge with TPC tracks, add TPC dE/dx PID remove pions misidentified as electrons.
● Merge with ITS tracks, impact parameter cut.● Background reduction by factor 10.
Conclusion
● Merge tracks from the different sub-detectors.● Need HLT tracking for ITS and TRD.● Only implemented for the TPC, however some
debugging is still needed. Must reproduce offline results.