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