The quest for the QGP: 20 years of heavy ion physics

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The quest for the QGP20 years of heavy ion
physics
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Explorations
Search for the QGP
Search for a sea passage to India
A Mid-Fifteenth-Century European World Map
(1466) The Mediterranean basin, known to Ptolemy
and later Europeans, is fairly accurately
depicted, but the Eastern portions of the map are
very incomplete since they were based on
often-fictitious travelers accounts rather than
observation.
Original idea from H. Satz and D. Karzheev, Hard
probes WS, Portugal, 2004 https//webh04.cern.ch/e
vent-hardprobes04/
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Explorers
Columbus visionary, enthusiastic adventurer Not
afraid to venture far into the unknown with
little guidance and marginal preparation. As
befits the brave (and lucky), he made a BIG
discovery.
In 1493, Columbus wrote a brief report
concerning his discoveries of "Islands of India
beyond the Ganges." It was intended as a public
notice to announce his discoveries and to garner
support for another voyage. The first edition of
this letter was printed in Spanish in Barcelona
in April 1493. Quote from US library of Congress
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Explorers
Vasco da Gama methodical explorer Building on
years of systematic experimental discoveries,
one step at a time.. As befits the diligent, he
reached his goal in due time
For the last leg, VdG was guided by an Indian
pilot, arranged for by Ahmed ibn Majid in Malindi.
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20th Century Explorers
Bikash, the Indian pilot
Hans, the visionary adventurer
Louis, the systematic explorer

• Lessons from the 15th century
• - there are different approaches to make a
  discovery
• you dont always find what you set out to
  discover
• - when venturing into the unknown, have the
  Indians on board

• India Strong and recognized partner in quest for
  QGP
• gt 60 physicists, gt 8 Institutes
• - participation in SPS, RHIC and LHC programs
• 5th largest nation in ALICE
• strong Theory community

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What are we looking for ?
15th century explorers direct trade route to
the Origin of Spices
20th century explorers understanding
the Origins of Matter
NA35 streamer chamber picture, ca 1990
Da Gama arriving in India, 1498
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QGP The Original State of Matter

• QGP true ground state of QCD
• melting matter gt deconfinement study phase
  diagram of matter
• melting vaccum (gluon condensate) gtchiral
  symmetry restoration
• dynamical origin of constituent mass
• Phase transitions involving elementary
  quantum fields
• phase transitions and spontaneous symmetry
  breaking central to HEP
• QCD transition is the only one accessible
  dynamically
• Cosmology Astrophysics
• early Universe at 1 ms
• interior of neutron stars
• new domain of hot dense QCD
• surprises ?

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Melting Matter
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The Dark Mystery of Matter
What stuff is the Universe made of ??

• Elementary Particles 0.1
• 12 matter particles (quarks, leptons)
• only 4 relevant today (u, d, e, n)
• 13 force particles (3 massive, 10 massless)
• Composite Particles (hadrons) 4
• hundreds
• only 2 are relevant (p,n), making nuclei

• Dark Matter 23
• made of unknown particles
• Dark Energy 73
• vacuum energy
• of completely unknown origin
• should be infinite or exactly 0

We dont know how and why for 5 We dont even
know what for the other 95
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Recent Lattice QCD Maps

• recent progress
• improved actions
• improved symmetries
• larger lattices
• crit. temperature
• energy density
• EOS

Tc 175 8 8 MeV
ec (62) Tc4
(e-3P) ¹ 0
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Heavy Ion Collision
QGP
pre-equilibrium
hard collisions
hadron gas
freeze-out
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Experimental Facilities

• AGS (1986 - 1998)
• Beam Elab lt 15 GeV/N, Ös 4 GeV/N
• Users 400 Experiments 4 big, several small
• SPS (1986 - 2003)
• Beam Elab lt 200 GeV/N, Ös lt 20 GeV/N
• Users 600 Experiments 6-7 big, several
  small
• RHIC (gt2000)
• Beam Ös lt 200 GeV/N
• Users 1000
• Experiments 2 big, 2 small
• LHC (gt2007)
• Beam Ös lt 5500 GeV/N
• Users 1000
• Experiments 1 dedicated HI, 3 pp expts

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Very complex reactions can be measured and
analyzed

• large systems
• thousand of particles
• Volume gt 4000 fm3
• energy density up to 3 GeV/fm3
• strongly interacting system
• hadronic rescattering
• collective phenomena (flow)
• thermal particle ratios f(T, m)
• signs of new state of matter
• ee- pairs (chiral symmetry rest. ?)
• J/y suppression (deconfinement ?)

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Soft Probes Elliptic Flow

• Flow Correlation between coordinate and
  momentum space
• close particles move at similar velocity and
  direction
• flow builds up in an interacting medium with
  pressure gradients
• for given boundary conditions, flow profile
  depends on
• Equation of State EoS and viscosity h of fluid
• Hydrodynamics of perfect fluid h 0, l 0
  (strongly interacting)

Elliptic Flow reduces spatial anisotropy -gt acts
at early times
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First Flow Measurement at SPS

• Remember Columbus
• Elliptic Flow not expected at SPS
• PMD meant to look for photon/hadron fluctuations
  (Centauro like events), discovered flow instead

WA93/98 PMD detectors measures azimuthal
anisotropy of photons Presented by Indian group
(Y. Viyogi) at QM95

• Implications
• strongly interacting matter
• collective expansion
• 1/2 ideal hydrodynamics

Particle emission is correlated !
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Photons Thermal Radiation ?

• Thermal photons
• heat radiation from initial hot phase
• El Dorado of QGP physics
• rate T4 gt sensitive to early phase
• rate lifetime gt contribution from hadronic
  phase
• very challenging measurement
• high pt direct QCD hard scattering
• medium pt p0 decay photons
• finally sighted at very low pt ???

CERN Press release in 2000 on Evidence for new
state of matter It is expected that the present
"proof by circumstantial evidence" for the
existence of a quark-gluon plasma in high energy
heavy ion collisions will be further
substantiated by more direct measurements (e.g.
electromagnetic signals which are emitted
directly from the quarks in the QGP) ...
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Hard Probes J/Psi suppression
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SPS Experiments
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Current hunting ground for Quark Gluon Plasma
The Relativistic Heavy Ion Collider
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RHIC Experiments
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Flow at RHIC

• matter at RHIC perfect fluid with zero mean
  free path !
• huge effect (almost 21 at high pt)
• almost perfect agreement with hydro f(impact
  parameter, pt, particle mass)

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Hard Probes Jet Quenching
jet quenching measures radiation length of
QGP dE mD2 x L2 mD Debye screening mass

• high pt partons
• Vacuum fragment into hadrons gt JETS
• Matter additional scattering gt more gluon
  radiation
• normal cold matter small effect
• QGP strong effect (up to several 10 GeV)
• observables of jet quenching
• leading parton looses energy
• energy shows up in soft partons around jet axis

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India or America ?

• SPS/AGS new state of matter
• solid evidence for collective, thermal hadronic
  matter
• new effects quarkonia suppression low mass
  lepton pair spectrum
• RHIC dense (thermalized ?) partonic matter
• elliptic flow compatible with hydrodynamical
  limit
• Hydro limit of zero mean-free-path gt strongly
  interacting fluid,¹ gas !
• almost ideal fluid, h/s 0.1 (much better than
  water !)
• jet quenching compatible with complete
  absorption from interior
• strength of interaction seems mysteriously high

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QG-Plasma or QG-Molasses ?

• QGP weakly interacting gas of quarks and
  gluons
• deconfined, chiral symmetry restored
• sQGP strongly interacting partonic fluid

Columbus Having now accomplished the
undertaking upon which I set out, I advanced
forward, thinking that I could find some town -
but at length, perceiving that nothing new was
likely to appear - I determined to make no
further search.
The journey must go on !
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Future place for studying the Quark Gluon Plasma
The Large Hadron Collider
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ALICE Set-up
TOF
TRD
HMPID
TPC
PMD
ITS
Muon Arm
PHOS
Size 16 x 26 m Weight 10,000 tons
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ALICE Collaboration
1000 Members (63 from CERN
MS) 30 Countries 80 Institutes
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The ALICE Magnet ready for the
experiment to move in!
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Inside the ALICE TPC
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India in Alice
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Past-Present-Future

• AGS/SPS 1986 1994
• existence properties of hadronic phase
• chemical thermal freeze-out, collective flow,
• SPS 1994 2003
• 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 (s)QGP ?
• parton flow, parton energy loss
• LHC 2007 - ??
• go west or find the Island of India beyond
  the Ganges
• precision spectroscopy of ideal plasma QGP
• heavy quarks (c,b), Jets, Y, thermal photons

We are on an exciting and wondrous exploration,
not taking any chances We have the Indian pilot
and his crew on board