Modern Nuclear Physics with STAR @ RHIC:

Recreating the Creation of the Universe

Rene BellwiedRene Bellwied

Wayne State UniversityWayne State University((bellwied@physics.wayne.edubellwied@physics.wayne.edu))

Lecture 1: Why and How ?Lecture 1: Why and How ? Lecture 2: Bulk plasma matter ?Lecture 2: Bulk plasma matter ? Lecture 3: Probing the plasmaLecture 3: Probing the plasma

Let there be light The Hertzsprung-The Hertzsprung-

Russell DiagramRussell Diagram Relation betweenRelation between mass mass

andand temperature, light temperature, light output, lifetime.output, lifetime.Stars shine because of Stars shine because of nuclear fusion reactions in nuclear fusion reactions in their core. The more their core. The more luminous they are, the luminous they are, the more reactions are taking more reactions are taking place in their cores.place in their cores.

Doppler Effect with Stars A star's motion causes a wavelength shift in its light A star's motion causes a wavelength shift in its light

emission spectrum, which depends on speed and emission spectrum, which depends on speed and direction of motion. direction of motion.

If star is moving If star is moving towardtoward you, the waves are you, the waves are compressed, so their wavelength is compressed, so their wavelength is shorter = shorter = blueshiftblueshift. .

If the object is moving If the object is moving awayaway from you, the waves are from you, the waves are stretched out, so their wavelength is stretched out, so their wavelength is longer = longer = redshiftredshift. .

Relativity and Universe Expansion

The doppler effect tells you about the The doppler effect tells you about the relativerelative motion motion of the object with respect to you. of the object with respect to you.

Important fact:Important fact: The spectral lines of nearly all of the galaxies in the The spectral lines of nearly all of the galaxies in the

universe are shifted to the red end of the spectrum. universe are shifted to the red end of the spectrum. This means that the galaxies are moving away from This means that the galaxies are moving away from

the Milky Way galaxy.the Milky Way galaxy. This is evidence for the expansion of the universe. This is evidence for the expansion of the universe.

Uniform Expansion

The The Hubble lawHubble law, speed = , speed = HHoo × distance, says the × distance, says the

expansion is uniform. expansion is uniform. The The Hubble constantHubble constant, , HHoo,, is the slope of the line is the slope of the line

relating the speed of the galaxies away from each relating the speed of the galaxies away from each other and their distance apart from each other. other and their distance apart from each other. It indicates the rate of the expansion. It indicates the rate of the expansion. If the slope is steep (large If the slope is steep (large HHoo),), then the expansion rate then the expansion rate

is large and the galaxies did not need much time to get is large and the galaxies did not need much time to get to where they are now. to where they are now.

Hubble Law

Hubble and Humason (1931): Hubble and Humason (1931): the Galactic recession speed = the Galactic recession speed = HH × distance, × distance,

where where HH is a number now called the is a number now called the Hubble Hubble constant.constant.

This relation is called the This relation is called the Hubble LawHubble Law and the and the Hubble constantHubble constant is the slope of the line. is the slope of the line.

Age of the Universe

Age of the universe can be estimated from the simple Age of the universe can be estimated from the simple relation of relation of time = distance/speed.time = distance/speed.

The Hubble Law can be rewritten The Hubble Law can be rewritten 1/1/HHoo = distance/speed. = distance/speed.

The Hubble constant tells you the age of the universe, The Hubble constant tells you the age of the universe, i.e., how long the galaxies have been expanding away i.e., how long the galaxies have been expanding away from each other: from each other: Age = 1/Age = 1/HHoo. .

Age upper limit since the expansion has been slowing Age upper limit since the expansion has been slowing down due to gravity. down due to gravity.

Evidence for the Big Bang Galaxies are distributed fairly uniformily across the sky Galaxies are distributed fairly uniformily across the sky

between a lot of void (Obler’s paradox)between a lot of void (Obler’s paradox) Background radiation was predicted, and has been found, Background radiation was predicted, and has been found,

to be exactly 2.73 K everywhere in the universe. to be exactly 2.73 K everywhere in the universe. Variations as measured by a NASA satellite named COBE Variations as measured by a NASA satellite named COBE (Cosmic Background Explorer) are less than 0.0001 K.(Cosmic Background Explorer) are less than 0.0001 K.

Star Count in the Galaxy RoughRough guess of the number of stars in our guess of the number of stars in our

galaxy obtained by dividing the Galaxy's galaxy obtained by dividing the Galaxy's total mass by the mass of a typical star (e.g., total mass by the mass of a typical star (e.g., 1 solar mass). 1 solar mass). The result is about 200 billion stars! The result is about 200 billion stars!

The actual number of stars could be several The actual number of stars could be several tens of billions less or more than this tens of billions less or more than this approximate value.approximate value.

All of these numbers are based on All of these numbers are based on luminous matter !luminous matter !

A Mass Problem The stars and gas in most galaxies The stars and gas in most galaxies

move much quicker than expected move much quicker than expected from the luminosity of the galaxies. from the luminosity of the galaxies.

In spiral galaxies, the rotation curve In spiral galaxies, the rotation curve remains at about the same value at remains at about the same value at great distances from the center (it is great distances from the center (it is said to be ``flat''). said to be ``flat'').

This means that the enclosed mass This means that the enclosed mass continues to increase even though continues to increase even though the amount of visible, luminous the amount of visible, luminous matter falls off at large distances matter falls off at large distances from the center. from the center.

Something else must be adding to the gravity of the Something else must be adding to the gravity of the galaxies without shining. We call it Dark Matter ! galaxies without shining. We call it Dark Matter ! According to measurements it accounts for 90% of the According to measurements it accounts for 90% of the mass in the universe.mass in the universe.

The Hubble Key Project determined in 2000 how fast the universe is expanding. The group concluded that the universe is expanding at a rate of 74 km/sec/megaparsec (one parcsec is 3.26 light-years) with an uncertainty of 10%.

The universe is accelerating ???Based on supernovae measurements

Dark Energy – the new puzzle of physics

What is Dark Matter ? We don’t know (yet)

White dwarfs, brown dwarfs, black holes, massive neutrinos, White dwarfs, brown dwarfs, black holes, massive neutrinos, although intriguing are very unlikely to account for most of the although intriguing are very unlikely to account for most of the dark matter. The dwarfs are generally called Massive compact dark matter. The dwarfs are generally called Massive compact halo objects (MACHOS)halo objects (MACHOS)

New exotic particles or formations are more likely:New exotic particles or formations are more likely: Weakly interacting massive particles (WIMPS)Weakly interacting massive particles (WIMPS) Matter based on exotic quark configurations (e.g. Matter based on exotic quark configurations (e.g. strange strange

Quark matterQuark matter))

If these states exist somewhere in the universe If these states exist somewhere in the universe wouldn’t they have been produced in the early wouldn’t they have been produced in the early universe ?universe ?

Where did it all start ?

Witten’s ‘Cosmic Separation of phases’ Witten’s ‘Cosmic Separation of phases’ (Phys.Rev.D 30 (1984) 272) and his idea of (Phys.Rev.D 30 (1984) 272) and his idea of strange quark matter. strange quark matter.

The impact on cosmology might be far reaching The impact on cosmology might be far reaching and definitely affected the search for strangeness and definitely affected the search for strangeness enhancement in general and strange quark matter enhancement in general and strange quark matter in particular.in particular.

Strange Quark Matter is still considered a Strange Quark Matter is still considered a possibility for stable or metastable matter in the possibility for stable or metastable matter in the universeuniverse

Two recent examples in astrophysicsFundamental paper on ‘How to identify a strange star’ Fundamental paper on ‘How to identify a strange star’

by Jes Madsen, PRL 81 (1998) 3311by Jes Madsen, PRL 81 (1998) 3311

Recent measurements by Drake et al. and Helfand et al. in Recent measurements by Drake et al. and Helfand et al. in 2002 with the Chandra X-ray telescope2002 with the Chandra X-ray telescope

These two NASA Chandra X-ray Observatory images show two stars - one too small, one too cold - These two NASA Chandra X-ray Observatory images show two stars - one too small, one too cold - that reveal cracks in our understanding of the structure of matter. (AFP) that reveal cracks in our understanding of the structure of matter. (AFP)

RXJ18563C58

Did quark matter strike the earth ?Two anomalous seismic events occurred in 1993, and were Two anomalous seismic events occurred in 1993, and were measured independently by 9 monitoring stations.measured independently by 9 monitoring stations.

Strange quark matter should pass through the earth at 400 km/s (40 times the speed Strange quark matter should pass through the earth at 400 km/s (40 times the speed of seismic waves), i.e. search for seismic events not connected with traditional of seismic waves), i.e. search for seismic events not connected with traditional seismic disturbances e.g. earth quakes. (Herrin et al., SMU, 2002) seismic disturbances e.g. earth quakes. (Herrin et al., SMU, 2002)

What can we do in the laboratory ?

The idea of strange quark matter did not only The idea of strange quark matter did not only initiate strangelet searches but led also to potential initiate strangelet searches but led also to potential signatures for the QGP phase transition.signatures for the QGP phase transition.

Increasing strangeness enhancement as a signal Increasing strangeness enhancement as a signal for QGP and strangeness equilibration as a signal for QGP and strangeness equilibration as a signal for thermalization of the particle emitting source for thermalization of the particle emitting source were for years at the forefront of our research.were for years at the forefront of our research.

A Cosmic Timeline AgeAge Energy Energy Matter in universe Matter in universe 00 10101919 GeV GeV grand unified theory of all forcesgrand unified theory of all forces

1010-35-35 s s 10101414 GeV GeV 11stst phase transition phase transition

(strong: q,g + electroweak: g, l,n)(strong: q,g + electroweak: g, l,n)

1010-10-10 ss 101022 GeV GeV 22ndnd phase transition phase transition(strong: q,g + electro: g + weak: l,n)(strong: q,g + electro: g + weak: l,n)

1010-5-5 s s 0.2 GeV0.2 GeV 33rdrd phase transition phase transition(strong:hadrons + electro:g + weak: l,n)(strong:hadrons + electro:g + weak: l,n)

3 min.3 min. 0.1 MeV0.1 MeV nucleinuclei

6*106*1055 years years 0.3 eV0.3 eV atomsatoms

NowNow 3*103*10-4-4 eV = 3 K eV = 3 K(15 billion years)(15 billion years)

An Inflationary Universe

The universe expanded to a point where the The universe expanded to a point where the unified forces of nature started to decouple. unified forces of nature started to decouple. When the strong force decoupled a major When the strong force decoupled a major amount of energy was released and the amount of energy was released and the universe expanded by a factor 10universe expanded by a factor 103030 in less in less than 10than 10-36-36 seconds. This rapid expansion is seconds. This rapid expansion is called called inflationinflation

Let’s revisit the timelines The beginningThe beginning

The universe is a hot plasma of fundamental particles … quarks, leptons, force particles (and other The universe is a hot plasma of fundamental particles … quarks, leptons, force particles (and other particles ?)particles ?)1010-43-43 s s Planck scale (quantum gravity ?)Planck scale (quantum gravity ?) 10101919 GeV GeV1010-35-35 s s Grand unification scale (strong and electroweak)Grand unification scale (strong and electroweak) 10101515 GeV GeV

Inflationary period 10Inflationary period 10-35-35-10-10-33-33 s s1010-11-11 s s Electroweak unification scaleElectroweak unification scale 200 GeV200 GeV

Micro-structureMicro-structure1010-5-5 s s QCD scale - protons and neutrons formQCD scale - protons and neutrons form 200 MeV200 MeV3 mins3 mins Primordial nucleosynthesisPrimordial nucleosynthesis 5 MeV5 MeV33101055 yrs yrs Radiation and matter decouple - atoms formRadiation and matter decouple - atoms form 1 eV1 eV

Large scale structureLarge scale structure1 bill yrs1 bill yrsProto-galaxies and the first starsProto-galaxies and the first stars3 bill yrs3 bill yrsQuasars and galaxy spheroidsQuasars and galaxy spheroids5 bill yrs5 bill yrsGalaxy disksGalaxy disksTodayToday Life !Life !

The Cosmic Timeline

Going back in time

Let’s go for the ‘Mini-Bang’ We need a system that is small so that we can We need a system that is small so that we can

accelerate it to very high speeds. accelerate it to very high speeds. (99.9% of the speed of light)(99.9% of the speed of light)

But we need a system (i.e. a chunk of matter and But we need a system (i.e. a chunk of matter and not just a single particle) so that the system can not just a single particle) so that the system can follow simple rules of thermodynamics and form a follow simple rules of thermodynamics and form a new state of matter in a particular phase.new state of matter in a particular phase.

We use heavy ions (e.g. a Gold ion which is made We use heavy ions (e.g. a Gold ion which is made of 197 protons and neutrons). It is tiny (about a of 197 protons and neutrons). It is tiny (about a 10-10-1414 m diameter) but it is a finite volume that can m diameter) but it is a finite volume that can be exposed to pressure and temperaturebe exposed to pressure and temperature

What are we trying to do ? We try to force matter we know (e.g. our Gold We try to force matter we know (e.g. our Gold

nucleus) through a phase transition to a new state nucleus) through a phase transition to a new state of matter predicted by the Big-Bang, called a of matter predicted by the Big-Bang, called a Quark-Gluon Plasma (QGP)Quark-Gluon Plasma (QGP)

atom

nucleons

Quarks andgluons

Quantum Chromodynamics (QCD)

Main features of QCDMain features of QCD ConfinementConfinement

At large distances the effective coupling between quarks is large, resulting At large distances the effective coupling between quarks is large, resulting in confinement.in confinement.

Free quarks are not observed in nature.Free quarks are not observed in nature. Asymptotic freedomAsymptotic freedom

At short distances the effective coupling between quarks decreases At short distances the effective coupling between quarks decreases logarithmically.logarithmically.

Under such conditions quarks and gluons appear to be quasi-free.Under such conditions quarks and gluons appear to be quasi-free. (Hidden) chiral symmetry(Hidden) chiral symmetry

Connected with the quark massesConnected with the quark masses When confined quarks have a large dynamical mass - constituent massWhen confined quarks have a large dynamical mass - constituent mass In the small coupling limit (some) quarks have small mass - current massIn the small coupling limit (some) quarks have small mass - current mass

Confinement The strong interaction potentialThe strong interaction potential

Compare the potential of the strong & e.m. interactionCompare the potential of the strong & e.m. interaction

Confining term arises due to the self-interaction property of the Confining term arises due to the self-interaction property of the colour fieldcolour field

Vem q1q2

40r

cr

Vs c

r kr c, c , k constants

QED QCDCharges electric (2) colour (3)Gauge boson (1) g (8)Charged no yesStrength em

e2

4

1137

s 0.1 0.2

q1 q2

q1 q2

a) QED or QCD (r < 1 fm)

b) QCD (r > 1 fm)

r

It is more usual to think of coupling strength rather than chargeIt is more usual to think of coupling strength rather than charge and the momentum transfer squared rather than distance.and the momentum transfer squared rather than distance.

In both QED and QCD the coupling strength depends on distance.In both QED and QCD the coupling strength depends on distance. In QED the coupling strength is given by:In QED the coupling strength is given by:

where where = = ((QQ2 2 0) 0) = = ee22/4/4 = 1/137= 1/137 In QCD the coupling strength is given by:In QCD the coupling strength is given by:

which decreases at large which decreases at large QQ22 provided provided nnff < 16 < 16..

Asymptotic freedom - the coupling “constant”

2M Q2 W 2 M2 M initial state mass energy transfer

W final state mass Q momentum transfer

em Q2

1 3 ln Q2 m2

s Q2 s 2

1 s 2 33 2n f 12

ln Q2 2

Q2»m2

Q2 = -q2

e e

Asymptotic freedom - summary Effect in QCDEffect in QCD

Both q-qbar and gluon-gluon loops contribute.Both q-qbar and gluon-gluon loops contribute. The quark loops produce a screening effect analogous to eThe quark loops produce a screening effect analogous to e++ee-- loops in QED loops in QED But the gluon loops dominate and produce an anti-screening effect.But the gluon loops dominate and produce an anti-screening effect. The observed charge (coupling) decreases at very small distances.The observed charge (coupling) decreases at very small distances. The theory is asymptotically free The theory is asymptotically free quark-gluon plasma ! quark-gluon plasma !

““Superdense Matter: Neutrons or Asymptotically Free Quarks”Superdense Matter: Neutrons or Asymptotically Free Quarks”J.C. Collins and M.J. Perry, Phys. Rev. Lett. 34 (1975) 1353 J.C. Collins and M.J. Perry, Phys. Rev. Lett. 34 (1975) 1353

Main pointsMain points Observed charge is dependent on the distance scale probed.Observed charge is dependent on the distance scale probed. Electric charge is conveniently defined in the long wavelength limit (Electric charge is conveniently defined in the long wavelength limit (r r ).). In practice In practice emem changes by less than 1% up to 10 changes by less than 1% up to 102626 GeV ! GeV ! In QCD charges can not be separated.In QCD charges can not be separated. Therefore charge must be defined at some other length scale.Therefore charge must be defined at some other length scale. In general In general ss is strongly varying with distance - can’t be ignored. is strongly varying with distance - can’t be ignored.

Quark deconfinement - medium effects Debye screeningDebye screening

In bulk media, there is an additional charge screening effect.In bulk media, there is an additional charge screening effect. At high charge density, At high charge density, nn, the short range part of the potential becomes:, the short range part of the potential becomes:

and and rrDD is the Debye screening radius. is the Debye screening radius. Effectively, long range interactions (Effectively, long range interactions (r r >> r rDD) are screened.) are screened.

The Mott transitionThe Mott transition In condensed matter, when In condensed matter, when rr < < electron binding radiuselectron binding radius

an electric insulator becomes conducting.an electric insulator becomes conducting. Debye screening in QCDDebye screening in QCD

Analogously, think of the quark-gluon plasma as a colour conductor.Analogously, think of the quark-gluon plasma as a colour conductor. Nucleons (all hadrons) are colour singlets (qqq, or qqbar states).Nucleons (all hadrons) are colour singlets (qqq, or qqbar states). At high (charge) density quarks and gluons become unbound.At high (charge) density quarks and gluons become unbound.

nucleons (hadrons) cease to exist.nucleons (hadrons) cease to exist.

V(r) 1r

1r

exp rrD

where rD

1n3

Debye screening in nuclear matter High (color charge) densities are achieved byHigh (color charge) densities are achieved by

Colliding heaving nuclei, resulting in:Colliding heaving nuclei, resulting in:1. Compression.1. Compression.2. Heating = creation of pions.2. Heating = creation of pions.

Under these conditions:Under these conditions:1. Quarks and gluons become deconfined.1. Quarks and gluons become deconfined.2. Chiral symmetry may be (partially) restored.2. Chiral symmetry may be (partially) restored.

Note: a phase transition is Note: a phase transition is notnot expected in binary nucleon-nucleon collisions. expected in binary nucleon-nucleon collisions.

The temperature inside a heavy ion collision at RHIC can exceed The temperature inside a heavy ion collision at RHIC can exceed

1000 billion degrees !! (about 10,000 times the temperature of the sun)1000 billion degrees !! (about 10,000 times the temperature of the sun)

Chiral symmetry Chiral symmetry and the QCD LagrangianChiral symmetry and the QCD Lagrangian

Chiral symmetry is a exact symmetry only for massless quarks.Chiral symmetry is a exact symmetry only for massless quarks. In a massless world, quarks are either left or right handed In a massless world, quarks are either left or right handed The QCD Lagrangian is symmetric with respect to left/right handed quarks.The QCD Lagrangian is symmetric with respect to left/right handed quarks. Confinement results in a large dynamical mass - constituent mass.Confinement results in a large dynamical mass - constituent mass.

chiral symmetry is broken (or hidden).chiral symmetry is broken (or hidden). When deconfined, quark current masses are small - current mass.When deconfined, quark current masses are small - current mass.

chiral symmetry is (partially) restoredchiral symmetry is (partially) restored

Example of a hidden symmetry restored at high temperatureExample of a hidden symmetry restored at high temperature Ferromagnetism - the spin-spin interaction is rotationally invariant.Ferromagnetism - the spin-spin interaction is rotationally invariant.

In the sense that any direction is possible the symmetry In the sense that any direction is possible the symmetry isis still present. still present.

T < Tc T > Tc

Below the Curie temperature the underlying rotational symmetry is hidden.

Above the Curie temperature the rotational symmetry is restored.

Modelling confinement: The MIT bag model

Modelling confinement - MIT bag modelModelling confinement - MIT bag model Based on the ideas of Bogolioubov (1967).Based on the ideas of Bogolioubov (1967). Neglecting short range interactions, write the Dirac equation so that the Neglecting short range interactions, write the Dirac equation so that the

mass of the quarks is small inside the bag (mass of the quarks is small inside the bag (mm) and ) and veryvery large outside large outside ((MM))

Wavefunction vanishes outside the bag if Wavefunction vanishes outside the bag if MM and satisfies a linear boundary condition at the bag surface.and satisfies a linear boundary condition at the bag surface.

SolutionsSolutions Inside the bag, we are left with the free Dirac equation.Inside the bag, we are left with the free Dirac equation. The MIT group realised that Bogolioubov’s model violated The MIT group realised that Bogolioubov’s model violated EE--pp

conservation.conservation. Require an external pressure to balance the internal pressure of the Require an external pressure to balance the internal pressure of the

quarks.quarks. The QCD vacuum acquires a finite energy density, The QCD vacuum acquires a finite energy density, BB ≈ 60 MeV/fm ≈ 60 MeV/fm33.. New boundary condition, total energy must be minimised wrt the bag New boundary condition, total energy must be minimised wrt the bag

radius.radius.B

Bag model results

RefinementsRefinements Several refinements are needed Several refinements are needed

to reproduce the spectrum of to reproduce the spectrum of low-lying hadronslow-lying hadrons

e.g. allow quark interactionse.g. allow quark interactions Fix Fix BB by fits to several hadrons by fits to several hadrons

Estimates for the bag constantEstimates for the bag constant Values of the bag constant Values of the bag constant

range from range from BB11/4/4 = 145-235 MeV = 145-235 MeV ResultsResults

Shown for Shown for BB11/4/4 = 145 MeV = 145 MeV and and ss = 2.2 = 2.2 and and mmss = 279 MeV = 279 MeV

T. deGrand et al, Phys. Rev. D 12 (1975) 2060

Summary of QCD input QCD is an asymptotically free theory.QCD is an asymptotically free theory. In addition, long range forces are screened in a dense In addition, long range forces are screened in a dense

medium.medium. QCD possess a hidden (chiral) symmetry.QCD possess a hidden (chiral) symmetry. Expect one or perhaps two phase transitions connected Expect one or perhaps two phase transitions connected

with deconfinement and partial chiral symmetry with deconfinement and partial chiral symmetry restoration.restoration.

pQCD calculations can not be used in the confinement pQCD calculations can not be used in the confinement limit.limit.

MIT bag model provides a phenomenological description MIT bag model provides a phenomenological description of confinement.of confinement.

Mapping out the Nuclear Matter Phase DiagramMapping out the Nuclear Matter Phase Diagram Perturbation theory highly successful in Perturbation theory highly successful in

applications of QED.applications of QED. In QCD, perturbation theory is only applicable In QCD, perturbation theory is only applicable

for very hard processes.for very hard processes. Two solutions:Two solutions:

1. Phenomenological models1. Phenomenological models2. Lattice QCD calculations2. Lattice QCD calculations

Estimating the critical parameters, Tc and c

Lattice QCDQuarks and gluons are Quarks and gluons are

studied on a discrete studied on a discrete space-time lattice space-time lattice

Solves the problem of Solves the problem of divergences in pQCD divergences in pQCD calculations (which arise calculations (which arise due to loop diagrams)due to loop diagrams)

There are two order There are two order parametersparameters

aa

Ns3 N

1. The Polyakov Loop L ~ Fq2. The Chiral Condensate ~ mq

(F. Karsch, hep-lat/9909006)

/T4

T/Tc

Lattice Results Tc(Nf=2)=1738 MeVTc(Nf=3)=1548 MeV

0.5 4.5 15 35 GeV/fm375

T = 150-200 MeV ~ 0.6-1.8 GeV/fm3

Lattice QCD: the latest news(critical parameters at finite baryon density)

Phenomenology I: Phase transition The quark-gluon and hadron equations of stateThe quark-gluon and hadron equations of state

The energy density of (massless) quarks and gluons is derived from Fermi-Dirac The energy density of (massless) quarks and gluons is derived from Fermi-Dirac statistics and Bose-Einstein statistics.statistics and Bose-Einstein statistics.

where where is the quark chemical potential, is the quark chemical potential, qq = - = - qq and and = 1/ = 1/TT.. Taking into account the number of degrees of freedomTaking into account the number of degrees of freedom

Consider two extremes:Consider two extremes:

1. High temperature, low net baryon density (1. High temperature, low net baryon density (TT > 0, > 0, BB = 0 = 0).).

2. Low temperature, high net baryon density (2. Low temperature, high net baryon density (TT = 0, = 0, BB > 0 > 0).).

g 1

2 2p3dp

ep 1 g

2T 4

30

q 1

2 2p3dp

e p 1 q q

7 2T 4

120

2T 2

4

4

8 2

TOT 16g 12 q q

B = 3 q

Phenomenology II: critical parameters High temperature, low density limit - the High temperature, low density limit - the

early universeearly universe Two terms contribute to the total energy Two terms contribute to the total energy

densitydensity

For a relativistic gas:For a relativistic gas:

For stability:For stability:

Low temperature, high density limit - neutron Low temperature, high density limit - neutron starsstars

Only one term contributes to the total Only one term contributes to the total energy densityenergy density

By a similar argument:By a similar argument:

qg 37 2

30T 4

Pqg 1

3qg

Pnet Pqg B 0

Tc 90

37 2 B

1 4

100 170 MeV

q 3

2 2 q4

c 2 2B 1 4300 500 MeV

~ 2-8 times normal nuclear matter densitygiven pFermi ~ 250 MeV and ~ 23/32

How to create a QGP ?energy = temperature & density =

pressure

Let’s collide two heavy nuclei (1)

Let’s collide two heavy nuclei (2)

Let’s study all phases of the process

Freeze-out

Hadron Gas

Phase Transition

Plasma-phase

Pre-EquilibriumHard scattering

If the QGP was formed, it will only live for 10-21 s !!!!BUT does matter come out of this phase the same way it went in ???

time

temperature

~ 100 s after Big Bang

Nucleosynthesis begins

In the beginning quark – gluon

plasma

~ 10 s after Big Bang

Hadron Synthesisstrong force binds quarks and gluons in massive objects: protons, neutrons mass ~ 1 GeV

STARSTAR

The RHIC Complex

1. Tandem Van de Graaff

2. Heavy Ion Transfer Line

3. Booster

4. Alternating Gradient Synchrotron (AGS)

5. AGS-to-RHIC Transfer Line

6. RHIC ring

1. Tandem Van de Graaff

2. Heavy Ion Transfer Line

3. Booster

4. Alternating Gradient Synchrotron (AGS)

5. AGS-to-RHIC Transfer Line

6. RHIC ring

11

33 44

66

22

55

The STAR Experiment 450 scientists from 50 international institutions

Conceptual Conceptual OverviewOverview

Conceptual Conceptual OverviewOverview

The STAR Experiment construction from 1992-2000

data taking from 2000-2010 (?)

Overview while Overview while under under

constructionconstruction

Overview while Overview while under under

constructionconstruction

The STAR Detector

MagnetMagnet

CoilsCoils

Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)

ZCalZCal

Time Time Projection Projection

ChamberChamber(TPC)(TPC)

Barrel EM Cal Barrel EM Cal (BEMC)(BEMC)

Silicon Vertex Silicon Vertex Tracker (SVT)Tracker (SVT)Silicon Strip Silicon Strip Detector (SSD)Detector (SSD)Vertex DetectorVertex Detector

(2006)(2006)

FTPCFTPCEndcap EM CalEndcap EM CalFPDFPD

TOFp, TOFrTOFp, TOFr

The STAR Experiment (TPC)

Construction in progressConstruction in progress

The STAR Experiment (SVT)Construction in progressConstruction in progress

The STAR Experiment (SVT)

The happy crew The happy crew after 8 long yearsafter 8 long yearsThe happy crew The happy crew

after 8 long yearsafter 8 long years

Actual Collision in STAR (1)

Actual STAR data Actual STAR data

for a for a

peripheral collisionperipheral collision

Actual STAR data Actual STAR data

for a for a

peripheral collisionperipheral collision

Actual Collision in STAR (2)

Actual STAR data Actual STAR data for a central for a central

collisioncollision

Actual STAR data Actual STAR data for a central for a central

collisioncollision

What is going on ?

A Au nucleus consists of 79 protons and 118 neutrons = 197 A Au nucleus consists of 79 protons and 118 neutrons = 197 particles -> 394 particles totalparticles -> 394 particles total

After the collision we measure about 10,000 particles in the After the collision we measure about 10,000 particles in the debris!debris!

measured particles: p, measured particles: p, , K, , K, , d, D, J/, d, D, J/Y, BY, B many particles contain s-quarks, some even c- and b-quarksmany particles contain s-quarks, some even c- and b-quarks Energy converts to matter, but does the matter go through a Energy converts to matter, but does the matter go through a

phase transition ?phase transition ?

What do we have to check ?

If there was a transition to a different phase, then this phase could If there was a transition to a different phase, then this phase could only last very shortly. The only evidence we have to check is the only last very shortly. The only evidence we have to check is the collision debris.collision debris.

Check the make-up of the debris:Check the make-up of the debris: which particles have been formed ?which particles have been formed ? how many of them ?how many of them ? are they emitted statistically (Boltzmann distribution) ?are they emitted statistically (Boltzmann distribution) ? what are their kinematics (speed, momentum, angular what are their kinematics (speed, momentum, angular

distributions) ?distributions) ? are they correlated in coordinate or momentum space ?are they correlated in coordinate or momentum space ? do they move collectively ?do they move collectively ? do some of them ‘melt’ ?do some of them ‘melt’ ?

What do we measure in a collider experiment ? particles come from the vertex. They have to traverse certain detectors but should particles come from the vertex. They have to traverse certain detectors but should

not change their properties when traversing the inner detectors not change their properties when traversing the inner detectors DETECT but don’t DEFLECT !!!DETECT but don’t DEFLECT !!! inner detectors have to be very thin (low radiation length): easy with gas (TPC), inner detectors have to be very thin (low radiation length): easy with gas (TPC),

challenge with solid state materials (Silicon).challenge with solid state materials (Silicon). Measurements: Measurements: - momentum and charge via high resolution - momentum and charge via high resolution

tracking in SVT and TPC tracking in SVT and TPC in magnetic field (and in magnetic field (and FTPC)FTPC) - - PID via dE/dx inSVT and TPC and time of flightPID via dE/dx inSVT and TPC and time of flight in TOF in TOF - - PID of decay particles via impactPID of decay particles via impact parameter parameter from SVT from SVT and TPCand TPC

particles should stop in the outermost detectorparticles should stop in the outermost detector Outer detector has to be thick and of high radiation length (e.g. Pb/Scint calorimeter)Outer detector has to be thick and of high radiation length (e.g. Pb/Scint calorimeter) Measurements:Measurements: - deposited energy for event and specific particles- deposited energy for event and specific particles - e/h - e/h

separation via shower profileseparation via shower profile - photon via - photon via shower profileshower profile

Signatures of the QGP phase

Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. entropy (i.e. # of degrees of freedom. entropy (i.e. # of degrees of freedom.

The temperature (or energy) is used to increase the number of degrees of freedom rather than heat the The temperature (or energy) is used to increase the number of degrees of freedom rather than heat the existing form of matter. existing form of matter.

In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity. In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity.

At the step some signatures dropAt the step some signatures drop

and some signatures riseand some signatures rise

Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. entropy (i.e. # of degrees of freedom. entropy (i.e. # of degrees of freedom.

The temperature (or energy) is used to increase the number of degrees of freedom rather than heat the The temperature (or energy) is used to increase the number of degrees of freedom rather than heat the existing form of matter. existing form of matter.

In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity. In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity.

At the step some signatures dropAt the step some signatures drop

and some signatures riseand some signatures rise

How do we know what happened ?

We have to compare to a system that did definitely We have to compare to a system that did definitely not go through a phase transition (a reference not go through a phase transition (a reference collision)collision)

Two options:Two options: A proton-proton collision compared to a Gold-A proton-proton collision compared to a Gold-

Gold collision does not generate a big enough Gold collision does not generate a big enough volume to generate a plasma phasevolume to generate a plasma phase

A peripheral Gold-Gold collision compared to a A peripheral Gold-Gold collision compared to a central one does not generate enough energy central one does not generate enough energy and volume to generate a plasma phaseand volume to generate a plasma phase

The idea of two phase transitionsDeconfinementDeconfinement

The quarks and gluons deconfine because energy or The quarks and gluons deconfine because energy or parton density gets too high parton density gets too high (best visualized in the bag model). (best visualized in the bag model).

Chiral symmetry restorationChiral symmetry restorationMassive hadrons in the hadron gas are massless Massive hadrons in the hadron gas are massless partons in the plasma. Mass breaks chiral symmetry, partons in the plasma. Mass breaks chiral symmetry, therefore it has to be restored in the plasma therefore it has to be restored in the plasma

What is the mechanism of hadronization ? How doWhat is the mechanism of hadronization ? How dohadrons get their mass ?hadrons get their mass ?

Evidence: Some particles are suppressed If the phase is very dense (QGP) than certain particles get absorbedIf the phase is very dense (QGP) than certain particles get absorbed

?

If things are produced in pairs then one might make it out and the other one not.

Central Au + Au

Peripheral Au + Au

STAR Preliminary

If things require the fusion of very heavy rare quarks they might be suppressed in a dense medium

Evidence: Some particles are enhanced Remember dark matter ? Well, we didn’t find clumps of it yet, but we Remember dark matter ? Well, we didn’t find clumps of it yet, but we

found increased production of strange quark particlesfound increased production of strange quark particles

What is our mission ?• Discover the QGP

• Find transition behavior between an excited hadronic gas and another phase

• Characterize the states of matter • Do we have a hot dense partonic phase and how

long does it live ?• Characterize medium in terms of density,

temperature and time• Is the medium equilibrated (thermal,

chemical)