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Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Nuclear Matter
Course IProperties of strongly interacting systems
Course IICreating and investigating nuclear matter under extreme conditions
Joachim Stroth, GSI/Univ. Frankfurt
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Discovery of the Micro-Cosmos
It all started with the observation of Radioactivity. In the late 19th Century Henri Becquerelle discovered Ionising Radiation emerging from Uranium. We now know that and -Rays stem from transitions in the nucleus. This event can be viewed as the birth of Nuclear Physics.
Further Discoveries:
– In Cathode Rays:Electron (Thompson)
– In Cosmic Rays:Positron, Myon (Anderson), Pion (Powell)
– With Accelerators:Anti-Proton, and and and
Decay patterns for the dacay of pions of the type + + + e+ + 3
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Atomic Nucleus
Ernest Rutherford, the real father of nuclear physics found something very heavy and tiny in the interior of atomic nuclei.
The observed angular distribution of -particles was in agreement with the assumption of pure electromagnetic scattering off an object with
– M >> M
– R < 3 10 –14 m
The probability for an interaction can be calculated for thin targets:
%3g200
106.0
cm
g1cm1010d
24
2224
mol
A
mol
AAu =×
×===== −
MN
xM
NMA
NAA
AP ρσσσ
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Electron Beam as Particle Microscope
Scattering of electrons off point-like objects is ...
.. excellently described by:
Exchange of PhotonsExchange of Photons
⎟⎠
⎞⎜⎝
⎛ −=Ω 2
sin1)(
)(4d
d
Formula-Mott
224
22 θ
βσ
qc
EZe
ee
e
EEv
ppq
′−=
′−=
e
E,pE´,p´
Z
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Charge Distribution of Nuclei
Experiments on elastic scattering of Electrons at Energies of < 1 GeV ( 0.2fm)
22 )(d
d
d
d
Mott
qFΩ
=Ω
σσ
Nobel Price Nobel Price in Physics 1961in Physics 1961
HofstaedterHofstaedter
e e
Z
Fourier-Transform ofthe Form Factor yields the Charge DistributionCharge Distribution
Pb
Ca
0 2 4 6 8 10R [fm]
0.02
0.08
ρ [f
m-3]
[Grad]
dσ/
dΩ[
rel.
Ein
h.]
20 30 40 50 60
100
10-2
10-4
10-6
10-8
10-10
48Ca
40Ca
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Struktur des Nukleons
Experiments with Electron Beams at the SLAC up to 20 GeV ( 0.1fm)
Essential Observations:
– Nucleons do have diffuse surfaces
– Nucleons can be transformed into excited states
– Nucleons are composite particles which contain point-like constituents
Nobel Price 1990Nobel Price 1990
Kenndall, Friedmann, TaylorKenndall, Friedmann, Taylor
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Constituents of the Atomic Nucleus
<qq> 0
<qq> = 0
Protons
Neutrons
up- and down-Quarks
Gluons and virtual Quarks and Anti-Quarks
R 1fm; m 1GeV
Nucleus (R 1-10 fm)
R < 10-4 fm; m 10 MeV
Strong Interaction: QCD
99.9% of the Matter around us 99.9% of the Matter around us consits out of Nucleonsconsits out of Nucleons
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Nucleon is a Complex Object
Hadrons are very complex excitations of valence quarks in the present of quark and gluon condensates.
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Particle ZooAccording to current understanding point-like particles
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Nature of the Strong ForceAlong the successful description of electro-weak interaction by gauge theory, the strong interaction can be described by the exchange of gluons.
Property QED QCD
Charge electric colour
Bosons photon(carries no charge)
gluons(carry charge)
Mass of boson 0 0
Screening reduces bare charge
amplifies bare charge
Strength s= 25
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
QCD: Confinement
If the distance between two quarks gets larger, more and more gluons contribute to the interaction between the quarks. Hence the potential energy grows with increasing distance.At some point, enough energy is stored in the field to produce a pair of quarks out of the vacuum.
Krr
crV s +−=
34
)(hα
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Origin of Matter
Criteria of Sacharov for the cre-ation of matter out of radiation:
C and CP ViolationThe decay rate of quarks and anti-quarks are different
Violation of Baryon Number ConservationLeptons decay in quarks and vice versa
No thermal equillibriumB=0 if baryon number is not onserved
10-43s
10-10s
10-34s
GUT
QGP
Hadronisation
t
x
Matter was produced about 1 s second after the Big Bang
Since particles are always produced in pairs, why is there only matter and no anti-matter left
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Production of Heavy Nuclei
In the Bing Bang only the light-est nuclei could be formed !
Production of heavier nuclei:
– Thermonuclear burning in starsup to Iron !
– Supernova Explosions:Neutron absorbtion with subsequent beta-decay !
• r-processNeutron Drip Line
• s-process
1 10
1E-90
1E-80
1E-70
1E-60
1E-50
1E-40
1E-30
1E-20
1E-10
1
HAGEDORNProduction in Secondary Reaction
Rel
ativ
e Y
ield
Atomic Mass Number
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Nuclear Matter has Exotic Properties
Let‘s quote some macroscopic properties of Nuclear Matter
Nuclear matter is extremely heavy 280 Million Tons per cm280 Million Tons per cm33
– Less than a mm3 is enough to built an aircraft carrier.
– However, if one would burn it completely, the energy gain would be equivalent to 50 GW for a whole year.
Although we know Nuclear Matter only in small portions inside atoms, it exists in nature also in big portions:
– Neutron Stars have a diameter of typically 10 km.
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Equation of State
Around normal nuclear ground-state density the compressibility can be determined from Giant Monopole Resonances.
At higher densities the proper-ties can only be extracted from experiment on the basis of theoretical models.
Conditions: E/A(ρ) = -16 MeV
(E/A)(ρ)/ρ
Compressibilityρ(E/A)/ ρ200 - 400 MeV
Com
pre
ssio
nal
En
ergy
E/A
Density
hard EoS = 380 MeVsoft EoS = 200 MeV
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Effective Interactions between Nucleons
Hideki Yukawa described in 1934 the force between nucleons as an exchange of virtual particles. If the exchanged particles carry mass, the range of the interaction is finite:
⎭⎬⎫
⎩⎨⎧−=
hmcr
r
grV exp
4)(
2
π
fm7.0MeV1372
fmMeV20022
2 ≈×
≈→≈Δ→≈ΔΔ Dhh ctcmctE
Meson Mass[MeV]
TypeI[JP]
140 1[0-]
σ 400-1200 0[0+]
ρ 770 1[1-]
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Nuclei can be described assuming nucleons moving independently in a mean nuclear potential:
– PhenomenologicalSquare-well, Harmonic, Woods-Saxon
– Self-consistentHartree-Fock
The Formation of Nuclei
Nuclei form because of the strong effective interaction between nucleons. Although this „residual“ interaction is weaker than the bare strong force between quarks and gluons, it still overcomes Coulomb repulsion of protons by far.
⎟⎟⎠
⎞⎜⎜⎝
⎛⎥⎦
⎤⎢⎣
⎡ −+
=
d
arrV
exp1
1)(
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Nucleus as a Liquid Drop
The nucleus in the ground state is cold Fermi liquid. At moderate excitation energies (E/nucleon << EB) nuclei behave like little droplets of water.
The Coulomb Barrier:
Potential energy of two touching spheres (if r=R0)
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Heating Nuclear Matter
Nuclei store additional energy by transfering nucleons into levels between the Fermi-surface and the barrier:
– Single Particle excitations
– Collective Excitations
It can thermalize by forming a Compound Nucleus
And cool down by
– (Fragmentation)
– Particle Decay (,p,n)
– Electromagnetic transitions ()
At E/A of 5 MeV the nuclei transform to a gas of nucleons.
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Hadronic Matter
Nucleons are composite particles and can therefore transform into excited states. Is the temperature of nuclear matter high enough, internal degrees of the nucleons are excited.
e.g.: N + N = N + Δ= N + N +
These excited states are often called resonances, since their decay width is rather large (due to the strong interaction).
ρ
k,
p,n
N(1440)
N(1520)
M[GeV]
0
1
a1
Mesonen
Baryonen
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Melting of Resonances
Exiting nucleons by inelastic electron scattering
– on liquid hydrogen (protons):Resonances are clearly visible (most prominent the Δ33)
– on nuclei:no higher-lying resonances seem to survive
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
QCD: Spontaneous Breaking of Chiral Symmtery
The groundstate of QCD is characterized by a non-vanishing field of quark – anti-quark pairs, the so-called chiral condensate.
This is a non-perturbative effect of QCD
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
ρ
k,
p,n
N(1440)
N(1520)
M[GeV]
0
1
a1
Vakuum<qq> 0
Mesonen
Baryonen
ρ
k,
p,n
N(1440)
N(1520)
M[GeV]
0
1a1
Vakuum<qq> > 0
Mesonen
Spontaneously Broken Chiral Symmetry
How can almost massless quarks combine to hadron with a mass of typicall 1 GeV and more?
The ground state of QCD is spotaneously broken – the vaccum is filled by a condensate of scalar quark – anti-quark pairs!
Light mesons (M<<1 GeV), , K
No parity doubletts M(ρ) M(a1)
The bare quarks gain dynamically mass by coupling to the quark – ant-quark pairs.
ρ
k,
p,n
N(1440)
N(1520)
M[GeV]
0
1
a1
Vakuum<qq> 0
Mesonen
Baryonen
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Probing the Chiral Condensate
Expectation value of the chiral condensate in a simplified model, as a function of baryon density and temperature of nuclear matter.Already in ordinary nuclei the condensate is reduce as compared to vacuum.
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Medium Modifications of Hadrons
Spectral function of the ρ-meson in medium
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Quark-Gluon Phase of Nuclear Matter At very high energies and/or densities quarks are deconfined
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Characteristic Energy Regimes
Heavy Ion Accellerators around the world
Coulomb Barrier
Fermi-Energy Regime
Resonance Matter
Quark-Gluon Matter
E/nucl. [GeV] 0,01 0,1 10 100 10000
Tandems, Linacs
Cyclotrons Synchrotrons (recently also colliders)
Many Univ. and Instituts
GANIL, MSU, RIKEN
GSI(SIS), LBL(Bevalac),
BNL(AGS)
CERN(SPS) BNL(RHIC), CERN(LHC)
in 2006
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Dissipative Collisions
In a kinematically complete experiment the following obsevables are derived:
– T CM scattering angle
– TKEL Total Kinetc Energy Loss
– MR,E Mass of Recoil Ion and Ejectile
The data show evidence for a smooth transfer of collective energy of motion into internal degrees od freedom
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Multi-Fragmentation
The ALADIN Experiment!Projectile Fragmentation in inverse Kinematics
– Forward focusing (4 detection)
– No detector Thresholds
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Liquid-Gas Phase Transition
Results of the ALADIN collaboration show evidence for transition from a liquid to a vapour phase of nuclear matter.
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Creating Nuclear Fireballs
At energies above a few 100 MeV/u the non-overlapping parts of the nuclei are abraised and continue on straight trajectories.
Nucleons in these „pole caps“ are called spectators.
The nucleons in the overlapp zone form the fireball and are called participants.
A correlation plot of the two helps to select impact parameter, which is no direct observable:
– ZSUM (Small Angle Hodoscope) Sum of all Charge
– M (Large Angle Hodoscope) Multiplicity
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Cross Properties of Expanding Fireballs
A nuclear fire ball is a hot, rapidly expanding gas of hadrons.
Below some critical density, all collisions between the particle stop and the system freezes out.
In the spectrometer all particles are identified by their mass and charge.
From the spectral shape it can be inferred, that the energy of the particles is composed of a thermal and collective part
Kinetic Energy of a Particle:Ek = Eth + Eflow = 3/2 kT + m/2flow2
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
A Typical 4 Experiment
Particle IDentification:
– Momentum from the bending in a magnetic field
– Chargeby Ionization Power
– Mass from time-of-flight (combined with momen-tum measurement)
Z
pB =ρ
2
d
dZ
x
E∝
p
m =
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Particle Spectra
The emission pattern of part-icles show a rich structure if correlated with the reaction plane.
[ ])2cos(2)cos(21d
d21 Ψ+Ψ+∝
Ψvv
σ
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Creation of New Particles (Resonance Matter)
Short-lived particles (resonances) can be detected via particle correlations.
Observable Invariant Mass
e.g.: N+N N+Δ33 N+N+∑== iinv pPPPM ;νμ
Resonance
Mass[MeV]
I(JP)
P11 1440 ½(½+)
D13 1520 ½(1½-)
S11 1535 ½(½-)
P33 (Δ33) 1232 1½(1½+
)
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Pions are Complicated
The pion is the lightest hadron. Its existence in nuclear matter is tightly linked to the excitation of the Δ33 resonance.
Data described by „two temperatures“ fit
⎥⎦⎤
⎢⎣⎡+⎥⎦
⎤⎢⎣⎡∝
22
113
3
expexpdp
dT
ECTEC
σ
Δ33
hole
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Strangeness Production
The KAOS Spectrometer features a compact dipole combined with a large quadrupole to enlarge acceptance.Various focal-plane detectors allow a dedicated kaon trigger.
At 1 AGeV the energy in a single nucleon nucleon is not sufficient to produce kaons.
In contrast to pion production is the kaaon production rising as the number of participating nucleons increases.
Clear evidence for multi-step production mechanism
N K+, ΔN K+N
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Medium Modification of KaonsIn medium kaons/anti-kaons experience a density dependent potential which lowers/increases their effective mass. Hence the production of anti-kaons close to the production threshold is enhanced.
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
A Thermal Model for the Fireball
The Thermal Model assumes that all particles stem from a thermalized fireball, where all inelastic collisions stop at the same temperature.
By adjusting only two parameters, the baryon chemical potential and the temperature, relative particle yields can be explained.
( )∫
⎭⎬⎫
⎩⎨⎧ ±−−
=1
1exp
d
2
2
2
iSiBi
ii
SBET
ppg
μμπ
ρ
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Central Collision of two Gold NucleiAbout 95% of the velocity of light
Simulation: Univ. Frankfurt, Institut für Theoretische Physik
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
p
n
Δ++
K
ρ= 2-3ρ0
T < 100 MeV
e.g. Au+Au @ 1 GeV/u
Probing the Interior of Fire Balls
p
e+
e-
ρ
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The HADES-Spectrometer
GeometryGeometry
inin
Online Pattern RecognitionOnline Pattern Recognition
RICH (Ring Imaging Cherenkov
Detectors)
TOF (Organic Scintillators)
SHOWER (Lead-Shower Detector)
TrackingTracking
ILSE (Super Conducting Magnet)
MDC (Multiwire Drift Chambers)
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Low-mass Dilepton Pairs
Sensitive to changes of in-medium properties of vector mesons (restoration of chiral symmetry)
Experimental findings:
– Strong enhancement of lepton pairs below the vector meson region
– Enhancement already at Bevalac energies
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Multistrange Hyperons
Strangeness enhancement in the QGP should influence in particular the production of multi-strange baryons (hyperons).
Strong enhancement of Ω over over found (ΩΩ : AA/pp = 17/1 : AA/pp = 17/1)
WA97 F. Antinori et al, Nucl. Phys. A 661 (1999) 130c
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Suppression of Charmonium
Anomalous suppression if screening in a deconfined phase occurs.
– Effect establishes as a function of centrality
NA50
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Composition of a Neutron Star
Each arrow indicatesa different model for the neutron star
Each model represents an other EOS
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
The Phase Diagram of Nuclear Matter …
... yet another version
Nuclear MatterJoachim Stroth, GSI/Univ. Frankfurt
Experimental Concept
Detector components: Detector components:
1. magnet (1-2T)
2. Silicon pixel/strip detectors:
, , , Ω
3. RICH: particles with = 10-100:
electrons, (pions, kaons)
4. TRD: electrons ( 2000): J/
5. TOF-start (diamond pixel
detector) and TOF-stop (RPC):
particle identification
( pions, kaons, protons, …)
1.-5. needed for D mesons
Trigger:Trigger:1. level: reactions, centrality, hits in TRD and
RICH2. level: electrons, momentum, hit matching,
rings in RICH3. level: displaced vertex