Study of jet trigger with ALICE EMCALfor PbPb 5.5TeV
Masato Sano
University of Tsukuba
Lawrence Berkeley National Laboratory
Research Fellow of the Japan Society for the Promotion of ScienceOutline• Motivation• ALICE Detector• Annual jet yield with ALICE : PbPb 5.5TeV• ALICE trigger architecture• Jet trigger performance : PbPb 5.5TeV• Summary2Motivation
Phys.Rev.Lett.91(2003) 072304• RHIC has discovered partonic energy loss in QGP▫ These results are from the measurement of leading hadrons• If jets can be measured in heavy ion environment, it must be moredirect probe for parton energy loss and QGP property itself

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ALICE Detector• ITS, TPC, TRD :▫

Δφ<2π、¦η¦<0.9▫ charged particle momentum
determination.
▫ Δp/p ~ 5% at 100GeV/c• EMCAL :▫ Δφ<110 、¦η¦<0.7▫ π0 and γ measurement▫ ΔE/E ~ 11%/√E4

Annual jet yield at ALICE
Annual Yield for inclusive jet
Pb+Pb minbias at sNN=5.5TeV

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Annual Yield (E >Ecut)
T

10

10

10

10binary scaling from p+p
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L=0.5/mb/s; 1 year=10 s
Jets by Fastjet(Anti-Kt)
8Jet(R=0.2) in EMCAL• Annual jet yield▫ Nominal PbPb luminosity▫ 1 running year
▫ Binary scaling from p+p (pythia6)▫ FastJet, anti-kt algorithm is appliedfor jet reconstruction.
▫  see next talk by D. Sakata

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10Jet(R=0.4) in EMCAL▫ 200k jets/year above100GeV▫ We have lots of opportunity to use
jets as a probe for the properties ofQGP

6200k105• ALICE canʼt record all events
 Need to trigger

1040• Huge cross section for jetproduction!

20 40 60 80 100 120 140 160 180 200Ecut
T for jet[GeV]5ALICE trigger architecture• Limitations on data flow
▫ TPC gating frequency (500Hz)▫ High level trigger input bandwidth (25GB/sec)▫ Data taping bandwidth (1.25GB/sec)• We have to select the interesting event efficiently
trigger levels in ALICE (L0(1.2μs), L1(6.6μs), L2 and High level trigger)• For heavy ion jet measurement with EMCAL, the trigger decision is at L1
and High level trigger
L1 output should be< 500Hz (TPC gating frequency)< 25GB/sec (High level trigger input bandwidth)
PbPb L0 frequency : 4kHz
Data rate : 80GB/sec

High level trigger output should be< 1.25GB/sec (Data taping bandwidth)

L1

High Level Trigger

Subsystem information only

Fully reconstructed event6Jet trigger enhancement with EMCAL• Trigger gain :▫ Comparison between
Jets triggered by and reconstructed with EMCAL
andJets by geometrical triggers and reconstructed with TPC▫ Applicable for ETJet>100GeV• Jet trigger with EMCAL will enhance high pt jet yield
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Study of jet trigger performance : PbPb 5.5 TeV• To evaluate the jet trigger performance in PbPb collision with ALICEEMCAL, I analyzed the PYTHIA events merged with HIJING events, andapplied the L1 trigger and High level trigger.
• L1 trigger▫ Patch trigger algorithm is used with subsystem information only (EMCAL, V0) Search the square patch which have maximum amplitude in EMCAL acc.
 If the amplitude is above the threshold, we accept the eventEMCAL• High level trigger▫ Fully reconstructed event information (tracks, clusters in EMCAL,▫ Fastjet Anti-kt algorithm (R=0.4), etc)

 Search the jet which have maximum pT inside EMCAL acc.
 If the pT is above the threshold, we accept the event

8Background rejection : PbPb 5.5TeV
L1 Accepted Event Frequency [Hz]L1 Rejection vs Accepted Event Frequency
4kHz Event Frequency is assumed.
L1 PatchSize:0.1x0.1
L1 PatchSize:0.2x0.2

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L1 PatchSize:0.3x0.3
L1 PatchSize:0.4x0.4

110Hz
10202

468

10

121416182022 24
L1 Rejection• Left plot :▫ Maximum patch amplitude distribution weighted by data volume▫ Background only (HIJING)▫ Applied cut to reduce data volume by factor 10• Right plot :▫ L1 rejection vs L1 output frequency▫ Rejection 10  L1 output 110Hz, 8GB/sec
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Jet Yields [a.u.]

Trigger bias on jet yield : PbPb 5.5TeV• Upper plot :1Trigger Bias for Jet Yeild, L1Patch:0.3x0.3
10-1▫ Jet yield as a function of jet pT forpythia before/after trigger

MinBias10-2

L1:1/10• Bottom plot :L1:1/10 HLT:1/40-310▫ Jet trigger efficiency

10-4• Rejections are 10 and 40 for L1trigger and High level trigger
respectively-510-6

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Jet Trigger Efficiency

10-7-8101.21▫ L1 output : 110Hz , 8GB/sec▫ HLT output : 0.2GB/sec• We have 90 % efficiency at above
80GeV/c for these rejections

90%

0.80.60.4

0.2002040

60

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100

120

140160180
p for jet [GeV/c]
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Summary• Jet Trigger performance was evaluated for PbPb 5.5TeV• Jet trigger efficiency is greater than 90% above 80GeV/cwith the following rejections
L1 : 1/10
HLT : 1/40

L1 output
HLT output: 8GB/sec, 110Hz: 0.2GB/sec▫ These output are satisfied with the requirements(TPC gating frequency, High level trigger input bandwidth and data tapingbandwidth)

Outlook• Centrality dependence of jet trigger performance• Jet trigger performance with the jet quenching model• Jet trigger performance for pp
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Back up12

ALICE Detector• ITS, TPC, TRD :▫

Δφ<2π、¦η¦<0.9▫ charged particle momentum
determination.
▫ Δp/p ~ 5% at 100GeV/c• EMCAL :▫ Δφ<110 、¦η¦<0.7▫ π0 and γ measurement▫ ΔE/E ~ 11%/√E• JCAL :▫ Upgrade of electro magnetic
calorimeter in ALICE▫ Sitting on back to back side of existent
EMCAL in azimuthal angle▫ Δφ< 60 ,Δη<1.4▫ Dijet, pi0-jet, gamma-jet correlation
measurement.

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Annual jet yield at ALICE
Annual Jet Yield
Annual Yield (E >ET )Pb+Pb minbias at sNN=5.5TeV• Annual yield for various jets arecalculated.

Tcut

13101012

binary scaling from p+p
L=0.5/mb/s; 1 year=106 s

1011

Jets by Fastjet(Anti-Kt)
1010

Jet in EMCAL R=0.2
Jet in EMCAL R=0.4

910

Jet1 in JCAL(R=0.2, >50GeV/c) Jet2 in EMCAL(R=0.2)!0 in JCAL(>20GeV/c) Jet in EMCAL(R=0.4)810" in JCAL(>20GeV/c) Jet in EMCAL(R=0.4)

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610





Inclusive jet with R=0.4 in EMCAL
Inclusive jet with R=0.2 in EMCAL
Jet1 (in Jcal) ‒ jet2(in EMCAL)
π０ (in Jcal) ‒ jet (in EMCAL)γ (in Jcal) ‒ jet (in EMCAL)▫ Nominal PbPb luminosity for 2months.
▫ Binary scaling from p+p (pythia6)▫ FastJet, anti-kt algorithm is appliedfor jet reconstruction.

510• We have lots of opportunity touse jets as a probe for theproperty of QGP !!

1043101020204060 80 100 120 140 160 180 200
cut
Y.Miake, P.Jacobs, H.Yokoyama, M.Sano,ET for jet[GeV]14

L1 rejection vs Threshold for PbPb
L1 Rejection

L1 Threshold vs Rejection

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L1 PatchSize:0.1x0.1
L1 PatchSize:0.2x0.2
L1 PatchSize:0.3x0.3

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L1 PatchSize:0.4x0.4

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Threshold [a.u.]15

Response of the L1 & HLTpythiappythia vs pMaxPatch, PatchSize=0.3x0.3

pTpMaxPatch [a.u.]

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6000

10500010400010-4200

vs pMaxJet, Rparam=0.4
T
10-2

pMaxJet [GeV/c]

TT

180-310160
TT-3140

10-4

120-5

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10100-51080-6

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10100010-7-61060
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10-7

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20406080 100 120 140 pythia
160 180 200
p[GeV/c]
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•

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20406080 100 120 140 pythia
160 180 200
p[GeV/c]

10T

Left plot : for L1
▫
▫

•

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Correlation between “ jet pT in pythia(X axis)” and “amplitude of MaxPatch for L1 in pythia+Hijing(Y axis)”.
For L1 we can use only partial information like EMCAL cell, V0 and etc. therefore broad correlation can beseen.

Right plot : for HLT▫
▫

Correlation between “jet pT in pythia(X axis)” and “pT of Maximum Jet for HLT in pythia+Hijing(Y axis)”.
For HLT we can use the fully reconstruced information, so much sharper correlation can be seen than L1.

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Patch size : 0.1x0.1

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Patch size : 0.2x0.2

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Patch size : 0.3x0.3

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Patch size : 0.4x0.4

20Jet Yields [a.u.]

1Trigger Bias for Jet Yeild, L1Patch:0.3x0.3
101010101010

Jet Trigger Efficiency

10-1

MinBias-2

L1:1/5 HLT:1/20
L1:1/10 HLT:1/40-3-4-5-6-7-8

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0020

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140160180
p for jet [GeV/c]
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Jet trigger efficiency : pp 5.5TeV

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V0 hits vs EMCAL total energy : Background subtraction23Jet energy resolution
ALICE –EMCAL technical design report24