HIGH ENERGYHEAVY ION COLLISIONSAT LHC
Tatsuya Chujo (Univ. of Tsukuba)
7th Italy-Japan Symposium on Nuclear Physics
Nov.20 ‒ 23, 2012, Milano, ITALYOutline
1. Introduction
2. Paton energy loss in QGP
3. QGP properties probing via hadrons
4. ALICE-DCal project (Italy-Japan collaboration)
5. Summary

QGP  :
Quark  Gluon
PlasmaTime：after  10  µ  sec  after  the  Big  Bang
Temperature  ：  T  =  2  x  1012  K

La#ce	  QCD	  calcula,ons:Tc	  =	  150-­‐200	  MeV,	  cross	  over	  phase	  transiKon	  from	  hadronic	  phase	  to	  partonic	  phase	  (QGP).
Wuppertal-­‐Budapest’s	  LQCD	  EOSJHEP	  1011	  (2010)77

Energy  density：
ε  =  1  GeV/fm3

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QGP: probing phasetransitions
Strong Int.
Weak Int.

Big Bang

EM int.

Gravity

t=0 sec 10-44 sec

10-36 sec 10-11 sec• QCD phase transition• Chiral symmetry restoration

410-6 secHeavy ion program @ CERN-LHC
CMS
jet, hard probes,
di-muons

ALICE
Excellent PID
low pT tracking
photons, e, muons
ATLAS
jet, hard probes

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“Phase	  transition”	  in	  our	  research:	  From	  discovery	  to	  the	  understanding	  of	  QGPβT,	  Tfo

6µB,	  Tchη/s,	  initial	  condition

Energy	  loss	  Temperature	  (Tc)

See	  R.	  
Thermalization Nania’s	  talk1. PARTON ENERGY LOSS
Jet quenching

One	  way	  to	  measure	  QGP	  property;
paton	  energy	  loss•••

In	  QGP,	  parton	  loses	  energy	  mainly	  due	  to	  the	  gluon	  radiaKon,	  and	  jet	  produced	  by	  the	  hard	  parton	  scaUering	  is	  quenched	  (jet	  quenching).
On	  the	  other	  hand,	  photon	  from	  hard	  scaUering	  does	  not	  lose	  energy	  in	  QGP	  (EM	  int.)
Using	  these	  jets	  and	  (direct)	  photons,	  one	  can	  perform:	  – QGP	  tomography– Study	  of	  medium	  response• low	  pT	  parKcle	  spectra,	  ﬂow,	  HBT,	  etc.	  with	  jet	  axis.

QGP jet-jet,
γ-jet tomography

PET
89

YieldSoft particle
production

Hard parton
scattering (jet)soft-hardtransition ~ 4 GeV/cpT (GeV/c)

1011

Nuclear	  modiﬁcation	  factor	  (RAA	  )for	  light	  hadrons●Hadrons with pT > 8 GeV/c are equally suppressed.

●A Large baryon enhancement at intermediate pT (2-5 GeV/c), recombination.

12RAA	  Summary	  @LHC	  -­‐	  Hadron:	  strong	  yield	  suppression,	  dip	  at	  ~7	  GeV.
-­‐	  EM	  probes:	  do	  not	  suppressed.

jet	  RAA

Instead of leading hadron, one can reconstruct “jet” directly.
- Strong jet suppression observed (RAA ~ 0.5).
- A hit of stronger suppression at lower jet pT (ALICE).

First	  p+Pb	  data	  at	  LHC••

Sep. 13, 2012(ALICE)
test run, p+Pb
collisions

Successful	  p+Pb	  pilot	  run	  (Sep.	  13,	  2012)
p+Pb	  Physics	  run	  (Jan.	  –	  Feb.,	  2013)–Beam	  energy:	  √sNN	  =	  5.02	  TeV–Expected	  staKsKcs:	  	  ~	  30	  nb-­‐1	  à rare	  probe	  staKsKcs	  equivalent	  to	  0.15	  nb-­‐1	  of	  Pb-­‐Pb.

p-Pb results (ALICE)
No suppression for
p-Pb collisions.
Indicated thatsuppression seen incentral Pb-Pb is the
final state effect, notthe initial state
effect.
arXiv:1210.4520 (ALICE)

Di-­‐jets

AJ:	  di-­‐jet	  asymmetry

CMS R=0.5• Quantify jet energy imbalance by the asymmetry ratio.
• Large asymmetry is seen in energy imbalance in central
Pb-Pb

Large AJ : low momentum particle (< 4 GeV/c) emitted atlarge angle on away side.

γ-­‐jet:jet	  quenching	  study	  with	  energy	  calibrated	  probes	  (photons)

γ-­‐Jet	  momentum	  balance	  (CMS)
arXiv:1205.0206•Momentum	  raKo	  (pT	  Jet/pT	  gamma)	  shids/decreases	  with	  collisions	  centrality.

2. PROPERTIES OF QGP
Probing via spectra, yield, flowTexpanding
sourcelightT, βheavy
pT

1/pT dN/dpT

pure thermal
source1/pT dN/dpT

To characterize the global properties
on expanding source; introduce
common velocity field;“radial flow”

lightheavypT

Identified hadron spectra at LHCs ALICE	  data	  for	  pions,	  K,	  ps Lines	  =	  blast-­‐wave	  ﬁtscParameters	  of	  the	  system	  at	  the	  kinetic	  freeze-­‐out	  (Tf0,	  βT).

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PID	  spectra	  and	  radial	  ﬂow

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Hydro	  Prediction
RHIC

Cen

trality	  Blast	  Wave	  Fit-­‐-­‐-­‐-­‐

Very	  signiﬁcant	  changes	  in	  slope	  compared	  to	  RHIC
Most	  dramatically	  change	  for	  protons
Very	  strong	  radial	  ﬂow,	  	  β	  ≈	  0.66	  (10%	  higher	  than	  RHIC)	  Even	  larger	  than	  predicted	  by	  most	  recent	  hydro	  (e.g.	  protons)	  RHIC

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Thermal	  Model	  Comparisons All	  ratios	  other	  than	  p/π	  are	  predicted	  accuratelys Protons:	  diﬀerent	  Tch	  than	  	  strange/multi-­‐strange,	  	  indicating	  the	  importance	  of	  re-­‐scattering	  at	  hadronic	  phase.	  

A.	  Andronic	  et	  al,	  PLB	  	  673:	  142-­‐145	  (2009)

LHC
Pb-Pb (2.76 TeV)
0-20% central

Braz. J. Phys. vol.37 no.2c São Paulo June 2007
http://dx.doi.org/10.1590/S0103-97332007000500024
N. Xu

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Anisotropic flow;
sensitive to the early time ofcollisions, pressure gradients, EOS.

Elliptic flow; v230

strongly coupled system
at 10-6 KWorld at 10-6 K
6Li (optical laser cooling)

Fermi gas system＝strongly coupled system
Very similar at 1012 K= strongly coupled QGP(sQGP)

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Identiﬁed	  particle	  v232s Large	  mass	  splitting	  at	  LHC	  compared	  to	  RHIC	  as	  predicted	  by	  hydrodynamics	  models.
s Pion	  v2:	  described	  well	  by	  hydro.	  predictions	  with	  MC-­‐KNL	  CGC	  initial	  conditions	  and	  η/s	  =	  0.2.
s (K	  and	  )	  Anti-­‐protons:	  overestimated	  by	  the	  same	  calc.	  for	  central	  collisions.

Higher	  order	  harmonics;	  vnψRPPRL 107, 032301(2011), ALICEψ3ψ2s v3	  sensitive	  to	  shear	  viscosity	  η/s	  and	  to	  initial	  conditions	  (Glauber,	  CGC)	  .
s No	  simultaneous	  description	  of	  v2	  and	  v3	  with	  the	  same	  η/s.

33η/sNitrogen

Heliumη/s ~ 0.1
Water
LHC/RHIC
HIC @1012
K

Temperature (K)
RHIC v2 data : η/s ~ 0.1.
Smallest η/s in the world, approaching the quantum
viscosity bound (1/4pi)

Fourier	  decomposition	  in	  di-­‐hadron	  corr.

35s Extract	  1D	  Δϕ correlations	  by	  integrating	  the	  C(Δη,Δϕ)	  in	  0.8<|Δη|<1.8	  range	  and	  do	  a	  Fourier	  decompositions 5	  components	  describe	  completely	  the	  correlations	  at	  large	  Δη and	  low	  pTarXiv:1109.2501

WMAP vs. Heavy Ion Collisions

Power spectrum

WMAP

Heavy ion collisions

Cosmological parameters

initial condition, QGP properties (e.g. eta/s)
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3. ALICE-DCAL
From view point of Italy-Japan
collaboration

ALICE	  Dijet	  Calorimeter	  (DCal)•

Extension of the acceptance of EMCal .

•Lead-scintillator sampling type EMC with
APD readout.
– EMCal: Δφ = 110°
– DCal: Δφ = 60° (on opposite side ofEMCalàgood uniformity, less sys.
uncertainty)– Δη = 0.7 for both EMCal and DCal +PHOS– Energy resolution: ~10%/√E•measurements in ALICE, with R = 0.4 jetcone radius, up to pT ~ 150 GeV/c.

DCal
PHOS

Allow back-to-back hadron-jet, di-jet•

Enhance jet, γ trigger capability.

•Full energy scale for γ: 250 GeV.

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ALICE-DCal Collaboration
China
Huazhong Normal University (CCNU), Wuhan
Finland
University of Jyvaskyla
FranceLPSC Grenoble, Subatech Nantes, IPHC Strasbourg
Italy
INFN Catania (Armando Palmeri, Angela Badala), LNF Frascati (Alessandra Fantoni)
Japan
Hiroshima University, University of Tokyo, University of Tsukuba
Switzerland
CERN
USA
Lawrence Berkeley National Laboratory, Wayne State University, University of Houston,
University of Tennessee, Lawrence Livermore National Laboratory, Yale University, OakRidge National Laboratory, Creighton University, Cal Poly San Luis Obispo, Purdue University
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DCal	  components

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42

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All modules are in Subatech / Grenoble, will install in
LHC long shutdown (2013-2014), physics in 2015.

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Perspec,ve	  of	  physics	  with	  DCal:	  Medium	  response	  with	  jets

3+1 hydro + jet (Tachibana, Hirano) QM2012• Excellent hadron PID (0.15 – 20 GeV/c), suitable detector to measure the medium

response with PID, jet ID and trigger by EMCal.
• Bulk properties (PID spectra, v2, HBT, etc.) with a large jet energy imbalance.
• Key to access cs, EOS?

SUMMARY• Rich harvest of LHC new HI data by
the complimentary measurements by
ALICE, ATLAS, CMS.
• Hottest, small eta/s, strongly coupled
QGP produced at LHC heavy ion
collisions.
• A lot of progress towards theprecession measurements of QGP
properties for next decade.

BACK UP SLIDESVery	  similar	  v2	  at	  RHIC	  and	  LHC49

PRL 105 (2010) 252302

s At	  LHC,	  pT	  integrated	  v2	  increases	  by	  30%	  compared	  to	  RHIC	  data	  at	  √sNN=200	  GeV.	  
s v2	  vs.	  pT	  does	  not	  change	  within	  uncertainties	  between	  √sNN=200	  GeV	  and	  2.76	  TeV

50Quark	  number	  scaling	  of	  v2pT/nqKET/nqs Just simple pT/nq scaling does not work at LHC.
s Scaling works better as a function of transverse
energy, but not perfect.