The Quest for the Quark-Gluon-Plasma: The High-Energy Frontier

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The Quest for the Quark-Gluon-Plasma The
High-Energy Frontier

• Why Heavy Ions at the LHC?
• Where we stand
• What lies ahead

Paolo Giubellino INFN Torino Duality 2005 LNF
June 7th
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At the moment the hunting ground for the Quark
Gluon Plasma is across the Ocean
The Relativistic Heavy Ion Collider At
Brookhaven National Laboratory
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But the future place for studying the Quark
Gluon Plasma is back in Europe!
The Large Hadron Collider
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Nuclear accelerators
(transparency from H. Specht, 1992)
/ 2007

• The LHC latest of a series of successful
  accelerators
• After many problems have been overcome, both
  technical and financial, startup is foreseen for
  2007, with first HI run in 2008

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One Dedicated HI experiment ALICE
One pp experiment with a HI program CMS

• One pp experiment considering HI ATLAS

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Heavy-Ion Physics _at_ LHC

• 1100 participants
• 1000 ALICE
• 60 CMS
• 25 ATLAS
• A large community which has been constantly
  growing over the years, and still grows! gt
  VERY lively field!!!

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Not an Easy Task.
SPS Pb ions since 1995 _at_ 158 Gev/nucleon
NA49 experiment A Pb-Pb event
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Even worse _at_ RHIC Started in 2000
A central Au-Au event _at_ 130 GeV/nucleon CM
energy
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The ALICE challenge
Nch(-0.5lt?lt0.5)8000
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Space-time Evolution of the Collision
time
g
e
? Expansion ?
space
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Diagnostic Tools (Probes) the experimental
challenge to observe in the final state the
signatures of the phase transition

• Low-pt soft probes

Caveat pure hadronic effects can mimic expected
QGP signaturures
thermal particle production from QGP

• single particle spectra
• flow patterns
• two particle correlations
• particle abundances and ratios

Therefore one needs

• Experimentally
  establish a solid baseline studying pp, pA
  collisions and use these data as a reference

• High-pt hard probes

during formation phase parton scattering
processes with large Q2 create high mass or high
momentum objects that are sensitive to the
nature of the medium
beams of hard probes jets, J/y .

• color screening in partonic phase ?
  J/y suppression
• dE/dx by strong interaction ? jet
  quenching

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The method works!
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Past/Present/Future of Nuclear Physics
high-energy frontier

• AGS/SPS 1986 1994
• existence properties of hadronic phase, proof
  of principle of the method
• chemical thermal freeze-out, collective flow,
• SPS 1994 2003 (new results just coming NA60)
• Building a coherent picture. 'compelling
  evidence' for new state of matter with many
  properties predicted for QGP
• J/Y suppression (deconfinement ?)
• low mass lepton pairs (chiral restoration ?)
• RHIC 2000 - ?
• compelling evidence -gt establishing the QGP ?
• parton flow, parton energy loss Huge flux of
  results!
• however soft semihard lifetime hadron
  parton phase
• LHC 2007 - ?? (typ. gt 10 yrs, see CDF)
• (semi)hard gtgt soft, lifetime parton gtgt hadron
  phase
• precision spectroscopy of ideal plasma QGP
• heavy quarks (c,b) Both Quarkonia and Open Charm
  Beauty, Jets, Y, thermal photons

LHC will open the next chapter in HI
physics significant step over above existing
facilities THE place to do frontline research
after 2007
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Why at the LHC? - I
Qualitatively new regime!
RHIC sQGP Still strongly interacting
LHC T well above Tc gt possibly ideal gas
behavior
mu md ms mu md mu md ms ? mu,d HQ
suppressed exp(-mc,b,t/T)
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Why at the LHC? - II
Quantitatively new regime!
SPS RHIC LHC
vsNN (GeV) 17 200
dNch/dy 500 850
t0QGP (fm/c) 1 0.2
T/Tc 1.1 1.9
e (GeV/fm3) 3 5
tQGP (fm/c) 2 2-4
tf (fm/c) 10 20-30
Vf(fm3) few 103 few 104








few 105

5500 X 28



0.1 faster




3.0-4.2 hotter






10 longer
30-40 longer


1500-8000 ?





15-60 denser

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Why at the LHC?-IIIHeavy Quarks

• Copiously produced
• Y ds/dy LHC 20 x RHIC
• ALICE also measures B D production gt proper
  normalization!

c/b Quarkonia in ALICE 1 month statistics of
PbPb vsNN5.5 TeV
0
2.5 lth lt 4
Mmm- (GeV)
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Why at the LHC?-IV New Tools
Hard probes have provided the most remarkable
RHIC results RAA dep. on PT, away-jet
disappearance etc

• _at_LHC Hard processes contribute significantly to
  the total AA cross-section
• Bulk properties dominated by hard processes
• Very hard probes are abundantly produced.
• Hard processes are extremely useful tools
• probe matter at very early times (QGP) !!
• hard processes can be calculated by pQCD ?
  predicted
• Weakly interacting probes become accessible.

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Hard Scattering to Probe the Hot Bulk QCD Medium
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Jets in ALICE hlt0.9
pp L 1030cm-2s-1

• ideal energy for jet-quenching
  around 100 GeV
• pQCD applicable
• jets measurable above soft background
• energy loss still relatively large effect
• DE/E O(10), decreasing with E !

Pb Pb rates
Reasonable rate up to ET 300 GeV
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50 100 GeV jets in PbPb
At large enough jet energy jet clearly
visible But still large fluctuation in underlying
energy
?f lego plot with ?? 0.08 ? ?f 0.25
Central PbPb event (HIJING simulation) with 100
GeV di-jet (PYTHIA simulation)
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But also signals observed at RHIC in the soft
domain will benefit of the high energy to
inderstand their nature e.g. Elliptic Flow
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?
LHC
?
Approaching Hydro or just crossing it? In the
latter case, oversimplified picture!
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Heavy Ions at the LHC

• Energy
• Ebeam 7 x Z/A TeV
• Ös 5.5 TeV/A (Pb-Pb), 14 TeV (pp)
• Beams
• possible combinations pp, pA, AA
  
• Expected Heavy-Ion running
• Initial few years (1HI year 106 effective s,
  like at SPS)
• 2 - 3 years Pb-Pb L
  1027 cm-2s-1
• 1 year p - Pb
  L 1029 cm-2s-1
• 1 year light ions (eg Ar-Ar) L
  few 1027 to 1029 cm-2s-1
• pp run at Ös 14 TeV L
  1029 and lt 3x1030 cm-2s-1
• Later options different ion species, lower
  energy AA and pp

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ALICE Design Philosophy

• General Purpose Heavy Ion Detector
• one single dedicated HI expt at LHC
• ATLAS/CMS will participate, but priority is pp
  physics
• AGS/SPS several (6-8) 'special purpose expts'
• RHIC 2 large multipurpose 2 small special
  purpose expts
• cover essentially all known observables of
  interest
• comprehensive study of hadrons at midrapidity
• large acceptance, excellent tracking and PID
• state-of-the-art measurement of direct photons
• excellent resolution granularity EM calo
  (small but performing !)
• dedicated complementary systems for
  di-electrons and di-muons
• cover the complete spectrum from soft (10's of
  MeV) to hard (100's of GeV)
• stay open for changes surprises (in fact the
  ALICE design has evolved considerably along the
  years!)
• high throughput DAQ system powerful online
  intelligence ('PC farm,HLT)
• flexible scalable minimum design prejudice on
  what will be most interesting

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An extraordinary experimental challenge gt a lot
of RD

• In DAQ Computing gt in progress
  now
• scalable architectures with consumer electornics
  commercial components (COTS)
• high perf. storage media
• GRID computing

• In detector Hardware and VLSI Electronics
• gt successfully completed
• across the decade of the 1990's
• Inner Tracking System (ITS)
• Silicon Pixels (RD19)
• Silicon Drift (INFN/SDI)
• Silicon Strips (double sided)
• low mass, high density interconnects
• low mass support/cooling
• TRD
• bi-dimensional (time-space) read-out, on-chip
• trigger (TRAP chip)
• TPC
• gas mixtures (RD32)
• advanced digital electronics
• low mass field cage
• EM calorimeter
• new scint. crystals (RD18)
• PID

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Example ITS Electronics Developments(all
full-custom designs in rad. tol., 0.25 mm process)
ALICE PIXEL CHIP 50 µm x 425 µm pixels 8192
cells Area 12.8 x 13.6 mm2 13 million
transistors 100 µW/channel
ALICE SSD FEE HAL25 chip 128 channels Preamps/h
serial out
ALICE SDD FEE Pascal chip 64 channel preamp
256-deep analogue memory ADC Ambra chip 64
channel derandomizer
chip
And extreme lightweight interconnection
techniques
SSD tab-bondable Al hybrids
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ExampleTime Of FlightBreakthrough after gt 5
years of RD
for p, K, p PID p, K for p lt2 GeV/c p for p lt4
GeV/c
- 0.9 lt ? lt 0.9 full f
150 kchann. over 150 m2
Multigap Resistive Plate Chambers
full size TOF modules under test
Typical time spectrum
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ALICE LAYOUT TRACKING (and
event characterization)
Inner Tracking System (ITS) 6 Si Layers (pixels,
drift, strips) Vertex reconstruction,
dE/dx -0.9lt?lt0.9
TPC Tracking, dE/dx -0.9lt?lt0.9
TRD Tracking and High-Pt Trigger -0.9lt?lt0.9
ZDC (impact parameter) Forward Multiplicity
Detectors T0 detectors (event time) V0 detectors
(trigger)
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ALICE LAYOUT PID
TRD Identification of electrons (pgt1
GeV/c) -0.9lt?lt0.9

• HMPID High Momentum Particle Identification (?,
  K, p)
• RICH
• Hard Probes

TOF PID (K,p,?) -0.9lt?lt0.9

• MUON arm
• Dimuons and vector mesons
• 2.4 lt? lt 4

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ALICE LAYOUT photons

• PMD Photon Multiplicity Detector
• Preshower detector with fine granularity
• Coverage 2.3lt h lt3.5, 270 k channels
• E-by-E fluctuaction, DCC, flow

• PHOS high-granularity, high-resolution ?
  detector
• PbWO4 crystals
• photons and neutral mesons
• ?-jet tagging

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ALICE tracking can fully exploit the high pt
signals which will become accessible at the LHC,
even at the highest multiplicities
ALICE PPR CERN/LHCC 2003-049
Dp/p ()
50
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9 100 GeV/c
10
100
50
10
ALICE momentum resolution at high pt
pt (GeV/c)
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ALICE PID performance
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Examples Hadronic Observables
particle spectra (single event)
two particle HBT correlations
reaction plane resolution
multiplicity, pseudorapidity reconstruction
multiplicity in ALICE central detector
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Signals which are just hints at RICH becomes
tools at the LHC need Luminosity and the higher
cross-section given by the higher Energy!
D0 ?K-p in ALICE
Search for thermal charm production and essential
normalization for quarkonia
Example of the power of ALICE tracking PID
vertexing
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J/? from B in ee- channel
B(D) ? e X

• Very important element in understanding the J/y
  yield c? 300?400 ?m for D and B mesons, so for
  B(D) ? e X the d0 of the electron can be
  measured with the ITS

e impact parameter d0
ee- mass spectrum for d0 gt cut
B?J/?
d0 lt cut ? resonances d0 gt cut ? D,B mesons
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If EMCAL gt trigger and g-jet, improve
resolution on Ejet
g-jet with PHOSEMCAL TPC
Proposed EMCAL hlt0.7 Df 120o
TPC
8
2
h
PHOSEMCAL
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Building ALICEwhere do we stand?
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• still largest magnet
• magnet volume 12 m long, 12 m high
• 0.5 T solenoidal field

The ALICE Magnet ready for the
experiment to move in!
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The Space Frame
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The Muon Magnet

• 0.7 T and 3Tm
• 4 MW power, 800 tons
• Worlds largest warm dipole

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Muon Chambers
Station 3-4 Slats
Quadrant mother board with MANU
Trigger RPC
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The TPC
drift gas 90 Ne - 10CO2
largest ever
88 m3, 570k channels
End Plates
HV membrane (25 mm)
Field Cage
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ITS modules
Pixel

• Now being produced in series.

Drift
Strip
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TPC-ITS Integration Test
Space Frame
TPC
V0
Absorber
Beam Pipe
T0
Space Frame
TPC
TPC
ITS
Absorber
Absorber
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TOF cosmic test set-up
Muon Chambers Support Panels
FMD inner prototype 2 x 512 strips
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And a lot more (just very few examples!)
TRD stack under test
ZDC
PHOS PbWO4 Crystals
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Also for the EMCal the infrastructure is being
prepared
EMCal rail
EMCal rail
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Computing Phase Transition
The Problem

• Online storing up to 1.2 Gbyte/s
• whole WWW in few hours on tape !
• 10 x RHIC !
• Offline 22 MegaSI2000
• 22000 PC's in 2004 (2800 Mhz)
• 6 PB on disk per year
• cheap mass market components
  Industry Moore's law
• make 100,000 mice do the work of one elephant
  new computing paradigm
• The GRID

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Summary

• LHC is the ultimate machine for Heavy Ion
  Collisions
• very significant step beyond RHIC
• excellent conditions for experiment theory
  (QCD)
• ALICE is a powerful next generation detector
• first truly general purpose HI experiment
• addresses most relevant observables from
  super-soft to ultra-hard
• many evolutionary developments
• SSD, SDD, TPC, em cal,
• some big advances in technology
• electronics, pixels, TOF, computing
• Both the experiment and the machine are getting
  ready and even thinking of upgrades!

Heavy Ion Community can look forward
to eventually exploit this unique combination !
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Event Geometry ALICE Zero-Degree Calorimeters
Determination of the impact parameter of the
collision by measuring the energy carried by the
spectator nucleons Where hadronic calorimeters
at 116 m from IP
spectators
participants nucleons in nuclear overlap
spectators
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Multiplicity Measured in ITS and FMD (one
central PbPb event)
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? ? - channel

• ?M 94.5 MeV/c2 at the ?
• Separation of ?, ?, ?
• Total efficiency 75
• Expected statistics (significance 1 yr)
• central min. bias J/? 310
  574
• ? 12 23
• ? 39 69
• ? 19 35
• ? 12 22
• from min. bias events
• 8k ? and 700k J/? /yr

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Jets in ALICE using all tracking
detectors the TRD
triggering capability
Use high-pT leading particle as seed
30-50 GeV
50-80 GeV
Measure fragmentation pT
distribution, particle composition, pT- y
correlations, multiplicity correlations,
120-170 GeV
80-120 GeV
Example evolution of hard fragmentation
as ETjet increases
230-330 GeV
170-230 GeV
Jet Fragment pT Distribution in Jet Cone
440-600 GeV
330-440 GeV
Normalized background pT distribution in Jet Cone
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Jet quenching with reconstructed jets

• Excellent jet reconstruction but challenging to
  measure medium modification of its shape
• Et100 GeV (reduced average jet energy fraction
  inside R)
• Radiated energy 20
• R0.3 DE/E3
• EtUE 100 GeV

Medium induced redistribution of jet energy
occurs inside cone.
Modest jet energy loss
C.A. Salgado, U.A. Wiedemann hep-ph/0310079
Energy lost at high PT reappears below 1 GeV/c
gt important low-PT capability
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Fragmentation functions
zpt/
pjet
Look also for transverse fragmentation function
(kt)
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Centrality Dependence of Suppression at RHIC
AuAu 130 GeV
Phys. Rev. Lett. 89, 202301 (2002)
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CMS as a Detector for Heavy Ion Physics

• High Resolution and High Granularity Calorimetry
• DhxDf (barrel)
• ECAL0.0174x0.0174
• HCAL 0.087x0.087
• Resolution (barrel)
• ECAL0.027/?E?0.0055
• HCAL1.16/?E?0.05
• Hermetic coverage up to hlt5 (hlt7 proposed
  using CASTOR)
• Zero Degree Calorimeter (proposed)
• Tracking m from Z0, J/?, ?
• Wide rapidity range hlt2.4
• Efficient suppression of p, K? m background
• ECAL at 1.3 m from the beam
• m chambers behind HCAL
• reject kinks using tracker
• Excellent Mmm mass resolution 50 MeV _at_ ?

m chambers
HCAL
ECAL
Si Tracker including Pixels

• DAQ and Trigger
• High rate capability for AA, pA, pp
• High Level Trigger capable of full reconstruction
  of most HI events in real time

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Understanding parton energy loss
(Jet quenching)

• Requires high statistics (luminosity and a good
  trigger)
• Requires good separation from background of
  underlying soft production (need high energy)
• Requires a detailed description of the final
  state
• High efficiency tracking over a wide range of
  momenta (Fragmentation function)
• Identification of particles (energy loss parton
  specific)
• g measurement (Correlation with opposite side
  photon)

ALICE _at_ LHC has all of the above
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Importance of p-Pb data the message from RHIC

• The hadron spectra at RHIC from p-p, Au-Au and
  d-Au collisions establish existence of a new
  final-state effect - early parton energy loss
  from strongly interacting, dense matter in
  central Au-Au collisions

Au Au Experiment
d Au Control Experiment
Preliminary Data
Final Data
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Summary ALICE Physics goals (have
evolved along the years, to cover practically all
relevant observables)
(in one experiment what at the SPS was done by
6-7 experiments, at RHIC by 4)

• Global observables
  Multiplicities, ? distributions
• Degrees of freedom as a function of T hadron
  ratios and spectra, dilepton continuum, direct
  photons
• Early state manifestation of collective
  effects
  elliptic flow
• Energy loss of partons in quark gluon plasma
  
  jet quenching, high pt spectra, open charm
  and open beauty

• Deconfinement
  charmonium and bottonium spectroscopy
• Chiral symmetry restoration neutral to
  charged ratios, res. decays
• Fluctuation phenomena - critical behavior
  
  event-by-event particle comp. and spectra
• Geometry of the emitting source
  HBT,
  impact parameter via zero-degree energy flow
• pp collisions in a new energy domain

• Large acceptance
• Good tracking capabilities
• Selective triggering
• Excellent granularity

• Wide momentum coverage
• P.I.D. of hadrons and leptons
• Good sec. vertex reconstr.
• Photon Detection

Use a variety of experimental techniques!
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Short Term Upgrade Plans

• Initial detector largely finished in place by
  2007
• exception TRD coverage only 60 financed
• New detectors under discussion
• based on recent physics results (RHIC) and
  theory developments since 1990
• pixel trigger electronics ( few 100 k)
• allows better study of pp min bias events
• PID for large momenta (5 20 GeV) ( few
  M )
• based on Cherencov radiation (aerogel, gas
  radiator ?)
• large em calorimeter for jet physics (
  10 M )
• 200 m2 high granularity, shashlik type
  sampling calorimeter
• interested groups in US, Brazil, France, Italy,