Jet quenching: future experiments and ‘End Game’ · 7.01.2018 · Jet quenching: future...

Jet quenching: future experiments  and ‘End Game’

Marco van Leeuwen, Nikhef, CERN

JETSCAPE Workshop, 5-7 January 2018LBNL, Berkeley

Jet quenching: future experiments  and ‘End Game’

Marco van Leeuwen, Nikhef, CERN

JETSCAPE Workshop, 5-7 January 2018LBNL, Berkeley

Disclaimer:We are (I am) not in a position yet to design the End Game yet,  but will try to do the next best thing….

The physics of parton energy loss — what do want/can we aim to learn?

2

Plus a host of technical questions, e.g. role of event-by-event/geometry fluctuations

Two broad categories: nature of energy loss mechanism and nature of the medium

Nature of the energy loss mechanism

Nature of the medium


• Flavour dependence of energy loss• Path length dependence of energy loss• Interference: do jets lose energy as a single parton?

• Also formation time effects• Transverse broadening: relate transverse and longitudinal dynamics

• Testing our understanding of the medium/dominant process

2









2


• Density of the medium/value of qhat (vs temperature)• Distribution of radiated energy; approach to thermalisation?• Nature of the scattering centers?

• Large angle deflection








2


• Density of the medium/value of qhat (vs temperature)• Distribution of radiated energy; approach to thermalisation?• Nature of the scattering centers?

• Large angle deflection




Goal of the field: answer as many of these questions as we can, as well as we canTechnical questions have lower priority, but some may need answers to get to the interesting ones!

Corollary: connections — Need coherent modeling of multiple observables

Part I: basic observables‘the bread and butter’

Simple observables; program and plan

• Observables/measurements:• Single particle RAA, vn • Di-hadron, recoil suppression IAA• Heavy flavor RAA, vn

4

Progress to be made by:- Coherent modeling of multiple observables- Improving precision, pT reach, comparing RHIC+LHC

• Density of the medium: value, time evolution of qhat• Path length dependence of energy loss• Heavy flavour energy loss;  

dead cone effect, importance of elastic scattering vs radiation• Scale dependence of energy loss, medium properties?

Address an important subset of the questions raised in the intro

0

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RAA

(pT)

pT (GeV/c)

CUJET2.0(αmax,fE,fM)

CMS 0-5%ALICE 0-5%

(0.20,1,0)(0.21,1,0)(0.22,1,0)(0.23,1,0)(0.24,1,0)(0.25,1,0)(0.26,1,0)(0.27,1,0)(0.28,1,0)(0.29,1,0)(0.30,1,0)(0.31,1,0)(0.32,1,0)

Example of a systematic exploration: RHIC and LHC

5

Burke et al, JET Collaboration, arXiv:1312.5003

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RAA

(pT)

pT (GeV/c)


PHENIX 0-5% 2012PHENIX 0-5% 2008(0.20,1,0)(0.21,1,0)(0.22,1,0)(0.23,1,0)(0.24,1,0)(0.25,1,0)(0.26,1,0)(0.27,1,0)(0.28,1,0)(0.29,1,0)(0.30,1,0)(0.31,1,0)(0.32,1,0)

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p

/fm2=1.4, 1.8, 2.2, 2.6, 3.0 GeV0

q

CMS (0-5%)Alice (0-5%)

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R

(GeV)T

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/fm2=0.8, 1.0, 1.2, 1.4, 1.7 GeV0

q

PHENIX 2008 (0-5%)

PHENIX 2012 (0-5%)

RHIC

RHIC

LHC

LHCSystematic comparison of energy loss models with dataMedium modelled by Hydrodynamics (2+1D, 3+1D)

pT dependence matches reasonably well

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RAA

(pT)

pT (GeV/c)


CMS 0-5%ALICE 0-5%

(0.20,1,0)(0.21,1,0)(0.22,1,0)(0.23,1,0)(0.24,1,0)(0.25,1,0)(0.26,1,0)(0.27,1,0)(0.28,1,0)(0.29,1,0)(0.30,1,0)(0.31,1,0)(0.32,1,0)

Example of a systematic exploration: RHIC and LHC

5


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RAA

(pT)

pT (GeV/c)


PHENIX 0-5% 2012PHENIX 0-5% 2008(0.20,1,0)(0.21,1,0)(0.22,1,0)(0.23,1,0)(0.24,1,0)(0.25,1,0)(0.26,1,0)(0.27,1,0)(0.28,1,0)(0.29,1,0)(0.30,1,0)(0.31,1,0)(0.32,1,0)

10 20 30 40 50 60 70 80 90 1000

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AA

R

(GeV)T

p

/fm2=1.4, 1.8, 2.2, 2.6, 3.0 GeV0

q

CMS (0-5%)Alice (0-5%)

6 8 10 12 14 16 18 200

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1

AA

R

(GeV)T

p

/fm2=0.8, 1.0, 1.2, 1.4, 1.7 GeV0

q

PHENIX 2008 (0-5%)

PHENIX 2012 (0-5%)

RHIC

RHIC

LHC

LHCSystematic comparison of energy loss models with dataMedium modelled by Hydrodynamics (2+1D, 3+1D)

pT dependence matches reasonably well

RHIC:

LHC:

(Ti = 370 MeV)

(Ti = 470 MeV)

What do we learn from ‘knowing’ qhat?

6

RHIC:

LHC:

(Ti = 370 MeV)

(Ti = 470 MeV)

i.e.


6

RHIC:

LHC:

(Ti = 370 MeV)

(Ti = 470 MeV)

i.e.

Arnold and Xiao, arXiv:0810.1026

HTL expectation:

relation qhat - T depends on number of degrees of freedom, 𝛼S


6

RHIC:

LHC:

(Ti = 370 MeV)

(Ti = 470 MeV)

i.e.


HTL expectation:


Conclusion for now: values are in the right ballpark — we semi-quantitatively understand parton energy loss


6

RHIC:

LHC:

(Ti = 370 MeV)

(Ti = 470 MeV)

i.e.


HTL expectation:


Conclusion for now: values are in the right ballpark — we semi-quantitatively understand parton energy loss

Future direction: can we make this quantitative?  E.g. determine number of degrees of freedom with a meaningful uncertainty?  Or constrain T-dependence of qhat?

What do we learn II: transport coefficient and viscosity

7

H. Song et al, PRC

83, 054912

0 20 40 60 80centrality

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0.02

0.04

0.06

0.08

0.1v

2

RHIC: η/s=0.16LHC: η/s=0.16LHC: η/s=0.20LHC: η/s=0.24

STAR

ALICEv

2{4}

MC-KLNReaction Plane

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1

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3

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0.2 0.25 0.3 0.35 0.4 0.45 0.5

Au+Au at 0.2 TeV

Pb+Pb at 2.76 TeVqN/T3 (DIS)effˆ

T (GeV)

0

q/T

3ˆ

≈≈

??

????

NL

O S

YM

Hints of increase of η/s and decrease of q/T3  could have a common origin?

Elliptic flow

(Scaled) viscosity slightly larger at LHC Scaled transport coefficient  slightly smaller at LHC

Parton gas expectation: qhat and eta are inversely relatedMajumder, Muller and Wang, PRL99, 192301

NB: effects not significant (yet); can we narrow down the uncertainties?

Transport coefficient from RAA

More systematics: compare soft scattering formalism

8

Armesto et al, arXiv:1606.04837

q̂ = 2K ✏3/4

pQCD expectation:K = 1 (by definition)

↵S =1

3

Similar fit to the data, as the JET paper, but using multiple-soft equations

Large difference (factor ~2)between scale factor at RHIC and LHC

Energy loss: BDMPS-ASW multiple soft scatteringMedium: Hydrodynamics; Hirano, Luzum&Romatschke

Conclusion seems different from JET collaboration workShould follow up to find out what drives this

Points to modeling uncertainties? Can we reduce those?

5 6 7 8 9 10pT [GeV]

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R AA

PHENIX in planePHENIX out of plane2+1d ideal2+1d vCGC2+1d vGlb3+1d ideal

20 - 30 %, ASW

(a)

High-pT v2, RAA in and out of plane

9

Xu et al, CU

JET, arXiv:1402.2956

T. Renk, arXiv:1010.1635

Sensitive to medium evolution models (freeze-out temp)

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v 2(p

T)

pT (GeV/c)

ALICE Pb+Pb 2.76ATeV h± 20-30%ATLAS Pb+Pb 2.76ATeV h± 20-30%

CMS Pb+Pb 2.76ATeV h± 20-30%CUJET2.0 π (0.23,1,0) ∆φ=0° & (0.26,1,0) ∆φ=90°

CUJET2.0 π (0.20,1,0) b=7.5fm @LHC(0.21,1,0)(0.22,1,0)(0.23,1,0)(0.24,1,0)(0.25,1,0)(0.26,1,0)(0.27,1,0)(0.28,1,0)(0.29,1,0)(0.30,1,0)(0.31,1,0)(0.32,1,0)(0.33,1,0)(0.34,1,0)(0.35,1,0)

Current state: Hydro+E-loss models do not produce enough v2

Potential with more precise data, and some effort:Use high-pT data to co-validate/constrain medium evolution (models)

CUJETYaJEM

RHICLHC

Qin and Majumder, arXiv:0910.3016

Various points under discussion:- Effect of fluctuations

- HT gets higher v2?Noronha-Hostler et al, arXiv:1602.03788

Another handle on path length dependence: di-hadrons

10

8 < pT,trig < 15 GeV

Near side trigger,  biases to small E-loss

Away-side large L

STA

R P

RL 95, 152301

Away-side (recoil) suppression IAA  samples longer path-lengths than inclusive RAA

Can be modelled with the same tools as inclusive particle production

IAA modeling

11

Armesto et al, J.Phys. G

37, 025104

RAA and IAA fit with similar density

Confirms ~L2 dependence Calculations with elastic loss give too little suppressionH

Zhang et al, PRL 98, 212301

→π

± ±

±

ε0

→π

± ±

±

χ2

Medium model: Glauber profileEnergy loss: Higher Twist

Medium model: (ideal) HydroEnergy loss: BDMPS-ASW multiple soft

T. Renk, PRC, arXiv:1106.1740

IAA modeling

11

Armesto et al, J.Phys. G

37, 025104

RAA and IAA fit with similar density

Confirms ~L2 dependence Calculations with elastic loss give too little suppressionH

Zhang et al, PRL 98, 212301

→π

± ±

±

ε0

→π

± ±

±

χ2

Medium model: Glauber profileEnergy loss: Higher Twist

Medium model: (ideal) HydroEnergy loss: BDMPS-ASW multiple soft


So far, model calculations only exist for RHIC: - Would like to see LHC calculations to put modeling to the test- Experimentally: extend pT range

IAA at the LHC

12

Transition enhancement → suppression @ pT ~ 2 GeV

CMS-PA

S-HIN-12-010

19.2 - 24.0 GeVpTtrig (GeV):

14.0 - 28.8 GeV 28.8-35.2 GeV 35.2-48.0 GeV

peripheral 50-60%

central 0-10%

)c (GeV/T

assocp0 1 2 3 4 5 6 7 8 9

AA

I

0

1

2

3

4

5

6 = 2.76 TeVNNsALICE, 0-10% Pb-Pb,

c < 16 GeV/trigT

p8 < | < 1.1)π-ϕ∆Away side (|

bkg)n

-hadron (v0π

AMPT model

JEWEL model

NLO pQCD model

ALICE, PLB 763, 238 PRL 108, 092301

Data already exist —  it’s really ‘just’ a matter  of running the models/calculations !

Heavy flavour RAA; mass dependence

13

〉part

N〈0 50 100 150 200 250 300 350 400

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

(empty) filled boxes: (un)correlated syst. uncert.

|

Relating heavy and light flavor modeling: Ds and

14

qhat(T=400 MeV) = 3 GeV2/fm

However, perturbative estimate Ds = 30/2 𝜋 T —> qhat ~ 0.6 GeV2/fm

E.g.: Why is the perturbative estimate of Ds so large?LO: Svetitsky, PRD 37, 2484

2⇡ TDs = 8⇡CFCA

T 3

q̂(approximate relation;  Ds and qhat are different regimes)

Trying out some numbers:

Cao, Qin, Bass, PRC 88, 044907

Ds = 6/2 𝜋 T

q̂

Should connect heavy and light flavor phenomenology

Jets: multi-parton states

High-pT jets vs hadrons

16

[GeV]T

p

AAR

0

0.5

1

1.5

100 200 300 400 500 600 900000

= 5.02 TeV, this analysisNNsATLAS,

= 2.76 TeV, arXiv: 1411.2357NNsATLAS,

PreliminaryATLAS = 0.4 jetsR tkanti-

0 - 10 %| < 2.1y|

-12015 Pb+Pb data, 0.49 nb-1 data, 25 pbpp2015

Jets: RAA < 1 out to high pT

Single particles: consistent with expected constant (log E) dependence

CMS, JHEP 04, 039

ATLAS-CONF-2017-009

Charged particle RAA Jet RAA

pT-dependence driven by energy dependence of E-loss Different for single particles and jets! ?

Jets suggest increase of ΔE vs E

Tentative interpretation: in jets, multiple partons lose energy; more partons in high-E jets —> more E-loss

High-pT jets vs hadrons

16

[GeV]T

p

AAR

0

0.5

1

1.5

100 200 300 400 500 600 900000

= 5.02 TeV, this analysisNNsATLAS,

= 2.76 TeV, arXiv: 1411.2357NNsATLAS,

PreliminaryATLAS = 0.4 jetsR tkanti-

0 - 10 %| < 2.1y|

-12015 Pb+Pb data, 0.49 nb-1 data, 25 pbpp2015

Jets: RAA < 1 out to high pT

Single particles: consistent with expected constant (log E) dependence

CMS, JHEP 04, 039

ATLAS-CONF-2017-009

Charged particle RAA Jet RAA

pT-dependence driven by energy dependence of E-loss Different for single particles and jets! ?

Jets suggest increase of ΔE vs E

Tentative interpretation: in jets, multiple partons lose energy; more partons in high-E jets —> more E-loss

First glimpse of jets as scale-dependent probes !Opens up a field of study: pT-dependence of jet modifications

First look at the models

17

Zapp, Krauss, Wiedemann,   arXiv:1212.1599

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10 100 1000

RA

A

pt [GeV]

charged hadrons

CMS data, 0-5% centrality

ALICE data, 0-5% centrality

JEWEL+PYTHIA

Eyalavalli and Zapp, JHEP 1707, 141

w/ Recoils, 4MomSubw/ Recoils, GridSub1w/ Recoils, GridSub2w/o Recoilsanti-k⊥ R=0.4 jetsp

jet⊥ > 100 GeV

|ηjet| < 2

100 150 200 250 300 350 4000

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1

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1.6JEWEL+PYTHIA (0-10%), Pb+Pb

√s = 2.76 TeV

p⊥ [GeV]R

AA

JetsCharged particles

JEWEL Hybrid model

JEWEL seems to capture the trends quite wellSome quantitative questions to be worked out;  e.g. increase of hadron RAA too slow at 5 TeV? Hybrid model: similar conclusion at first sight:

increase of jet RAA less steep than hadron RAAAlso consistent with energy shift + small corrections?

Take home message: need large pT range to draw strong conclusionssmall range: flat vs increase hard to disentangle; limited precision of models and data

D Pablos, this meeting

Where does the lost energy go ?

18

Results clearly show that lost energy  goes to large angle and soft particles

Should try to go beyond this qualitative statement

• Is the transport to large-angle consistent with  expectations from pQCD?

• Does it require ‘thermalisation’?• Can we learn more about coherence effects?

Several studies exist: JEWEL, Hybrid model, CCNUgive partial answers…

∆0.5 1 1.5

[GeV

]〉|| Tp〈

-20

-10

0

ppCMS (2.76 TeV)-15.3 pb

InclusiveJA

∆〉

||

Tp〈pp

∆0,〉||

Tp〈pp

[GeV]∆,

Ttrkp

〉||

Tp〈

| < 2.4trkη|

0.5-1.01.0-2.02.0-4.04.0-8.08.0-300.0

∆0.5 1 1.5

-20

-10

0

PbPb 30-100% (2.76 TeV)-1bµ166

R = 0.3tanti-k

∆〉

||

Tp〈PbPb

∆0,〉||

Tp〈PbPb

∆0.5 1 1.5

-5

0

5 (PbPb 30-100%) - pp

∆〉

||

Tp〈PbPb - pp

∆0.5 1 1.5

-20

-10

0

> 50 GeVT,2

> 120; pT,1

p/6π > 5

1,2φ∆| < 0.6;

2η|,|

1η|

PbPb 0-30%

∆0.5 1 1.5

-5

0

5 (PbPb 0-30%) - pp

CMS, JHEP 01 (2016) 006Requires careful modeling of soft physics — not easy

and exploration of model uncertainties

Fragmentation functions/hadron distributions

19

CMS-PAS-FTR-17-002Mehtar-Tani and Tywoniuk, Phys. Lett. B744(2015) 284

jetξ

0.5 1 1.5 2 2.5 3 3.5 4 4.5

jet

ξdtrk

dN je

tN1

0

1

2

3

4

5PbPb Cent. 0-10 %Current Unc.Projected Unc.

pp (smeared)Current Unc.Projected Unc.

> 1 GeV/ctrkT

p

jet R = 0.3Tanti-k

> 30 GeV/cjetT

p

| < 1.6jetη|

> 60 GeV/cγT

p

| < 1.44γη|

8π7 >

γjφ∆

= 5.02 TeVNNs-1, pp 650 pb-1PbPb 10 nb

CMSProjection

0

1

2

3

4

5

dN

/

dℓ

0.5

1

1.5

2

0 1 2 3 4 5

Ratio

ℓ

CohCoh + Decoh

VacuumCMS Prelim.: medium, 0-10%

CMS Prelim.: vacuum

CohCoh + Decoh

CMS Preliminary, 0-10%

High-z: hadron vs jet RAA; scale dependence of energy lossLow-z: mechanism of thermalisation in the medium vs soft fragmentation

Effects tend to be small: Experimentally: need good precision and study pT dependenceModels: need to consider systematic uncertainties on models/missing physics

Jet acoplanarity

20

Gaussian width: sensitive to momentum broadening

Potential for direct sensitivity to scattering centers in the medium

0 5 10 15 20 250.00

0.05

0.10

0.15

0.20

0.25

q?(GeV)

1 �d� dq

?

RHIC

HJ [9, 30]+[12, 18]

HJ [9, 30]+[18, 48]

HH [5, 10]+[3, 5]

HH [5, 10]+[5, 10]

HH [12, 20]+[3, 5]

LHC

HJ [9, 30]+[18, 48]

HJ [20, 50]+[60, 90]

HH [5, 10]+[5, 10]

Chen, Qin, et al, arXiv:1607.01932

2.4 2.6 2.8 3.00.0

2.0

4.0

6.0

ptrigT,h = [9, 30] GeV

passoT,J = [18, 48] GeV

��

1 �d� d��

STAR 60-80%

STAR 0-10%

hp2?i = 0 GeV2

hp2?i = 13 GeV2

K Rajagopal, this workshop

Relation momentum broadening - energy loss depends on nature of medium

hq2?i = q̂L q̂ = KT 3

Tails:‘Rutherford scattering’

K = 2-5 in QCDlarger in strong coupling

Competing effects for acoplanarity: Sudakov broadening and E loss

21

0 5 10 15 20 250.00

0.05

0.10

0.15

0.20

0.25

q?(GeV)

1 �d� dq

?

RHIC

HJ [9, 30]+[12, 18]

HJ [9, 30]+[18, 48]

HH [5, 10]+[3, 5]

HH [5, 10]+[5, 10]

HH [12, 20]+[3, 5]

LHC

HJ [9, 30]+[18, 48]

HJ [20, 50]+[60, 90]

HH [5, 10]+[5, 10]

Chen, Qin, et al, arXiv:1607.01932Hybrid model, Solana et al, arXiv:1609.05842

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3

0� 10%

PLt > 35 GeV, PSt > 10 GeV, |⌘| < 2

EventFraction

��

K=0

K=20

K=40

K=100

Vacuum

Energy loss causes narrowing (shift from high to low pT)

0

1

2

3

4

5

6

7

8

0 0.5 1 1.5 2 2.5 3

0� 10%

PLt > 35 GeV, PSt > 10 GeV, |⌘| < 0.5

EventFraction

��

K=0

K=5

K=20

K=50

Vacuum

RHIC

LHC

Natural width of h-jet, jet-jet distributions

hq2?i = (2� 5 GeV)2

Putting things together: dialing the biasesLeveraging the differences in geometric and energy loss bias in observables

Conceptually powerful, but needs simultaneous modeling of  geometry, energy loss, and experimental selection

23

T. Renk, arXiv:1212.0646RHIC

LHC

h-h jet-h jet-jet (AJ)

Surface bias differs between probes: largest for hadrons and energy/collider: stronger at RHIC

Main ingredients: surface bias vs fluctuations

Using biases: examples/ideas

• Disentangle geometric effects and fluctuations• Inclusive vs recoil• gamma-jet (or EW boson-jet) vs di-jets

• Select quark/heavy quark jets• Dial the biases to tease out the small acoplanarity signals?• Select jets that experience a large energy loss to increase ‘signal’

• ‘Natural’ fluctuations from geometry and the intrinsic process are very large; ‘average’ not always useful• Explicitly study energy loss dependence on e.g. opening angle?  

Needs development/study: ideally have two classes of variables:• Variable(s) that preserve properties of the ‘vacuum jet’, i.e. not (much) affected by energy loss• Variable(s) that are explicitly sensitve to energy loss

24

Using biases: examples/ideas

• Disentangle geometric effects and fluctuations• Inclusive vs recoil• gamma-jet (or EW boson-jet) vs di-jets

• Select quark/heavy quark jets• Dial the biases to tease out the small acoplanarity signals?• Select jets that experience a large energy loss to increase ‘signal’

• ‘Natural’ fluctuations from geometry and the intrinsic process are very large; ‘average’ not always useful• Explicitly study energy loss dependence on e.g. opening angle?  

Needs development/study: ideally have two classes of variables:• Variable(s) that preserve properties of the ‘vacuum jet’, i.e. not (much) affected by energy loss• Variable(s) that are explicitly sensitve to energy loss

24

This is where jet shape variables have great potential!Many options under study; unfortunately no time to review…

Example: AJ at RHIC

25

JA0.2− 0 0.2 0.4 0.6 0.8

Fraction

0

0.05

0.1

0.15

0.2

0.25

>2 GeV/c:CutT

With p>20 GeV/c

T,lead p

>10 GeV/cT,sublead

p

Au+Au, 0-20%, R=0.4TAnti-k

>2 GeV/c:CutT

p Au+Au MB⊕p+p HT

Au+Au HT

>0.2 GeV/c, Matched:CutT

p Au+Au MB⊕p+p HT

Au+Au HT

STAR, arXiv:1609.03878

Observation: di-jet imbalance small at RHICwhen selecting ‘hard-core jets’

Is this driven by the hard core selection?—> Hard core selects jet (pairs) that lose little energyCan be tested at LHC

What about other biases/effects:- Steeper spectrum at RHIC- Smaller overall energy loss at RHIC vs LHC?- Quark vs gluon jets?

Promising avenue, needs follow-up to extract the physics

Example II: compare 𝛾-jet and jet-jet

26

z

2−10 1−10 1

ratio

of D

(z)

0.6

0.8

1

1.2

1.4

1.6

PreliminaryATLASpp0-30% Pb+Pb /

-tagged jets 5.02 TeVγ

inclusive jets 2.76 TeV(0-10%)

ATLAS-CONF-2017-074

Comparing 𝛾-jet and jet-jet changes:- Energy loss bias 

reco jet energy is ‘after energy loss’ - Flavour content 

quark vs gluon jets

Leads to difference in frag function modification

Leverage this with models + increasing data precisionto extract the physics

Example III: h-jet at RHIC and LHC

27

LHC: recoil jet suppressionΔIAA ~ 0.5 with R=0.2

STAR, PRC96, 024905

)c(GeV/chT,jet

p0 10 20 30 40 50 60 70 80 90 100

PY

TH

IAre

coil

∆/P

bP

bre

coil

∆=

AA

I∆

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

ALICE data

Shape uncertainty

Correlated uncertainty

= 2.76 TeVNNs0-10% Pb-Pb

Ha

dro

n T

rig

ge

r T

hre

sho

ld

= 0.2R charged jets, TkAnti- < 0.6ϕ∆ − π

TT{8,9}− TT{20,50}

ALICE

RHIC: recoil jet suppressionΔIAA ~ 0.3 with R=0.2

Suppression numerically quite different at RHIC and LHC. What drives this? Kinematic selection, different surface bias, …

ALICE, JHEP 09 (2015) 170

Future experiments: HL-LHC

28

https://indico.cern.ch/event/647676/timetable/J.Jow

ett, HL-H

C w

orkshop

1 nb-1 PbPb ~ 43 NN-equiv pb-1

HL-LHC: expect factor ~3 increase of lumi; 2.8 nb-1/year

Current target lumi : 10 nb-1 in run 3 + 4 (2021-2029)(ALICE request)

Increase in statistics compared to run 1, 2:- 5x for triggers in ATLAS+CMS- 10x for triggers in ALICE- 100x for MB-like in ALICE

0.7 nb-1

LHC HI lumi over the years

https://indico.cern.ch/event/647676/timetable/http://www.apple.com

Future experiments: HL-LHC

28

https://indico.cern.ch/event/647676/timetable/J.Jow

ett, HL-H

C w

orkshop

1 nb-1 PbPb ~ 43 NN-equiv pb-1

HL-LHC: expect factor ~3 increase of lumi; 2.8 nb-1/year

Current target lumi : 10 nb-1 in run 3 + 4 (2021-2029)(ALICE request)

Increase in statistics compared to run 1, 2:- 5x for triggers in ATLAS+CMS- 10x for triggers in ALICE- 100x for MB-like in ALICE

0.7 nb-1

LHC HI lumi over the years

The HI program for run 3, 4 and beyond is  being discussed in a series of workshops→ European Strategy for Particle Physics

https://indico.cern.ch/event/647676/timetable/http://www.apple.com

Future experiments: sPHENIX at RHIC

29

Slide from: G Roland,  CERN HI jet workshop 2017

Planned start:  2022 ~ LHC run 3

Instead of a summary…

30

sPHEN

IX, G. Roland

Main directions

• Increased precision and pT reach  Non-trivial improvement of physics potential!

• More differential studies Leveraging the biases

• Better overlap between RHIC and LHC

Theory/modeling:• Need coherent/simultaneous description  of multiple observables to constrain the physics

• Need competing/alternative models/mechanisms to compare and contrast Also within a single group/code!

Experiment:

Thanks for your attention!

More distant future: FCC and HE-LHC

32

√s = 27 TeV pp, √sNN = 10.6 TeV Pb-PbEarliest possible realisation 2040

FCCFuture Circular Collider very large project; requires new tunnel ~ 100 km

√s = 100 TeV for pp, √sNN = 39.4 TeV for Pb-Pb

More info: see HL-LHC workshops and FCC weeks, e.g.: http://fcw2018.web.cern.ch

HE-LHCHigh-Energy LHC

http://fcw2018.web.cern.ch

Simple observables; how to model them?

• A lot of experience exists with simple modeling:• Production, energy loss, and fragmentation• Plus full hydro background or a good approximation in most cases

• Main advantage: keeps the model tractable (clear what is put in)• Disadvantage: no natural extension to jet observable

• Simple modeling may be good enough for single particle observables• Except, maybe via jet functions, but long and tedious road

• Also not always obvious how to implement path-length dependence in a non-uniform medium

33

Note: should not forget model uncertainties/freedoms- Important part of the story; may point to new questions/directions!- Several aspects have been explored; many connections still missing

Summary of transport coefficient study

34

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3 0.4 0.5

McGill-AMY

HT-M

HT-BW GLV-CUJET

MARTINI

Au+Au at RHIC

Pb+Pb at LHCqN/T

3 (DIS)eff

ˆ

T (GeV)

q/T

3ˆ

RHIC:

LHC:


(Ti = 370 MeV)

(Ti = 470 MeV)

values from different models consistent


34

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3 0.4 0.5

McGill-AMY

HT-M

HT-BW GLV-CUJET

MARTINI

Au+Au at RHIC

Pb+Pb at LHCqN/T

3 (DIS)eff

ˆ

T (GeV)

q/T

3ˆ

RHIC:

LHC:


(Ti = 370 MeV)

(Ti = 470 MeV)


HTL expectation:Sizeable uncertainties from 𝛼S, treatment of logs etc expected



34

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3 0.4 0.5

McGill-AMY

HT-M

HT-BW GLV-CUJET

MARTINI

Au+Au at RHIC

Pb+Pb at LHCqN/T

3 (DIS)eff

ˆ

T (GeV)

q/T

3ˆ

RHIC:

LHC:


(Ti = 370 MeV)

(Ti = 470 MeV)


HTL expectation:Sizeable uncertainties from 𝛼S, treatment of logs etc expected

Values found are in the right ballpark compared (p)QCD estimateMagnitude of parton energy loss is understood


Transport coefficient and viscosity

35

Transport coefficient:momentum transfer per unit path length

basically measures the density


35



Viscosity: General relation:


35



Viscosity: General relation:

Expect for a QCD medium

Majumder, Muller and Wang, PRL99, 192301

MC tools: JEWEL

36

Ti = 530 MeV @ 𝜏0 = 0.5 fm/c

Zapp, Krauss, Wiedemann, arXiv:1212.1599

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

10 100 1000

RA

A

pt [GeV]

charged hadrons

CMS data, 0-5% centrality

ALICE data, 0-5% centrality

JEWEL+PYTHIA

0

0.2

0.4

0.6

0.8

1

4 6 8 10 12 14 16 18 20 22 24 26

RA

A

pt [GeV]

π0

PHENIX data, 0-10% centrality

JEWEL+PYTHIA

RHIC LHC

Elastic+radiative energy loss; follows BDMPS-Z in appropriate limits Medium: Bjorken-expanding Glauber overlap

Ti = 350 MeV @ 𝜏0 = 0.8 fm/c

Good agreement with JET collaboration values

Publicly available

T vs t in EPOS/MC@HQ

37

EPOS2, b=0PbPb

s =2.76 TeV

1.0 10.05.02.0 20.03.01.5 15.07.0

1.00

0.50

0.20

0.30

0.15

0.70

tHfmêcL

THGeVL

JET collabTinit = 470 MeV

P Gossiaux, private comm

Medium parameters in MC@HQ agree well with light flavour fits

Q: how does the relation compare?

Werner, et al, arXiv:1203.5704

x [fm]-8 -6 -4 -2 0 2 4 6 8

y [fm

]

-8

-6

-4

-2

0

2

4

6

8

0

50

100

150

200 = 0.35 fm/c) τ= 0.0 , sη] (

3energy density [GeV/fm

�E(T )

Model(ing) uncertainties for high-pT v2

• Initial time/treatment• Freeze-out temperature/treatment• Length sampling in a non-uniform medium• Event-by-event fluctuations

38

When reporting a model/calculation; make sure to specify these things

Noronha-Hostler et al: fluctuations

39

Observation: high-pT v2 is  measured wrt to low pT v2

Noronha-Hostler et al, arXiv:1602.03788

Fluctuations bias v2

Basically, measure ⌦v22↵

NB: no energy loss fluctuations; not so clear how geometry was implemented (L)

v2 in CUJET

40

aS runs, with cut-off at low Q

Cut-off is the main model parameter

0

0.04

0.08

0.12

0.16

10 20 30 40 50

v 2(p

T)

pT (GeV/c)

ALICE Pb+Pb 2.76ATeV h± 20-30%ATLAS Pb+Pb 2.76ATeV h± 20-30%

CMS Pb+Pb 2.76ATeV h± 20-30%CUJET2.0 π (0.23,1,0) ∆φ=0° & (0.26,1,0) ∆φ=90°

CUJET2.0 π (0.20,1,0) b=7.5fm @LHC(0.21,1,0)(0.22,1,0)(0.23,1,0)(0.24,1,0)(0.25,1,0)(0.26,1,0)(0.27,1,0)(0.28,1,0)(0.29,1,0)(0.30,1,0)(0.31,1,0)(0.32,1,0)(0.33,1,0)(0.34,1,0)(0.35,1,0)

CUJETXu et al, C

UJET, arXiv:1402.2956

Black dashed line: depends onAdds v2 ‘by hand’

GLV-based E-loss

Standard settings underpredict v2

However, see also: CUJET3.0Xu et al, arXiv:1509.00552

↵max

��

v2 in Higher Twist

41

Qin and Majumder, arXiv:0910.3016

Relating qhat to medium density, or T

42

[GeV]partonE0 5 10 15 20 25 30 35 40 45 50

/fm]

2 [G

eVq

1

10

210

Quark-Gluon Gas2µ> = 2 = 2

Comparison to LBT

43

Cao, et al, arXiv:1703.000822

Factor ~1.5 between LBT fits and JET values; probably within uncertainties

Heavy+light energy loss

Di-hadrons and single hadrons at LHC

44

Need simultaneous comparison to  several measurements  to constrain geometry and E-loss

Here: RAA and IAA

Three models: ASW: radiative energy loss YaJEM: medium-induced virtuality YaJEM-D: YaJEM with L-dependent   virtuality cut-off (induces L2)

Di-hadron modeling

45


L2 (ASW) fits data L3 (AdS) slightly below

Modified shower  generates increase at low zT

L (YaJEM): too little suppression L2 (YaJEM-D) slightly above

Model ‘calibrated’ on single hadron RAA

Clear sensitivity to L dependence

Di-hadron with high-pT trigger

46

pttrig > 20 GeV at LHC: strong signals even at low pTassoc 1-3 GeVCMS-PAS-HIN-12-010

19.2 - 24.0 GeVpTtrig (GeV): 14.0 - 28.8 GeV 28.8-35.2 GeV 35.2-48.0 GeV

CMS-PAS-H

IN-12-010

CMS di-hadrons: near side

47

19.2 - 24.0 GeVpTtrig (GeV):

14.0 - 28.8 GeV 28.8-35.2 GeV 35.2-48.0 GeV

Transition enhancement → suppression @ pT ~ 3 GeV

also compatible with IAA=1 at pT > 3 GeV?

peripheral 50-60%

central 0-10%

CMS-PA

S-HIN-12-010

Some open and partially-answered questions

48

Energy loss mechanismphysics of hard partons in a plasma

Nature of the mediumdensity, character of constituents

Flavor dependence of energy loss

Role of interference effects Do all partons in a jet lose energy?

Angular broadeninglarge-angle scattering

Thermalisation of the lost energy

Path length dependence of energy loss—> tomography of the medium

Scale dependence  of energy loss?

Jet quenching: future experiments and ‘End Game’ · 7.01.2018 · Jet quenching: future...

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