Transcript Document

Bulk Properties of QCD Matter
Many thanks to organizers !
Kai Schweda, University of Heidelberg / GSI Darmstadt
1/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Outline
 Introduction
 Hadron Abundances - Tch
 Collective Flow - Tfo, 
 Heavy Quarks - open charm and
quarkonia
2/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Introduction
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Quark Gluon Plasma
Source: Michael Turner, National Geographic (1996)
Quark Gluon Plasma:
(a) Deconfined and
(b) thermalized state of quarks and gluons
 Study partonic EOS at RHIC and LHC
(?) Probe thermalization using heavy-quarks
4/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Nuclear phase diagram
Energy scan
1) Heavy quarks with ALICE at LHC:
- Study medium properties
- pQCD in hot and dense environment
2) FAIR/GSI program:
- Search for the possible phase boundary.
- Chiral symmetry
restoration
XXIII Graduate
Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Colliding Heavy Nuclei
6/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
High-Energy Nuclear Collisions
Time 
CYM & LGT
1) Initial condition: 2) System evolves:
3) Bulk freeze-out
PCM & clust. hadronization
-Baryon transfer
- parton/hadron expansion - hadronic dof
NFD
- ET production
- inel. interactions cease:
NFD & hadronic TM
particle ratios, Tch, mB
-Partonic dof
string & hadronic TM
PCM & hadronic TM
Plot: Steffen A. Bass, Duke University
7/62
- elas. interactions cease
Particle spectra, Tth, <T>
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Collision Geometry
Au + Au sNN = 200 GeV
Non-central Collisions
Uncorrected
Number of participants: number of incoming nucleons in the overlap region
Number of binary collisions: number of inelastic nucleon-nucleon collisions
Charged particle multiplicity
Reaction plane: x-z plane
8/62
 collision centrality
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Hadron Abundances
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Particle Multilplicities
PHOBOS fit
HIJING BBar
Armesto et al.
AMPT
Eskola
CGC
KLN
ASW
DPMJET-III
EHNRR
 at LHC, dN/dh  1000  3000
1
1 dE
 estimate energy density  Bj   R 2  dyT
0
PHOBOS compilation: W. Busza, SQM07.
10/62
Theory points: HI at LHC – last call for predictions, CERN, May 2007.
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
EoS from Lattice QCD
1) Large increase in  !
SPS
RHIC
LHC ?
 Large increase in Ndof:
Hadrons vs. partons
2) TC ~ 160 MeV
3) Boxes indicate max. initial
temperatures
 Longest expansion
duration at LHC
 Expect large partonic
collectivity at LHC
Z. Fodor et al, JHEP 0203:014(02)
C.R. Allton et al, hep-lat/0204010
F. Karsch, Nucl. Phys. A698, 199c(02).
11/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
HI - Collision History
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
 Tc(ritical): quarks and gluon  hadrons, Tc(ritical) = 160 MeV
 Tch(emical): hadron abundancies freeze out
 Tfo: particle spectra freeze out
Plot: R. Stock, arXiv:0807.1610 [nucl-ex].
12/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Solar Spectrum
Wavelength and Intensity solely determined by temperature Tsolar = 5500 °C
(at the sun’s surface)
Graphik: Max-Plack-Institut für Plasmaphysik
13/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Wie heiss ist die Quelle ?

1000
 Lichtquelle  Teilchenquelle
N
Teilchenhäufigkeit
 Häufigkeit von Teilchen am
K+
100.
besten beschrieben durch
L
K0
K- h
N
10.0
T = 2 000 000 000 000 C
X
f
L
= 2 Trillionen C
W
1.0
 100 000 mal heisser als
im Innern der Sonne !
X
W
0.1
0
0.4
0.8
1.2
1.6
E = mc2 (GeV)
14/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Chemical Freeze-out Model
Hadron resonance ideal gas
Refs. J.Rafelski PLB(1991)333
P. Braun-Munzinger et al., nucl-th/0304013
Density of particle i
Qi : 1 for u and d, -1 for u and d
si : 1 for s, -1 for s
gi : spin-isospin freedom
mi : particle mass
mB = 3mq
mS = mq-ms
Tch
mq
ms
V
gs
: Chemical freeze-out temperature
: light-quark chemical potential
: strange-quark chemical potential
: volume term, drops out for ratios!
: strangeness under-saturation factor
All resonances and unstable particles are decayed
Compare particle ratios to experimental data
15/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Hadron Yield  Ratios
1) At RHIC:
Tch = 160 ± 10 MeV
mB = 25 ± 5 MeV
2) gS = 1.
 The hadronic
system is
thermalized at RHIC.
3) Short-lived resonances
show deviations.
 There is life after
chemical freeze-out.
RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184;
Statistical Model calculations: P. Braun-Munzinger et al. nucl-th/0304013.
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Chemical Freeze-Out vs Energy
With increasing energy:
•
Tch increases and saturates
at Tch = 160 MeV
•
Coincides with Hagedorn
temperature
•
Coincides with early lattice results
 limiting temperature for
hadrons, Tch  160 MeV !

mB decreases, mB = 1MeV at LHC
 Nearly net-baryon free !
A. Andronic et al., NPA 772 (2006) 167.
17/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
QCD Phase Diagram
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
18/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Baryon Ratios
With increasing energy:
•
Baryon ratios approach unity
•
At LHC, pbar / p  0.95
 with increasing
collision energy,
production of matter
and anti-matter gets
closer
Compilation: N. Xu
19/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
‘Elementary’ p+p Collisions
 Low multiplicities
 use canonical ensemble:
Strangeness locally
conserved!
 particle yields are well
reproduced
 Strangeness not
equilibrated ! (gs = 0.5)
Statistical Model Fit: F. Becattini and U. Heinz, Z. Phys. C 76, 269 (1997).
20/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
HI - Collision History
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
 Tc(ritical): quarks and gluon  hadrons, Tc(ritical) = 160 MeV
 Tch(emical): hadron abundancies freeze out, Tch(emical) = 160 MeV
 Tfo: particle spectra freeze out
Plot: R. Stock, arXiv:0807.1610 [nucl-ex].
21/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Collective Flow
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Pressure, Flow, …
Thermodynamic identity
 – entropy
p – pressure
U – energy
V – volume
 = kBT, thermal energy per dof
d  dU  pdV
In A+A collisions, interactions among constituents
and density distribution lead to:
pressure gradient  collective flow



23/62
number of degrees of freedom (dof)
Equation of State (EOS)
cumulative – partonic + hadronic
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Momentum Distributions*
2
dN
[(GeV/c)-1 ]
2 dpT dy


K (dE/dx)
p
K (dE/dx)
Tth=107±8 [MeV]
<t>=0.55±0.08 [c]
n=0.65±0.09
2/dof=106/90
solid lines: fit range
p
L
•
Typical mass ordering in inverse slope
from light  to heavier L
•
Two-parameter fit describes yields of
, K, p, L
•
Tth = 90  10 MeV
•
<t> = 0.55  0.08 c
 Disentangle
collective motion from thermal
L
random walk
pT [GeV/c]
*Au+Au @130 GeV, STAR
24/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
(anti-)Protons From RHIC
More central collisions
Au+Au@130GeV
mT 
pT2  mass 2
Centrality dependence:
- spectra at low momentum de-populated, become flatter at larger momentum
 stronger collective flow in more central coll.! STAR: Phys. Rev. C70, 041901(R).
25/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Thermal Model + Radial Flow
Fit
Source is assumed to be:
– in local thermal equilibration: Tfo
– boosted in transverse radial direction: r = f(s)
boosted
E.Schnedermann, J.Sollfrank, and U.Heinz, Phys. Rev. C48, 2462(1993)
d 3N
(u m p m )/T fo
E 3 e
pd m 
dp 
random
 m coshr   p sinh r 
R
dN
  0 rdrmT K1 T
I0  T

mT dmT
 Tfo   Tfo 
r  tanh1 T
26/62
 r 
T   S  
 R
  0.5, 1, 2
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
D-meson collective flow
Large collective flow
velocity
 Spectrum moves to
larger momentum
27/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
HI - Collision History
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
 Tc(ritical): quarks and gluon  hadrons, Tc(ritical) = 160 MeV
 Tch(emical): hadron abundancies freeze out, Tch(emical) = 160 MeV
 Tfo: particle spectra freeze out, Tfo  100 MeV :, K, p
Plot: R. Stock, arXiv:0807.1610 [nucl-ex].
28/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Kinetic Freeze-out at RHIC
1) Multi-strange hadrons f
and W freeze-out earlier
than (, K, p)
 Collectivity prior to
hadronization
STAR Preliminary
2) Sudden single freeze-out*:
Resonance decays lower Tfo
for (, K, p)
 Collectivity prior to
hadronization
 Partonic
Collectivity ?
STAR Data: Nucl. Phys. A757, (2005 102),
*A. Baran, W. Broniowski and W. Florkowski, Acta. Phys. Polon. B 35 (2004) 779.
29/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Anisotropy Parameter v2
coordinate-space-anisotropy

momentum-space-anisotropy
y
x
 y2  x2
 2
 y  x2
py
v 2  cos2 ,   tan ( )
px
1
Initial/final conditions, EoS, degrees of freedom

v2 in the Low-pT Region
- v2 approx. linear in pT, mass ordering from light  to heavier L
characteristic of hydrodynamic flow !
 sensitive to equation of state
31/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Non-ideal Hydro-dynamics
h
s
 finite shear viscosity h reduces elliptic flow

 many caveats, e.g.:
- initial eccentricity  (Glauber, CGC, …)
- equation of state
- hadronic contribution to h/s
 6/4
String theory
predicts:
h/s > 1/4
M.Luzum and R. Romatschke, PRC 78 034915 (2008); P. Romatschke, arXiv:0902.3663.
32/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Elliptic Flow vs Collision Energy
Glauber initial conditions
 Centrality dependence:
- initial eccentricity 
- overlap area S
QuickTime™ and a
decompressor
are needed to see this picture.
 Collision energy dep.:
- multiplicity density dNch/dy
 in central collisions
at RHIC, hydro-limit
seems reached !
NA49, Phys. Rev. C68, 034903 (2003);
STAR, Phys. Rev. C66, 034904 (2002);
Hydro-calcs.: P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev.C62, 054909 (2000).
33/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
v2 of f and multi-strange W
 Strange-quark flow - partonic collectivity at RHIC !
QM05 conference: M. Oldenburg; nucl-ex/0510026.
34/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Collectivity, Deconfinement at
RHIC
- v2, spectra of light hadrons
and multi-strange hadrons
- scaling with the number of
constituent quarks
At RHIC, it seems we have:
 Partonic Collectivity
 Deconfinement
 Thermalization ?
PHENIX: PRL91, 182301(03)
STAR: PRL92, 052302(04)
S. Voloshin, NPA715, 379(03)
Models: Greco et al, PRC68, 034904(03)
X. Dong, et al., Phys. Lett. B597, 328(04).
….
35/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Collectivity  Energy Dependence

Collectivity parameters <T>
and <v2> increase with
collision energy

strong collective
expansion at RHIC !
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
<T>RHIC  0.6

expect strong partonic
expansion at LHC,
<T>LHC  0.8, Tfo  Tch
K.S., ISMD07, arXiv:0801.1436 [nucl-ex].
36/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Partonic Collectivity at RHIC
1) Copiously produced hadrons freeze-out ,K,p:
Tfo = 100 MeV,
T = 0.6 (c) > T(SPS)
2) Multi-strange hadrons freeze-out:
Tfo = 160-170 MeV (~ Tch), T = 0.4 (c)
3) Multi-strange v2:
f and multi-strange hadrons X and W do flow!
4) Model - dependent h/s: (0?),1 - 10 x 1/4
Deconfinement &
Partonic (u,d,s) Collectivity !
37/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Heavy Quarks
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Heavy  flavor: a unique probe
mc,b >> LQCD : new scale
mc,b  const., mu,d,s ≠ const.
Q2
• initial conditions:
 cc bb
test pQCD, mR, mF
probe gluon distribution


• early partonic stage:
diffusion (g), drag (), flow
probe thermalization
X. Zhu, M. Bleicher, S.L. Huang, K.S., H. Stöcker,
N. Xu, and P. Zhuang, PLB 647 (2007) 366.
time
• hadronization:
chiral symmetry restoration
confinement
statistical coalescence
J/ enhancement / suppression
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Limitations in PDFs

Most charm created from
gluons, e.g. g+g  c + cbar

increasing uncertainties in gluon
distribution at smaller Bjorken x:

Assume y=0, pT=0, x1=x2

2 x mcharm  3 GeV
RHIC (s=0.2TeV): x = 0.015
LHC (s=14TeV): x = 2x10-4
40/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Heavy  Quark Production
Heavy-quark
production at
LHC,
compared to
RHIC expect
factors
Charm  10
Beauty  100
(i) Heavy-quarks abundantly produced at LHC energies !
(ii) Large theoretical uncertainties  energy scan (LHC,FAIR) will help !
Plots: R. Vogt,Eur. Phys. J. C, s10052-008-0809-x (2008).
41/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Heavy  quark Correlations
PYTHIA: p + p @ 14 TeV

c-cbar mesons are correlated
•
Pair creation: back to back
•
Gluon splitting: forward
•
Flavor excitation: flat

Exhibits strong correlations !

Baseline at zero:
clear measure of
vanishing correlations !
 probe thermalization
among partons !
X. Zhu, M. Bleicher, S.L. Huang, K.S., H. Stöcker,
N. Xu, and P. Zhuang, PLB 647 (2007) 366.
G. Tsildeakis, H. Appelshäuser, K.S., J. Stachel, arXiv: 0908.0427.
42/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
How to measure HeavyQuark Production
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
43/62

e.g., D0, c = 123 mm

displaced decay vertex is signature of heavy-quark decay

need precise pointing to collision vertex
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Heavy  Flavor production at RHIC
 large discrepancy between
STAR and PHENIX:
factor > 2 (!)
 need Si-vertex upgrades
(> 2011)
 large theoretical
uncertainties (factor > 10)
 Measure charm production
at RHIC, LHC, FAIR and
provide input to theory:
- gluon distribution,
- scales mR, mF
Plot: J. Dunlop (STAR), QM2009, Open Heavy-flavor in heavy-ion collisions,
Calcs: R. Vogt,Eur. Phys. J. C, s10052-008-0809-x (2008),
M. Cacciari, 417th Heraeus Seminar, Bad Honnef (2008).
44/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Where does all the charm
go?
J
Lc
Ds
D

D0
Total charm cross section: open charm hadrons,
e.g. D0, D*, Lc, … or c,b  e(m) + X

Hidden-charm mesons, e.g. J/ carry ~ 1 % of total charm
Statistics plot: H. Yang and Y. Wang, U Heidelberg.
45/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
D0  + + K- Reconstruction
+
D 0,
c = 123 mm
K-
Plot: A. Shabetai
46/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Open  Charm Performance

Measure secondary decay vertex
 Direct reconstruction of D0
 address heavy-quark production
with 1st year of data taking

Many other channels, e.g. D+, D*

Also: single-electrons from heavy-flavor
decays
ALICE: PPR.vol.II, J. Phys. G 32 (2006) 1295.
Simulation: 109 p+p, 108 p+Pb, 107 Pb+Pb collisions
47/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
D* meson Identification

D*+  D0 + +
 Identify D*+
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
through
M[D*+ - D0]
 Subtract resonance
decay to D0
 Two different
methods to address
total charm
production
D*± analysis: Yifei Wang, Ph.D. thesis, University of Heidelberg, in preparation.
48/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Viele neue interessante Signale in ALICE bei LHC:
z.B.
Hadronen mit schweren Quarks
(charm und beauty)
D0, D+, D*, Ds, J/ ’, Lc Lb  
49/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Quarkonia
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Charmonium

Bound state of charm- and anti-charm quark

Hidden-charm meson

mJ/ = 3.1 GeV, rJ/ = 0.45 fm, mJ/' = 3.6 GeV, JP = 1- states

Minimum formation time  = rJ/ / c = 0.45 fm

Charm-quark production at time scale tc~ 1/2mc  0.08 fm

Separation between initial production and hadronization (factorization)
51/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Debye Screening
52/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Quarkonia as a Thermometer

Check for melting of bottomonium (b-bbar)
at Tdeconfined  2 Tc

Check for melting of charmonium (c-cbar)
at Tdeconfined  1.2 Tc

53/62
Absolute numbers model-dependent Tfo:
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
J/ Production
P. Braun-Munzinger and J. Stachel, Nature 448 (2007) 302.
 suppression,
compared to
scaled p+p
(SPS)
 regeneration,
enhancement
Low energy (SPS):
few ccbar quarks in the system  suppression of J/
High energy (LHC):
many ccbar pairs in the system  enhancement of J/
 Signal of de-confinement + thermalization of light quarks !
54/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Statistical Hadronization of Charm
 large charm production at LHC
 strong generation of J/
cc
 striking centrality dependence
 Signature for QGP
formation !
 Initial conditions at LHC ?
 Need to measure total
charm production in PbPb !
 Assumes kinetic
equilbration of charm !
A. Andronic, P. Braun-Munzinger, K. Redlich, J. Stachel, Phys. Lett. B 652 (2007) 259.
55/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Charmonium production

In central Pb+Pb collisions at
top SPS energy:

J/’ to J/ ratio approaches
thermal limit

Indicates kinetic equilibration
of charm
56/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
 Examples of the ALICE physics potential
- Open charm: D0  K- + +
(already shown)
- Quarkonia: J/, 
- Global event properties
 Will be addressed in first year of pp collisions
57/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
First Physics with ALICE
 Results from simulations
 1 day of data taking
 Address:
- multiplicity
- mean transverse momentum
- hadro-chemistry
58/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Charmonia via Di-Electron
Measurement
• electron ID with TPC and TRD
• expect 2500  mesons per Pb+Pb year
with good mass resolution and S/B
Simulation: pp coll.
c1 c2
J/
Simulation: 2·108 central PbPb collisions
59/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
Heavy Flavor in Muon Channel
•
muon channel: J/,   m+m- (2.5 <h<
4)
60000 J/ and 2000 
•
initial sample sufficient to study
production rates of J/ and 
states in muon channel
J/
bm

60/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
LHC: Schedule
1st pp collisions
very short run at 900 GeV
Nov 2009:
Long run of pp collisions at 7- 10 TeV
end of 2010:
3 - 4 weeks Pb+Pb collisions
at 2.8 - 3.9 TeV
*short technical stop
over Christmas period
61/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda
ALICE  Ready for Physics !
62/62
XXIII Graduate Days, Heidelberg, 5  9 Oct, 2009
Kai Schweda