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Heavy Ions: Experiment. Federico Antinori (INFN Padova, Italy). A-A collisions in the LHC!. John Jowett - LHC. Contents. Introduction Selection of results (hard choices were required…) Particle multiplicity Correlations High p T suppression Identified particles Quarkonia Jets

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heavy ions experiment

Heavy Ions: Experiment

Federico Antinori

(INFN Padova, Italy)

a a collisions in the lhc
A-A collisions in the LHC!

John Jowett - LHC

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

contents
Contents
  • Introduction
  • Selection of results (hard choices were required…)
    • Particle multiplicity
    • Correlations
    • High pT suppression
    • Identified particles
    • Quarkonia
    • Jets
    • Heavy flavours
  • Conclusions
ultrarelativistic aa collisions
Ultrarelativistic AA Collisions

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

basic idea: compress large amount of energy in a very small volume

  • produce a “fireball” of hot matter:

temperature O(1012 K)

    • ~ 105 x T at centre of Sun
    • ~ T of universe @ ~ 10 µs after Big Bang
  • how does matter behave under such extreme conditions?
    • study the fireball properties
    • QCD predicts state of deconfined quarks and gluons (Quark-Gluon Plasma)
lattice qcd
Lattice QCD

3 flavours; (q-q)=0

  • in lattice QCD, non-perturbative problems are treated by discretization on a space-time lattice  cure ultraviolet divergences
  • zero baryon density, 3 flavours
  • e changes rapidly around Tc
  • Tc = 170 MeV:

 ec = 0.6 GeV/fm3

  • at T~1.2 Tce settles at about 80% of the Stefan-Boltzmann value for an ideal gas of q,q g (eSB)

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

qcd phase diagram

~ 10 ms after

Big Bang

LHC

Early Universe

RHIC

Quark-Gluon

Plasma

Tc ~ 170 MeV

SPS

AGS

Hadron gas

Temperature

Nuclear

Neutron Star

matter

~ 5 - 10 nuclear

r

Baryon density

ec ~ 1 GeV/fm3

QCD phase diagram

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

geometry of a pb pb collision
Geometry of a Pb-Pb collision
  • central collisions
    • small impact parameter b
    • high number of participants high multiplicity
  • peripheral collisions
    • large impact parameter b
    • low number of participants low multiplicity

for example: sum of the amplitudes in the ALICE V0 scintillators

reproduced by Glauber model fit (red):

  • random relative position of nuclei in transverse plane
  • Woods-Saxon distribution inside nucleus
  • deviation at very low amplitude expected due to non-nuclear (electromagnetic) processes

b

peripheral

central

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

particle multiplicity
Particle multiplicity

ALICE: PRL105 (2010) 252301

log extrapolationfails (finally!)

2.2 x central Au+Au

(√sNN=0.2 TeV)

1.9 x pp (NSD)

(√sNN=2.36 TeV)

√sNN=2.76 TeV Pb+Pb, 0-5% central, |η|<0.5

2 dNch/dη / <Npart> = 8.3  0.4 (sys.)

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

for the most central collisions: ~ 1600 charged particles per unit of η

centrality dependence
Centrality dependence

ALICE: PRL 106 (2011) 032301

Helena Santos - ATLAS

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • model comparisons
    • DPMJET (with string fusion)
    • HIJING 2.0 (no quenching)
      • centrality-dependent gluon shadowing
      • tuned to multiplicity in 0-5%
    • saturation models

(sometimes too much?)

  • very similar centrality dependence at LHC & RHIC
    • once corrected for difference in absolute values
azimuthal asymmetry
Azimuthal asymmetry
  • transfer of this asymmetry to momentum space provides a measure of the strength of collective phenomena
  • Large mean free path
    • particles stream out isotropically, no memory of the asymmetry
    • extreme: ideal gas (infinite mean free path)
  • Small mean free path
    • larger density gradient -> larger pressure gradient -> larger momentum
    • extreme: ideal liquid (zero mean free path, hydrodynamic limit)
  •  quantified by second coefficient (v2) of Fourier expansion of azimuthal distribution

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

… in the transverse momentum distribution of produced particles

  • why is it important?
  • non-central collisions are asymmetric in azimuth

azimuth = angle in the plane of the screen

slide14
v2
  • v2 still large at the LHC
  • system still behaves very close to ideal liquid (low viscosity)
  • v2(pT) very similar at LHC and RHIC

 same hydrodynamical behaviour?

ALICE: PRL 105 (2010) 252302

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

structures in
Structures in (Δη,Δφ)

near side jet peak

two shoulders

on away side

(at 120 and 240 )

aka “the Mach cone”

long range structure

in η on near side

aka “the ridge”

Helena Santos – ATLAS

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

fluctuations v 3
Fluctuations  v3

Matt Luzum (QM 2011)

v2

v3

ALICE: PRL 107 (2011) 032301

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • “ideal” shape of participants’ overlap is ~ elliptic
    • in particular: no odd harmonics expected
    • participants’ plane coincides with event plane
  • but fluctuations in initial conditions:
    • participants plane  event plane
    • v3 (“triangular”) harmonic appears

[B Alver & G Roland, PRC81 (2010) 054905]

  • and indeed, v3  0 !
  • v3 has weaker centrality dependence than v2
  • when calculated wrt participants plane, v3 vanishes
    • as expected, if due to fluctuations…
long range correlations
Long-η-range correlations

Andrew Adare – ALICE (QM2011)

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • “ultra-central” events: dramatic shape evolution in a very narrow centrality range
  • double hump structure on away-side appears on 1% most central
    • visible without any need for v2 subtraction!
  • first five harmonics describe shape at 10-3 level
    • “ridge” and “Mach cone”
    • explanations based on medium response to propagating partons were proposed at RHIC
    • Fourier analysis of new data suggests very natural alternative explanation in terms of hydrodynamic response to initial state fluctuations
nuclear modification factor r aa
Nuclear modification factor (RAA)

Yen-Jie Lee – CMS

CMS: PAS HIN-10-005

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • RAA: particle yield in AA relative to pp scaled with number of binary nucleon-nucleon collisions
  • RAA(pT) for charged particles produced in 0-5% centrality range
    • minimum (~ 0.14) for pT ~ 6-7 GeV/c
    • then slow increase at high pT
    • still significant suppression at pT ~ 100 GeV/c !
  • essential quantitative constraint for parton energy loss models!
suppression vs event plane
Suppression vs event plane
  • significant effect, even at 20 GeV!
  • further constraints to energy loss models

 path-length dependence of energy loss (L2, L3, …)

Alexandru Dobrin – ALICE (QM2011)

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

p t spectra vs hydrodynamics
pT spectra vs hydrodynamics

Roberto Preghenella - ALICE

Michele Floris – ALICE (QM2010)

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • comparison of identified particle spectra with hydro predictions
    • (calculations by C Shen et al.: arXiv:1105.3226 [nucl-th])
  • OK for π and K, but p seem to “misbehave” (less yield, flatter spectrum)
v 2 vs hydrodynamics
v2 vs hydrodynamics

Raimond Snellings

ALICE (QM2010)

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • comparison of identified particles v2(pT) with hydro prediction
    • (calculation by C Shen et al.: arXiv:1105.3226 [nucl-th])

 again, protons are off…  what’s going on with protons?

quarkonium suppression
Quarkonium suppression

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • Quark-Gluon Plasma “signature” proposed in the 80’s

[T Matsui & H Satz, Phys. Lett. B 178 (1986) 416]

  • in the plasma phase the interaction potential is expected to be screened beyond the Debye length λD (analogous to e.m. Debye screening)
  • cc and bb states with radius > λD will not bind  their production will be suppressed
j @ lhc forward y low p t
J/ψ @ LHC: forward y, low pT
  • LHC: 2.5 < y < 4, pT > 0 (ALICE)

Livio Bianchi – ALICE

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • less suppression than

RHIC: 1.2 < y < 2.2, pT > 0 (PHENIX)

  • ~ as suppressed as

RHIC: |y| < 0.35. pT > 0 (PHENIX)

j @ lhc central y high p t
J/ψ @ LHC: central y, high pT
  • LHC: |y| < 2.4, pT > 6.5 GeV/c (CMS)

prompt J/ψ

  • more suppressed than

RHIC: |y| < 1. pT > 5 GeV/c (STAR)

inclusive J/ ψ

  • LHC |y| < 2.5, pT > 3 GeV/c (ATLAS)

Catherine Silvestre – CMS

CMS: PAS HIN-10-006

Helena Santos – ATLAS

ATLAS: PLB 697 (2011) 294

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

slide28

Yen-Jie Lee – CMS

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

slide29

Yen-Jie Lee – CMS

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

di jet imbalance
Di-jet imbalance

Frank Ma - CMS

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • Pb-Pb events with large di-jet imbalance observed by ATLAS & CMS
  • recoiling jet strongly quenched!
slide32
AJ
  • with increasing centrality:
  • enhancement of asymmetric di-jets
    • with respect to pp & HIJING + PYTHIA

Helena Santos - ATLAS

ATLAS: PRL105 (2010) 252303

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

di jet
Di-jet Δφ

e.g.: Frank Ma – CMS

CMS: arXiv:1102.1957

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

no visible angular decorrelation in Δφ wrt pp collisions

jet nuclear modification factor
Jet nuclear modification factor
  • suppression of jet production
    • in central Pb-Pb wrt binary-scaled peripheral
  • very weak centrality dependence

Helena Santos - ATLAS

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

slide35

Yen-Jie Lee – CMS

Frank Ma – CMS

CMS: arXiv:1102.1957

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

c and b quenching @ lhc
c and b quenching @ LHC
  • substantial suppression of heavy flavour production
    • beauty, too!

Diego Stocco – ALICE

Catherine Silvestre - CMS

  • study parton mass and colour charge dependence of interaction with medium!

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

[compilation courtesy of Andrea Dainese]

slide38
D vs π
  • charm ~ as suppressed as pions
    • maybe a hint of RAAD > RAAπ at low pT …

 to be continued with higher statistics…

  • quarks (CR = 4/3) expected to couple weaker than gluons (CR = 3)
  • at pT ~ 8 GeV, factor ~ 2 less suppression expected for D than for light hadrons in BDMPS-ADSW

Diego Stocco – ALICE

N Armesto et al., PRD 71 (2005) 054027

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

conclusions
Conclusions

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • in November 2010, the field of ultrarelativistic nuclear collisions has entered a new era with the start of heavy ion collisions at the LHC
    • abundance of hard probes
    • state-of-the art collider detectors
  • exciting results already from first, limited data samples
    • death of ridge and Mach cone?
    • anomalies in proton yields & momentum distributions
    • pattern of jet and heavy flavour suppression challenges Eloss models
  • the future looks very bright
    • precision measurements  constrain dynamic and coupling properties of medium
    • look out for surprises!!!
merci
Merci…

Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  • … aux organisateurs

for the invitation to present this plenary talk

  • … à:

Peter Braun-Munzinger, Brian Cole, Andrea Dainese, David d’Enterria, Paolo Giubellino, Raphaël Granier de Cassagnac, Barbara Jacak, Peter Jacobs, John Jowett, Karel Šafařík, Carlos Salgado, Jürgen Schukraft, Edward Shuryak, Peter Steinberg, Xin-Nian Wang, Urs Wiedemann, Nu Xuand many others…

  • … à vous tous