Heavy Ion Physics Lecture 1 Thomas K Hemmick Stony Brook University.

Heavy Ion Physics Lecture 1 Thomas K Hemmick Stony Brook University

COURAGE INTENTION 2

l This talk is not targeted at the experts. l Students should EXPECT to understand. l Whenever the speaker fails to meet this expectation: INTERRUPT! Thomas K Hemmick 3 For the Students!

Thomas K Hemmick 4 What Physics do You See?

Physics beyond the diagram! l The water droplets on the window demonstrate a principle. l Truly beautiful physics is expressed in systems whose underlying physics is QED. Stony Brook University Thomas K Hemmick 5 l Does QCD exhibit equally beautiful properties as a bulk medium. l ANSWER: YES!

Axel Drees ~ 10 s after Big Bang Hadron Synthesis strong force binds quarks and gluons in massive objects: protons, neutrons mass ~ 1 GeV/c 2 ~ 100 s after Big Bang Nucleon Synthesis strong force binds protons and neutrons bind in nuclei

Axel Drees ~ 10 s after Big Bang T ~ 200 MeV Hadron Synthesis strong force binds quarks and gluons in massive objects: protons, neutrons mass ~ 1 GeV/c 2 ~ 100 ps after Big BangT ~ 10 14 GeV Electroweak Transition explicit breaking of chiral symmetry inflation Planck scale T ~ 10 19 GeV End of Grand Unification

Travel Back in Time l QGP in Astrophysics early universe after ~ 10 s l possibly in neutron stars l Quest of heavy ion collisions l create QGP as transient state in heavy ion collisions l verify existence of QGP l Study properties of QGP l study QCD confinement and how hadrons get their masses neutron stars Quark Matter Hadron Resonance Gas Nuclear Matter SIS AGS SPS RHIC & LHC early universe BB T T C ~170 MeV 940 MeV 1200-1700 MeV baryon chemical potential temperature Thomas K Hemmick

Estimating the Critical Energy Density normal nuclear matter 0 critical density: nave estimation nucleons overlap R ~ r n nuclear matter p, n Quark-Gluon Plasma q, g density or temperature distance of two nucleons: 2 r 0 ~ 2.3 fm size of nucleon r n ~ 0.8 fm Thomas K Hemmick

Critical Temperature and Degrees of Freedom l In thermal equilibrium relation of pressure P and temperature T l Assume deconfinement at mechanical equilibrium l Internal pressure equal to vacuum pressure B = (200 MeV) 4 l Energy density in QGP at critical temperature T c Noninteracting system of 8 gluons with 2 polarizations and 2 flavors of quarks (m=0, s=1/2) with 3 colors Thomas K Hemmick

Stony Brook University Thomas K Hemmick 11 Lattice Calculations The onset of QGP is far from the perturbative regime ( s ~1) l Lattice QCD is the only 1 st principles calculation of phase transition and QGP. l Lattice Calculations indicate: q T C ~170 MeV C ~1 GeV/fm 4

Stony Brook University Thomas K Hemmick 12 Outline of Lectures l What have we done? q Energy Density q Initial Temperature q Chemical & Kinetic Equilibrium q System Size l Is There a There There? q The Medium & The Probe q High Pt Suppression Control Experiments: direct, W, Z l What is It Like? q Azimuthally Anisotropic Flow q Hydrodynamic Limit q Heavy Flavor Modification q Recombination Scaling l Is the matter exotic? q Quarkonia, Jet Asymmetry, Color Glass Condensate l What does the Future Hold? } } Lecture 1 Lecture 2 Lecture 3

Stony Brook University Thomas K Hemmick 13 RHIC Experiments STAR

LHC Experiments Stony Brook University Thomas K Hemmick 14 ALICE CMS ATLAS

Axel Drees 100% 0 % Participants Spectators Collisions are not all the same l Small impact parameter (b~0) q High energy density q Large volume q Large number of produced particles l Measured as: q Fraction of cross section centrality q Number of participants q Number of nucleon-nucleon collisions Impact parameter b

Stony Brook University Thomas K Hemmick 16 Terminology l Centrality and Reaction Plane determined on an Event-by-Event basis. l N part = Number of Participants q 2 394 Peripheral CollisionCentral CollisionSemi-Central Collision 100% Centrality 0% Reaction Plane l Fourier decompose azimuthal yield:

Stony Brook University Thomas K Hemmick 17 What have we done? Energy Density l Lets calculate the Mass overlap Energy: l Bjorken Energy Density Formula: RHIC: = 5.4 +/- 0.6 GeV/fm 2 c LHC: = 16 GeV/fm 2 c Overly Simplified: Particles dont even have to interact! Measured Assumed

l Hot Objects produce thermal spectrum of EM radiation. l Red clothes are NOT red hot, reflected light is not thermal. Thomas K Hemmick 18 Remote Temperature Sensing Red Hot Not Red Hot! White Hot Photon measurements must distinguish thermal radiation from other sources: HADRONS!!!

19 Number of virtual photons per real photon: Point-like process: Hadron decay: m ee (MeV) About 0.001 virtual photons with m ee > M pion for every real photon Direct photon 00 1/N dN ee /dm ee (MeV -1 ) Avoid the 0 background at the expense of a factor 1000 in statistics form factor Real versus Virtual Photons Direct photons direct / decay ~ 0.1 at low p T, and thus systematics dominate.

20 Observation of Direct Virtual Photons

Experimental Result Proton-Proton Photons T i = 4-8 trillion Kelvin Emission rate and distribution consistent with equilibrated matter T~300-600 MeV Number of Photons Photon Wavelength 2 x 10 -15 m0.5 x 10 -15 m Gold-Gold Photons

Stony Brook University Thomas K Hemmick 22 Thermal Equilibrium l Well consider two aspects of thermal predictions: q Chemical Equilibrium u Are all particle species produced at the right relative abundances? q Kinetic Equilibrium u Energetic sconsistent with common temperature plus flow velocity? l Choose appropriate statistical ensemble: q Grand Canonical Ensemble: In a large system with many produced particles we can implement conservation laws in an averaged sense via appropriate chemical potentials. q Canonical Ensemble: in a small system, conservation laws must be implemented on an EVENT-BY-EVENT basis. This makes for a severe restriction of available phase space resulting in the so- called Canonical Suppression. q Where is canonical required: u low energy HI collisions. u high energy e+e- or hh collisions u Peripheral high energy HI collisions

Stony Brook University Thomas K Hemmick 23 Chem Eql: Canonical Suppression Canonical Suppression is likely the driving force behind strangeness enhancement

Stony Brook University Thomas K Hemmick 24 Thermal or Chemical yields As you know the formula for the number density of all species: here g i is the degeneracy E 2 =p 2 +m 2 B, S, 3 are baryon, strangeness, and isospin chemical potentials respectively. l Given the temperature and all m, on determines the equilibruim number densities of all various species. The ratios of produced particle yields between various species can be fitted to determine T, .

Chemical Equilibrium Fantastic l Simple 2- parameter fits to chemical equilibrium are excellent. l Description good from AGS energy and upward. l Necessary, but not sufficient for QGP Stony Brook University Thomas K Hemmick 25

Stony Brook University Thomas K Hemmick 26 Kinetic Equil: Radial Flow l As you know for any interacting system of particles expanding into vacuum, radial flow is a natural consequence. q During the cascade process, one naturally develops an ordering of particles with the highest common underlying velocity at the outer edge. l This motion complicates the interpretation of the momentum of particles as compared to their temperature and should be subtracted. q Although 1 st principles calculations of fluid dynamics are the higher goal, simple parameterizations are nonetheless instructive. l Hadrons are released in the final stage and therefore measure FREEZE-OUT Temp.

Stony Brook University Thomas K Hemmick 27 Radial Flow in Singles Spectra l Peripheral: q Pions are concave due to feeddown. q K,p are exponential. q Yields are MASS ORDERED. l Central: q Pions still concave. q K exponential. q p flattened at left q Mass ordered wrong (p passes pi !!!) Peripheral Central Underlying collective VELOCITIES impart more momentum to heavier species consistent with the trends

Stony Brook University Thomas K Hemmick 28 Decoupling Motion: Blast Wave l Lets consider a Thermal Boltzmann Source: If this source is boosted radially with a velocity boost and evaluated at y=0: where l Simple assumption: uniform sphere of radius R and boost velocity varies linearly w/ r:

Stony Brook University Thomas K Hemmick 29 Blast Wave Fits Fit AuAu spectra to blast wave model: S (surface velocity) drops with dN/d S (surface velocity) drops with dN/d T (temperature) almost constant.T (temperature) almost constant. p T (GeV/c)

Stony Brook University Thomas K Hemmick 30 Intensity Interferometry l All physics students are taught the principles of amplitude interferometry: q The probability wave of a single particle interferes with itself when, for example, passing through two slits. l Less well known is the principle of intensity interferometry: q Two particles whose origin or propagation are correlated in any way can be measured as a pair and exhibit wave properties in their relative measures (e.g. momentum difference). q Correlation sources range from actual physical interactions (coulomb, strong; attractive or repulsive) to quantum statistics of identical bosons or fermions. l Measurement of two-particle correlations allows access space-time characteristics of the source.

Stony Brook University 31 Boson Correlations l The two paths (a 1,b 2) and (a 2,b 1) are indistinguishable and form the source of the correlation: l The intensity interference between the two point sources is an oscillator depending upon the relative momentum q=k 2 -k 1, and the relative emission position! l Consider two particles emitted from two locations (a,b) within a single source. l Assume that these two are detected by detector elements (1,2). a b

Stony Brook University Thomas K Hemmick 32 Integrate over Source l The source density function can be written as l We define the 2-particle correlation as: l To sum sources incoherently, we integrate the intensities over all pairs of source points: l Here q,K are the 4-momentum differences and sums, respectively of the two particles.

Stony Brook University Thomas K Hemmick 33 Famous Nave Mistakes If S(x,K) = (x) (K), the momentum dependence cancels! q No. If the source contains any collective motions (like expansion), then there is a strong position-momentum correlation. l Geethe correlation function is simply the Fourier Transform of S(x,K). All we need do is inverse transform the C(q,K) observable!! q Umno. Particles are ON SHELL. l Must use parameterized source.

Stony Brook University Thomas K Hemmick 34 Building Intuition l The under-measure of the source size for a flowing source depends upon the flow velocity: q Higher flow velocity, smaller source. l We expect that the measured Radius parameters from HBT would drop with increasing K (or K T ).

Stony Brook University Thomas K Hemmick 35 Some Results l R(Au) ~ 7 fm, R(HBT)

Stony Brook University Thomas K Hemmick 39 Calibrating the Probe(s) l Measurement from elementary collisions. l The tail that wags the dog (M. Gyulassy) p+p-> 0 + X Hard Scattering Thermally- shaped Soft Production hep-ex/0305013 S.S. Adler et al. Well Calibrated

If no effects: R AA < 1 in regime of soft physics R AA = 1 at high-p T where hard scattering dominates Suppression: R AA < 1 at high-p T Stony Brook University Thomas K Hemmick 40 R AA Normalization / inel p+p nucleon-nucleon cross section 1. Compare Au+Au to nucleon-nucleon cross sections 2. Compare Au+Au central/peripheral Nuclear Modification Factor: AA

41 Discovered in RHIC-Year One l Quark-containing particles suppressed. Photons Escape! l Gluon Density = dN g /dy ~ 1100 QM2001

Suppression Similar @LHC l Suppression of high momentum particles similar at RHIC and LHC. l Both are well beyond the phase transition. Stony Brook University Thomas K Hemmick 42

Control Measures for R AA l R AA intrinsically scales the pp reference by as the denominator. l Validity of this for colorless probes should be established. l At RHIC was use direct photons at large p T. l At LHC, there are more: direct q W q Z

Stony Brook University Thomas K Hemmick 44 Jet Tomography l Tomography, a fancy word for a shadow! l Jets are produced as back-to-back pairs. l One jet escapes, the other is shadowed. l Expectation: q Opaque in head-on collisions. q Translucent in partial overlap collisions. Escaping Jet Near Side Lost Jet Far Side In-plane Out-plane X-ray pictures are shadows of bones Can Jet Absorption be Used to Take an X-ray of our Medium?

45 Back-to-back jets Back-to-back jets Central Au + Au Peripheral Au + Au l Given one jet particle, where are its friends: q Members of the same jet are in nearly the same direction. q Members of the partner jet are off by 180 o l Away-side jet gone (NOTE: where did the energy go?) STAR In-plane Out-plane

Singles to Jets l Parton pairs are created at the expected rate (control measure). l Parton pairs have a k T due to initial state motion. l Partons interact with medium (E-loss,scattering?) l Fragment into Jets either within or outside the medium. l To be Learned: q E-loss will created R AA {Jets} < 1. q Scattering will make back-to-back correl worse (higher k T ) q Fragmentation function modification possible.

Moving from Singles to Jets l LHC shows loss of Jets similar to loss of hadrons. l Huge Asymmetry signal in ATLAS and CMS. l Must understand the nature of this loss

Jet Direction l Overwhelmingly, the direction of the Jets seems preserved. l This is a shock l How can you lose a HUGE amount of longitudinal momentum and not have a random walk that smears back-to-back. l Top Puzzle from LHC.

Summary Lecture 1 l Heavy Ion collisions provide access to the thermal and hydrodynamic state of QCD. l RHIC and LHC both provide sufficient energy to create the form of matter in the plateau region. l The matter is opaque to the propagation of color charge while transparent to colorless objects. l Coming in Lecture #2: q The medium behaves as a perfect fluid. q Fluid is capable of altering motion of heavy quarks (c/b). q Descriptions from string theory (AdS/CFT duality) are appropriate. q Indications of yet another new phase of matter (Color Glass Condensate) are beginning to emerge. Stony Brook University Thomas K Hemmick 49

Heavy Ion Physics Lecture 1 Thomas K Hemmick Stony Brook University.

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Transcript of Heavy Ion Physics Lecture 1 Thomas K Hemmick Stony Brook University.