0. Beam Energy Programs in HIC Part I: Past
Christoph Blume
University of Frankfurt

1. Christoph Blume, Dubna Aug. 2012
Outline: Experiments
Beam energy scan programs with heavy ions
Part I: Past
AGS: e.g. E895
SPS: NA49 (NA45, NA57)
Part II: Present
RHIC: STAR, PHENIX
SPS: NA61
Part III: Future
NICA: MPD
FAIR: CBM
Christoph Blume, Dubna Aug. 2012

2. Christoph Blume, Dubna Aug. 2012
Outline: Physics
Scan of the QCD phase diagram
Search for the onset of deconfinement
Locate the phase boundary to QGP
Order of the phase transition
(cross over ↔ 1st order)
Search for the QCD critical point
Systematic scan of relevant
area in phase diagram
Search for new QCD phases and exotica
E.g. Quarkyonic matter
Christoph Blume, Dubna Aug. 2012

3. Christoph Blume, Dubna Aug. 2012
The QCD Phase Diagram
Topic of this lecture
Part of phase diagram with μB > 0
μB = 0: LHC physics
Questions to experiments
1) Is it possible to locate the
onset of deconfinement ?
2) Is there any evidence for a
1st order phase transition ?
3) Can one find any indication
for a possible critical point ?
RHIC
SPS
FAIR
NICA
Christoph Blume, Dubna Aug. 2012

4. Analogy: Phase Diagram of Water
Cross over
Critical point
1st order
phase boundary
Christoph Blume, Dubna Aug. 2012

5. Christoph Blume, Dubna Aug. 2012
Beam Energy Scan
Control parameter: √sNN
Allows to scan different regions of phase diagram
System freezes out at different positions along freeze-out curve
Trajectory might cross critical area
Variation of system size
Program of
H. Stöcker, E.L. Bratkovskaya,
M. Bleicher, S. Soff, and X. Zhu,
JPG31, S929 (2005)
Y.B. Ivanov, V.N. Russkikh,
V.D. Tonnev,
PRC73, (2006)
3-fluid hydro
Christoph Blume, Dubna Aug. 2012

6. Christoph Blume, Dubna Aug. 2012
Beam Energy Scan
Region of high baryon density
RHIC
SPS
FAIR / NICA (/ AGS)
RHIC
sNN = GeV
SPS
sNN = 6–17 GeV
AGS
sNN = 2.7–5 GeV
Christoph Blume, Dubna Aug. 2012

7. Alternating Gradient Synchrotron
Christoph Blume, Dubna Aug. 2012

8. HIC Experiments at the AGS
Beam
Technology
Observables
E802 Si
Single arm magnetic spectrometer
Spectra (, p, K), HBT
E810
TPCs in magnetic field
Strangeness (K0s, )
E814
Magnetic spectrometer + calorimeters
Spectra (p) + Et
E859
E nd level PID trigger
Strangeness ()
E866 Au
2 magnetic spectrometers (TPC, TOF)
Strangeness (Kaons)
E877
Upgrade of E814
E891
Upgrade of E810
E895
EOS TPC
E896
Drift chamber + neutron detector
H0 Di-baryon, 
E910
EOS TPC + TOF
p+A Collisions
E917
Upgrade of E866
Christoph Blume, Dubna Aug. 2012

9. Christoph Blume, Dubna Aug. 2012
The E895 Experiment
Time Projection Chamber
EOS-TPC
Beam energy scan
Au+Au
2.4 < √sNN < 4.8 GeV
2 < Elab < 10.8 A GeV
Observables
π±, p, K0s, Λ, Ξ-
Spectra, HBT,
directed and elliptic flow
Christoph Blume, Dubna Aug. 2012

10. CERN Accelerator Complex
Christoph Blume, Dubna Aug. 2012

11. CERN Accelerator Complex
North Area
SPS
LHC
West Area PS
Christoph Blume, Dubna Aug. 2012

12. HIC Experiments at the SPS
Beam
Technology
Observables
NA34
16O, 32S
Muon spectrometer + calorimeter
Di-leptons, p, , K, 
NA35
Streamer chamber
-, K0s, , HBT
NA36
TPC
K0s, 
NA38
Di-muon spectrometer (NA10)
Di-leptons, J/
WA80/WA93
Calorimeter + Plastic Ball
, 0, 
WA85
Mag. spectrometer with MWPCs
K0s, , 
WA94
WA85 + Si strip detectors
NA44
16O, 32S, 208Pb
Single arm magnetic spectrometer
, K, p
NA45
Cherenkov + TPC
Di-leptons (low mass)
NA49
208Pb
Large volume TPCs
, K, p, K0s, , , , ...
NA50
NA38 upgrade
NA52
Beamline spectrometer
Strangelets
WA97
Mag. spectrometer with Si tracker
h-, K0s, , , 
WA98
Pb-glass calorimeter + mag. spectrom.
NA57
WA97 upgrade
NA60
114In
NA50 + Si vertex tracker
Christoph Blume, Dubna Aug. 2012

13. Beam Energy Scan at the SPS
Pb+Pb:
6.3 < √sNN < 17.3 GeV
Christoph Blume, Dubna Aug. 2012

14. Christoph Blume, Dubna Aug. 2012
The NA49 Experiment
Christoph Blume, Dubna Aug. 2012

15. Christoph Blume, Dubna Aug. 2012
The NA49 Experiment
Christoph Blume, Dubna Aug. 2012

16. Christoph Blume, Dubna Aug. 2012
The NA45 Experiment
Christoph Blume, Dubna Aug. 2012

17. Christoph Blume, Dubna Aug. 2012
The NA57 Experiment
Christoph Blume, Dubna Aug. 2012

18. Baryon-Number DistributionsyP yT y0
y’T
y’p
Lower energies:
Higher energies:
Christoph Blume, Dubna Aug. 2012

19. Christoph Blume, Dubna Aug. 2012
How to Measure Them
Net-proton distributions: Protons - Antiprotons - =
Other contributions (neutrons, hyperons) usually ignored
(difficult to measure)
Christoph Blume, Dubna Aug. 2012

20. Energy Dependence of Net-Protons
NA49 preliminary
BRAHMS: PRL93, (2004)
Christoph Blume, Dubna Aug. 2012

21. Energy Dependence of y
RHIC (sNN = 200 GeV):
E = 25.7 ± 2.1 TeV
E/Nucleon = 72.0 ± 6.0 GeV
Rapidity shift:
Energy loss:
Christoph Blume, Dubna Aug. 2012

22. Inelastic Energy per NN Collision
Central data
Energy of single net-baryon:
Total inelastic energy
per NN collision:
Christoph Blume, Dubna Aug. 2012

23. Inelasticity of Heavy Ion Collisions
Central data
 p+p
Inelasticity:
⇒ ≈ 70% of available energy
is transformed into particle
production and expansion
of fireball (p+p ≈ 50%)
Christoph Blume, Dubna Aug. 2012

24. Rapidity Distributions of Baryons
Central Pb+Pb,
158A GeV
dn/dy (a.u.) y
Net-protons:
3 valence Quarks (uud )
Omegas:
3 produced Quarks (sss )
Net s:
1 valence (d ) +
2 produced Quarks (ss )
Net s:
2 valence (ud ) +
1 produced Quark (s )
Christoph Blume, Dubna Aug. 2012

25. Antibaryon/Baryon Ratios
√sNN dependence gets
reduced with increasing strangeness content
But even Ω-/Ω+ ratio not
energy independent
S = -3
S = -2
S = -1
S = 0
PRC78, (2008)
Christoph Blume, Dubna Aug. 2012

26. Christoph Blume, Dubna Aug. 2012
Particle Production
Particle yields
Lots of data on lighter particles
(π, K, Λ) for central collisions
(system size less well covered)
Data on heavier particles (φ, Ξ, Ω)
still relatively scarce
Different energy dependences
Steeper rise at low energies
for K+ and Λ
Interplay between net-baryon
density and strangeness production
AGS
NA49
BRAHMS
Christoph Blume, Dubna Aug. 2012

27. Major Strangeness Carriers: K and Λ
Strangeness Conservation  =
Isospin Symmetry
K0 (ds)
K+ (us) 
K- (us)
 (uds)
>> 
If baryon density is high
Christoph Blume, Dubna Aug. 2012

28. Relative Strangeness Production
Maximum around √sNN = 7-8 GeV
Christoph Blume, Dubna Aug. 2012

29. Particle Production: Hyperons
/ −
-/
+/
 = 1.5 (+ + -)
|y| < 0.4
|y| < 0.5
Christoph Blume, Dubna Aug. 2012

30. Particle Production: K/π Ratios
Pronouned maximum for K+/π+ ratio (aka “The Horn”)
Not described by transport models
Sharper than early statistical model predictions
Proposed as signature for the onset of deconfinement
M. Gaździcki and M.I. Gorenstein, APPB30, 2705 (1999)
Christoph Blume, Dubna Aug. 2012

31. Chemical Freeze-Out Curve
Provides relation between T and μB
Christoph Blume, Dubna Aug. 2012

32. Energy Dependence of T and B
A. Andronic et al,
NPA772 (2006), 167
Christoph Blume, Dubna Aug. 2012

33. Particle Production: Stat. Model
Latest version of stat. model
T(√sNN) and μB(√sNN) parameterized
T and μB connected via freeze-out curve
Better fit after introduction of additional high mass resonances (Hagedorn-res.)
⇒ Increase of pion yield
Decrease of μB ⇒ maximum also in Λ/π
A. Andronic et al., PLB673, 142 (2009)
Christoph Blume, Dubna Aug. 2012

34. Strangeness in Heavy Ion Physics
Strangeness enhancement as a QGP signature
J. Rafelski and B. Müller, PRL48, (1982)
P. Koch, B. Müller, and J. Rafelski, Phys. Rep. 142, 167 (1986)
Strangeness has to be produced (no s-Quarks in nucleons)
Thresholds are high in hadronic reactions
E.g..: N + N  N + K+ +  (Ethres  700 MeV)
Fast equilibration in a QGP via partonic processes
E.g. gluon-fusion
⇒ Enhancement of strange particle production in A+A relative
to p+p expected (in particular multi-strange particles)
Christoph Blume, Dubna Aug. 2012

35. Strangeness Enhancement
√sNN (GeV)
Contrary to naive expectation
Same behavior for multi-strange particles? More data needed
Christoph Blume, Dubna Aug. 2012

36. Christoph Blume, Dubna Aug. 2012
QGP Signature ?
Is it a dominantly partonic effect or can hadronic processes lead to the same fast equilibration?
Multi-meson fusion processes
C. Greiner and S. Leupold, J. Phys. G 27, L95 (2001)
Dynamic equilibration at the phase boundary?
T-μB freeze-out curve follows phase boundaries (QGP or quarkyonic matter)
P. Braun-Munzinger, J. Stachel, and C. Wetterich, Phys. Lett. B 596, 61 (2004)
Hadronization generally a statistical phenomenon?
U. Heinz, Nucl. Phys. A 638, 357c (1998), R. Stock, Phys. Lett. B 456, 277 (1999)
Christoph Blume, Dubna Aug. 2012

37. Radial Expansion and mt-Spectra
1/mT dN/dmT mT
1/mT dN/dmT
No radial flow:
exponential spectrum
(p+p collisions)
With radial flow:
add. boost by expansion (vT)
⇒ blue shifted spectrum
Christoph Blume, Dubna Aug. 2012

38. mt-Spectra: Charged Kaons
Sudden change in the Kaon slope parameters (aka “The Step”)
Evolution of radial flow changes around √sNN = 7-8 GeV
Difficult to model in hadronic transport models
Indication for a change of Equation of State (EOS) ?
Christoph Blume, Dubna Aug. 2012

39. Energy Dependence of 〈mT〉
NA49: PRC77, (2008)
Christoph Blume, Dubna Aug. 2012

40. Christoph Blume, Dubna Aug. 2012
The QCD Phase Diagram
K. Rajagopal, CPOD Conference 09
Christoph Blume, Dubna Aug. 2012

41. Critical Point Predictions
Lattice QCD calculation
at finite μB
Z. Fodor and S. Katz
JHEP 0404, 050 (2004)
But current predictions scatter quite a lot
The CP might even not exist at all ...
P. de Forcrand and O. Philipsen, JHEP01, 077 (2007)
M. Stephanov,
CPOD conference 09
Christoph Blume, Dubna Aug. 2012

42. Critical Point Predictions
Larger critical area possible
Y. Hatta and T. Ikeda,
PRD67, (2003)
Focusing effect
Proximity of critical point might
influence isentropic trajectories
M. Askawa et al.,
PRL101, (2008)
Christoph Blume, Dubna Aug. 2012

43. Critical Point Observables
Critical opalescence
Correlation lengths and
susceptibilities diverge
Heavy ion reactions
System size limited ⇒ critical region
Correlation length ξ ≈ radius of system
Enhanced fluctuations
Multiplicity
Average pt
Particle ratios
Conserved quantities
Strangeness S
Baryon number B
Charge Q
Higher moments more sensitive
M. Cheng et al.,
PRD79, (2009)
μB = 0
Christoph Blume, Dubna Aug. 2012

44. Christoph Blume, Dubna Aug. 2012
Fluctuations
Probe the medium response (susceptibilities)
Study of hadronization properties
Might be sensitive to QGP phase
Hadron gas reacts differently than QGP
Different number of degrees of freedom
Nature of the phase transition
Order of the transition (cross over ⇔ 1st order)
Existence of critical point
⇒ sudden increase of fluctuations
Christoph Blume, Dubna Aug. 2012

45. Christoph Blume, Dubna Aug. 2012
Fluctuations
Charged multiplicity n
Extensive quantity
tight centrality selection (1%)
to reduce volume fluctuations
Scaled variance 
Energy dependence of 
Data narrower than Poisson ( < 1)
Trend reproduced by UrQMD
Pb+Pb,
158A GeV
1 < y < ybeam
Christoph Blume, Dubna Aug. 2012

46. Comparison to CP Expectations
Average pt fluctuations
Quantified by Φpt
Multiplicity fluctuations
Quantified by scaled variance
No √sNN dependence seen
Critical point expectation
central
Pb+Pb
K. Grebieszkow, SQM11
B from stat. model fit:
F. Becattini et al.,
PRC73, (2006)
Position of critical point:
Z. Fodor and S. Katz
JHEP 0404, 050 (2004)
Amplitude of fluct. :
M. Stephanov et al.
PRD60, (1999)
Width of critical region:
Y. Hatta and T. Ikeda,
PRD67, (2003)
NA49, PRC79, (2009)
Christoph Blume, Dubna Aug. 2012

47. Particle Ratio Fluctuations
Examples: K/π, p/π, K/p
Dynamical fluctuations quantified
relative to mixed events reference
S/B fluctuation as QGP signal
V. Koch, A. Majumder, and J. Randrup,
PRL95, (2005)
T < Tc: S and B can be unrelated
(Kaons: S = -1, B = 0)
T > Tc: S and B are correlated
(s-Quark: S = -1, B = 1/3)
Experimentally: K/p fluctuations
Christoph Blume, Dubna Aug. 2012

48. Particle Ratio Fluctuations
Comparison NA49 ↔ STAR
Good agreement for p/π
Deviations for K/π + K/p at lowest √sNN
Likely due to different acceptances:
K/π
NA49, PRC83, (2011)
NA49, PRC79, (2009)
STAR, PRL103, (2009)
p/π
T. Tarnowsky, SQM11
J. Tian, SQM11
T. Schuster, QM11
K/p
Christoph Blume, Dubna Aug. 2012

49. Christoph Blume, Dubna Aug. 2012
Summary Part I
Beam energy scans at AGS and SPS
Produced already a substantial amount of data
Baseline for ongoing and future programs
Main observations
Strong variation of net-baryon density ⇒ change of μB
Maximum of relative strangeness production around √sNN = 7-8 GeV
Sharp maximum in K+/π+ ratio. Interpretation?
Evolution of radial flow changes around √sNN = 7-8 GeV
No evidence for critical point yet (first attempts)
Christoph Blume, Dubna Aug. 2012

50. Christoph Blume, Dubna Aug. 2012

51. Center-of-Mass Energy
Center-of-mass energy in nucleon-nucleon system:
One particle in rest (fixed target):
Example: p+p at the SPS (450 GeV beam energy):
⇒ Fixed target: √s = 29.1 GeV
⇒ Collider: √s = 900 GeV
Christoph Blume, Dubna Aug. 2012

52. Christoph Blume, Dubna Aug. 2012
Luminosity L
Na(b) = number of particles per bunch
j = number of bunches
v = velocity of the bunches
u = circumference of collider
A = beam cross section at collision point
Christoph Blume, Dubna Aug. 2012

53. Time Projection Chamber: ALICE
Field cage
Readout chamber
E-Field
510 cm
HV electrode (100 kV)
Volume: 88 m3
Drifttime 93 μs
#channels:
Christoph Blume, Dubna Aug. 2012

54. Christoph Blume, Dubna Aug. 2012
ALICE-TPC
Christoph Blume, Dubna Aug. 2012

55. Christoph Blume, Dubna Aug. 2012
TPC Readout
Christoph Blume, Dubna Aug. 2012

56. Specific Energy Loss dE/dx
Christoph Blume, Dubna Aug. 2012

57. Christoph Blume, Dubna Aug. 2012
Bethe-Bloch Equation
Christoph Blume, Dubna Aug. 2012

58. Christoph Blume, Dubna Aug. 2012
dE/dx-Measurement
Christoph Blume, Dubna Aug. 2012

59. Christoph Blume, Dubna Aug. 2012
Weak Decay Topologies
V0 Topology (K0s, Λ):
Ξ- (Cascade) Ω- Topology:
Christoph Blume, Dubna Aug. 2012

60. Strangeness Production in π+p-  K0 p +
Associated production:
Christoph Blume, Dubna Aug. 2012

61. Reconstruction via Decay Topology
NA49
NA57
NA57
Christoph Blume, Dubna Aug. 2012

62. Armenteros-Podolanski Plot
Christoph Blume, Dubna Aug. 2012

63. Invariant Mass Spectra (K0s, -, - )
Entries
minv(+,-) (GeV/c2)
Entries -
K0s
Christoph Blume, Dubna Aug. 2012