Download Aspects of Heavy-Ion Collisions with the FOPI detector at SIS Energies

Overview of Relativistic HeavyIon Collisions
at SIS Energies
고려대학교
홍병식
12-8-2002
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Schematic Understanding of the Relativistic HI Collisions
Evolution
PreThermalization
equilibrium
QGP?
Mixed phase
Hadronization
(Freeze-out)
+
Expansion
Compression
Thermalization
V>0.9c
Some of the energy they had before is transformed into heat
and
new particles right here
!
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Nuclear Phase Diagram
T(MeV)
Early Universe
(RHIC)
Quark-Gluon Plasma
~150
Phase Transition
SIS explores
Nonperturbative
regime of QCD
Hadron Gas
Atomic Nuclei
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Color Superconductor
Neutron Star
~10
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Density(n0)
3
HE Heavy-Ion Accelerators
Accelerator
c.m. Energy
(GeV)
Status
SIS 18
(GSI, Germany)
2A
(A=mass number)
Running
AGS
(BNL, USA)
5A
Finished
SIS 200
(GSI, Germany)
8A
Just approved; Plan
to run from ~2010
SPS
(CERN, Switzerland)
20A
Finish soon
RHIC
(BNL, USA)
200A
Running since 2000
LHC
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(CERN, Switzerland)
5500A
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Plan to run from
4
~2007
Heavy-Ion Collisions at SIS
• Properties of hot and dense nuclear matter
by studying
– Nuclear Equation-of-State (EoS)
– In-medium properties of hadrons
 Test of QCD
• Experimental Observables
–
–
–
–
–
Nuclear stopping phenomenon
Nonstrange meson production
Collective flow
Strangeness production
Comparison to various models
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Experiments at GSI
HADES
CBM
KaoS
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FOPI
6
FOPI Setup
[email protected]
1 K- in 104 events
-IPNE Bucharest, Romania
-ITEP Moscow, Russia
-CRIP/KFKI Budapest, Hungary
-Kurchatov Institute Moscow, Russia
-LPC Clermont-Ferrand, France
-Korea University, Seoul, Korea
-GSI Darmstadt, Germany
-IReS Strasbourg, France
-FZ Rossendorf, Germany
-Univ. of Heidelberg, Germany
-Univ. of Warsaw, Poland
-RBI Zagreb, Croatia
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KaoS Setup
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PID & Detector Acceptance
Examples of FOPI
Ru+Ru at 400A MeV
Phase-space covered
by the FOPI detectors
p
dE/dx vs p/Z in drift chambers
Bethe-Bloch parameterization
Additional use of plastic to differentiate Z
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Collision Centrality
Peripheral
Central
• FOPI invented the
Erat variable which
is extremely
sensitive,
especially, for the
most central
collisions.
E

E
 ,i
Erat
i
||,i
i
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Particle Spectra
B. Hong et al., (FOPI)
Phys. Rev. C66, 034901 (2002)
Ru+Ru at 400A MeV
• Two independent
detectors (CDC and
HELITRON) give
identical results.
• Nice backward and
forward symmetry
• Dotted lines: fit
functions by the
SiemensRasmussen blast
model
– PRL 42, 880(1979)
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Particle Spectra
free
 NN   NN
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Stopping
Mean rapidity shift of
protons defined by
0( )
y p 

| y ( 0 )  yt ( b ) | (
 ( 0 )
0( )

 ( 0 )
(
dN
(0)
)
dy
dy ( 0 )
dN
(0)
)
dy
dy ( 0)
where yb(yt) is the
beam(target) rapidity
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Stopping
Introduce a new
variable to test a
nuclear transparency
Rp 
N yRu Zr
N yZr  Ru
We use the heaviest
isobaric nuclei
available(9644Ru & 9640Zr)
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B. Hong et al., (FOPI)
Phys. Rev. C66, 034901 (2002)
Stopping
0.4A GeV Ru(Zr)+Ru(Zr)
• Experimental data
support the
transparency
scenario.
• We need higher
energy data to
figure out which
model is valid:
– More stopping
(CBUU model)
– More
transparency
(IQMD model)
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B. Hong et al., (FOPI)
Nucl. Phys. A 721, 317c (2003)
Stopping
1.5A GeV Ru(Zr)+Ru(Zr)
• Rp steeper
– More transparency
• Trend predicted
by IQMD.
• Absolute values of
Rp are not
described
quantitatively.
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Stopping
0.4A GeV Ru(Zr)+Ru(Zr)
Zr+Zr
Ru+Ru
2Ny Ny
mix
R
Z

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N
ZrZr
ZrZr
y
Ny
RuRu
Ny
RuRu
d
N
d
projectile
traget
y
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( 0)

(0) d
1
(1  0.437 y )
2
d
N
y
( 0)
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Stopping
1.5A GeV Ru(Zr)+Ru(Zr)
2Ny Ny
mix
R
Z

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N
ZrZr
ZrZr
y
Ny
projectile
traget
RuRu
Ny
RuRu
dN
d
y
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(0)

(0) d
1
(1  0.856 y ) N( 0)
2
dy
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Comparison
Eb(GeV)
dyp/yb
Nf 1)
Nb 2)
Mpr 3)
0.4A
0.256
9.46
6.14
0.21
1.5A
0.258
23.4
9.70
0.41
Remark
More
Transparent
1) Number of projectile nucleons in forward hemisphere
2) Number of projectile nucleons in backward hemisphere
3) Mixing parameter: more transparent for a larger Mpr
N

M
N
f
 Nb
f
 Nb
pr
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Collective Flow
Reaction plane
reaction plane
transverse plane
(at midrapidity)
v1<0
v1 >0
sideward flow
v2<0
v2 >0
elliptic flow
z
y
x
Fourier expansion of azimuthal
distribution gives the phase
space distribution w.r.t. the
reaction plane.
     R
d 3N
 (1  2v1 cos( )  2v 2 cos( 2 )  ...)
pt dpt dyd 
S. Voloshin & Y. Zhang, Z. Phys. C70, 665 (1996)
px
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J.Y. Ollitrault,
Nucl. Phys. A638, 195c (1998)
= v1 pt
RN=(1+ v2)/(1-v
20 2)
Sideward Flow –integrated
FOPI Collaboration,
Phys. Rev. C67, 034907 (2003)
• pt integrated sideward
flow is sensitive to
– EoS
– MDI (especially at
projectile rapidity)
– σNN (especially at low
beam energies less than
~100A MeV)
• SM(soft EoS with MDI)
well describe data
• Better agreement for
larger collision system
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Sideward Flow –differential
• Differential directed
flow (DDF) for
– Au+Au collisions at
400A MeV
• DDF shows a clear
sensitivity on the
EoS.
• IQMD deviates at
large y and large pt
for Z=1.
• SM(soft EoS with
MDI) well describe
data.
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Sideward Flow -warning
• IQMD fails to reproduce
the measured integrated
sideward flow for Z=2
particles at 90A MeV
• Remember that IQMD
also fails to reproduce
the centrality
dependence of the
nuclear stopping for
Ru+Ru at 400A MeV
– previous slides
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Elliptic Flow -systematic study
FOPI Collaboration,
Nucl. Phys. A679, 765 (2001)
Centrality
dependence
Eb dependence
pt dependence
A dependence
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Elliptic Flow –transition energy
• Our data agree
well with the
Plastic Ball data.
• Transition from
in-plane to outof-plane
azimuthal
enhancement
near 100A MeV
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Elliptic Flow -comparison
• Model cannot explain the experimental
observation.
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Strangeness Production
• Motivation (reminder)
– Study
• the in-medium effect
due to the chiral
symmetry restoration

• Equation-of-State
– By using
• the production yields
• the momentum
distribution
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Phase-space distribution
Ni+Ni 1.93A GeV
central (b≤4.4 fm)
KaoS Collaboration, Phys. Lett. B 495, 26 (2000)
non-central
Isotropic thermal source
1 d 3
Fit function : 2 3  exp( mT / T )
mT dp
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FOPI measures the target rapidity region:
Eur. Phys. J. A9, 515 (2000)
Nucl. Phys. A 625, 307 (1997)
K-/K+ Ratio
RBUU calculation by
E.Bratkovskaya,
W.Cassing (Giessen)
similar trends by
G.Q.Li (Stony Brook)
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with
without
in-medium potentials
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Equivalent Energy Analysis
KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997)
Ni+Ni at various beam energies
 Use equivalent beam energies to correct
for different production thresholds
 1.0 GeV/u for K+
 1.8 GeV/u for K each corresponds to
s  sth  0.23GeV
40° < θlab < 48°
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 K+ yield at 1.0 GeV/u is almost
the same as K- yield at 1.0 GeV/u.
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Equivalent Energy Analysis
KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997)
Considering the pp→K+/-+X
cross section, there is about
factor of 7 enhancement in
K- production in medium.
Parameterizations by
H. Müller, ZPA353, 103 (1995)
Indicates the importance of the multiple
collisions for the strangeness production
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Determination of the EoS
KaoS Collaboration, Phy. Rev. Lett. 86, 39 (2001)
 Comp. between Au+Au & C+C
① Purpose: disentangle soft EoS
effect and in-medium effect
② Baryon density (ρB) depends on
the nuclear compressibility
③ Au+Au will reach much higher ρB
④ Subthreshold K+ production by
multiple scattering means ~ρB2 at
least → will increase the K+ yield
in larger collision system → more
important at lower beam energies
⑤ But UKN depends linearly or less
than linearly on ρB → will reduce
the K+ yield in larger collision
system
 MAuAu/MCC(K+) favors the soft
Equation-of-State.
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Collective Flow of K+ (v1)
Ni+Ni 1.93A GeV
FOPI Collaboration,
Z. Phys. A 352, 355 (1995)
Striking results on
the kaon sideflow
from the FOPI
triggered a lot of
discussions.
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Collective Flow of K+ (v1)
•
K+
sideflow can be
used to study inmedium effect
– Strong ptdependence
– Antiflow w.r.t.
baryons at small pt
– Flow in baryon
direction at large pt
– Magnitude of flow
changes with
collision centrality
– Favors repulsive
potential and
increased kaon mass
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FOPI Collaboration,
Phys. Lett. B486, 6 (2000)
1.7A GeV Ru + Ru
Rapidity interval: -1.2 < y(0) < -0.5
<bgeo>=3.8fm
<bgeo>=2.3fm
RBUU model calculations by
E.Bratkovskaya & W.Cassing
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Collective Flow of K+ (v2)
KaoS Collaboration,
Phys. Rev. Lett. 81, 1576 (1998)
Au+Au 1A GeV
b≤5 fm 5<b≤10 fm
N (90  )  N (90  ) 1  2v 2
R



N (0 )  N (180 ) 1  2v2
b>10 fm
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due to the absorption
due to the scattering
35
Collective Flow of K+ (v2)
RBUU model
calculations by
with in-medium potential
G.Q. Li et al.,
Phys. Lett. B 381, 17 (1996)
without in-medium potential
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F Production
• K+K- invariant mass spectra
FOPI Collaboration,
Nucl. Phys. A714, 89 (2002)
Ni+Ni at 1.93A GeV
-
Φ-yield = K -yield at the same incident energy!
Systematics: Φ/K = 10 - 20 %
Theoretical Expectations: ??
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Long-Term Future
Exploring nuclear matter at the highest-density
B. Friman et al.,
Eur. Phys. J. A3, 165(1998)
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Motivation-Strangeness
Unique maximum in AA
QGP already
at 30A GeV?
When this
enhancement
of hyperons starts?
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Motivation-e+e- pair
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Motivation-Charm
SIS18: strangeness production
near threshold (1-3 n0)
SIS200: charm production near
threshold (5-10 n0)
In-medium effects
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Simple Estimates of Open Charms
PYTHIA calculation for
open charm meson production
Quark-meson Coupling model
Sibirtsev, K. Tsushima, A.W. Thomas,
EPJA6, 351 (1999)
(dc)
(dc)
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Simple Estimates
B. Hong, JKPS43, 685 (2003)
More explicit channel, e.g.,
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More Motivations
• Indications for deconfinement at high baryon
density
– Anomalous charmonium suppression
• Temperature of Hot Nuclear Matter
– Virtual photons decaying into e+e- pairs
• Equation-of-State
– Flow measurement (direct, v2, radial, etc.)
• Critical Point
– Event-by-Event fluctuations
• Color Superconductivity
– Precursor effects at T > TC
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How?
• Accelerator Side
– Require high intensity for rare particle measurements:
~109 ions/sec (cf. ~107 ions/sec at the SPS)
– High spill fraction: 0.8 (cf. 0.25 at the SPS)
• Detector Side
– Identification of hadrons at high momentum with high
track density environment (~1000 for 25A GeV Au+Au)
– Identification of electrons with pion suppression by 104
– 105 (need two electron detectors)
– Reconstruction of particle vertices with high resolution
– Large acceptance
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2nd Generation Fixed Target Exp.
• Magnetic field: 1-2 T
• Silicon Pixel/Strip:
hyperons and D’s
• RICH: electrons, high
momentum pions &
kaons
• TRD: electrons from
the J/Psi decay
• TOF
CBM Detector Concept
– Start: diamond pixel
– Stop: RPC
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Conclusions
• Stopping
– New experimental approach exploiting N/Z shows
incomplete mixing for the most central collisions.
• Collective flow
– Fourier analysis of azimuthal distributions reveals the
detailed event shape over full phase-space.
• Particle Production
– Pion spectra provides an information of the Coulomb
interaction and the modification of the delta-spectral
function.
– Kaon yields and spectra favor the in-medium
modification of kaon masses (it also favors a soft EoS).
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Conclusions –continued• Nuclear EoS is not understood yet.
– But many promising experimental observables such as
collective flow and strangeness production are available
to constrain it.
• Evidence for in-medium effects from strange
particle observables.
– It exists, but more accurate (high statistics) data are
needed.
– But difficult near threshold energy
• Future
– CBM experiments at the future GSI facility
– We can start the CBM experiment in ten years (far future).
– But it takes more than ten years to design and build it.
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