Measurement of jet spectra reconstructed with charged
particles in Pb-Pb collisions at √sNN=5.02 TeV
with the ALICE detector at the LHC(LHC-ALICE実験 √sNN=5.02 TeV 鉛鉛衝突実験における荷電粒子ジェットの測定)

Hiroki Yokoyama
LPSC, Université Grenoble-Alpes, CNRS/IN2P3
University of Tsukuba, Japan
01/09/2017 Tsukuba Weekly Meeting1Outline
Introduction
Quark-Gluon Plasma and Jet Quenching
LHC-ALICE Experiment
Development and commissioning of the ALICE Calorimeter L1 Triggersystem
Inclusive Charged jet measurement with √sNN = 5.02 TeV Pb-Pb collisions
Summary2

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )• Introduction• Development and commissioning of the ALICE Calorimeter L1 Trigger system• Inclusive Charged jet measurement with √sNN = 5.02 TeV Pb-Pb collisions

3

Quark Gluon Plasma
What is QGP ?
Quark-Gluon Plasma (QGP)
Hot & dense color thermalized QCD matter prevailing at the early Universe ~1μs after big bang
Deconfined state of quarks and gluons
Theoretically inferred through lattice gauge simulations of QCD

LHC HI programme

How to create ?
‘Little Bang’high-energy head-on nucleus-nucleus collisions atparticle acceleratorsRecreate QGP droplets for a brief period of time toquantitatively map out the QCD phase diagram

4Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Jets in HI Collisions ( Hard Probes of the QGP )What’s a Jet ?

Jet Quenching
Attenuation or disappearance of observed Jets
in Pb-Pb

Collimated spray of hadrons producedby the hard scattering of partons at the initialstage of the collision

due to partons' energy loss in the QGP

high-Q2 process, pT ≳ 20 GeV

jet shape broadening
evaluation of the degree of the attenuation
allows to assess QGP properties

5

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Jets in HI Collisions ( Hard Probes of the QGP )What’s a Jet ?

Jet Quenching
Attenuation or disappearance of observed Jets
in Pb-Pb

Collimated spray of hadrons producedby the hard scattering of partons at the initialstage of the collision

due to partons' energy loss in the QGP

high-Q2 process, pT ≳ 20 GeV

jet shape broadening

Why Jets ?

evaluation of the degree of the attenuation
allows to assess QGP properties(e.g. dE/dx)

The QGP lifetime is so short ( ~10-23 s ) thatcharacterisation by external probes is ruled out
self-produced probes
Occur at early stage : τ ~ 1/Q
probe the entire medium evolution
Production rate calculable within pQCD
well calibrated probes
Large cross-section at the LHC
copious production
Reconstructed jet enables to access
4-momentum of original parton

two-particle angular correlations

jet structure (energy re-distribution)

4 < pTtrig [GeV/c] < 6, 2 < pTasso [GeV/c] < pTtrig
Phys. Rev. Lett. 91, 072304 (2003)

6Hiroki Yokoyama : TAC seminar ( 01/09/2017 )ALICE Jet Quenching Measurements in Pb-Pb
Nuclear modification factor : RAA
if RAA = 1, NO modification

High-pT Hadrons

Jetsstrong suppression : RAA~0.2

strong suppression : RAA~0.4

proxy for Jet ( parton ) : pT >10 GeV/c

Jet shape broadens?
where is the lost energy?
RAA

fragmentation of quenched partons
1.2

ALICE Pb-Pb

sNN = 2.76 TeV

Anti-kT R = 0.2| η | < 0.5
jetplead,ch> 5 GeV/ cT1
Data 0 - 10%

Correlated uncertainty

Data 10 - 30%

Shape uncertainty

0.80.6

Correlated uncertainty
Shape uncertainty

JEWEL

JEWEL

YaJEM

YaJEM

0.4
0.2
0050

ALI−PUB−92182

Centrality Dependence of Charged Particle Production at Large Transverse
Momentum in Pb-Pb Collisions at √sNN = 2.76 TeV , PLB 720 (2013) 52

100pT,jet (GeV/c)50

100pT,jet (GeV/c)

Measurement of jet suppression in central Pb-Pb collisionsat √sNN = 2.76 TeV , PLB 746 (2015) 1

7Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Jet Measurement in LHC-ALICE
ALICE detector focus on Heavy Ion ExperimentLHC Run2 period started from 2015

√s =trigger
13 TeV pp implementation
1st topic : dedicated Jet/photon√sNN = 5.02 TeV Pb-Pb, pp√sNN = 8 TeV p-Pb

Charged Particles : |η| < 0.9, 0<φ<2π
ITS : silicon tracking detector
TPC : Time Projection Chamber
Charged constituents

PHOS
EMCal

Neutral particles : |η| < 0.7

Charged Jet

EMCal, (DCal : Run2 from 2015-)
Pb-Scintillator sampling calorimeter

DCal

PHOS
lead-tungsten
2nd topic
crystal: evaluation(PWO) based calorimeterof charged jet suppression in Pb-Pb
Neutral constituents
PHOS
8

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )My Activity
2014 Apr.

12015 May.

2

LHC Long Shutdown 1

LHC Run2

Trigger Upgrade (FW development)2015 Nov. - Dec.

2016 Feb.

pp, Pb+Pb 5.02 TeV

Trigger Upgrade (commissioning)

Trigger Upgrade (QA)

(1) 2015 Mar. 日本物理学会第70 回年次大会 : “Development of EMCALs' Trigger System in LHC-ALICE”(2) 2015 Sep. Quark Matter 2015 : [poster] “A Summary Trigger Unit for the ALICE Electromagnetic
Calorimeters”
国際ワークショップでの口頭発表（4回）

2016 Mar.

2016 Sep.

3

2017 Mar.

4

LHC Run2

Stay in
CERN : ~15 months
Grenoble LPSC : ~5 months

Jet Analysis(3) 2016 Sep. Hard Probes 2016 : [oral] “Measurement of Inclusive Charged Jet Production in pp andPb-Pb collisions at √sNN = 5.02 TeV with ALICE”(4) 2017 Mar. 日本物理学会第72 回年次大会 : “The nuclear modification of charged jets in √sNN = 5.02
TeV Pb-Pb collisions at LHC-ALICE”
国際ワークショップでの口頭発表（3回）

9Hiroki Yokoyama : TAC seminar ( 01/09/2017 )• Introduction• Development and commissioning of the ALICE Calorimeter L1 Trigger system• Inclusive Charged jet measurement with √sNN = 5.02 TeV Pb-Pb collisions

10Motivation
ALICE calorimeter upgrade for Run2
new calorimeter : DCAL
trigger hardware retrofitness on PHOS
trigger algorithm
et al…
new Jet/photon trigger implementation is required

11

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Trigger System of ALICE Calorimeters
PHOS
PHOS
FEE TRU
PHOS
PHOSTRU
TRU

fastOR amp(analog)

PHOSPHOS
TRU TRU
PHOS
PHOSTRU
TRU

L0_localfastOR amp*28TRUs

DCAL
DCAL
FEE TRU
DCAL
DCALTRU
TRU

fastOR amp(analog)

DCAL
DCAL
TRUTRUDCAL
DCALTRU
TRU*14TRUsEMCALDCALFEETRUDCAL
DCALTRU
TRUfastOR amp(analog)

EMCAL
DCAL
TRUTRUDCAL
DCALTRU
TRU

PHOS
STU

PHOS_L0
PHOS_L1_photon_low
PHOS_L1_photon

CTP

subregion data

L0_localfastOR amp

DCAL
STU

DCAL_L0
DCAL+PHOS_L1_Jet_low
DCAL+PHOS_L1_Jet
DCAL_L1_photon_low
DCAL_L1_photon

background density

L0_localfastOR amp

EMCAL
STU

EMCAL_L0
EMCAL_L1_Jet_low
EMCAL_L1_Jet
EMCAL_L1_photon_low
EMCAL_L1_photon*32TRUs

Analog sum
inside 1fastOR

digitise fastOR Amp
L0 trigger calculation

L1 photon/Jet
Trigger calculation
12

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Summary Trigger Unit
TTC (Trigger Trigger Clock)
clock management (40 MHz)
new L1/L2 Class message

40 serial communications with TRU,(STU)

DDL (Detector data Link)
DAQ for trigger
new data header (CDH v3)

FPGA

Trigger Information
trigger setting
raw data etc…
DCS
Control Command

Xilinx Vertex V

DDL

Trigger Output
DCS

TTC

new command
Trigger Busy Signal
Trigger Output
FastOR Amplitude
L0 localmost of all modules(functions) are controlled
by FPGA on STU

Mean BKG signal, Jet Primitive signal
13

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Level 1 Trigger Algorithmz

L1 Photon patch
2x2 FastOR
sliding window algorithm based on FastOR
On-the-Fly calculations
to reduce HW resource

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phi

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Level 1 Trigger Algorithmz

L1 Jet patch
2x2 or 4x4 jet primitivessliding window algorithm
based on jet primitive(4x4 FastOR)

jet-patch(2x2)jet-patch(4x4)X

jet primitive

150

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101012323232323234545454

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101232323232323454545454545010101010101232323232323454545454545012345012345phi

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Level 1 Trigger Algorithm
Large background energy deposit superimposed to the jet energy
event-by-event correction using the background measured on the opposite side
To avoid jet bias on background estimate
To obtain a reliable event-by-event backgroundEMCALModulejet primitive(8x8 Module Sum)

BKG estimation

BKG subtraction

Comparison

threshold

Modulejet primitive(8x8 Module Sum)

BKG estimation

BKG subtraction

Comparison

BKG_density(EMCAL)L1 outDCAL

BKG_density(DCAL)

L1 outthreshold16

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Trigger Performance
Trigger Efficiency =Number of Jet Patch in Triggered Events
Number of Jet Patch in MB Events

Trigger rejection
To define threshold which satisfy theBandWidth restriction of the data taking

Trigger eﬃciency
clear turn-on at set values of10 GeV (L1-photon) and 20 GeV (L1_Jet)

L1-Jet Rejection

1Trigger Eﬃciency

EMCal
DCal

10− 1−210−31010− 4

1.2
EMCAL Jet_H
DCAL Jet_H

1EMCAL Gamma_H
DCAL Gamma_H

0.8

0.6

0.4

0.2

−510efficiency

Rejection

Trigger Rejection~1000 for L1-Jet @20GeV threshold−40−2002040006080100Threshold[GeV]Trigger Threshold [GeV]

102030HIROKI YOKOYAMA

4050607080
FEE amp in JP/GP [GeV]

Energy in Jet/photon patch

All L1-Jet/photon Triggers by Calorimeters Worked Well in 2015 Pb-Pb Runs!
17

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )• Introduction• Development and commissioning of the ALICE Calorimeter L1 Trigger system• Inclusive Charged jet measurement with √sNN = 5.02 TeV Pb-Pb collisions

18

Motivation
Jetscloser probes to the partons than handons
powerful tools for study of QGP properties
strong suppression observed at central Pb+Pb collisions
Nuclear modification factor RAA
extreme condition ( highest energy in the world : √sNN = 5.02 TeV )-> systematic understanding of parton energy loss in QGP

19

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Analysis Flow ( Pb-Pb collisions )DatasetEvent Selection√sNN = 5.02 TeV, Pb-Pb collisions
MB triggered events( 3.36M events, ~5% of full statistics)

Track Selection

Charged track selection| η | < 0.9, pTtrack > 0.15 GeV/c
Jet reconstruction

Jet Reconstruction

UE density : ρanti-kT jet reconstruction algorithm
R = 0.2

Underlying Eventsubtraction| η | < 0.7, pTlead > 5 GeV/c

UE fluctuation : δpT

Underlying Event subtraction
background is subtracted fromreconstructed jetUnfolding
PYTHIA detector RM

Unfoldingto correct for detector effects andbackground fluctuations

Inclusive Jet spectrum

Jet finding eﬃciency

RAA

pp inclusive Jet spectrum

Inclusive jet spectrum, RAA
fully corrected to charged particle level,
assess nuclear modification
20

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Jet Reconstruction
Correspondence between detector level,
hadron level and parton level.
Jet Reconstruction
using observable particles
sequentially combine or classify theseparticles into clusters (Jet candidates)

21

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Underlying Event Density
Challenge in Heavy-Ion Collisions
large background contribution to jet energy
dNch/dη ~ 1300 ( 0-10% centrality )Jet Background Subtraction
background density : ρ
median kT excluding the highest two clusters

ρ ~ 145 GeV/c for 0-10% ( ~18 GeV/c for R=0.2 jets )background subtraction
background is estimated event-by-event and subtracted
from each jet
minimum leading constituent pT > 5 GeV/c requirement
suppresses combinatorial jets in low momentum

22Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Underlying Event Fluctuation

UE fluctuation : δpT
δpT is used as a measure for background fluctuation
for the correction of measured spectrum

δpT width (magnitude of UE fluctuation)
fluctuations larger in central than in peripheral collisions~5 GeV/c for R=0.2, 0-10% centrality

23

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Unfolding
Detector
effectcorrection NEEDED!
More

Detector eﬀect (e.g. smearing)

MC simulation

background fluctuation

Unfolding techniqueBackground Fluctuations

Detector Eﬀects

Mm = Gm,d · Dd

Dd = Gd,t · Tt

Measuredjet spectrum

Responsematrix

spectrum corrected
for BKG fluctuation

Responsematrix“unknown” true
jet spectrum

Inverted Response matrix gives “TRUE” jet spectrum via

Mm = Gm,d · Gd,t · Tt = Gm,t · Tt
24

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )pp Inclusive Jet Cross Section
Jet cross section

Ritsuya Hosokawa

well described by POWHEG NLO
calculations within systematic
uncertainties

25

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Nuclear Modification Factor : RAANuclear modification factor : RAA
RAA > 1, enhancement of yield
RAA < 1, suppression
RAA in each centrality bin
Increased suppression from peripheral~0.8 to central ~0.4

26

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Nuclear Modification Factor : RAA
RAA (5.02TeV) is comparable to RAA (2.76TeV)
denser medium stronger jet suppression

smaller RAA

harder collision flatter jet spectrum

larger RAA

effect of flattening of the spectrum compensated by stronger jet suppression ?

ALI-PREL-114190

27

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )SummaryJet Quenching
Attenuation of jets in central Heavy-Ion collisions-> jets are good probe to access QGP property
development & commissioning of ALICE-EMCals’ L1 trigger system
Jet/photon triggers working well in Run2
achieves expected performance
Inclusive charged jets RAA in √sNN = 5.02 TeV Pb-Pb Collisions
Jet measurement at highest energy in the world.
strong suppression at central collisions ( ~0.4 at 0-10 centrality )suppression weaken at peripheral collisions ( ~0.8 at 50-90% centrality )comparable to RAA in √sNN = 2.76 TeV-> balance b/w spectrum flattering and stronger suppression?

28

Hiroki Yokoyama : TAC seminar ( 01/09/2017 )Outlook
1analysis
withfullstatisticsp> 5 GeV/c0−1

kinematic reach : 90 GeV/c -> 130 GeV/c at00-10%- 10 %
0 - 10 %centrality 10plead> 10 GeV/cT

0−210−1

plead> 10 GeV/cT−2

IR : 2-4kHz−3−3evaluate
jet radius dependence
R = 0.2

0−410

IR : 4-5.5kHz−5−6100

p150
T,ch.jet200[GeV/c]10−7− 50

10−20 - 10 %IR : 5.5kHz-−310−5−650plead> 10 GeV/c
T

10−610010−110100plead> 5 GeV/cT

R = 0.2

jet shape ( broadning )−51−4100plead> 2 GeV/cT

R = 0.2−400−7− 50plead> 5 GeV/cTev

lead
T

1/N

1dNch,jet/dp

plead> 2 GeV/cT

plead> 0.15 GeV/c
T

10ev

plead
> 2 GeV/c
T

1/Nplead> 0.15 GeV/c
TdNch,jet/dpp> 0.15 GeV/cusing~5% of full statistics
10leadT

10102

T,ch.jet

102

T,ch.jet

02

10050

100p29150
T,ch.jet200[GeV/c]10−7− 50

050

100

p150
T,ch.jet200[GeV/c]Hiroki Yokoyama : TAC seminar ( 01/09/2017 )