Recent Results and Surprises from Ultrarelativistic Heavy-Ion - - PowerPoint PPT Presentation

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions

Jan Fiete Grosse-Oetringhaus, CERN

• XIII. Strong and Electroweak Matter

June 2018

CMS LHCb ALICE ATLAS PHENIX STAR sPHENIX

Short recapitulation: Basic Concepts

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 2

A Heavy-Ion Collision

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 3

t = 0 fm/c collision pre-equilibrium hydrodynamic evolution chemical freeze-out hadronization kinetic freeze-out t = ~1 fm/c t = 10 fm/c Time particle detection t = 4 cm/c dNch/dh up to 2000 particles

• Activity depends strongly on impact parameter b

– Few to 1600 nucleon-nucleon collisions

• Accessible experimentally

– Nch and SET grows with decreasing b

• Soft (low pT) ~ participants (Npart)
• Hard (high pT) ~ collisions (Ncoll)

4

Centrality & Glauber

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus Plot: A. Toia

Multiplicity vs. b Central b ~ 0 e.g. “0-5%” Peripheral b ~ R e.g. “60-90%” from Glauber calculations / MC

Flow

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 5

• Overlap region of colliding nuclei is not isotropic
• Spatial anisotropy (almond shape)

 different pressure gradient  momentum-space anisotropy (particle level)

• “Classical” picture: Overlap of nuclei  elliptic flow (v2)
• “Today’s” picture

– Initial state density fluctuations  higher-order anisotropies

• Fourier coefficients vn of single-particle distribution

wrt nth order participant plane

 



   

n n n

n v A d dN ) ( cos 2 1   e3 e4

Traditional wisdom: needs significant reinteractions between medium constituents / small Knudsen number x y

Particle Production and Hadronization

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 6

Particle Yields in Pb-Pb 5 TeV

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 7

12 different particles 7 orders of magnitude p K K0 K* f p L X W d 3

LH 3He

Experimental Effort: Particle Identification

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 8

Direct particle identification p K p d 3He 3H Displaced vertices K0

S  p p (ct = 2.7 cm)

L p p (ct = 7.9 cm) p p p L X Cascade X  L + p  p p p W  L + K  p p K Invariant mass f  K K K*  K p

Particle Yields in Pb-Pb 5 TeV

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 9

p K K0 K* f p L X W d 3

LH 3He

Particle yields well described by equilibrium thermal models over 7

• rders of magnitude

Fit with statistical (thermal) model

• Relativistic ideal quantum gas of

hadrons

• 3 parameters: V, T, mB
• At LHC, mB ~ 1 MeV, fixed by

antip/p ratio T = 153 MeV (3 MeV lower than at 2.76 TeV due to proton yield)

System Comparison

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 10

Strangeness enhancement Deuteron enhancement pp p-Pb Pb-Pb K* Suppression p ?

Particle Yields in Pb-Pb 5 TeV

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 11

p K K0 K* f p L X W d 3

LH 3He

Nuclei!

• Heavy and fragile objects in agreement with

thermal model at chemical freeze out

• Open puzzle: No re-scattering of anti-nuclei

in hadronic phase despite large dissociation cross-section

• Naïve coalescence after kinetic freeze-out

does not describe the data

12

Nuclei: Production Mechanism

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

S3 = 1 S3 vs. sNN

Parton-Medium Interactions

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 13

• HI collision more than superposition of nucleon-

nucleon collisions with incoherent fragmentation?

• Charged particles up 400 GeV/c
• Jets up to 1 TeV
• pT dependence

– Hadrons: consistent with constant DE – Jets: suggest increase of ΔE vs E – More insight: D. Pablos @ QM

14

RAA

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

T pp coll T AA AA

dp dN N dp dN R / / 

RAA = 1  no modification RAA != 1  medium effects Particles RAA vs. pT Jets RAA vs. pT

• Photon: fixes initial parton energy

15

g-Jet Correlations

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus ATLAS-CONF-2018-009

g Significant difference central Pb-Pb vs. pp xJg = pT,jet / pT,g pT,jet pT,g dN/dxJg vs. xJg

• Techniques applied in pp collisions

extended to Pb-Pb collisions

• Resolve inner structure of a jet
• Challenge: large background contribution

from underlying event

• Example: zg of two leading sub jets

16

Jet Substructure

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

2 1 2 1

) , min(

T T T T g

p p p p z  

PRL 120 (2018) 142302

asymmetric splittings  increase symmetric splittings  decrease dN/dzg vs. zg

• Are there sufficient interactions between medium

and heavy quarks?

– Charm v2 > 0 – Charm quarks flow with the medium

• How are charmed hadrons

formed at freeze out?

– Lc/D ratio larger than in pp – Ds/D0 ratio larger than in pp – Lc and Ds give large contribution to total cross-section

17

Charm

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

Lc/D0 vs. pT v2 vs. pT Ds/D0 vs. pT

• Sequential suppression for Y family

– Y(3S) limit for now

• Clear hierarchy, no clear turn-on
• Smooth evolution of T with centrality

18

Y Suppression

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus CMS-HIN-16-023 arXiv:1805.04387

RAA vs. Npart RAA vs. Npart RAA vs. Npart

Parity Violation in the Strong Interaction

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 19

• Spectator charge causes large magnetic

field (~1018 Gauss)

– Aligns spins

• Domains with non-zero topological charge

(local)  chirality flip

• Leads to charge separation
• Experimental correlator

– Same sign = signal – Opposite sign = control

20

Chiral Magnetic Effect

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

Y

• Signal observed increasing with increasing

centrality

• Magnitude similar at 0.2 TeV (STAR) and

2.76 TeV (ALICE)

• Magnitude similar in Pb-Pb and p-Pb
• Issue: Large backgrounds due to local charge

conservation (resonance decays, momentum conservation, parton fragmentation)

21

Earlier Results

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus PRL110 (2013), 012301 PRL118 (2017), 122301

g112 vs. centrality g112/v2 vs. Nch

• Large event-by-event variation of vn
• Final-state v2 correlated with initial-state eccentricities e2

(hydro with small h/s)

• At fixed centrality, split events by event-by-event v2 (q vector)

[Schukraft, Timmins, Voloshin (PLB719 (2013) 394)]

• CME backgrounds proportional to v2

– Possibility to constrain background

22

Event Shape Engineering

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

nucl-ex/0701025

Large q2  large v2 Small q2  small v2 v2 vs. pT

PRC 93, 034916 (2016)

central peripheral elliptic round

• Event shape engineering, modelling of magnetic

field + initial state models allows limit on CME

• fCME = maximal signal contribution in correlator

– Limit set on signal 7% at 95 C.L.

• Isobar run planned at RHIC this year

– Test Z2 magnetic field dependence

23

Latest Results

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus ALICE, PLB 777, 151 CMS, PRC 97 (2018) 044912

fCME vs. centrality fCME vs. Nch

Small Systems

p-Pb d-Au pp

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 24

Paradigm Shift

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 25

Traditional wisdom: needs significant reinteractions between medium constituents / small Knudsen number

 



   

n n n

n v A d dN ) ( cos 2 1  

Significantly challenged in recent years !

Two-Particle Correlation

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 26

Near-side jet + resonances, ... (D ~ 0, Dh ~ 0) Away-side jet + flow (D ~ p, elongated in Dh) Near-side flow ridge (D ~ 0, elongated in Dh)

Beam axis h f

Pb-Pb vs. pp

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 27

Pb-Pb pp

Near-side ridge (flow) only in Pb-Pb

at least everyone thought so for a long time…

Near-Side Ridge

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 28

• …observed in very high-multiplicity pp collisions

– 0.005% events with highest multiplicity

• …observed in high multiplicity p-Pb collisions

– ~40% events with highest multiplicity

– Surprisingly large magnitude

CMS, PLB718 (2013) 795

3.1% of MB Noffline,trk > 110 pp

CMS, JHEP09(2010)091

0.005% of MB p-Pb here: h = hlab

• Subtraction procedure to “isolate” ridge contribution from jet correlations

– No ridge seen in 60-100% and similar to pp

29

The Double Ridge

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

–

0-20% 60-100%

=

ALICE, PLB719 (2013) 29

here: h = hlab Discovery!  two ridges!

• Large number of observations of effects in p-Pb collisions which

were traditionally associated with Pb-Pb only

• Even in pp collisions, some of these effects observed
• Absence of these effects in archived e+e- data (LEP)

30

Where are we today?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

In the following, overview of selected highlights

Higher-Order Cumulants

Is the observed structure a multi-particle effect?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 31 PLB 765 (2017) 193

pp p-Pb Pb-Pb

• Yes! At least 8 particles involved in Pb-Pb and p-Pb.
• Even in pp collisions, at least 6 particles involved
• Magnitude of v2 similar in pp, p-Pb and Pb-Pb
• Differences in details, e.g. v2{2} ~ v2{4} in pp, but v2{2} > v2{4} in larger systems

v2 vs. Nch

Identified Particles

How does the observed effect behave for different particles?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 32

v2 vs. pT

PLB 726 (2013) 164

protons pions kaons p-Pb

arXiv:1804.09767

v2 vs. pT p-Pb

• Mass ordering at low pT ( radial flow and expansion)
• Crossing at intermediate pT

as observed in Pb-Pb collisions

Charm & Beauty

Can similar effects be observed for heavy quark?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 33

• Signal observed for D, J/y, leptons from HF decays
• Heavy quarks participate in the collective effects observed

p-Pb J/y D p-Pb v2 vs. pT v2 vs. pT

Initial or final state effect?

What is the relation to the shape of the initial state?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 34 arXiv:1805.02973

RHIC geometry scan Triangular initial state  large v3 p-Au d-Au

3He-Au

v2 v3 Prediction by hydrodynamic models vn vs. pT

e+e- (archived ALEPH data)

Can we observe the same structures in e+e- collisions?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 35 Yen-Jie Lee, Quark Matter 2018

No ridge found in ee collisions! Y(Df) vs. Df

36

Strangeness Production

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus Nature Phys.13(2017)535

K0/p L/p X/p W/p pp p-Pb Pb-Pb

• Strange baryon production increases

with increasing multiplicity

– K0, L, X, W – Smooth across system (pp, p-Pb, Pb-Pb) – Multiplicity only relevant variable here?

• Need more overlap for final answer
• Traditional MC codes fail to reproduce trend
• Tjorben Sjostrand (QM ’18):

“need new framework for baryon production”

Energy loss?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 37

No significant signal observed in RpA for hadrons, D and B hadrons D mesons J/y from B

PRL110 (2013) 082302

RpA vs. pT RpA vs. pT RpA vs. pT

• RAA ~ 0.8 in peripheral Pb-Pb collisions

– Npart ~ 5-10, like in p-Pb and there the RpA ~ 1

• Shown to be caused by biases

– Event selection – Nucleon-nucleon impact parameter: in peripheral Pb-Pb collisions, the average NN impact parameter is larger than in pp

• Above 80% reproduced by simple

superposition model HG-PYTHIA

(Loizides, Morsch, Phys.Lett. B773 (2017) 408-411)

38

Solved Puzzle: Peripheral RAA

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus arXiv:1805.05212

No need to involve energy loss in peripheral collisions RAA vs. pT RAA vs. centrality

What Next?

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 39

• The quest for the QGP has turned into a precision exercise
• The questions remain puzzling

40

Open Questions

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

• QGP onset in light of the discoveries in small systems
• Collective effects in small and dilute systems?

Christian Bierlich, Workshop on physics at HL-LHC, 31.10.17

• What is the underlying dynamics?

– Model describing long wavelength (ideal fluid) and short wave-length ("quenching") behavior

• What are the (relevant) degrees of freedom / microscopic structure?
• How to derive behavior from QCD?

• Historic smoking gun observables

– RAA, Flow, Strangeness

• Different turn-on expected as underlying

dynamics driven by different variable

• Smooth increase to first order

– Connect small and large systems

• Fine structure to second order
• Potential to learn about

– underlying dynamics – their driving variables

41

QGP Onset

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus ALICE, arXiv:1805.05212 (at 7 GeV/c)

dNch/dh Relative Effect pp p-Pb Pb-Pb

AA central AA

R R

,

Disclaimer: numerous caveats in this comparison

 central

v v

2 2 2 2

/ / e e

 central

p p / / W W

CMS, PLB 724 (2013) 213

RAA at 7 GeV/c v2/e2 W/p

ALICE, Nature Phys.13(2017)535

W/p ratio

bias corr.

The Next 10 Years

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus 42

LHC run 2 RHIC run Upgrades “LHC LS2”

• LHC: collimators + injectors
• ALICE: Tracking, DAQ (rate x100)
• ATLAS: Fast tracker trigger (rate x2)
• CMS: pixel detector (rate x2)
• LHCb: VELO, tracker, DAQ (rate x10)

LHC Run 3 + 4 (numbers for Pb-Pb)

• L = 6 · 1027 cm-2s-1 ~ 50 kHz rate
• 10 nb-1 (ALICE, CMS, ATLAS)

2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 RHIC run sPHENIX

• 1011 events read out
• Sampled 50 nb-1

STAR

• 109 events read out

Upgrades “LHC LS3”

ATLAS:

• Tracker (acc x2)
• Timing

CMS:

• Tracker (acc x2)
• Encap Calorimeter

LHCb:

• TOF?

sPHENIX const. STAR upgrades

SPS, FAIR, NICA not shown here

• Significant detector upgrades at LHC for ALICE, ATLAS, CMS,

LHCb and for STAR at RHIC

• New detector sPHENIX replaces PHENIX at RHIC
• Accelerators + detectors willl be factories for D, B, J/y, Y, thermal

dileptons, nuclei and jets

43

Detector Upgrades

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

1011 MB events 106 pp events Nch > 12 <Nch> (250 particles in |h| < 1.5) 1011 MB events 10 nb-1 Pb-Pb (LHC) 35 nb-1 Au-Au* (RHIC) 200 pb-1 pp* (LHC) * not yet approved

• How does charm recombine from the QGP?

– Baryon/meson ratios Ds/D, Lc/D, Lb/B – Very challenging: e.g. Lc ct ~ 60 mm

• Influence of recombination and radial flow
• Influence of melting and regeneration

– Compare states with different binding energy

• Validation of recombination and

coalescence models

44

Charm Hadronization

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

Lc/D vs. pT

ALICE

CERN-LHCC-2013-024

RAA y(2S)/J/y vs. Npart

ALICE Upgrade

current stat. unc ~ 70%

• Do heavy quarks thermalize?
• Light vs. heavy-quark flow
• Constrain temperature dependence
• f diffusion coefficient

45

Heavy Quarks

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

D v2 vs. pT RAA vs. Npart

• Beauty transport coefficients

compared to lattice QCD

• Bottomonia flow in reach

• Precise medium tomography
• Di-jet imbalance, g-jet, Z0-jet
• Path-length dependence with

event-shape engineering

46

Energy Loss

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

• Quark-mass dependence
• Flavour identified fragmentation fct
• Path-length dependence through v2

bjet v2 vs. pT dN/xJg vs. xJg

• Access space-time evolution of medium
• Temperature ( 10-25% uncertainty)
• Radiation from all stages of the expansion
• Change of r spectral function connected

to chiral symmetry restoration

47

Thermal Radiation & Nuclei

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

• Precision era for (anti-)(hyper-)nuclei

production

• Production mechanism: (advanced)

coalescence vs. thermal model

• Input to astrophysical background, e.g.

for AMS

CERN-LHCC-2013-024 ALICE Projection

r Thermal radiation dN/dMee vs. Mee 0-10%

4 LH 4 LHe

S vs. Lint

• Can reach extremely rare (10-11) pp events

– 200 pb-1 | Sampling 1013 events

• Significant overlap between pp and PbPb

– In multiplicity up to ~65% centrality

• If pp behaves HI, we shall see “standard” HI physics

– Including jet quenching if effects driven by final state – If not, we can see the differences

• In addition: MB sample for low-multiplicity limit

– What is smallest droplet of matter showing collective behavior? – Origin of collectivity in few particle system? (color reconnection, gluon interference, escape, …)

48

Collectivity in Small Systems

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

Pb-Pb p-Pb pp Today 65% central 14-16 <Nch> >25k events P(Nch) vs. Nch

• 100 km circumference

– sNN = 39 TeV (Pb-Pb) | 63 TeV (p-Pb) | 100 TeV (pp)

• Future Circular Collider @ CERN

– 35-110 nb-1 per month (12-40x LHC) – Conceptual Design Report by fall 2018 – Further reading: Physics case | FCC week

• SPPC in China

– Combined with e+e- machine – Funding for R&D available – Further reading: Physics case | Pre CDR

49

Future Collider Projects

(2040-50)

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

LHC FCC dNch/dh 3600 V 11000 fm3 e (t = 1 fm/c) 35-40 GeV/fm3 Pb-Pb

Manqi Ruan, Hard Probes 2016

Geneva

• ne of several site

candidates (close to Hong Kong)

• Precision measurements from RHIC and LHC experiments

– Transition from “simple fine tuning” to comprehensive modelling – Agreement/discrepancy of details may contain key to understanding

• Paradigm shift followed by discoveries small systems

– Ample evidence for collective phenomena – No significant parton energy loss – Hints that collective phenomena exist in few particle systems

• Data sample will be increased by factor 100 in next ten years

50

Summary

Recent Results and Surprises from Ultrarelativistic Heavy-Ion Collisions - Jan Fiete Grosse-Oetringhaus

Thank you for your attention