Measurement of Quenched Energy Flow for Dijets in PbPb collisions with CMS · PDF fileFor the...

Yen-Jie Lee (MIT)

Yen-Jie Lee (MIT)

For the CMS Collaboration

NPA Seminar

Yale, USA

15 October, 2015

Measurement of Quenched Energy Flow for

Dijets in PbPb collisions with CMS

Yen-Jie Lee (MIT) NPA Seminar @ Yale

Relativistic Heavy Ion Collisions

Trying to answer two important questions in the high density QCD:

Where is the critical point of the QCD phase diagram?

What is the property of Quark Gluon Plasma?

2

Yen-Jie Lee (MIT)

Ideal World

NPA Seminar @ Yale

High Energy Quark

Medium

Quark Gluon Plasma Brick

3

Yen-Jie Lee (MIT)

Parton Cascade in Vacuum

NPA Seminar @ Yale

HadronizationParton shower

Hadrons

High Energy Jet

Large Virtuality Q

4

Yen-Jie Lee (MIT)

Parton Cascade in Medium

NPA Seminar @ Yale

HadronizationParton shower

High Energy Jet

Large Virtuality Q

Hadrons

Medium

Medium Changes vs. Time

Space-time information is also important in heavy ion environment

5

Yen-Jie Lee (MIT)

Parton Energy Loss Models

NPA Seminar @ Yale

Collisional

energy lossRadiative

energy lossAdS/CFT “drag force”

Perturbative QCD

Weak coupling limit

Holographic calculationStrong coupling limit

Two theoretical approaches:

6

Yen-Jie Lee (MIT) NPA Seminar @ Yale 7

The High Energy Frontier

Large Hadron Collider

LHC

Pb+Pb collisions

2.76 TeV (2010-13)

14x jump with respect to RHIC!

2015: 5.1 TeV

7

Lake Geneva

27 km circumference

CMS

ATLAS

LHCb

ALICE

France

Switzerland

RHIC

7


CMS Detector

8


CMS Detector

Inner tracker:

charged particles

vertex, isolation

solenoid

EM and Hadron calorimeters

photons, isolation, jet reconstruction

Muon

HCAL

ECAL

Tracker |η|< 2.5

|η|< 3.0

|η|< 5.2

|η|< 2.4

Pb

Pb

9

Yen-Jie Lee (MIT)

Particle Reconstruction with CMS

NPA Seminar @ Yale

μ±

γ

Neutral Hadron

Charged Hadron

e±

10

Yen-Jie Lee (MIT)

Heavy Ion Collision Recorded by the CMS Detector

NPA Seminar @ Yale 11

Yen-Jie Lee (MIT)

Underlying Event Background

NPA Seminar @ Yale

Jet

Goal: To study high pT jets event-by-event

How do we subtract the background from soft scatterings?

Take advantage of the large acceptance CMS detector:

Predict with the measured energy in the forward calorimeter

3<η<5-5<η<-3 |η|<2.5

12


Underlying Event in Heavy Ion Collisions

Training done with minimum-bias events (optimized by SVD method)

CMS DP 2013/018

13

Yen-Jie Lee (MIT)

Jet Reconstruction and Composition

NPA Seminar @ Yale

Anti-kT algorithm is used in the

most CMS publications

On average, charged hadrons

carry ~65% of the jet momentum

Measure the known part

Correct the rest by MC simulation

Optimize the use of calorimeter and tracker

Example: “Particle Flow” in CMS A typical high pT jet

Clustering

JetUE subtracted particles

14

Yen-Jie Lee (MIT)

CMS Jet Reconstruction Strategy

NPA Seminar @ Yale

Remove underlying

events contribution

MC Simulation

PYTHIA

Validated with dijet,

photon(Z)-jet data

Raw jet energyBackground

subtraction

Jet energy

correctionJet energy

correction

15


Jet Transverse Momentum SpectraN

ucle

ar

Modific

ation F

acto

r

Nuclear Modification Factor (RAA):

Ratio of the jet cross-section in PbPb

and pp scaled by the number of

nucleon-nucleon collisions

pPb Collisions

No significant modification

Head-on PbPb Collisions

Large suppression of high pT jet

Large final state effect observed in PbPb collisions

Is the jet structure modified in PbPb collisions?

16

Yen-Jie Lee (MIT)

Inclusive Jet Shape and “Fragmentation Function”

NPA Seminar @ Yale

Jet shape PbPb / pp Charged particle in cone PbPb - pp

RJet

Energy

Jet Fragmentation function: how transverse momentum is distributed inside the jet cone

Jet shape: “the jet energy distribution” as a function of R

17

Yen-Jie Lee (MIT)

Inclusive Jet Shape and “Fragmentation Function”

NPA Seminar @ Yale

Jet shape PbPb / pp Charged particle in cone PbPb - pp

Observation of energy redistribution inside the jet cone

(Some modification at large R; ~ one more low track pT)

The bulk of the Jet structure is actually pretty similar to that in pp

R

R

120 < Jet pT < 300 GeV/c

One more low pT particle

in the jet cone R=0.3

0-10% PbPb

Jet

Energy

18

Yen-Jie Lee (MIT)

Probe the QGP with High Energy Quarks and Gluons

PP PbPb

medium

Increased rate of

asymmetric dijets

in central PbPb collisions


Yen-Jie Lee (MIT)

Probe the QGP with High Energy Quarks and Gluons

PP PbPb PRC 84 (2011) 024906

PLB 712 (2012) 176

Small AJLarge AJ

(AJ~0.5)

Where does the

energy go?

medium

Increased rate of

asymmetric dijets

in central PbPb collisions


Yen-Jie Lee (MIT)

Tracks in

the jet cone

ΔR<0.8

Tracks out of

the jet cone

ΔR>0.8

CMS

PRC 84 (2011) 024906

Significant Energy Flow Out of the Jet Cone


Yen-Jie Lee (MIT)

Tracks in

the jet cone

ΔR<0.8

Tracks out of

the jet cone

ΔR>0.8

CMS

PRC 84 (2011) 024906


Jet collimation

Casalderrey-Solana, Milhano, WiedemannJ.Phys. G38 (2011) 035006

• Partons undergo Brownian motion

• Medium ”trims away” soft component to large angle


Yen-Jie Lee (MIT)

Ex: Mehtar-Tani, SalgadoPLB 707 (2012) 156-159

Ex: Mehtar-Tani, SalgadoPLB 707 (2012) 156-159

Tracks in

the jet cone

ΔR<0.8

Tracks out of

the jet cone

ΔR>0.8

CMS

PRC 84 (2011) 024906


Decoherence

Jet collimation

Mehtar-Tani, SalgadoPLB 707 (2012) 156-159

• Color coherence (angular ordered radiation) is

destroyed in the strongly interacting medium

• Open up the phase space for wide angle radiation


Yen-Jie Lee (MIT)

Tracks in

the jet cone

ΔR<0.8

Tracks out of

the jet cone

ΔR>0.8

CMS

PRC 84 (2011) 024906


Jet collimation

Turbulance cascade

Decoherence

• Effect of multiple branchings in medium:

“Quasidemocratic branching”

• Effective mechanism which brings soft

partons to large angle

Blaizot, Iancu, Mehtar-TaniPRL 111 052001 (2013)


Yen-Jie Lee (MIT)

Tracks in

the jet cone

ΔR<0.8

Tracks out of

the jet cone

ΔR>0.8

CMS

PRC 84 (2011) 024906


Jet collimation

Turbulance cascade

Decoherence

Third jet quenching

• Vacuum-like parton shower also extend to

large angle as large as R~1.0

• The third jet may be quenched and produce

soft particles out of the small jet cone R=0.3


Yen-Jie Lee (MIT)

Tracks in

the jet cone

ΔR<0.8

Tracks out of

the jet cone

ΔR>0.8

CMS

PRC 84 (2011) 024906


Jet collimation

Turbulence cascade

Decoherence

Third jet quenching

Strongly coupling

approach, hydro

• The medium takes energy away from the high

energy parton and turns that energy into heat /

collective motion of the medium.

• Produce extra soft particles in the final state

Casalderrey-Solana, Gulhan, Mihano, Pablos, Rajagopal, …


Yen-Jie Lee (MIT)


Jet collimation

Turbulance cascade

Decoherence

Third jet quenching

Strongly coupling

approach, hydro

(1) How many particles are carrying

the missing energy?

(2) What is the angular distribution of the

quenched energy flow with respect to

the dijet axis?


Yen-Jie Lee (MIT)

Measurement of the Quenched Energy Flow

NPA Seminar @ Yale

Difficulty: Large PbPb

underlying event (UE)

Leading jet

Subleading jet

Idea: Use all charged particles (pT>0.5 GeV/c)

Study the transverse momentum balance

28

Yen-Jie Lee (MIT)

Datasets and Event Selection

pp

• 5.3 pb-1

• Jet trigger with pT > 80 GeV/c

• Track reconstruction:

• pT > 0.2 GeV/c

• Anti-kT Calorimeter jet

• With R=0.3

PbPb

• 150 μb-1

• Jet trigger with pT > 80 GeV/c

• Track reconstruction:

– pT > 0.4 GeV/c

• Anti-kT Calorimeter jet

– with R=0.3

– HF/Voronoi UE

subtraction

• Dijet selection:

– pT,1 > 120 GeV/c

– pT,2 > 50 GeV/c

– |η1|, |η2| < 1.6 (0.5)

– Δφ > 5π/6

• Charged particles:

– pT > 0.5 GeV/c

– |η| < 2.4

= 2.76 TeV


Yen-Jie Lee (MIT)

Multiplicity Difference

What is the multiplicity of

the particles that balance the “extra”

lost pT?

φ1

φ2


Yen-Jie Lee (MIT)

Multiplicity Difference



lost pT?

Compare the multiplicities in the leading and

subleading jet hemispheres

Direction of the dijet is defined as:

(In contrast to PRC 84 (2011) 024906, where

the leading jet direction was used)

Provide UE cancellation differential in ΔR

φ1

φ2

φdijet

φdijet =½(φ1 + (π-φ2))


Yen-Jie Lee (MIT)

Multiplicity Difference (subleading – leading jet)



lost pT?

Compare the multiplicities in the leading and

subleading jet hemispheres

Direction of the dijet is defined as:

(In contrast to PRC 84 (2011) 024906, where

the leading jet direction was used)

Provide UE cancellation differential in ΔR

φ1

φ2

φdijet

φdijet =½(φ1 + (π-φ2))

Nch in subleading

jet hemisphere-Δmult =

NPA Seminar @ Yale

Nch in leading jet

hemisphere

32

Yen-Jie Lee (MIT)


φ1

φ2

φdijet

Multiplicity difference between the subleading and leading hemisphere

is increasing vs. dijet asymmetry in pp and peripheral PbPb.

There are more charged particles in the subleading hemisphere

AJ = (pT,1-pT,2)/(pT,1+pT,2)

Three / multi-jet

events

Symmetric Dijet

Events

NPA Seminar @ Yale

arXiv 1509.09029

33

Yen-Jie Lee (MIT)


• This increase is larger in central PbPb

• The enhancement in PbPb compared to pp increases with centrality

• Large AJ, 0-10%: ~16 extra particles (pT>0.5 GeV) in the subleading jet hemisphere

φ1

φ2

φdijet

AJ = (pT,1-pT,2)/(pT,1+pT,2)

PbPb-PP

NPA Seminar @ Yale

arXiv 1509.09029

34

Yen-Jie Lee (MIT)

Missing pT||

? ?

φ1

φ2

φdijet

½(φ1 + (π-φ2))

φi, pTi

What is the multiplicity and

pT spectra of the particles that

balance the lost pT?

NPA Seminar @ Yale

Dijet axis

Charged particle

azimuthal angle

Projection to dijet axis

35

Yen-Jie Lee (MIT)

Missing pT|| vs. AJ

NPA Seminar @ Yale

PP 0-10% PbPb

More energy flow

in the leading jet direction

More energy flow

in the subleading jet direction

arXiv 1509.09029

The momentum imbalance inside the jet cone is restored

if we consider all particles in the event

(in both pp and PbPb collisions)

36

Yen-Jie Lee (MIT)

Missing pT|| vs. AJ

• Missing pT from high pT particles increases as a function of AJ

• In pp Balanced by 2-8 GeV/c particles

• In 0-10% PbPb Balanced by particles with pT < 4 GeV/c

NPA Seminar @ Yale

PP 0-10% PbPb

More energy flow

in the leading jet direction

More energy flow

in the subleading jet direction

arXiv 1509.09029

37

Yen-Jie Lee (MIT)

φ1

φ2

φdijet

Missing pT|| vs. Δ

? ?Calculate the missing pT for charged

particles that fall in slices of Δ

φ2

What is the angular distribution of

these particles with respect to the

dijet system?


Yen-Jie Lee (MIT)

φ1

φ2

φdijet

Missing pT|| vs. Δ

φ2

NPA Seminar @ Yale





dijet system?

39

Yen-Jie Lee (MIT)

φ1

φ2

φdijet

Missing pT|| vs. Δ

φ2

NPA Seminar @ Yale





dijet system?

40

Yen-Jie Lee (MIT)

Missing pT|| vs. Δ in pp

NPA Seminar @ Yale

Integrated curve

from 0-ΔR

Contribution from third jet

Asymmetry inside the jet conearXiv 1509.09029

Subleading jet direction

Leading jet direction

0.5-300 GeV/c

41

Yen-Jie Lee (MIT)

Missing pT|| vs. Δ in pp

NPA Seminar @ Yale

Integrated curve

from 0 to Δ

Contribution from third jet

Asymmetry inside the jet conearXiv 1509.09029



42

Yen-Jie Lee (MIT)

Missing pT|| vs. Δ

NPA Seminar @ Yale

Inclusive AJ



arXiv 1509.09029

43

Yen-Jie Lee (MIT)

Missing pT|| vs. Δ

NPA Seminar @ Yale

Inclusive AJ



arXiv 1509.09029

Open circles:

Integrated over

particle pT

Slight modification of the

cumulative energy flow

44

Yen-Jie Lee (MIT)

Missing pT|| vs. Δ

High pT imbalance

at small Δ

NPA Seminar @ Yale

arXiv 1509.09029

Inclusive AJ





45

Yen-Jie Lee (MIT)

Missing pT|| vs. Δ

High pT imbalance

at small Δ

Balanced by low pT particles

in subleading jet direction

Extends upto large Δ

NPA Seminar @ Yale

arXiv 1509.09029

Inclusive AJ





46

Yen-Jie Lee (MIT)

Anti-kT Jets with Different R Parameters

Jets reconstructed with

R=0.5 gives ”wider” jet

Jets reconstructed with

R=0.2 gives ”narrower” jet

Jet shape from PYTHIA

• Jets are only meaningful if the algorithm is defined

• Different parameter R select different sets of dijet events!!

• Jet width dependent studies


Yen-Jie Lee (MIT)

“Shooting Jets with Different Width” through the Medium

NPA Seminar @ Yale

pp

PbPb

PbPb - pp

R= 0.2 R= 0.3 R= 0.4 R= 0.5

48

Yen-Jie Lee (MIT)


NPA Seminar @ Yale

Narrower jets Wider jets

• Quenched energy distribution depends on the R parameter

used in the Anti-kT algorithm

49

Yen-Jie Lee (MIT)


NPA Seminar @ Yale


• Quenched energy distribution depends on the R parameter

used in the Anti-kT algorithm

• Hint of narrower leading jet (or wider subleading jet) in

PbPb collisions?

50

Yen-Jie Lee (MIT)


NPA Seminar @ Yale


• Quenched energy distribution depends on the

R parameter used in the Anti-kT algorithm

• Hint of narrower leading jet (or wider

subleading jet) in PbPb collisions?

51

Yen-Jie Lee (MIT)

•Outlook

NPA Seminar @ Yale

LHC Run II (2015)

Comparison to Theory and Outlook

52

Yen-Jie Lee (MIT)

Significant Energy Flow Out of the Jet ConeJet collimation

NPA Seminar @ Yale

Turbulence cascadeDecoherence

Third jet quenching Strongly coupling

approach, hydro

0-10% PbPb collision

~16 extra particles (pT>0.5 GeV) in the

subleading jet hemisphere

53

Yen-Jie Lee (MIT)

Significant Energy Flow Out of the Jet ConeJet collimation

NPA Seminar @ Yale

Turbulence cascadeDecoherence

Third jet quenching Strongly coupling

approach, hydro

54

Yen-Jie Lee (MIT)

Jet Data vs. JEWEL event generator

NPA Seminar @ Yale

JHEP03(2013)080

A Jet Quenching Monte Carlo based

on weak coupling approach:

Reasonable description of jet FF, jet

RAA and charged hadron RAA

Hadron RAA Jet RAA

Jet Fragmentation Function

55

Yen-Jie Lee (MIT)

Hybrid Model with Strong Coupling Approach

NPA Seminar @ Yale

JHEP 1410 (2014) 19

Jet RAA

Dijet Asymmetry

Jet FF

Quark/Gluon Ratio

Motivate high pT flavor tagged jet analysis: (heavy) quark vs. gluon jets

PYTHIA+”Ads Drag”

56

Yen-Jie Lee (MIT)

Heavy Flavor Meson

NPA Seminar @ Yale

Very high pT heavy flavor meson (from quark jets):

complementary to the high pT heavy flavor jets

PRL 108, 022301 (2012)

PLB 666, 320 (2008)

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Yen-Jie Lee (MIT)

Particle Identification with CMS

NPA Seminar @ Yale

Υ(1S)

Υ(2S)

D0

Excellent capability of (decay) particle identification with CMS

58

Yen-Jie Lee (MIT)

Flavor Dependence of Jet QuenchingCMS-PAS-HIN-15-005

b→J/ψ

D0

Fully reconstructed D0 → K-π+ over a wide kinematic range

Charged Hadrons


Yen-Jie Lee (MIT)

Outlook:Identified Heavy Flavor Jet and Mesons

NPA Seminar @ Yale

B meson

b-jet

2013 5.02 TeV pPb data (35/nb)

2015-17 5.1 TeV PbPb data (~1.5/nb)

B meson

b-jet

2011 2.76 TeV PbPb data (0.15/nb)

b-jet

HL-LHC (10/nb): (b)-jet quenching at O(TeV)

D(*) meson

(Artist’s impression)

c-jet

c-jet

D(*) meson

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Yen-Jie Lee (MIT)

• An iterative feedback cycle between theory and experiment has started!

• Quenched jet event generator

• A systematical comparison between models and data

• LHC Run II:

• High statistics Photon-Jet and the first Z-Jet measurements

• High statistics (di-)jet measurement up to pT ~ 1 TeV

• Multi-jet correlation

• Flavor dependence of the parton energy loss from low to high pT with jets and mesons

Outlook

NPA Seminar @ Yale

… Stay tuned!!!

Generator Experiment

Used to derive correction or to compare with data

Feedback and improve the generator / model

61

Yen-Jie Lee (MIT)

BACK-UPBackup slides

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Measurement of Quenched Energy Flow for Dijets in PbPb collisions with CMS · PDF fileFor the...

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