Modern Nuclear Physics with RHIC: Recreating the Creation of the Universe Rene Bellwied Wayne State University

The STAR experiment at RHIC What are we doing ? What are we doing ? Why do we do it ? Why do we do it ? How do we do it ? How do we do it ? What are we doing ? What are we doing ? Why do we do it ? Why do we do it ? How do we do it ? How do we do it ?

Let there be light The Hertzsprung- Russell Diagram The Hertzsprung- Russell Diagram Relation between mass and temperature, light output, lifetime. Relation between mass and temperature, light output, lifetime. Stars shine because of nuclear fusion reactions in their core. The more luminous they are, the more reactions are taking place in their cores.

Doppler Effect with Stars A star's motion causes a wavelength shift in its light emission spectrum, which depends on speed and direction of motion. A star's motion causes a wavelength shift in its light emission spectrum, which depends on speed and direction of motion. If star is moving toward you, the waves are compressed, so their wavelength is shorter = blueshift. If star is moving toward you, the waves are compressed, so their wavelength is shorter = blueshift. If the object is moving away from you, the waves are stretched out, so their wavelength is longer = redshift. If the object is moving away from you, the waves are stretched out, so their wavelength is longer = redshift.

Relativity and Universe Expansion The doppler effect tells you about the relative motion of the object with respect to you. The doppler effect tells you about the relative motion of the object with respect to you. Important fact: Important fact:  The spectral lines of nearly all of the galaxies in the universe are shifted to the red end of the spectrum.  This means that the galaxies are moving away from the Milky Way galaxy.  This is evidence for the expansion of the universe.

Hubble Law Hubble and Humason (1931): Hubble and Humason (1931):  the Galactic recession speed = H × distance, where H is a number now called the Hubble constant. This relation is called the Hubble Law and the Hubble constant is the slope of the line. This relation is called the Hubble Law and the Hubble constant is the slope of the line.

Age of the Universe Age of the universe can be estimated from the simple relation of time = distance/speed. Age of the universe can be estimated from the simple relation of time = distance/speed. The Hubble Law can be rewritten The Hubble Law can be rewritten  1/H o = distance/speed. The Hubble constant tells you the age of the universe, i.e., how long the galaxies have been expanding away from each other: The Hubble constant tells you the age of the universe, i.e., how long the galaxies have been expanding away from each other:  Age = 1/H o. Age upper limit since the expansion has been slowing down due to gravity. Age upper limit since the expansion has been slowing down due to gravity. Present best estimate: 13.7 Billion years Present best estimate: 13.7 Billion years

Evidence for the Big Bang Galaxies are distributed fairly uniformily across the sky between a lot of void (Obler’s paradox) Galaxies are distributed fairly uniformily across the sky between a lot of void (Obler’s paradox) Background radiation was predicted, and has been found, to be exactly 2.73 K everywhere in the universe. Variations as measured by a NASA satellite named COBE (Cosmic Background Explorer) are less than K. Background radiation was predicted, and has been found, to be exactly 2.73 K everywhere in the universe. Variations as measured by a NASA satellite named COBE (Cosmic Background Explorer) are less than K.

Star Count in the Galaxy Rough guess of the number of stars in our galaxy obtained by dividing the Galaxy's total mass by the mass of a typical star (e.g., 1 solar mass). Rough guess of the number of stars in our galaxy obtained by dividing the Galaxy's total mass by the mass of a typical star (e.g., 1 solar mass).  The result is about 200 billion stars! The actual number of stars could be several tens of billions less or more than this approximate value. The actual number of stars could be several tens of billions less or more than this approximate value. All of these numbers are based on luminous matter ! All of these numbers are based on luminous matter !

A Mass Problem The stars and gas in most galaxies move much quicker than expected from the luminosity of the galaxies. The stars and gas in most galaxies move much quicker than expected from the luminosity of the galaxies. In spiral galaxies, the rotation curve remains at about the same value at great distances from the center (it is said to be ``flat''). In spiral galaxies, the rotation curve remains at about the same value at great distances from the center (it is said to be ``flat''). This means that the enclosed mass continues to increase even though the amount of visible, luminous matter falls off at large distances from the center. This means that the enclosed mass continues to increase even though the amount of visible, luminous matter falls off at large distances from the center. Something else must be adding to the gravity of the galaxies without shining. We call it Dark Matter ! According to measurements it accounts for 90% of the mass in the universe. Something else must be adding to the gravity of the galaxies without shining. We call it Dark Matter ! According to measurements it accounts for 90% of the 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

The cosmic connection of RHI physics The universe is accelerating according to the latest Supernova results Witten’s ‘Cosmic Separation of phases’ (Phys.Rev.D 30 (1984) 272) SNAP: Supernova Accelerating Probe

What is Dark Matter ? We don’t know (yet) White dwarfs, brown dwarfs, black holes, massive neutrinos, although intriguing are very unlikely to account for most of the dark matter. The dwarfs are generally called Massive compact halo objects (MACHOS) White dwarfs, brown dwarfs, black holes, massive neutrinos, although intriguing are very unlikely to account for most of the dark matter. The dwarfs are generally called Massive compact halo objects (MACHOS) New exotic particles or formations are more likely: New exotic particles or formations are more likely:  Weakly interacting massive particles (WIMPS)  Matter based on exotic quark configurations (e.g. strange Quark matter).  Witten’s ‘Cosmic Separation of phases’ (Phys.Rev.D 30 (1984) 272)  If these states exist somewhere in the universe wouldn’t they have been produced in the early universe and are they still around ?

Going back in time… Age Energy Matter in universe Age Energy Matter in universe GeV grand unified theory of all forces GeV grand unified theory of all forces s10 14 GeV1 st phase transition (strong: q,g + electroweak: g, l,n) s10 2 GeV2 nd phase transition (strong: q,g + electro: g + weak: l,n) s0.2 GeV3 rd phase transition (strong:hadrons + electro:g + weak: l,n) 3 min.0.1 MeVnuclei 6*10 5 years0.3 eVatoms Now 3*10 -4 eV = 3 K (15 billion years) RHIC, LHC & FAIR RIA & FAIR

What can we do in the laboratory ? a.) Re-create the conditions as close as possible to the Big Bang, i.e. a condition of maximum density and minimum volume in an expanding macroscopic system. Is statistical thermodynamics applicable ? b.) Measure a phase transition, characterize the new phase, measure the de-excitation of the new phase into ‘ordinary’ matter – ‘do we come out the way went in ?’ (degrees of freedom, stable or metastable matter, homogeneity) c.) Learn about hadronization (how do particles acquire mass) – complementary to the Higgs search but with the same goal. The relevant theory is Quantum Chromo Dynamics

Let’s go for the ‘Mini-Bang’ We need a system that is small so that we can accelerate it to very high speeds. (99.9% of the speed of light) We need a system that is small so that we can accelerate it to very high speeds. (99.9% of the speed of light) But we need a system (i.e. a chunk of matter and not just a single particle) so that the system can follow simple rules of thermodynamics and form a new state of matter in a particular phase. But we need a system (i.e. a chunk of matter and not just a single particle) so that the system can follow simple rules of thermodynamics and form a new state of matter in a particular phase. We use heavy ions (e.g. a Gold ion which is made of 197 protons and neutrons). It is tiny (about a m diameter) but it is a finite volume that can be exposed to pressure and temperature We use heavy ions (e.g. a Gold ion which is made of 197 protons and neutrons). It is tiny (about a m diameter) but it is a finite volume that can be exposed to pressure and temperature

What are we trying to do ? We try to force matter we know (e.g. our Gold nucleus) through a phase transition to a new state of matter predicted by the Big-Bang, called a Quark-Gluon Plasma (QGP) We try to force matter we know (e.g. our Gold nucleus) through a phase transition to a new state of matter predicted by the Big-Bang, called a Quark-Gluon Plasma (QGP) atom nucleons Quarks and gluons

Strong color field Force grows with separation !!! Analogies and differences between QED and QCD to study structure of an atom… “white” proton …separate constituents Imagine our understanding of atoms or QED if we could not isolate charged objects!! nucleus electron quark quark-antiquark pair created from vacuum “white” proton (confined quarks) “white”  0 (confined quarks) Confinement: fundamental & crucial (but not understood!) feature of strong force - colored objects (quarks) have  energy in normal vacuum neutral atom To understand the strong force and the phenomenon of confinement: Create and study a system of deconfined colored quarks (and gluons)

The main features of Quantum Chromodynamics (QCD) Confinement Confinement  At large distances the effective coupling between quarks is large, resulting in confinement.  Free quarks are not observed in nature. Asymptotic freedom Asymptotic freedom  At short distances the effective coupling between quarks decreases logarithmically.  Under such conditions quarks and gluons appear to be quasi-free. (Hidden) chiral symmetry (Hidden) chiral symmetry  Connected with the quark masses  When confined quarks have a large dynamical mass - constituent mass  In the small coupling limit (some) quarks have small mass - current mass

One goal: Proving asymptotic freedom in the laboratory. Measure deconfinement and chiral symmetry restoration under the conditions of maximum particle or energy density. Measure deconfinement and chiral symmetry restoration under the conditions of maximum particle or energy density. Gross, Politzer, Wilczek win 2004 Nobel Prize in physics for the discovery of asymptotic freedom in the theory of the strong interaction

Generating a deconfined state Nuclear Matter (confined) Hadronic Matter (confined) Quark Gluon Plasma deconfined ! Present understanding of Quantum Chromodynamics (QCD) heating compression  deconfined color matter !

Expectations from Lattice QCD  /T 4 ~ # degrees of freedom confined: few d.o.f. deconfined: many d.o.f. T C ≈ 173 MeV ≈ 2  K ≈ 130,000  T[Sun’s core]  C  0.7 GeV/fm 3

The phase diagram of QCD Temperature baryon density Neutron stars Early universe nuclei nucleon gas hadron gas colour superconductor quark-gluon plasma TcTc 00 critical point ? vacuum CFL

RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) 1 km v =  c  s NN =200 GeV

RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) STAR Collaboration: ~500 Collaborators (~300 authors) from 51 Institutions

The STAR Experiment 450 scientists from 50 international institutions Conceptual Overview

The STAR Experiment construction from data taking from (?) Overview while under construction

The STAR DetectorMagnetCoilsCentralTriggerBarrel(CTB)ZCalTimeProjectionChamber(TPC) Barrel EM Cal (BEMC) Silicon Vertex Tracker (SVT) Silicon Strip Detector (SSD)  Vertex Detector (2006) FTPC Endcap EM Cal FPD TOFp, TOFr

The STAR Experiment (TPC) Construction in progress

The STAR Experiment (SVT) Construction in progress

The STAR Experiment (SVT) The happy crew after 8 long years

Study all phases of a heavy ion collision If the QGP was formed, it will only live for s !!!! BUT does matter come out of this phase the same way it went in ???

Actual Collision in STAR (1) Actual STAR data for a peripheral collision Actual STAR data for a peripheral collision

Study all phases of a heavy ion collision If the QGP was formed, it will only live for s !!!! BUT does matter come out of this phase the same way it went in ???

Actual Collision in STAR (2) Actual STAR data for a central collision

Close-Up Solution for the high particle density problem: build a high resolution detector (zoom in on the problem)

What is going on ? A Au nucleus consists of 79 protons and 118 neutrons = 197 particles -> 394 particles total A Au nucleus consists of 79 protons and 118 neutrons = 197 particles -> 394 particles total After the collision we measure about 10,000 particles in the debris! After the collision we measure about 10,000 particles in the debris! measured particles: p, , K, , d, D, J/  Y, B measured particles: p, , K, , d, D, J/  Y, B many particles contain s-quarks, some even c- and b-quarks many particles contain s-quarks, some even c- and b-quarks Energy converts to matter (Einstein !), but does the matter Energy converts to matter (Einstein !), but does the matter go through a phase transition ?

What do we have to check ? 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 collision debris. 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 collision debris. Check the make-up of the debris: Check the make-up of the debris:  which particles have been formed ?  how many of them ?  are they emitted statistically (Boltzmann distribution) ?  what are their kinematics (speed, momentum, angular distributions) ?  are they correlated in coordinate or momentum space ?  do they move collectively ?  do some of them ‘melt’ ?

How Do We Measure Things ? particles go from the inside-out particles go from the inside-out they have to traverse certain detectors they have to traverse certain detectors they should stop in the outermost detector they should stop in the outermost detector the particle should not change its properties when traversing the inner detector the particle should not change its properties when traversing the inner detector DETECT but don’t DEFLECT !!! DETECT but don’t DEFLECT !!! inner detectors have to be very thin (low radiation length): easy with gas, challenge with solid state materials (Silicon). inner detectors have to be very thin (low radiation length): easy with gas, challenge with solid state materials (Silicon).

Different Techniques of Detection Tracking and Vertexing Tracking and Vertexing  gas or Silicon detectors Measure Time Of Flight Measure Time Of Flight  scintillators with phototubes Measure Energy Measure Energy  calorimeters

Calorimetry and Time of Flight Calorimetry Calorimetry  build a device that surrounds all other detectors made of many layers of very dense material (e.g. Pb) in which the particles stop and deposit all their energy. Measure energy by interspersing scintillator layers. Time Of Flight Time Of Flight  build a detector layer sufficiently far away (radially) from the intersection point to measure the flight time for each charged particle. The start time is the time of interaction the stop time is the impact time of the particle on the time of flight layer (made of scintillators). Different particle species have different time of flight for the same momentum due to their difference in mass.

Tracking Detector Schematic 1.) generate e-cloud 2.) drift e-cloud 3.) focus e-cloud 4.) record e-cloud (position and time) 1.) generate e-cloud 2.) drift e-cloud 3.) focus e-cloud 4.) record e-cloud (position and time)

How Do We Measure Things ? measure a track by connecting points in different radial planes (SVT has three planes, TPC has 45 planes) measure a track by connecting points in different radial planes (SVT has three planes, TPC has 45 planes) put the tracking detectors in a magnetic field -> the charged particle track will be curved ( r = mv/qB -> r = p/qB) put the tracking detectors in a magnetic field -> the charged particle track will be curved ( r = mv/qB -> r = p/qB) the radius is proportional to the particles momentum the radius is proportional to the particles momentum curvature direction tells us particle charge curvature direction tells us particle charge

How Do We Measure Things ? in inner detectors (SVT and TPC) the particles lose only a tiny bit of energy and are not or very little deflected in inner detectors (SVT and TPC) the particles lose only a tiny bit of energy and are not or very little deflected the tiny bit of energy is sufficient for an energy loss measurement = particle identification the tiny bit of energy is sufficient for an energy loss measurement = particle identification in outer detector (EMC) the particles are stopped and all their remaining energy is measured. in outer detector (EMC) the particles are stopped and all their remaining energy is measured.

What can we measure ? Global Observables Global Observables  multiplicity (= number of charged particles)  energy (= energy deposited in calorimeter) Specific Observables Specific Observables  particle specific yields  particle specific kinematic spectra  correlation between particles  fluctuations of any observable

Specific topic: decaying particles ? Our nature is made of elementary particles that contain only light quarks (u,d) and that are stable (protons, electrons) Our nature is made of elementary particles that contain only light quarks (u,d) and that are stable (protons, electrons) Elementary particles with heavy quark content (s,c,b,t) are not stable and rare but they can be produced in the laboratory. We suspect that a lot of these particles were produced during the Big Bang and subsequently decayed. Elementary particles with heavy quark content (s,c,b,t) are not stable and rare but they can be produced in the laboratory. We suspect that a lot of these particles were produced during the Big Bang and subsequently decayed. Of these, particles with strange quark are most abundant and have the longest lifetime. Of these, particles with strange quark are most abundant and have the longest lifetime. Let’s look at some of these particles. Let’s look at some of these particles.

A neutral strange particle decays… a neutral particle decays into two charged particles inside the active tracking volume e.g.  -> p  - (ct = 7.89 cm) a neutral particle decays into two charged particles inside the active tracking volume e.g.  -> p  - (ct = 7.89 cm)

How do we know what happened ? We have to compare to a system that did definitely not go through a phase transition (a reference collision) We have to compare to a system that did definitely not go through a phase transition (a reference collision) Two options: Two options:  A proton-proton collision compared to a Gold- Gold collision does not generate a big enough volume to generate a plasma phase  A peripheral Gold-Gold collision compared to a central one does not generate enough energy and volume to generate a plasma phase

Signatures of the QGP phase Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. 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 existing form of matter. In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity. At the step some signatures drop and some signatures rise Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. 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 existing form of matter. In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity. At the step some signatures drop and some signatures rise

Distinction between probe and medium We are producing ‘soft’ and ‘hard’ matter. An arbitrary distinction is coming from the applicability of pQCD which is generally set to p T > 2 GeV/c (hard). Below p T = 2GeV/c we expect thermal bulk matter production. We are producing ‘soft’ and ‘hard’ matter. An arbitrary distinction is coming from the applicability of pQCD which is generally set to p T > 2 GeV/c (hard). Below p T = 2GeV/c we expect thermal bulk matter production.  Medium: The bulk of the particles; dominantly soft production and possibly exhibiting some phase.  Probe: Particles whose production is calculable, measurable, and thermally incompatible with (distinct from) the medium (hard production)

Fate of jets in heavy ion collisions? p p ? Au+Au idea: p+p same  s NN = 200 GeV as reference ?: what happens in Au+Au to jets which pass through medium? Prediction: scattered quarks radiate energy (~ GeV/fm) in the colored medium:  decreases their momentum (fewer high p T particles)  “kills” jet partner on other side

We measure two predicted QGP signatures The ‘quenching’ of high pt particles due to radiative partonic energy loss. The ‘quenching’ of high pt particles due to radiative partonic energy loss. Energy loss 15 times higher (several GeV/fm 3 ) than in cold nuclear matter (compare STAR AA to HERMES eA) ? The disappearance of the away-side jet in dijet events traversing the opaque medium The disappearance of the away-side jet in dijet events traversing the opaque medium

What is our present conclusion ? The interpretation of bulk properties in heavy ion systems is complex. We have indications that we have produced strongly interacting partonic matter. An ideal plasma should be a weakly interacting state, but the produced matter behaves more like an ideal liquid. This is very exciting and unexpected ! We need to study the properties of this new phase of matter above the critical temperature. We will learn how particles acquire mass and why free partons are apparently massless, but partonic matter is not plasma-like.