Probing the hot, dense QCD matter with the ATLAS experiment at the LHC

Jiangyong JiaStony brook University and BNL

Space-time history of heavy ion collisions2

initial state pre-equilibrium QGP & expansion Phase transition Freeze-out

HEP HI

Probe the properties of Quark Gluon Plasma

Bulk hadrons ： Thermodynamic and hydrodynamic properties T, μ, EOS, viscosity, etc. Usually close to equilibrium

Hard probes ： Transport properties Energy loss and broadening, screening length etc. Usually far from equilibrium

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x

z

y

hadrons hadronsJ/Ψγeμ

AGS 5 GeV SPS 17 GeV RHIC 200 GeV LHC 2760-5500 GeV

hadronsJ/Ψ,Υ,c,bγeμ

hadronsJ/Ψ,Υ,c,bγeμ

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LHC Heavy Ion Data-takingDesign: Pb+Pb at √sNN=5.5 TeV

(1 month per year)Nov. 2010: 60M PbPb at √sNN=2.76 TeVNov. 2011: >1 Billion at √sNN=2.76 TeV

ATLAS detector & Pb+Pb measurement5

|η|<5

|η|<2.5

Bulk hadrons: hydrodynamic flow

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x

z

y

Centrality: the amount overlap, percentile of cross-section or number of participants (Npart)

Reaction plane(RP): orientation of the matter, defined by beam & impact parameter direction.

Φ

anisotropic expansion: elliptic flow

Pressure converts initial asymmetry into momentum anisotropy

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x

z

y

ϕΦ

Generalize into harmonic flow (vn)

Anisotropic distribution generalized by Fourier series

Related to initial spatial fluctuations of nucleons

vn and correlations between the n probe initial geometry and expansion mechanism

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2

3

4

cos( ) sin( )n n

n n

r n r n

r

n1 2v cos nn

dNn

d

Flow coefficients: vn(n,η,pT,cent)

Features of Fourier coefficients. vn coefficients are ~boost invariant.

vn coefficients rise and fall with pT.

vn coefficients rise and fall with centrality.

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1203.3087 n1 2v cos nn

dNn

d

Measured by correlating single particle ϕ with global Φn.

Ridge and Cone in two-particle correlation

Once the “ridge” and “cone” were thought due to “jet-medium” interactions…..

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Au+Au at RHIC √s=200 GeV3-4 x 1-2 GeV

Ridge

Jet1

Jet2

Double hump or cone

Fourier expansion of 2PC11

Long range structures exhausted by the first six harmonics v1,1-v6,6

|Δη|>2

Important to check the factorization relation

1203.3087

Check factorization 2PC vn

Factorization works well for n=2-6 Break down of v1,1 is due to global momentum conservation

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1203.3087

Reconstruct 2PC via single particle vn

“ridge” and “cone” reproduced by the single particle vn. They are consequences of global event properties –not due to jet fragmentation!!

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From 2PC method From single vn method

1203.3087

Connection to cosmology 14

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3

4

Infer initial geometry fluctuation via observation in momentum space

“little” bang

“big” bang

“Acoustic” damping of harmonic flow

Treat as sound wave seeded by the hot spot.

Sound horizon fixed at freezeout Damping of the second peak

sensitive to viscosity

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ATLAS Data compared with 1106.3243 (Shuryak)

4πη/s=0

4πη/s=14πη/s=1.9

v1,1(pTa,pT

b) and v1(pT) story Factorization of v1,1 to v1 breaks due to momentum conservation

CMB is dominated by dipole component from Doppler shift of observer.

Extract v1 via two component fit

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Red Points: v11 data

Black line : Fit to functional form

Blue line: momentum conservation component

1203.3087

Extracted v1(pT)

Significant v1 values observed: pT dependence similar to other vn

Comparable to v3: significant dipole moment in initial state

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1203.3087

Reaction Plane correlations

Further insights can be obtained by studying correlations between the n:

The procedure can be generalized to measure correlations involving three or more planes:

One way to think of the three-plane correlations is as combination of two plane correlations

• 246 =4262• 246 =4262• Thus three plane correlations are the correlation of two angles relative to the third.

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arXiv:1203.5095

arXiv:1205.3585

http://cdsweb.cern.ch/record/1451882

Two-plane correlations19

Three-plane correlations20

“2-3-5” correlation

Rich centrality dependence patterns are observed

“2-4-6” correlation “2-3-4” correlation

Expectation from Glauber model Plane directions in configuration space

Expected to be strongly modified by medium evolution in the final state

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arXiv:1011.1853, 1203.5095 1205.3585

Corr

elati

on

Corr

elati

on

Predictions from hydrodynamic models

Significant correlations are generated dynamically. Strong constraints to the model assumptions, in particular the viscosity.

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Teaney and Yan in preparation

Hard probes: single hadron,μ, jets, Z/W/γ, Quarkonium

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Single hadron suppression Quantify suppression with central/peripheral

ratio normalized by Ncoll

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“Enhancement” from flow

Jet quenching

Transition region

Single muon from c, b decay

Open heavy flavor production measured via c,bμ±. Probing jet quenching of the c/b jets

Expect less quenching than light quark jet and gluon jet. But no difference seen between heavy and light jet fragments at RHIC.

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Extracting the heavy flavor muon yield26

Suppression of heavy flavor muons

Evaluate Rcp using 60-80% peripheral reference

Factor of 2.0-2.5 relative suppression in 0-10%

Independent of muon pT

Trend different from inclusive hadron suppression

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Full jets probes

Beyond di-jet asymmetry!

Suppression of single jet yield

Jet fragmentation function, jet shape, jT distributions

multi-jet final states.

All of above relative to the reaction plane

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PRL

~140 citations

Single jet suppression

Single jet yield suppressed by x2 Smooth vs pT and centrality

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‣ Error bars: sqrt of diagonal elements of covariance matrix

‣ Systematic errors • Black band: fully correlated • Red boxes: partially correlated

Jet suppression vs radius

Evaluate jet radius dependence of Rcp correlated error cancels in the ratio

Modest but significant increase for larger R broadening?

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Jet suppression vs radius

Evaluate jet radius dependence of Rcp correlated error cancels in the ratio Modest but significant increase for larger R broadening? Models predicting strong R dependence ruled out.

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Modification of jet shape?

pT cut to suppress underlying event, bg subtracted. No strong modification of jet fragmentation between central

and peripheral collisions. Suggest energy lost by jet appears at large angle wrt jet axis

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Eletro-weak probes Isolated gamma, Z/W yield are not expected to be modified at final state, but can be affected by nuclear pdf

(shadowing, isospin etc) However low pT gamma (upto 50 GeV) might be generated by the QCD matter.

Important baseline for jet quenching measurement Unbiased tagging on away-side color probes : γ-jet, Z-jet etc.

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Isolated gamma measurement w/ 2011 data

Measured using isolation and shower shape cuts75% purity Consistent with NLO QCD multiplied by Ncoll

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https://cdsweb.cern.ch/record/1451913

Z measurement w/ 2011 data

Z yield scales with Ncoll

Similar story for W

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Quarkonium and dimuon continuum36

By yifei

Dilepton enhancement belowρ: Chiral symmetry restoration

Melting of heavy quarkonia states:Debye screening, recombination

IS & Jet quenching via Z, Z-tagged jet

decay of correlated ccbar,bbar or q+q-l+l-: Initial state, jet quenching

Strangeness enhancements, flow etc

ω, ϕJ/ψ

ψ’

Υ

bJ/Ψ+x

Analyses in progress.. But need manpower

J/Ψ suppression from RUN 2010 data

Clean J/Ψ peak in central Pb+Pb collisions J/Ψ pT >6.5 GeV, because eloss of muon in calorimeter

Less suppressed than inclusive hadrons

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Rcp

5μb-1

5μb-1

Summary

Flow coefficients vn and Φn correlations probe the geometry of the created matter and subsequent hydrodynamic evolution .

Significant harmonic flow measured for v1-v6constraints on viscosity.

Factorization from vn,n to vn valid for n=2-6non-flow is small.

v1,1 is consistent with dipolar flow v1 plus global momentum conservation. Naturally explains the exotic ridge and cone-like structures in 2PC Correlation between flow angle Φn probes into dynamics of hydro-evolution

Jet quenching of color probes provides insight on energy loss Single particle/jet suppression consistent with radiative energy loss Energy lost by jets seems to be redistributed to large angle. Heavy flavor jet suppression seems to be similar to light flavor.

Electro-weak probes constrains the initial condition Effect of nuclear pdf and other initial state effects are small Jet suppressions are mostly due to final state effects

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Opportunities We are just at the beginning, a lot more to do.

Measure γ-jet, Z-jet, multi-jet final state Understand the medium response, final state direct photons b-jets, b-tagged dijets, bJ/Ψ heavy quarkonium, Drell-Yan Flow and correlations of above with geometry. Ultra-peripheral physics

p+A base line measurement2012 Most measurements above can be done.

Precision determination of pdf

Saturation physics, cold nuclear matter effects

Full energy Pb+Pb run 2014 and beyond x6.5 luminosity and much larger cross sections.

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