hlt collaboration (28-jun-15) 1 high level trigger l0 l1 l2 hlt dieter roehrich uib trigger...
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HLT Collaboration (18 Apr 2023) 1
High Level Trigger
L0L0L1L1L2L2HLTHLT
Dieter RoehrichUiB
• Trigger• Accept/reject events
• Select • Select regions of interest within
an event
• Compress• Reduce the amount of data
required to encode the event as far as possible without loosing physics information
• Provide HLT-ESDs for online monitoring• Access to the results of the event
reconstruction
• Physics Requirements
HLT Collaboration (18 Apr 2023) 2
Physics Applications
• Quarkonium spectroscopy • Dielectrons• Dimuons
• Open Charm• Jets • Pileup removal in pp
Detectors
DAQ HLT
Mass storage
HLT Collaboration (18 Apr 2023) 3
Quarkonium• Dielectrons
– HLT task• Reject fake TRD triggers and reduce trigger rate by factor of more than 10
– Status• Fast TPC pattern recognition – done• Additional PID by dE/dx – done• Adaption of Kalman filter for HLT – done• Combined track fit TRD-TPC-ITS – in progess
– To do• Emulate the TRD Global Tracking Unit
(TRD tracklet merging and PID)
• Dimuons– HLT task
– Utilizing tracking chamber information and improving momentum resolution
– Sharpening of pt-cut– Rejection factors: low pt-cut: 5, high pt-cut: 100
– Status– Complete simulation including cluster finder – done– Full scale prototype HLT farm (UCT) – done– FPGA cluster finder – in progress– FPGA interface – in progress
T. Vik, PhD thesis, Oslo, 2005
HLT Collaboration (18 Apr 2023) 4
Open charm
• HLT task– Detection of hadronic charm decays: D0 K– + +
– About 1 D0 per event (central Pb-Pb) in ALICE acceptance
– After cuts
» signal/event = 0.001
» background/event = 0.01
• Status– Detailed study of timing profile of offline algorithm - done
– Adaption of ITS tracking to HLT and speed-up – done
– Optimization of D0 finder – in progress
– Combine HLT tracking and D0 algorithm – in progress
• To do– estimate the efficiency for appling D0-offline-cuts online
– extend study to D+, D*+
HLT Collaboration (18 Apr 2023) 5
Online • Available modules
• TPC cluster finder (CF)
• TPC track follower (TF)
• Kalman fitter
• TPC Hough transform tracker (1)
• TPC Hough transform tracker (2)
• TPC cluster deconvolution
• TPC performance monitor
• TPC dE/dx
• TPC data compression (1)
• TPC data compression (2)
• ITS tracker
• Dimuon cluster finder
• Dimuon tracker
• Jet cone finder
• D0 finder
• PHOS pulse shape analysis
HLT Collaboration (18 Apr 2023) 6
Tracking performance for CF/TF
Tracking efficiency Momentum resolution
Computing time: 13 sec per event (dn/dy=4000) on a 1kSPECInt machine
A. Vestbø, PhD thesis, Bergen, 2004
HLT Collaboration (18 Apr 2023) 8
Tracking performance for Hough transform – version 1
• Gray-scale Hough transform– Image space: raw ADC counts
– Transform space: circle parameters
– Histogram increment: charge
Local Hough transform
Clusteranalysis
Peaks=track candidates
too CPU-time consuming
A. Vestbø, PhD thesis, Bergen, 2004
HLT Collaboration (18 Apr 2023) 9
Tracking performance for Hough transform – version 2 (1)
• Linearized prehistoric Hough transform– Image space: conformal mapped cluster boundaries– Transform space: straight line parameters– Histogram increment: history of missing padrows, conditional
slice of TPC sector Corresponding Hough Space
Collaboration with the Offline group: Cvetan Cheshkov
HLT Collaboration (18 Apr 2023) 10
Tracking performance for Hough transform – version 2 (2)
Cvetan Cheshkov
Tracking efficiency
dN/dy=8000dN/dy=6000dN/dy=4000dN/dy=2000
B=0.5T
HLT Collaboration (18 Apr 2023) 11
Tracking performance for Hough transform – version 2 (3)
• Momentum resolution Pt/Pt=(1.8xPt+1.0)% (B=0.5T) ()=6.1mrad ()=5.5x10-3
• Computing time (1.3 kSpecInt machine)
Cvetan Cheshkov
dN/dy ~0 2000 4000 6000 8000
LUT Init 120ms
Hough Transform
0.7s(3ms/patch)
3.3s(15ms/patch)
5.9s(27ms/patch)
8.7s(40ms/patch)
11.3s(53ms/patch)
HLT Collaboration (18 Apr 2023) 12
ITS tracking (1)
• Offline tracking– Modified offline code
– Speed-up of up to a factor of 30 for some modules
ITS Clusterer
clusters
HLT TPCTracker
ITS Vertexer
TPC tracks
ITS TrackerJ. Belikov, C.Cheshkov
HLT Collaboration (18 Apr 2023) 13
ITS tracking (2)
J. Belikov, C.Cheshkov
• Tracking efficiency
TPC only (HT)ITS+TPCFakes
B=0.5T
Comparable to offline
HLT Collaboration (18 Apr 2023) 14
ITS tracking (3)
J. Belikov, C.Cheshkov
• Impact parameter resolution
Dominated by SPD -> ”offline” quality,i.e. 1 GeV/c track: transverse impact parameter resolution = 60 microns
HLT Collaboration (18 Apr 2023) 15
ITS tracking (4)
J. Belikov, C.Cheshkov
• Computing time (1.3 kSPECInt PC)
dN/dy Clusterer Vertexer Tracker
~0 0.5s 20ms 0.15s
2000 1.3s 45ms 0.45s
4000 1.5s 85ms 0.95s
6000 1.75s 150ms 1.70s
8000 2.0s 210ms 2.70s
HLT Collaboration (18 Apr 2023) 16
D0 finder
• Offline algorithm– Cut on impact parameter
– calculate
» Distance of closest approach
» Invariant mass
» Decay angle
» Pointing angle
• Timing results (0.3 kSPECInt PC)
dN/dy 1000 2000 4000 6000 8000
CPU time [sec] 0.4 1.4 6 11 23
HLT Collaboration (18 Apr 2023) 17
TPC Data Compression - Principle
Data model adapted to TPC tracking
Store (small) deviations from a model:(A. Vestbø et. al., to be publ. In Nucl. Instr. Meth. )
Cluster model dependson track parameters
Standard loss(less) algorithms; entropy encoders, vector quantization ... - achieve compression factor ~ 2 (J. Berger et. al., Nucl. Instr. Meth. A489 (2002) 406)
Tracking efficiency before and after comp. Relative pt-resolution before and after comp.
dNch
/d=1000
Tra
ckin
g ef
fici
ency
Rel
ativ
e pt
res
olut
ion
[%]
HLT Collaboration (18 Apr 2023) 19
TPC Data Compression - Results
Achieved compression ratios and corresponding efficiencies
Compression factor: 10
HLT Collaboration (18 Apr 2023) 20
PHOS Data Compression
• Data volume – 18k crystals
– Occupancy: ~10% (min. bias Pb+Pb, E > 10 MeV)
– 10 MHz sampling frequency
– 128 samples per pulse
– 2 channels per crystal
– 10 bits per sample
• Readout – all channels: 6 Mbyte/event
– discard empty channels (after zero-suppresion): 0.6 Mbyte/event
• Date rate– 2 kHz ’clean’ Pb+Pb interaction rate: 1.2 GByte/sec
HLT Collaboration (18 Apr 2023) 21
PHOS Data Compression
• Online pulse shape analysis– Fit amplitude -> energy
– Fit time offset -> TOF
» Peak method
» Slope method
Gamma-2 fit
Peak Method : Offline time referenceat peak ( y’ =0 )
Slope Method:Offline time referenceat max. slope ( y”=0 )
(both reference points are amplitude independent)
HLT Collaboration (18 Apr 2023) 22
• TPC– event reconstruction
» primary vertex
» primary vertex tracks
» secondary vertex tracks
» ghost (non-vertex) tracks
• ITS– SPD and SSD tracking
• TRD, PHOS, ...
• Full event reconstruction– data compression
– pile-up rejection
HLT task in pp
HLT Collaboration (18 Apr 2023) 23
Pattern recognition scenario in pp
• TPC tracking strategy• Cluster finder • Track follower (conformal mapping method)
• First pass with vertex constraint• Second pass in order to improve efficiencies for low-pt
and secondary tracks• input all unassigned clusters from the first pass• no vertex constrain is imposed on the track follower
(conformal mapping done with respect to the first associated cluster on track)
• Kalman filter for track extension into TRD and ITS• PID in TRD and TPC