Hard Probes 2006

1
Hard Probes 2006
The Not a Theory Summary-Talk
Urs Achim Wiedemann SUNY Stony Brook and RIKEN BNL
Asilomar, 15 June 2006
2
From elementary interactions to collective
phenomena
3
DIS - the most successful hard probe so far

• Deep inelastic scattering (DIS) is
• a hard probe of cold nuclear matter.

• What makes DIS so successful?

• properties of matter (pdfs)
• are field-theoretically well-defined OPE

• interaction between probe and medium
• (where probe ends and medium starts)
• described in controlled dynamical framework
• DGLAP

Lesson success of hard probe depends on
theoretical control of both 1.
the hard probe 2. the properties
of matter, which are probed.
4
Jet Quenching DIS on the QGP?
5
Accuracy of jet-quenching benchmarks
6
Modeling the medium seen by jets

• assumptions in all current jet quenching
  calculations are simplistic

Are static scattering centers sufficiently
realistic? What do they stand for?

• Is there a rigorous field-theoretic definition
  of the properties of
• ultra-dense QCD matter tested by jet
  quenching?

K. Rajagopal

• The role of collisional energy loss is an open
  question
• - numerically
• - conceptually
• Does the ratio of radiative vs. collisional
  energy loss depend on what
• constitutes the medium?
• Can one really separate radiative and
  collisional contributions?

X.N. Wang
M. Djordjevic
Radiative or Collisional?
7
Modeling the medium seen by jets - flow
8
Quarkonium in the QGP
Qualitative idea Thermometer of dense QCD
matter
H. Satz
9
Quarkonium in matter
10
Elmag. Probes
Qualitative idea Sufficient yield of elmag
probes particularly clean signal (no final
state effects) Basis for detailed
investigation of dense QCD matter
11
Elmag. Probes
12
AdS/CFT

• a novel and at present unique testing ground
  for those theoretical techniques,
• which are required by the most basic insights
  from RHIC
• (namely non-perturbatively strong coupling and
  strong collective dynamics),
• but which are not (yet) available in QCD.
• - AdS/CFT cousins of QCD exhibit much of what
  we are interested in
• confinement, mass gap, global symmetries,
  chiral symmetry breaking
• - can be studied in weak and strong coupling
  limit, thus allowing for
• comparison of perturbative and
  non-perturbative techniques

• non-abelian thermal gauge theories share
  important generic features
• - energy density in strong coupling 3/4 of
  energy density of free gas
• - universal viscosity to entropy density ratio
  
• -

K. Rajagopal, P. Kovtun
13
Parton energy loss from AdS/CFT
14
Punchline of this talk

• The connection between theory and data is only
  as strong as its weakest link.
• There are numerous examples, that for the
  sector of Hard Probes,
• the weakest link is currently the modeling of
  the produced matter.

• Many properties of the produced matter can be
  calculated in well-defined settings

• Lattice QCD ( strong coupling, - no real time
  dynamics)
• AdS/CFT ( strong coupling, real time
  dynamics, - not QCD)
• HTL (- weak coupling, real time
  dynamics)

• Embedding hard probes in a realistic geometrical
  and dynamical setting
• (hydrodynamics, dissipative hydrodynamics)
• is a prerequisite for
• - determining numerically sensible values for
  medium properties tested
• by hard probes
• - characterizing at least qualitatively many
  of the collective effects
• present in dense matter (I.e Mach cones)