Jet results in heavy ion collisions from CMS

Yen-Jie Lee (MIT) 12nd Conference on HI Collisions

Yen-Jie Lee (MIT)

For the CMS collaboration

2nd Conference on Heavy Ion Collisions in

the LHC era and beyond

Quy Nhon, Vietnam

26-31 July, 2015

Jet results in heavy ion

collisions from CMS

Yen-Jie Lee (MIT)

Probing the properties of the medium

22nd Conference on HI Collisions

Collisional

energy lossRadiative

energy loss

medium

Strong coupling: “AdS drag force”

Goal: understand the properties of the produced

medium

Status: validating the theoretical understanding

of jet quenching

Yen-Jie Lee (MIT)

Jet quenching without jets


EPJC 72 (2012) 1945

Yen-Jie Lee (MIT)

Why do we study jet quenching with jets?


EPJC 71 (2011) 1795

Jet


Jet as a versatile probe

Probe the Initial State Effects:

Extraction of nPDF

medium

Probe the Final State

Modification of JetsSearch for medium response

Where does the quenched energy go?



medium?

p(d)A collisions


Extraction of nPDF

Yen-Jie Lee (MIT)

(Di-)Jet production in pPb collisions at 5.02 TeV


Dijet pT ratio compared to PYTHIA from CMS.

No significant reduction of dijet pT ratio (<2%)Jet RpPb ~ 1.1 ± 0.2, Consistent with pQCD

calculation with EPS09 nPDF

Subleading Jet pT / leading jet pTInclusive (charged) jet RpPb

EPJC 74 (2014) 2951


Dijet dN/d𝛈 in pPb collisions at 5.02 TeV

Jet quenching from dijet analysis in pPb:

Dijet asymmetry <2%

No sizable deviation from unity

found in jet RpPb

Jets for nPDF studies!(pp PDF)

Anti-shadowing

Shadowing

EMC

Anti-shadowing

Shadowing

EMC

Boosted PYTHIA6 Z2@ 5.02 TeV

= (η1+η2)/2

(In the lab frame)

EPJC 74 (2014) 2951


Compare to CT10 and CT10+EPS09

Hannu’s QM14 talk

EPJC 74 (2014) 2951


Dijet dN/dη vs. event activity

(Too) large modification vs. event activity.

Can not be explained by centrality dependent nPDF

= (η1+η2)/2

Red: event with large forward energy

Blue: event with small forward energy

p p+π p+2π

…?

10

EPJC 74 (2014) 2951

Yen-Jie Lee (MIT)

Jet fragmentation pattern in pPb


• Track pT spectra inside the jet cone is measured

in pPb collisions

• Ratio of pPb and the interpolated pp reference is

consistent with unity

High pT jet

140-200 GeVLow pT jet

60-80 GeV

CMS-PAS-HIN-15-004




Extraction of nPDF

medium


Modification of Jets

Yen-Jie Lee (MIT)

Probe the QGP with high energy quarks and gluons

13

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

14

PP PbPb PRC 84 (2011) 024906

PLB 712 (2012) 176

Small AJLarge AJ

(AJ~0.5)

Increased rate of

asymmetric dijets

in central PbPb collisions


medium


Jet Fragmentation at LHC

CMS FF RAA compared to

ATLAS FF RCP

Z = p||Trk / pJet

Qualitative consistent results

between CMS and ATLAS

ATLAS : indication of

enhancement of low ξ

(high z) particles in the

jet cone

Using Jet Energy as a reference

High pT particles Low pT particles

CMS: PRC 90 (2014) 024908

ATLAS: PLB 739 (2014) 320-342

Yen-Jie Lee (MIT)

Photon-Jet correlation


xJ=pTjet/pT

pTjet

pT

Jet(info about “final parton energy”)Photon

(tag initial parton energy)

PLB 718 (2013) 773

CMS-PAS-HIN-13-006 • ~10% of the jet energy goes out of the jet cone

• Where does the quenched energy go?




Extraction of nPDF

medium


Modification of Jets

Search for medium response

Where does the quenched energy go?

Yen-Jie Lee (MIT) 18

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

2nd Conference on HI Collisions 19

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


Decoherence

Jet collimation

2nd Conference on HI Collisions 20


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


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


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

Strongly coupling

approach, hydro



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?


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

Measurement of quenched energy flow

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))

28

Nch in subleading

jet hemisphere-Δmult =


Nch in leading jet

hemisphere

Yen-Jie Lee (MIT)


29

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


CMS-PAS-HIN-14-010

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%: ~14 extra particles (pT>0.5 GeV) in the

subleading jet hemisphere

30

φ1

φ2

φdijet

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

PbPb-PP


CMS-PAS-HIN-14-010

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?


Dijet axis

Charged particle

azimuthal angle

Projection to dijet axis

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 < 2 GeV/c


PP 0-10% PbPb

More energy flow

in the leading jet direction

More energy flow

in the subleading jet direction

CMS-PAS-HIN-14-010

Yen-Jie Lee (MIT)

φ1

φ2

φdijet

Missing pT|| vs. ΔR

? ?Calculate the missing pT for charged

particles that fall in slices of ΔR

φ2

What is the angular distribution of

these particles with respect to the

dijet system?


Yen-Jie Lee (MIT)

φ1

φ2

φdijet


φ2






dijet system?

Yen-Jie Lee (MIT)

φ1

φ2

φdijet


φ2






dijet system?

Yen-Jie Lee (MIT)

Missing pT|| vs. ΔR in pp


Integrated curve

from 0-ΔR

Contribution from third jet

Asymmetry inside the jet coneCMS-PAS-HIN-14-010

Subleading jet direction

Leading jet direction

Yen-Jie Lee (MIT)



Inclusive AJ



CMS-PAS-HIN-14-010

Yen-Jie Lee (MIT)



Inclusive AJ



CMS-PAS-HIN-14-010

Cumulative energy

flow are similar

Open circles:

Integrated over

particle pT

Yen-Jie Lee (MIT)


39

High pT imbalance

at small ΔR


CMS-PAS-HIN-14-010

Inclusive AJ



Cumulative energy

flow are similar

Yen-Jie Lee (MIT)


40

High pT imbalance

at small ΔR

Balanced by low pT particles

in subleading jet direction

Extends upto large ΔR


CMS-PAS-HIN-14-010

Inclusive AJ



Cumulative energy

flow are similar



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)

Jet data vs. JEWEL


JHEP03(2013)080

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 FF

Yen-Jie Lee (MIT)

Description of the jet data with strong coupling approach


JHEP 1410 (2014) 19

Jet RAA

Dijet Asymm.

Jet FF

Quark/Gluon Ratio

Yen-Jie Lee (MIT)

Outlook

• LHC Run II: PbPb @ 5 TeV in 2015

• High statistics photon-jet sample

• Z-jet correlation

• Multi-jet correlation

• Flavor tagged jet

• Need an iterative feedback cycle between

theory and experiment

• Quenched jet event generator

• Tell us your favorite analysis with Run II data!


Yen-Jie Lee (MIT)

Backup slides



CMS Preliminary

Consistent picture: excess of low pT particle in the jet cone

STAR

PHENIX

Photon-tagged Hadron IAA

Jet-Hadron

Z = p||Trk / pJet

Z = p||Trk / pJet

Documents

Jet results in heavy ion collisions from CMS