12-8-2002 서울대 핵물리세미나 1 overview of relativistic heavy- ion collisions at sis...

12-8-2002 서울대 핵물리세미나 1

Overview of Relativistic Overview of Relativistic Heavy-Ion Collisions Heavy-Ion Collisions at SIS Energiesat SIS Energies

고려대학교홍 병 식


V>0.9c

Evolution

Hadronization (Freeze-out) + Expansion

Compression Thermalization

Pre-equilibrium

Thermalization QGP? Mixed phase

Some of the energy they had before is transformed into heat and new particles right here !

Schematic Understanding of the Relativistic HI Collisions


Nuclear Phase Diagram

T(MeV)

Density(n0)

~150

~10

Early Universe(RHIC)

Color SuperconductorNeutron Star

Hadron Gas

Quark-Gluon Plasma

Phase Transition

Atomic Nuclei

SIS explores Nonperturbative regime of QCD


HE Heavy-Ion Accelerators

Acceleratorc.m. Energy

(GeV)Status

SIS 18(GSI, Germany)

2A(A=mass number)

Running

AGS(BNL, USA)

5A Finished

SIS 200(GSI, Germany)

8AJust approved;

Plan to run from ~2010

SPS(CERN,

Switzerland)20A Finish soon

RHIC(BNL, USA)

200ARunning since

2000

LHC(CERN,

Switzerland)5500A

Plan to run from ~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


Experiments at GSI

HADES

KaoS

FOPI

CBM


FOPI Setup

HI-Beam

-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

[email protected] K- in 104 events


KaoS Setup


PID & Detector Acceptance

dE/dx vs p/Z in drift chambers Bethe-Bloch parameterization Additional use of plastic to differentiate Z

Ru+Ru at 400A MeVPhase-space covered by the FOPI detectors

p

Examples of FOPI

12-8-2002 서울대 핵물리세미나 10

Collision Centrality

• FOPI invented the Era

t variable which is extremely sensitive, especially, for the most central collisions.

ii

ii

rat E

EE

||,

,

Centr

al Peripher

al

12-8-2002 서울대 핵물리세미나 11

Particle SpectraRu+Ru at 400A MeV

• Two independent detectors (CDC and HELITRON) give identical results.

• Nice backward and forward symmetry

• Dotted lines: fit functions by the Siemens-Rasmussen blast model– PRL 42, 880(1979)

B. Hong et al., (FOPI)Phys. Rev. C66, 034901 (2002)

12-8-2002 서울대 핵물리세미나 12

Particle Spectra

freeNNNN

12-8-2002 서울대 핵물리세미나 13

Stopping

)(0

)0(

)0()0(

)(0

)0(

)0()0()(

)0(

)(

)(||

dydydN

dydydN

yy

ybt

p

Mean rapidity shift of protons defined by

where yb(yt) is the beam(target) rapidity

12-8-2002 서울대 핵물리세미나 14

Stopping

RuZry

ZrRuy

p N

NR

We use the heaviest isobaric nuclei available(96

44Ru & 96

40Zr)

Introduce a new variable to test a nuclear transparency

12-8-2002 서울대 핵물리세미나 15

Stopping

• 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)

B. Hong et al., (FOPI)Phys. Rev. C66, 034901 (2002)

0.4A GeV Ru(Zr)+Ru(Zr)

12-8-2002 서울대 핵물리세미나 16

Stopping

• Rp steeper– More transparency

• Trend predicted by IQMD.

• Absolute values of Rp are not described quantitatively.


B. Hong et al., (FOPI)Nucl. Phys. A 721, 317c (2003)

12-8-2002 서울대 핵물리세미나 17

Stopping

NNNNN

R RuRu

y

ZrZr

y

RuRu

y

ZrZr

y

mix

y

Z

2

yNy

yN

d

d

d

d tragetprojectile

)0(

)0(

)0()437.01(

2

1


Ru+Ru

Zr+Zr

12-8-2002 서울대 핵물리세미나 18

Stopping

yNy

yN

d

d

d

d tragetprojectile

)0(

)0(

)0( )856.01(2

1

NNNNN

R RuRu

y

ZrZr

y

RuRu

y

ZrZr

y

mix

y

Z

2


12-8-2002 서울대 핵물리세미나 19

Comparison

Eb(GeV) dyp/yb Nf 1) Nb

2) Mpr 3) Remark

0.4A 0.256 9.46 6.14 0.21

1.5A 0.258 23.4 9.70 0.41 More Transparent

1) Number of projectile nucleons in forward hemisphere2) Number of projectile nucleons in backward hemisphere3) Mixing parameter: more transparent for a larger Mpr

NNNN

Mbf

bf

pr

12-8-2002 서울대 핵물리세미나 20

Collective Flow

tim

e

reaction plane

transverse plane(at midrapidity)

v2<0 v2 >0 elliptic flow

RN=(1+ v2)/(1-v2)

v1<0 v1 >0sideward flow

px = v1 pt S. Voloshin & Y. Zhang, Z. Phys. C70, 665 (1996)J.Y. Ollitrault, Nucl. Phys. A638, 195c (1998)

Fourier expansion of azimuthal distribution gives the phase space distribution w.r.t. the reaction plane.

...))2cos(v2)cos(v21( 21

3

dyddpp

Nd

tt

R

x

yz

x

yz

x

yz

x

yz

Reaction plane

12-8-2002 서울대 핵물리세미나 21

Sideward Flow –integrated

• 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

FOPI Collaboration,Phys. Rev. C67, 034907 (2003)

12-8-2002 서울대 핵물리세미나 22

Sideward Flow –differential

• Differential directed flow (DDF) for – Au+Au collisions at 40

0A MeV• DDF shows a clear se

nsitivity on the EoS.• IQMD deviates at larg

e y and large pt for Z=1.

• SM(soft EoS with MDI) well describe data.

12-8-2002 서울대 핵물리세미나 23

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

12-8-2002 서울대 핵물리세미나 24

Elliptic Flow -systematic study

pt dependence

Centralitydependence

Eb dependence

FOPI Collaboration,Nucl. Phys. A679, 765 (2001)

A dependence

12-8-2002 서울대 핵물리세미나 25

Elliptic Flow –transition energy

• Our data agree well with the Plastic Ball data.

• Transition from in-plane to out-of-plane azimuthal enhancement near 100A MeV

12-8-2002 서울대 핵물리세미나 26

Elliptic Flow -comparison

• Model cannot explain the experimental observation.

12-8-2002 서울대 핵물리세미나 27

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 distributi

on

12-8-2002 서울대 핵물리세미나 28

Phase-space distributionKaoS Collaboration, Phys. Lett. B 495, 26 (2000)

Ni+Ni 1.93A GeVNi+Ni 1.93A GeV central (b≤4.4 fm)non-central

)/exp(1

3

3

Tmdp

d

m TT

Fit function :

Isotropic thermal source

2

12-8-2002 서울대 핵물리세미나 29

K-/K+ Ratio

withwithout

in-medium potentials

RBUU calculation byE.Bratkovskaya, W.Cassing (Giessen)similar trends byG.Q.Li (Stony Brook)

FOPI measures the target rapidity region:Eur. Phys. J. A9, 515 (2000)Nucl. Phys. A 625, 307 (1997)

12-8-2002 서울대 핵물리세미나 30

Equivalent Energy Analysis KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997)

Ni+Ni at various beam energies

40° < θ lab < 48°

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

GeVss th 23.0

K+ yield at 1.0 GeV/u is almost the same as K- yield at 1.0 GeV/u.

12-8-2002 서울대 핵물리세미나 31

Equivalent Energy AnalysisKaoS 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

12-8-2002 서울대 핵물리세미나 32

Determination of the EoS 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 ~ρB

2 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.

KaoS Collaboration, Phy. Rev. Lett. 86, 39 (2001)

12-8-2002 서울대 핵물리세미나 33

Collective Flow of K+ (v1)

FOPI Collaboration,Z. Phys. A 352, 355 (1995)

Ni+Ni 1.93A GeV

Striking results on the kaon sideflow from the FOPI triggered a lot of discussions.

12-8-2002 서울대 핵물리세미나 34


• K+ sideflow can be used to study in-medium effect– Strong pt- dependence– 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

FOPI Collaboration,Phys. Lett. B486, 6 (2000) 1.7A GeV Ru + Ru

RBUU model calculations by E.Bratkovskaya & W.Cassing

<bgeo>=3.8fm <bgeo>=2.3fm

Rapidity interval: -1.2 < y(0) < -0.5

12-8-2002 서울대 핵물리세미나 35

Collective Flow of K+ (v2)KaoS Collaboration,Phys. Rev. Lett. 81, 1576 (1998)

Au+Au 1A GeV

2

2

21

21

)180()0(

)90()90(

v

v

NN

NNR

b≤

5 fm

5<

b≤

10 fm

b>

10 fm

due to the absorption

due to the scattering

12-8-2002 서울대 핵물리세미나 36


RBUU model calculations by

G.Q. Li et al.,Phys. Lett. B 381, 17 (1996)

with in-medium potential

without in-medium potential

12-8-2002 서울대 핵물리세미나 37

Production• K+K- invariant mass spectra

Ni+Ni at 1.93A GeV

Φ-yield = K--yield at the same incident energy! Systematics: Φ/K- = 10 - 20 % Theoretical Expectations: ??

FOPI Collaboration,Nucl. Phys. A714, 89 (2002)

12-8-2002 서울대 핵물리세미나 38

Long-Term FutureExploring nuclear matter at the highest-density

B. Friman et al.,Eur. Phys. J. A3, 165(1998)

12-8-2002 서울대 핵물리세미나 39

Motivation-Strangeness

When this enhancement of hyperons starts?

QGP already at 30A GeV?

Unique maximum in AA

12-8-2002 서울대 핵물리세미나 40

Motivation-e+e- pair

12-8-2002 서울대 핵물리세미나 41

Motivation-Charm

SIS18: strangeness production near threshold (1-3 n0)SIS200: charm production near threshold (5-10 n0)In-medium effects

12-8-2002 서울대 핵물리세미나 42

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)

12-8-2002 서울대 핵물리세미나 43

More explicit channel, e.g.,

Simple EstimatesB. Hong, JKPS43, 685 (2003)

12-8-2002 서울대 핵물리세미나 44

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

12-8-2002 서울대 핵물리세미나 45

How?

• Accelerator Side– Require high intensity for rare particle measurements: ~10

9 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

12-8-2002 서울대 핵물리세미나 46

2nd Generation Fixed Target Exp.

• Magnetic field: 1-2 T• Silicon Pixel/Strip: hyp

erons and D’s• RICH: electrons, high

momentum pions & kaons

• TRD: electrons from the J/Psi decay

• TOF– Start: diamond pixel– Stop: RPC

CBM Detector Concept

12-8-2002 서울대 핵물리세미나 47

Conclusions

• Stopping– New experimental approach exploiting N/Z shows incomplet

e mixing for the most central collisions.

• Collective flow– Fourier analysis of azimuthal distributions reveals the detail

ed event shape over full phase-space.

• Particle Production– Pion spectra provides an information of the Coulomb interac

tion 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).

12-8-2002 서울대 핵물리세미나 48

Conclusions –continued-

• Nuclear EoS is not understood yet.– But many promising experimental observables such as collec

tive 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.

12-8-2002 서울대 핵물리세미나 1 overview of relativistic heavy- ion collisions at sis...

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