Exploring QGP with jets at LHC Yaxian MAO Central China Normal University

A symposium on future RHIC and LHC physics September 25th-26th, 2015 Yaxian MAO Central China Normal University

GyulassyFest, September 25-26, Wuhan 2015

Yaxian MAO Central China Normal University

GyulassyFest, September 25-26, Wuhan 2015

2

Jet quenching evidences at LHC

•

RAA: Nuclear modification factor 2 σ inel d N AA /dp T dη pp R AA = N coll d 2 σ pp /dp T dη 1.8 PbPb

1.6

∫

1.4

Jet RAA

1.2

sNN = 2.76 TeV

L dt = 129 µ b 100 < p 100 < p

jet T jet T

-1

|η|<2

Bayesian Uncorr statistical

(GeV/c) < 110 (GeV/c) < 300

Total systematics

1 0.8 0.6 0.4

CMS Preliminary

0.2

Anti-kT Particle Flow Jets

0

0

100

CMS PAS HIN-12-004

• •

200

R = 0.3 300

400

PLB 712 (2012) 176

Npart

About 50% of jets (RAA ~ 0.5) are lost at a given pT in most central PbPb Dijet pT ratio is imbalanced in most central PbPb collisions

➡

Jets are quenched in central PbPb collisions, how about b-jets? 3

Tagging and counting b-quark jets

•

Long lifetime of b (~1.5 ps) leads to measurable displaced secondary vertices (SV)

•

Subsequent charm decay may lead to a tertiary vertex (TV)

•

B-jets are tagged using reconstructed SV’s based on flight distance

•

Tagging efficiency estimated in a datadriven way

•

b-jet fraction (purity) is extracted by a template fit to the (tagged) SV mass PRL 113 (2014) 132301

4

b-jet suppression

PRL 113 (2014) 132301

• •

Evidence of b-jet suppression in central PbPb collisions b-jet RAA favours pQCD models that include strong jet-medium coupling 5

Anatomy of jets

•

Understand how jets interact with the QGP medium by studying the energy flow inside the jet

Vacuum (pp reference)

Jets in Medium (jet broadening)

➡ question to address: is the jet energy in PbPb redistributed radially?

•

Understand how jets interact with the QGP medium by studying the particle momenta projected onto the jet axis ➡ question to address: is the jet energy in PbPb redistributed in momentum space?

r = √(ηjet-ηch

ρ (r) =

1 1 1 fch δr N jet

)2+(φ

jet-φch

)2

ξ = ln(1/z) =

ln(pjet/p||)

low ξ

pT (r − δ r / 2, r + δ r / 2) ∑ , jet jets pT

high ξ

6

Jet structure analysis PYTHIA 100 GeV inclusive jet Anti-kT R=0.3 jet Charged particle energy fraction ~95% of energy in r < 0.2

PLB 730 (2014) 243

~95% of energy with pT > 4GeV particles

• Core of the jet (dominated by high pT particles) → no changes • Intermediate r (intermediate pT particles) → depletion/narrower • Large radii (low pT particles) →excess/broadening ➡Jet energy is redistributed inside jet cone 7

Inclusive jet FF vs. pT and ξ

PRC 90 (2014) 024908

Ejet = 100 GeV 100

50

10

4

3

2

1

pT (GeV/c)

ξ = ln(1/z) = ln(pjet/p||track) • high pT particles → no changes • intermediate pT particles → depletion • low pT particles →excess ➡Jet fragmentation is modified

8

Controlled Experiment: p + Pb ? pPb collisions

PbPb collisions

Jet

Jet

QGP Jet

Jet

• Clear signs of Quark-Gluon Plasma (QGP) • Strongly interacting particles affected by the presence of QGP • quenched jets and high pT

• modified jet structure

QGP? CGC?

• Can we understand the baseline for PbPb? • How do strongly interacting particles behave in cold nuclear matter? quenching?

•

Can we see nuclear structure? 9

Pb

NN

1.4

1.4

1.4

1.2

1.2

1.2

-2.0 < η

CM

0.4

1.8

100

-1.5 < η

CM

0.4 300

p [GeV/c]

400

T

500 1.8

100

1

200

300

p [GeV/c]

400

500 1.8

1.2

1.2

1.2

RpPb

1.4

0.4

1

CM

100

0.6

< 0.5

0.5 < η

CM

0.4

200

300

p [GeV/c] T

400

500

100

200

< -0.5

300

p [GeV/c]

400

500

T

1 0.8

0.8

-0.5 < η

CM

1.6

1.4

0.6

-1.0 < η

0.4

1.4

0.8

Luminosity uncertainties

0.6

< -1.0

T

1.6

1

CMS-HIN-14-001

0.8

0.6

< -1.5

200

1.6

RpPb

1

0.8

0.8 0.6

RpPb

1.6

1

-1

1.8

1.8 Anti-kT Particle Flow Jets: R = 0.3 1.6 1.6

total uncertainties

RpPb

RpPb

1.8

RpPb

p

Jet quenching in p + Pb? CMS Preliminary pPb s = 5.02 TeV ∫L dt = 35 nb

100

200

< 1.0

300

p [GeV/c] T

0.6

1.0 < η

CM

0.4 400

500

100

200

< 1.5

300

p [GeV/c]

400

500

T

• No strong jet pT dependence observed • Consistent with EPS09 description 10

Charged particles RpA p

Pb

EPJC 75 (2015) 237

• No suppression observed for charged hadron production in pPb collisions • High pT charged particles (50 < pT < 100) RpPb >1 using interpolated pp reference • EPS09 calculation is under predicted the data → possible baryon/meson difference? 11

Dijet η asymmetry François Arleo and Jean-Philippe Guillet http://lapth.cnrs.fr/npdfgenerator/

EPJC 74 (2014) 2951

p

Pb

ηdijet =

η1+η2 2

EMC

anti-shadowing

•

ηdijet =

Agreement between data and EPS09 calculation with systematics

η1+η2 2

shadowing 12

Probing nPDF with jets and hadrons x - fractional momentum from a colliding nucleon carried by the parton “backward”

p

Pb

“forward”

JHEP 0904 (2009) 065

large x from Pb

nPDF R= PDF

small x from Pb

x

•

Different pT and η region can probe different x-range

13

Probing nPDF with jets and hadrons x - fractional momentum from a colliding nucleon carried by the parton “backward”

p

Pb

“forward”

JHEP 0904 (2009) 065

large x from Pb

nPDF R= PDF

small x from Pb

x PYTHIA Z2

s= 5.02 TeV: Generator Level



1

10−1

-2.0 < η < -1.5 -1.5 < ηCM < -1.0 -1.0 < ηCM < -0.5 -0.5 < ηCM < 0.5 0.5 < η CM< 1.0 1.0 < ηCM < 1.5 CM

10−2

50

•

100

200

300 400

jet

p [GeV/c] T

Different pT and η region can probe different x-range

13

Probing nPDF with jets and hadrons x - fractional momentum from a colliding nucleon carried by the parton “backward”

p

Pb

“forward”

JHEP 0904 (2009) 065

large x from Pb

nPDF R= PDF

small x from Pb

x PYTHIA Z2

s= 5.02 TeV: Generator Level



1

10−1

-2.0 < η < -1.5 -1.5 < ηCM < -1.0 -1.0 < ηCM < -0.5 -0.5 < ηCM < 0.5 0.5 < η CM< 1.0 1.0 < ηCM < 1.5 CM

10−2

50

•

100

200

300 400

jet

p [GeV/c] T

Different pT and η region can probe different x-range

13

Charged particle and jet production asymmetry p

Pb

PARTICLE YIELD LEAD GOING SIDE

CMS Preliminary, pPb sNN = 5.02 TeV

YieldPb going/Yieldp going

1.5

∫

L dt = 35 nb

PARTICLE YIELD PROTON GOING SIDE

jets

-1

charged hadrons

Anti-kT Particle Flow Jets: R = 0.3

1

0.5

-1.5<η <-1.0/1.0< η <1.5 CM

CM

-1.0<η <-0.5/0.5< η <1.0 CM

0

50

200

100

CM

300 400

p [GeV/c] T

•

charged hadron: Yasym above 1 for pT < 10 GeV/c and close to unity for pT > 10 GeV/c within systematics uncertainty

•

A decreasing trend of Yasym at very high pT for both charged hadron and jets at large psedorapidity 14

dijet η and charged hadron asymmetry ηdijet =

η1+η2 2

EPJC 74 (2014) 2951

p

Pb

• “Peripheral” events with low HF activity: dijets shifted to p-going side, expect Yasym < 1 • “Central” events with high HF activity: dijets shifted to Pb-going side, expect Yasym > 1 15

Summary and outlook

•

So far so good…

•

consistent picture about jet quenching in PbPb collisions from different experiments

• • • •

high pT jets are strongly suppressed Jet fragmentation patterns are modified

No jet quenching observed in pPb collisions

But…still left with questions…

•

can be addressed and checked by more precise measurements with new LHC data from RunII and RunIII ➡ flash in the next few slides with the questions in my mind…

Yaxian MAO Central China Normal University

GyulassyFest, September 25-26, Wuhan 2015

16

How low pT Jet quenched?

Jet RAA

How are the low pT jets suppressed?

•

High pT RAA is in good agreement, however low pT behavior is different ➡ different jet cone size, can be revisited with RunII data under same condition 17

Flavour dependent energy loss? Is the energy loss depending on the quark flavour as predicted? parton

hot and dense medium

ENERGY LOSS light

M.Djordjevic PRL 94 (2004)

• •

RAA(b-jet) ≃ RAA(inclusive-jet) at high pT, no strong flavour dependence RAA(J/ψ←B)>RAA(D)≃RAA(π) ➡ More precise measurements down to low pT needed to conclude 18

Longitudinal or transverse broadening? Which direction of the jet broadening occurred?

r = √(ηjet-ηch)2+(φjet-φch)2

•

Di-hadron correlation study observed:

•

Broadening mainly in η direction and no increase in φ direction

➡Need precise study with jets for Δη and Δφ broadening 19

Color charge dependent jet FF and modifications?

PbPb/pp

FF

High z fragments modified? Different partons have different modification?

ATLAS: PLB 739 (2014) 320 CMS: PRC 90 (2014) 024908 PRD 84 (2011) 014034

• •

FF Rcp shows difference hints at high z between experiments ➡ need precise measurements with coming LHC data Theory predicted jet fragmentation pattern modified differently for different parton mass ➡ can be checked at LHC with coming data

20

Path length dependent medium effect? Feasible to probe medium density experimentally? xT =[0.5, 0.6]

xT =[0.9, 1.0]

EPJC 74 (2014) 2959

0-10%

20-30%

•

By selecting jet pair events using different asymmetry (xT) value, one can probe different medium lengths and density profile, and result different modification patterns

➡ can be studied at LHC with coming data

21

Consistency between jets and hadrons? p

CMS Preliminary, pPb sNN = 5.02 TeV

2

CMS (0-100%): |η |<0.5 CM

CMS: jet R = 0.3, Extrapolated pp

∫L dt = 35 nb

Pb

EPJC 75 (2015) 237

-1

ATLAS: jet R = 0.4,arXiv:1412.4092

RpPb

ATLAS(0-90%): |y*|<0.3

RpPbjets⊗RpPbFF =RpPbhadrons

1.5

1

30 40

100

200

p [GeV/c]

ATLAS, HP15

or

T

CMS, HP15

• CMS and ATLAS results are consistent for both jets and hadrons • Jets RpPb ~1 while hadrons RpPb >1 using interpolated pp reference → jet FF modified in pPb? ➡ Precision measurements with direct reference data is highly demanded 22

Thank you very much!

A new era just started!

Please stay tuned… Yaxian MAO Central China Normal University

GyulassyFest, September 25-26, Wuhan 2015

23

backup

Yaxian MAO Central China Normal University

Mini-workshop on jet physics, Wuhan April 14-15

24

jet FF modifications: CMS vs. ATLAS

•

Recalculate FF ratio for Rcp style using the published data in HEP

Yaxian MAO Central China Normal University

Mini-workshop on jet physics, Wuhan April 14-15

25

Anatomy of the dijet η distribution EPJC 74 (2014) 2951

Yaxian MAO Vanderbilt University

IS2013, 10/09/2013, Illa da Toxa, Spain

26

Anatomy of the dijet η distribution EPJC 74 (2014) 2951

Shadowing

Yaxian MAO Vanderbilt University

IS2013, 10/09/2013, Illa da Toxa, Spain

26

Anatomy of the dijet η distribution Anti-shadowing EPJC 74 (2014) 2951

Shadowing

Yaxian MAO Vanderbilt University

IS2013, 10/09/2013, Illa da Toxa, Spain

26

Anatomy of the dijet η distribution Anti-shadowing EPJC 74 (2014) 2951

EMC Shadowing

Yaxian MAO Vanderbilt University

IS2013, 10/09/2013, Illa da Toxa, Spain

26

Color charge dependent jet FF and modifications? Do different colored partons have different fragmentation pattern? e++e- s=180 GeV OPAL+DELPHI quark jets gluon jets

102 10

dN/dz

FF

103

quark FF

1

10-1

PbPb/pp

KKP π±

Du,d(z,Q2) 0

10-2

π±

Dgluon(z,Q2)

gluon FF

0

-3

10

10-4

• •

DELPHI, EPJC, 13 (2000) 573 OPAL, ZPC, 69 (1996) 543

0.2

0.4

0.6

0.8

1

z

OPAL and DELPHI measured quark and gluon has different PRD 84 (2011) 014034 fragmentation pattern in e+eTheory predicted jet fragmentation pattern modified differently for different parton mass ➡ can be checked at LHC with coming data 27

10

8

±

6

4

pp events at s = 7 TeV cluster trigger (mainly π0) charged trigger (h± ) ALICE Performance

2 0

10

jet-h ± gluon

10

zt = 1.0 8

jet-h ± quark

E

jet-h quark

inv xE slope in x ∈ (0.4,0.8)

jet-h ± gluon

E

inv xE slope in x ∈ (0.4,0.8)

Inverse xE slope

20

30

6

4

zt ≈ 0.5 pp events at s = 7 TeV

w/o isolation w/ isolation

2 0

20

30

pTt (GeV/c)

pTt (GeV/c)

•

10

ALICE Preliminary

cluster trigger (mainly π0) and charged trigger has similar slope on xE distribution

Yaxian MAO Central China Normal University

GyulassyFest, September 25-26, Wuhan 2015

28

Charged particle pp reference spectrum CDF: PRL 61 (1988) 1819, PRD 82 (2010) 119903 CMS: JHEP 08 (2011) 086, EPJC 72 (2012) 1945

Direct data interpolation method • Six datasets used from published papers with √s from 0.63 to 7 TeV • Only the 2.76 and 7 TeV data extend to high pT beyond 30-40 GeV/c • Technique for high-pT interpolation: use xT = 2 pT / √s • Total uncertainty: 10%

Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

29

Comparison to ALICE Charged Particles pPb Measured Spectra • ALICE and CMS results generally consistent within combined systematic uncertainty. • CMS results ~5-10% higher • Measured pPb spectra account for ~ 1/3 of the tension

Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

ALICE: arXiv:1405.2737 CMS: HIN-12-017

30

Comparison to ALICE Charged Particles Artificial pp Reference Spectra • ALICE and CMS references diverge at high-pT • Accounts for ~ 2/3 of the tension • Different methods used • NLO-scaling (ALICE) • Direct Interpolation (CMS) • Different underlying data used for ALICE and CMS Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

ALICE: arXiv:1405.2737 CMS: HIN-12-017

31

Comparison to ALICE Charged Particles Comparison of Methods • Perform NLO Scaling on CMS data to 5.5 TeV and • Compare with interpolation to 5.5 TeV • Two methods generally agree within 10% • No clear systematic trend above or below unity

Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

NLO – F. Arleo, D. d’Enterria, A. Yoon: JHEP 06 (2010) 035 CMS: HIN-12-017

32

Comparison to ALICE Charged Particles Comparison pp Data from CMS and ALICE • 7 TeV and 2.76 TeV datasets compared • Larger statistical uncertainty on high-pT ALICE data ALICE: EPJC 73 (2013) 2662 CMS: HIN-12-017

Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

33

Comparison to ALICE Charged Particles Comparison of NLO-Scaling with ALICE and CMS • Perform NLO-Scaling on both ALICE and CMS data to 5.5 TeV and • Compare with CMS interpolation to 5.5 TeV NLO – F. Arleo, D. d’Enterria, A. Yoon: JHEP 06 (2010) 035 CMS: HIN-12-017

Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

34

Major differences comes from pp reference Due to the pp reference

pP b FF Ana./CMS data from R pPb

•

re-analyzed pp data at √s = 7 TeV not agrees with published spectra

1.2

CMS Preliminary

1 1.4

0.8

CM S Preliminary

0.6 0.4 RpPb analysis: EPJC 75 (2015), 237

0.2 0

This analysis, inside jet cone This analysis, spectra analysis

0

50 100 150 pTtrack (GeV/c)

Yaxian MAO Central China Normal University

200

σ pp(Updated)/σ pp(R pPb)

•

1.2 1 0.8 0.6

pp √ = 0.9, 1.96, 2.76, 7 TeV → 5.02 TeV (R pPb): PRD 82 (2010) 119903, EPJC 72 (2012) 1945, JHEP 08 (2011) 086

0.4

(Updated): √ = 2.76 TeV from 2013 √ = 7 TeV from 2011

0.2 0

0

GyulassyFest, September 25-26, Wuhan 2015

50

100 150 (GeV/c)

200

p Ttrack

35

Jet shape results compare to theory

• The experimental results show quite consistent as theory (COM and jet energy different) 36

Motivation

• Final%State%Radia.on% %(FSR)%

{π ,K, p,n

Detector% ,… }

"

Had

Ini.al%State%Radia.on% %(ISR)%

Jet%

za3 o

n"

Beam% Remnants%

p% ="

(uud)"

Beam% Remnants%

ron i

Exploit high pT particles and jets to understand initial and final state properties of heavy-ion collisions:

•

p%

High pT partons produced in hard interactions in the initial phase of the collision...

="

•

(uud)"

•

in pp: understand and characterise the probe

...Undergo multiple interaction inside the collision region prior to hadronization

•

in pA: benchmark for AA, disentangle initial from final state effects, characterise nuclear PDFs

•

in AA: probe the QCD medium created in the collision, identify final state effects

37

Jet/hadron RpA vs. RAA

Nuclear Modification Factor Nuclear Modification Factor

2.5 2.5

PbPb sNN = 2.76 TeVµb-1 pPb L = 35 nb-1; PbPb L = 150

Charged R |η |η| < |1< 0.5 Inclusive jet particles R (0-100%) pA CM pA

CM

Charged R (0-5%) |η| < 1 Inclusive jet particles R (0-5%) AA |η| < 2

22

AA

1.5 1.5

11

0.5 0.5

00 0 0 50

100 20 15040200 250 60 30080350 400 100

2.5

Nuclear Modification Factor

pPbCMS sNNPreliminary = 5.02 TeV

Charged particles R

2

pA

AA

|η | < 1 CM

(0-5%) |η| < 1

1.5

1

0.5

0 0

T T

Vanderbilt University

pPb L = 35 nb-1; PbPb L = 150 µb-1

Charged particles R

p p[GeV/c] [GeV/c]

Yaxian MAO

CMS Preliminary

IS2014, 12/06/2014, Napa, CA

20

40

60

80

100

p [GeV/c] T

38

Summary from dijet η CMS PAS HIN-13-001

ηdijet =

• •

η1+η2 2

Mean of ηdijet increases v.s. forward calorimeter energy Width of ηdijet decreases v.s. forward calorimeter energy

Yaxian MAO Vanderbilt University

IS2014, 12/06/2014, Napa, CA

39