High Level Trigger – Applications
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High Level Trigger –Applications
• Open Charm physics• Quarkonium spectroscopy
• Dielectrons• Dimuons
• Jets
Assumptions
• Detector readout rate (i.e. TPC)
>> DAQ bandwidth mass storage bandwidth
• Physics motivation for a high level trigger• Need for an online rudimentary event reconstruction
for monitoring
Data volume and event rate
TPC detector
data volume = 300 Mbyte/event, data rate = 200 Hz
front-end electronics
DAQ – event building
realtime data compression & pattern recognition
PC farm = 1000 clustered SMP
permanent storage system
bandwidth
60 Gbyte/sec
15 Gbyte/sec
< 1.2 Gbyte/sec
< 2 Gbyte/sec
parallel processing
Data rate reduction
• Volume reduction– regions-of-interest and partial readout
• pile-up removal in p+p
– data compression• entropy coder• vector quantization• TPC-data modeling
• Rate reduction– (sub)-event reconstruction and (sub)-event rejection before
event building
Fast pattern recognition
Essential part of Level-3 system
– crude complete event reconstruction monitoring
– redundant local tracklet finder for cluster evaluation efficient data compression
– selection of (,,pT)-slices ROI
– high precision tracking for selected track candidates dielectrons, ...
Level-3 system structure
TPC:fast cluster finder + fast tracker
Hough transform + cluster evaluatorKalman fitter
TRD trigger
Dimuon trigger
Trigger detectors
Pattern Recognition
Dimuon arm tracking
PHOStrigger
Extrapolate to ITS
Extrapolate to TOF
Extrapolate to TRD
...
Level-1
Level-3
(Sub)-event Reconstruction
TPC Rate limitationsPb+Pb p+p
L [cm-2 s-1] 5 1026 21030
event rate 4 kHz 140 kHz
pile-up 10% 20
clean min. bias / central rate 1 kHz / 200 Hz
event size
(10 bit zero-suppressed & Huffman coded)
80 MByte
50 Mbyte
(central)
1.5 MByte
1 MByte
TPC readout rate 1 kHz / 200 Hz 1 kHz
front-end data rate / DDL 47 MByte/s
(central)
5.5 MByte/s
Level-3 input event rate 200 Hz (central) 1 kHz
Level-3 output event rate
(full TPC events)
10 Hz
(central)
1 kHz
pile-up removal
Level-3 output data rate 0.5 GByte/s <0.2 GByte/s
Open Charm Physics (1)
• Hadronic charm decays – D0 K– + +
– B.R. = 3.86%
– c = 124 m
– high pT of the decay products:
• 75% of decay pions have pT > 0.8 GeV/c
Open Charm Physics (2)Charm Filter
• HLT momentum filter– subevent rejection
– subevent = low- pT tracks
– 11% of charged particles have
pT > 0.8 GeV/c
Open Charm Physics (3) Charm Filter
• Trigger strategy– find high-pT tracks in outer sector of TPC (based on seeds
from TRD)
– extrapolate track back to vertex
– record raw data along trajectory
• Problem of overlapping clusters– for deconvolution of high-pT track clusters the knowledge
of track parameters of crossing tracks is necessary
• Solution– reconstruction of all tracks in the neighborhood
(same/neighboring sector and )
Open Charm Physics (4) Charm Filter
• Trigger efficiency– signal loss: <25%
– data volume reduction to 7 Mbyte/event (factor 10)
– pT > 0.8 GeV/c vs. all pT
Open Charm Physics (5) Charm Filter
• Trigger efficiency– signal loss: <35%– data volume
reduction to 10 Mbyte/event (factor 5)
Open Charm Physics (5)Event Abortion
• Level-3 trigger: event abortion– Trigger strategy
• high-precision reconstruction of high- pT tracks (Kalman + PID)
• extrapolation to ITS
• cuts on impact parameters, invariant mass etc.
– Trigger efficiency• signal/event = 0.0027*
• background/event = 0.15*
• event rejection rate of 85% (new result incl. PID and pt-cut: factor 10
higher)
* A. Dainese, ALICE-PR-2001-04
TPC tracking
Tracking in the ITS:PbPb central event, slice
83o-87o - primary vertex - secondary vertices => for Hyperons => for Charm and Beauty - dE/dx for particle identification (@low momenta)- improve TPC momentum resolution- stand-alone tracking for low-Pt particles
Heavy Quark Physics
• Detectors involved: – TRD, TPC, ITS– Dimuon arm, ITS
• Quarkonium spectroscopy– J/,
• D, B
Quarkonium spectroscopy - dielectrons (1)
• Trigger rates ptsingle > 1 GeV/c ptsingle > 0.8 GeV/c
ptpair > 3 GeV/cJ//event 0.007 0.0006
background/event 0.39 0.15
TRD @ 1kHzTPC @ 150 Hz
Online track reconstruction:1) selection of
e+e—pairs (ROI)
2) analysis of e+e—pairs
(event rejection)
HLT system
Quarkonium spectroscopy - dielectrons (2)
• Trigger strategy– precise tracking of dielectron candidates in TPC– additional PID by dE/dx– rejection of background tracks (mainly
misidentified pions) by combined (TRD+TPC) PID – rejection factor
• 5 (singles)• 25 (pairs)
– HLT output rate: 1- 40 Hz (full events or ROIs)
Quarkonium spectroscopy - dielectrons (3): event flow
TRDTrigger~2 kHz
GlobalTrigger
Zero suppressed TPC Data
Sector parallel
Other Trigger Detectors,L0pretrig.
L1
L2 accept(180 Links, 83 MB/evt)
L0
ReadoutTPC
Readoutother detectors
L1
Tracking ofe+e- candidates
inside TPC
Selectregions of
interest
Verify e+e-
hypothesis
TRDe+e- tracks
Rejectevent
Track segmentsAnd space points
e+e- tracksPlus ROIs
On-line Data reduction(tracking, reconstruction,
partial readout,compression)
seed
s
enable
L0
L1
L2
HLT
DAQ
Tim
e, c
ausa
lity
0.5-2 MB/evt) 4-40 MB/evt)
Detector raw data readout for debugging
Binary loss less Data compression (RLE, Huffman, LZW, etc.)
45 MB/evt)
Event sizes and number of links TPC only
Event sizes and number of links TPC only
Quarkonium spectroscopy - dimuons
• Sharpening of pt-cut
• Trigger rate reduction: >4