WG5: Future Physics Opportunity for High Density QCD with ...

Yen-Jie Lee

Yen-Jie Lee (MIT)On behalf of WG5

2nd Workshop on the physics of HL-LHC, and perspectives at HE-LHC

CERN, Geneva, Switzerland

18-20 June, 2018

WG5: Future Physics Opportunity for High

Density QCD with Ion and Proton Beams

Conveners: Urs Wiedemann (Theory), Jan Fiete Grosse-Oetringhaus (ALICE), Zvi Citron (ATLAS),

Michael Winn (LHCb), Yen-Jie Lee (CMS), John Jowett (Accelerator)

Yen-Jie Lee

Outline of WG5 Yellow Report

2WG5: Future Physics Opportunity for High Density QCD

• Future physics opportunities for high-density QCD with ions and proton beams at LHC (WG5 conv.)

• Accelerator performance with heavy ions (Roderik Bruce, John Jowett, Michaela Schaumann)

• Physics chapters (given here in random order), and coordinators

• Other opportunities

• Physics with lighter ions coordinated by Zvi Citron (ATLAS)

• Physics with gamma-gamma collisions Iwona Grabowska-Bold (ATLAS)

• Fixed-target with existing detectors (LHCb, ALICE?) to be presented briefly and refer to PBC report

• Inputs to cosmic-ray physics from p-nucleus collisions at LHC Hans Dembinski (LHCb)

• Opportunities with HI at HE-LHC (David d’Enterria, Carlos Salgado)

Jet ObservablesOpen Heavy FlavorQuarkonia Anton A (ALICE) +Chiral restoration via dileptons and thermal radiation via dileptons & photonsFlow/CorrelationsProduction of light nuclear states and net-particle fluctuationsEmergence of Hot and Dense QCD in Small SystemsnPDF/small-x

Marta V (CMS)Elena B (ALICE)Emilien C (CMS)Michael W (ALICE)Soumya M (ATLAS)Francesca B (ALICE)Jan Fiete (ALICE)Michael W (LHCb)

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QCD Phase Diagram


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Relativistic Heavy Ion Collisions


Two discs of almost real quarks and gluons

Time (fm/c)

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Parton Distribution Function (PDF)


Input Data for Nucleon PDF

Input Data for Ion PDF

Poor understanding of PDF due to

the limited amount of ion data

Lead Ion ≠ Superposition of Neutrons and Protons

Q2(G

eV2)

Q2(G

eV2)

x

x

45 Pb collider data vs.1200 proton collider data

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Opportunity at HL-LHC for nPDF


Ultra-peripheral collisions in PbPb and inclusive pPb collisions

; onset of gluon saturation?

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Observables in Ultra-Peripheral Collisions


Not Final

Present Data

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Measurements with Inclusive pPb Collisions


Constraint from Top production

Need ~2 /pb pPb collisions ( 10x Run 2)

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Time (fm/c)


Collision! Highest energy density state. Huge amount of soft (low momentum transfer) scatterings.

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Time (fm/c)

Midrapidity: thermalized QGP with very small baryon doping (μB)

Forward: QGP just created



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Time (fm/c)

Midrapidity: thermalized QGP with very small baryon doping (μB)

Forward: QGP just created

Hadronization of QGP, different from elementary collisions like e+e- or pp collisions

Based on particle correlation analyses, QGP is found to be

consistent with

“Near Perfect Liquid”Two discs of almost real

quarks and gluons


Yen-Jie Lee

Open Questions for Large System• Why does the system hydrodynamize so fast? How does the strongly

interacting medium emerge from an asymptotic free theory?

• What is the role of the pre-hydrodynamization phase? How big is the initial magnetic field? When is QGP formed?

• How does the QGP hadronize?

• What are the precise properties and inner workings of the QGP?


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Hard Probes


D, B

D, B

Heavy Quarks

C Cb b b b C C

Quarkonia

Jet

QGP

Jets

Electroweak Bosons

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Jet Quenching Observables


• HL-LHC data allow significant improvements on the statistical

accuracy of the boson-tagged jets measurements

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TeV Jet Quenching


• High pT reach of charged hadrons and jet RAA up to ~ 1 TeV

• The excitement is that the quenched energy will be significant

compared to underlying event energy density!

Charged Hadron RAA Jet RAA

Yen-Jie Lee

Jet Substructure


• High statistics jet sample delivered in HL-LHC:

• Opening a new era of jet quenching studies with jet substructure

• Constraints on the QGP scattering power with a completely

orthogonal observable (compared to jet or hadron spectra)

• Use of grooming techniques enable us to study

“Parton Shower Shape Dependence of Jet Quenching”

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Charmonia Production


Studies of the charmonia regeneration and ψ(2S) are crucial for

understanding the dynamics

Current HL-LHCCurrent

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Bottomonia Production


b

bb b

Recombination

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Heavy Flavor Mesons


D, B, non-prompt D, non-prompt J/y RAA, v2

D0 from B

J/y (ee) from B

ALICE Projection

• HL-LHC data could provide strong constraint on the heavy quark diffusion coefficient

Ds, characterizing the fundamental QCD force

• Very high precision measurement of heavy flavor meson spectra (from high pT to

pT~0): Total charm cross-section which provide strong constrains on the models

• High precision azimuthal anisotropy measurements become possible for the first time

Heavy Quark

Diffusion Coefficient

(Ds)

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Magnetic Field with Heavy Flavor Meson


• Heavy Quarks:

• More sensitive (than light flavor) to early magnetic fields and vorticity

• High precision measurement could be performed for the first time with HL-LHC data

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Modification of W mass in Top event


• Longer total delay time of the W (τtot) leads to smaller modification of

W mass in heavy ion collisions

• Probe the “start” and “end” time of the QGP!!

Negligible interaction between Top / W and the QGP

τm : quenching end time

“A Yoctosecond Chronometer.” (Gavin Salam)

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Sensitivity to the Medium End Time


Full exploitation of this probe only at FCC energies

• Sensitivity to medium end time (τm):

• HL-LHC PbPb Program (10 nb-1): 1.4 fm/c

• 1 month KrKr (30 nb-1): 1.8 fm/c

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Physics of (anti-)(hyper-)nuclei


1. Precision test of production models (coalescence, thermal production) via

measurement of (anti-)(hyper-)nuclei in pp, pA, AA

production sensitive to the size of the object relative to the size of the source

2. Search for rarely produced anti- and hyper-matter

Insights on the strength of the hyperon-nucleon interaction, relevant for

nuclear physics and nuclear astrophysics (neutron stars)

HL-LHC: first observation for anti-hyper-nuclei with A = 4

3. Constrain productions models with measurements in pp collisions

application in estimates of astrophysical background for dark matter searches

5σ

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Heavy Quark Hadronization


Lc/DDs RAA

Can we see modification of hadronization process in

heavy ion collisions with heavy flavor particles?• Strange quarks are enhanced in the quark soup

• Heavy quark recombination would enhance baryon or Ds (Bs) production

• HL-LHC: Precision measurement of Ds & Bs mesons enhancement with respect to D0

& B+ mesons. Λc and Λb production.

• Crucial for using heavy flavor mesons for medium property Ds extraction

ALICE Projection ALICE Projection CMS Place Holder

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Temperature of QGP: Thermal Photons / Dilepton


at ALICE

Photon Azimuthal Anisotropy

Dielectroninvariant mass

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QCD Equation of State at μB=0


Dark Lines:

Hadron Resonance Gas

Light bands: Quark Gluon Plasma

• Could we “measure” the QCD Equation of State from experimental data?

• Lattice QCD predicts a continuous cross-over between hadron gas and

quark gluon plasma

Yen-Jie Lee

QCD Equation of State at μB=0


Dark Lines:

Hadron Resonance Gas

Light bands: Quark Gluon Plasma

• Could we “measure” the QCD Equation of State from experimental data?

Net-protons fluctuation

High precision flow measurement enabledby HL-LHC data

Examples:

… and many more

observables enabled by

HL-LHC data

• Lattice QCD predicts a continuous cross-over between hadron gas and

quark gluon plasma

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“Ridge” signal in pp, pPb and PbPb collisions


pp pPb PbPb

QGP FormationEscape MechanismInitial State Correlation

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Open Questions for Small System


Emergence of hot QCD phenomena in small colliding systems• Standard descriptions of pp and AA physics may lack ingredients

• Higher luminosity and energy needed of more detailed studies

Is there a common paradigm to describe the underlying physics in all colliding systems?• If yes: QGP production in small system? Smooth transition from pp to AA?

• If no: What are the different mechanisms that come into plays?

• What about an intermediate scenario?

QGP FormationEscape MechanismInitial State Correlation

Yen-Jie Lee

Open Questions for Small System


Emergence of hot QCD phenomena in small colliding systems• Standard descriptions of pp and AA physics may lack ingredients

• Higher luminosity and energy needed of more detailed studies

Is there a common paradigm to describe the underlying physics in all colliding systems?• If yes: QGP production in small system? Smooth transition from pp to AA?

• If no: What are the different mechanisms that come into plays?

• What about an intermediate scenario?

Search for QGP-like signature in small systemsComparison between pp, pA and AA collisions at similar multiplicity

200 pb-1 high multiplicity pp program which will produce 25k events with

14-16x <Nch> which is equivalent to 60-65% central PbPb events

“Qualitatively new aspect of the comparison of pp and PbPb"

Yen-Jie Lee

Goals:• Precise control over initial state geometry/fluctuations

• Constrain initial and final state effect (flow fluctuations, …)

• Onset of collectivity

• Test various description (hydro, CGC, …)

Measurements (in pp and pPb):• Non-flow background free vn measurements

• Symmetric cumulants w/ and w/o subevents

• Fluctuation of P(vn)

• ID vn : o Light (p, K, p )

o Strange (K0s, …)

o Charm (D, J/y)

o Beauty (Y) [To be studied]

Flow Correlation in pPb Collisions


Not Final

Yen-Jie Lee

Strangeness Enhancement


Smooth transition between pp, pPb and PbPb in strange particle to pion yield ratios

• Will we reach the thermal limit in

pp/pPb?

• HL-LHC data will be able to provide unambiguous answer

Ω/π ratio vs. Nch

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Thermal Photon and Jet Quenching in pPb


dN/M vs. M

Search for thermal dilepton signal in pp and pPb• QGP thermal radiation in pp and/or

pPb?• Comparison with models (hydro,

transport) in pp and pPb

Jet Quenching in small system?• Observation or stringent upper limit

on energy loss• hadron-jet recoil yield ratio in pp and

pPb • Z-jet or gluon-jet in pp and pPb • Jet substructure

Recoil yield ratio vs. pT

arXiV

:17

12

.05

60

3

Current Data

Yen-Jie Lee

HI Baseline Plan From ALICE 2012 LoI


(adapted without permission)

p-p &

Pb-Pb Pb-Pb Pb-Pbp-pp-Pb Pb-Pb?

Pb-Pb Pb-Pbp-Pb

201320122011

LS1

2010

Pb-Pb Pb-Pbp-Pb!

p-Pb

Run 1

LHC will have done 12 ~one month heavy ion runs between 2010 and 2030 (LS4). 5/12 done already.

Xe-Xe

Yen-Jie Lee

Explore Opportunity with Light Ions


• Possibility to use different ions:

• Could get up to 20-100 times more hard probes with Ar+Ar collisions

compared to Pb+Pb collisions for CMS and ATLAS. Potential loss for ALICE

due to detector design and LHCb due to machine.

• Caveats:

• QGP fireball is smaller and shorter-lived

• Need accurate calculations of reduced medium effects in smaller AA to

assess physics reach

• Characterization of largest possible system in PbPb remains the priority

Ar+Ar

50x

Pb+Pb = 1

Yen-Jie Lee

Explore Opportunity with Light Ions

• Help to bridge small (pp) to large (PbPb) systems

• Opportunity to study the onset of jet quenching (system size scan from O+O to Ar+Ar)

• Provide more info about the atomic number A dependence of the nuclear PDF

• Provide new insights on the Color Glass Condensate:vary the saturation scale with system size

• pO collision: Solve the long standing issue of the modeling of pA collisions in the studies of cosmic ray


Yen-Jie Lee

Summary

• Significant progress on all the WG5 chapters, exploit• Pb+Pb: 13/nb at 5.5 TeV + pp reference

• p+Pb: 2/pb ATLAS/CMS, ~1/pb ALICE, ~0.5/pb LHCb, 8.8 TeV preferred

• p+p: 200/pb at low(er) pile-up μ=0.01 (ALICE) and 1-2 (ATLAS/CMS)

• Many thanks to all the contributors in the workshop!

• Exciting opportunities with light ion (O, Ar) explored

• Looking forward to new discovery with HL-LHC data!• Extraction of the QGP medium properties and QCD EoS

• Onset of QGP formation in small system

• Initial state correlation

• …


Yen-Jie Lee

• Backup slides


Yen-Jie Lee

Key questions with Heavy Flavor Mesons


Transport properties (Ds, q,…)

Impact of collisional / radiative en. loss

Radial distribution of energy lost

Understanding dead-cone effect

Hadronization: fragmentation vs

recombination

Magnetic effects on HF production

∧ Charm, beauty RAA

v2, v3, relation to bulk v2 (ESE)

Jets and correlations

Ds, Bs, charm and beauty

baryons

v1

RpPb

Angular correlations,

multiplicity dependence, v2

Cold Nuclear Matter effects

HF production mechanisms

Onset of medium-like effects for HF ?

QG

P p

rop

ert

ies

Sm

all

syste

ms

Yen-Jie Lee

“Light flavor” chapter

(Anti-)nuclei and (anti-)(hyper-)nuclei production yields sensitive to the chemical freeze-outtemperature and thermal properties of the medium puzzle of survival of loosely bound states in the hadronic phase

Fluctuations of conserved chargesHigher moments sensitive to the fluctuations near the chiral crossover

Direct comparison with lattice QCD

Direct experimental access to the critical behavior at the chiral phase transition

20-Jun-

18F. Bellini, N&F meeting

44

Focus on statistics-hungry measurements in the LF sector (PID) and searches

with L = 10 nb-1 min bias Pb-Pb (100x Run1+2) with ALICE as main player.

Status: ON TRACK

- Chapter editors assigned, writing in

summer

- Projections for (hyper-)nuclei and exotica

to be updated with dedicated MC

simulation

in progress

- Assessment of potentialities with nuclei in

pp

need more input from theory/astroph.

- Recent developments from lattice and

experiments shown at QM2018

discussion from theory side ongoing

- Statistics projections for fluctuations

require input from theory (signal) for toy

MC

in progress

Yen-Jie Lee

Contents and contributors

1. Introduction • Short general introduction, motivation to study light-flavors in Run 3+4• outline of the chapter, no figures foreseen

2. (Anti-)(hyper-)nuclei productionThermal production and nucleon coalescence models

1. Observables and projections for LHC Run 3 and 4 2. Nuclei in pp, pA and impact for astrophysics

3. Fluctuations of conserved chargesPhysics introduction and observables

1. State of the art from experiments and present limitations 2. Projections for LHC Run3 and 43. Complementarity with other facilities (RHIC BESII, FAIR, …)

4. Summary of experimental reach and sensitivity• Includes summary of section 2 and 3, outlook beyond HL-LHC• No figures foreseen

Contributors: M. Arslandok, F. Bellini, P. Braun-Munzinger, A. Kalweit, R. Lea, A. Mastroserio, A. Ohlson, S. Pathak, M. Puccio, K. Redlich, A. Rustamov, J. Stachel, S. Trogolo, E. Umaka

20-Jun-

18F. Bellini

45

Yen-Jie Lee

Timeline & planning

20-Jun-

18F. Bellini, N&F meeting

46

A. Dainese, WG5

meeting

Next appointements and deadlines

14-16 June: workshop on LF selected topics at CERN, including (hyper-)nuclei

[https://indico.cern.ch/event/732345/overview]

18-20 June: HL-LHC workshop public report on status of chapter

16 July Draft of the chapter on overleaf, meeting of N&F group

checkpoint for ALL projections, figures available (not final)

30 July Full text draft available

30 August Meeting of N&F group, review status of projections – finalization of contents

30 September Final version of chapter

https://indico.cern.ch/event/717641/contributions/3014728/attachments/1660005/2659076/Dainese_HLLHC_WG5_1June2018.pdf

Yen-Jie Lee 47WG5: Future Physics Opportunity for High Density QCD

Yen-Jie Lee

Opportunity with Light Ions


Yen-Jie Lee

Other opportunities


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Chiral Magnetic Effect


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Extraction of the Medium Scattering Power


From HF data

From jet substructure data

Weiyao Ko

One could only gain confidence if we could see a consistent picture

from different observables

From charged hadron data

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TOP Production


Negligible interaction between

Top / W and the QGP

“Turn off the QGP effect”

for a period of time!

“A Yoctosecond Chronometer.” (Gavin Salam)

Yen-Jie Lee

Flow Decorrelation


• HL-LHC data enable highly

differential flow

measurements

• Together with many other

measurements: strong

constrain on the medium

properties and the starting

time of the hydrodynamic

phase

Yen-Jie Lee 54WG5: Future Physics Opportunity for High Density QCD 54

Near Perfect LiquidCan be explained by

hydrodynamics calculation

+ Initial state fluctuation

Shear viscosity to

entropy ratio

Temperature

v2

v3

v4

QGP

Yen-Jie Lee

Criticality in Hot QCQ Matter


c

n

B =k

nn

B-n

B( )VT 3

F. Karsch, arXiv:1706.01620

O. Kaczmarek, arXiv:1705.10682

measure of criticality

Experiment (ALICE)Theory (LQCD)

A. Rustamov, arXiv:1704.05329

G. A. Almasi, B. Friman, K. Redlich, PRD96 (2017) 1, 014027

o Higher order cumulants are more sensitive probes

of criticality and are essential for understanding the

phase structure of QCD at LHC energies.

o HL-LHC is needed to go beyond 4th order cumulants

to be sensitive to criticality

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