STAR Level-3 C. Struck CHEP 98 1 Level-3 Trigger for the Experiment at RHIC J. Berger 1, M. Demello 5, M.J. LeVine 2, V. Lindenstruth 3, A. Ljubicic, Jr

STAR Level-3 C. Struck

CHEP 981

Level-3 Trigger Level-3 Trigger for the for the

Experiment at Experiment at RHICRHIC

J. Berger1, M. Demello5 , M.J. LeVine2, V. Lindenstruth3,A. Ljubicic, Jr.2, D. Roehrich1, E. Schaefer6,

J.J. Schambach4, D. Schmischke1, M.W. Schulz2, R. Stock1, C. Struck1,a , P. Yepes5

(1) University of Frankfurt(2) Brookhaven National Lab., Upton, NY(3) University of Heidelberg(4) University of Texas at Austin(5) Rice University, Houston, TX(6) Max-Plank-Institut fuer Physik, Munich(a) Yale University, New Haven, CT

Christof Struck August, 98University of FrankfurtYale University


CHEP 982

Solenoidal Tracker At RHICAu+Au at s = 200 GeV/nucleon pair5000-10000 charged particles/eventpolarized p+p at s = 500GeV baseline detector: large TPC

STAR Experiment

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CHEP 983

STAR DAQ• TPC organized in 24 geometrical sectors;

each sector delivers digitized data through 6 readout boards (custom built VME boards); same readout scheme for SVT (4 sectors) and FTPC (6 sectors)

• readout boards equipped with:

– buffer for 12 uncompressed events

– processing power (three i960 per board)

• STAR DAQ hierarchical system of VME systems - interconnected by a low latency and high bandwidth network:

SCI: event building, inter-crate communication/synchronization and for Level-3 data-passing

Global VME Crate

SCI Ring

TPC Sector Crate SVT Sector Crate

24 crates 4 crates

SCSI


CHEP 984

Level-3 Requirements

Au+Au collisions:TPC event rate after Level-0 Trigger: 100 Hz,expected event size: 100 MByte

2.0 GByte/secafter zero suppressionevent size 20 MByte

20 MByte/sec

10 8 bit translationzero suppression

Level-3

Tape / Offline


CHEP 985

Level-3 Trigger

• software trigger:select events according to

– event topology, kinematics

– specific signature

• selecting sub-events:store only raw data of interesting tracks(regions-of-interest, ROI),e.g. tracks of lepton candidates

• data compression

process the raw data:perform pattern recognition in real time at 100 Hz

Reduce data by a factor of 100, therefore use knowledge of physics of these collisions.

Possibilities:


CHEP 986

Software Triggeror

Regions-of-Interest

Estimated rates for J/ e+e–

and e+e– . 100 Au+Au collisions/sec

L3-Trigger sensitivity 1:100 assumed

J/ e+e–

pT(e)>1.5 GeV/c

e+e–

Signal/event 10-5 0.02

S/B 1:58 1:50

Background/event 6 · 10-4 1

Method L3-Trigger ROI

Signal/year with L3 104 2 · 107

Seff/year with L3 102 2 · 105

Seff/year without L3 1 2 · 103

Seff = S / (1+2B / S)


CHEP 987

Online Pattern Recognition

Reconstruction of full eventincluding track merging between different detectors

max. TPC event rate 100 Hz average time for one event 10 msec

DAQ receiver boards provide buffer for 12 uncompressed raw events Level-3 processing time 120 msec

tracking quality not as high as offline analysis, but precise enough to enable fast trigger decision

Input:• raw data of slow detectors:

TPC, SVT, FTPC• raw data of fast detectors:

CTB, MWC, VTC, VPD, ZDC, EMC


CHEP 988

Concept of Level-3

• scalable hierarchical structure of processors

• pattern recognition done sequentially

• DAQ readout boards:cluster findingtransform raw ADC data into space coordinates

• Sector Level-3: track findingperform track finding on sector level

• Global Level-3:collect all information from local nodes, merge tracks and make trigger decision


CHEP 989

Cluster Finder I

• runs on DAQ readout board processors (Intel i960)

• input:beginning and ending time of pixel sequences in each pad prepared in receiver board ASICs

• output:space coordinates and charge of found clusters

• optimized for speed

• includes deconvolution of merged clusters


CHEP 9810

Cluster Finder II

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Simulation: Au+Au, Venus + GEANT


CHEP 9811

Cluster FinderResults

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Simulation: Au+Au, Venus + GEANTpad row 16 - 20


CHEP 9812

Cluster FinderTiming

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CHEP 9813

Track Finder

• combines a number of space points to form track segments

• track segments are merged to form vertex and non-vertex tracks

• provides: – particle momenta– particle identification via dEdx

• algorithm: (P. Yepes at CHEP ‘97)

– conformal mapping to speed up fitting procedures– optimized data organization and memory management

• results:– efficiency between 80 - 90 % for pT > 0.4 GeV/c and

pseudorapidity < 1.2; comparable to offline track finder

– momentum resolution pT/ pT < 1.5 % forpT > 0.4 GeV/c (vertex constraint)


CHEP 9814

Track FinderResults

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CHEP 9815

Track FinderTiming

task PentiumPro

200 MHz

PentiumII

400 MHz

PowerPC750

266 MHz

Alpha21164

600 MHz

Alpha21264

667 MHzSPEC-95 int 8.7 15.8 12.4 18 44

SPEC-95 fp 6.7 12.4 8.4 27 66

fast tracker 200 msec 110 msec 150 msec 80 msec 30 msec

timing for one TPC sectorsimulated central Au+Au, Venus


CHEP 9816

Architecture

• distributed, symmetric, scalable processor system

• OS and Software:WinNT (or Linux/ Solaris) for processing nodes; VxWorks for DAQ nodes; software is written in C/C++

• SCI network connection between local sector units and global system to provide high bandwidth(poster, J. Schambach, CHEP ‘98)

• baseline configuration:12 local processing clusters

• later:24 TPC sectors, 4 SVT sectors and 6 FTPC sectors


CHEP 9817

Architecture:Sector Level-3

SB1

SBn

DAQ SCI Ring

SL31/1

Level-3 localSCI Ring 1

SL3 machine1 processor

Alpha 21264

SL31/4 SL3

1/4 SL31/4 SL3

1/4

SL3 SMP machine4 processors

Quad Pentium II

Level-3 localSCI Ring n

GL3


CHEP 9818

Architecture:Global Level-3

GL3Broker

SB1

SBn

EVB

DAQ SCI Ring

GL31/4 GL3

1/4 GL31/4 GL3

1/4

Level-3 globalSCI Ring

GL3 SMP machine 14 processors

GL3n/4 GL3

n/4 GL3n/4 GL3

n/4

GL3 SMP machine n4 processors

Token Manager

To Trigger System


CHEP 9819

Examples forLevel-3

• Au+Au collisionsSelect events with J/ candidates in e+e–-channel– find electron candidates

– loop over electron pair candidates» calculate mass with vertex constraint

» select events in mass window (e.g. 2.5 - 4 GeV)

• p+p collisions– remove pile-up in TPC:

select trigger event out of 600 - 800 visible events in the TPC

– select events based on threshold for jets,photons and electrons


CHEP 9820

Data Compression I

• zero suppression• general data compression methods, loss-

free (e.g. Huffman encoding) or lossy reduce only by a factor of 2 to 5

• later phase of the experimentdata modeling techniques reduce by a factor up to 15,keep only relevant information:– assume data model for cluster and tracks (helix

for STAR)– store only quantized differences to data model

of found tracks– pattern recognition can be redundant– detector performance has to be well understood

!!


CHEP 9821

Data Compression II

parameter size

curvature R 4 Byte (float)

begin (X,Y,Z) 12 Byte (float)

dip angle 4 Byte (float)

azimuthal angle 4 Byte (float)

track length 2 Byte (integer)

(average) cluster charge 2 Byte (fixed point)2 2 Byte (fixed point)

number of clusters 1 Byte (integer)

sum 31 Byte

track parameter for a helix model

parameter size

Flag empty cluster 1 Bittime 6 Bitpad 6 Bit

cluster charge 7 Bitshape 4 Bit

sum 24 Bit (3 Byte)

cluster parameter


CHEP 9822

Data Compression III

• typical event:8000 tracks with 45 cluster each(Venus simulation, worst case)

track data: 8000 • 32 Byte = 0.24 MByte

cluster data: 8000 • 45 • 3 Byte = 1.03 MByte

total: 1.3 MByte needed (lower limit)

• compare to

- raw data (zero suppressed) : 20 MByte

- cluster data: 2.7 MByte(8 Byte per cluster)


CHEP 9823

Summary / Outlook

• Level-3 Trigger is needed for most of the STAR physics programs

• reduction of data rate by a factor of 100 requires pattern recognition in real time at 100 Hz

• processed event rate of about 15 - 20 Hz can be achieved using the shown fast algorithms and either one Alpha 21264 or aQuad Pentium II (sufficient for year one)

• system is scalable by adding more CPUs higher event rates

What needs to be done?

• choose processors and OS– therefore timing results for Alpha 21264 needed

• prototype setup

• full simulation of trigger scenarios using the Level-3 chain (cluster finder + tracking)

Documents

STAR Level-3 C. Struck CHEP 98 1 Level-3 Trigger for the Experiment at RHIC J. Berger 1, M. Demello 5, M.J. LeVine 2, V. Lindenstruth 3, A. Ljubicic, Jr