What do we study Nucleosynthesis builds nuclei up to He Nuclear Force…Nuclear Physics Universe too hot for electrons to bind E-M…Atomic (Plasma) Physics E/M Plasma Too hot for quarks to bind!!! Standard Model (N/P) Physics Quark- Gluon Plasma?? Too hot for nuclei to bind Nuclear/Particle (N/P) Physics Hadron Gas Solid Liquid Gas Today’s Cold Universe Gravity…Newtonian/General Relativity

Structure of matter in the Universe scale ~ m scale ~ m Huge scale Iron Wood Universe Gravitational Electromagnetic Strong Leptons: electron, muon, etc Current building block

baryon meson hadrons Particles Leptons pion u d Force carriers Gluons Glue the quark together

Quarks are Confined inside Particles Strong Interaction (QCD) Strong interaction is mediated by gluons Both gluons and quarks has “color” charge. V(r) = -k 1 /r + k 2 r, k 2  1 GeV / fm, constant force. V(r) = -k 1 /r + k 2 r, k 2  1 GeV / fm, constant force. Electromagnetic Interaction Force (r) ~ 1/r 2 Two charges can be broken apart and set free As two quarks are pulling away, energy increase. Color string fragment into new pairs of quark. Single quarks are confined inside particles. When energy is high enough, it forms a jet.

How to Liberate Quarks and Gluons Increase Temperature and/or Pressure Bayon (pressure) pressure Water molecule is liberated with high T and P Librated Quarks and Gluons 1,500,000,000,000 K ~100,000 times higher temperature than the center of our sun.

One Way to Increase Temperature or Pressure Small “Bang” Heavy alien object hits the heavy earth Tremendous kinetic energy converted into tremendous heat and pressure.

One (Nuclear Physicist’) Way to Increase Temperature or Pressure Mini “Bang” Heavy (Au) Nuclei hits the heavy (Au) Nuclei Tremendous kinetic energy converted into tremendous heat

One (Real Nuclear Physicist’) Way to Increase Temperature or Pressure Mini “Bang” Heavy Nuclei hits the heavy Nuclei Tremendous kinetic energy converted into tremendous heat

Different Stage after the Collision Right before the collision. Instantly (< 1 fm/c) after the collision. Highest energy density (15GeV/fm3). After ~1fm, system thermalized, i.e. thermal equilibrium. Temperature is the same everywhere. Hadron continue to interact with each other elastically. Hadron is not changed but the momentum distribution does. At Kinetic freezout, the elastic interaction between hadrons stop. Hadron spree out and detected by the experiment System continue the expension and cool down. Quarks and gluons start to fragment into hadrons. The particle ratio kept on changing due to the chemical reactions. At the point of Chemical Freezout, the chemical reaction ceased

What are the probes. soft hadron: Pions, kions, protons, etc coming from the fragmentation process after chemical freezout. To study their behavior (cross section, correlation, suppression, etc) can leads to the estimation of the QGP properties, e.g. temperature, pressure, energy density. Penetrating probes: direct photons, jet, heavy flavor, etc Coming from the QGP, i.e. before the chemical freezout. Directly bring the information of the QGP properties.

What are Detected Detector in Rphi plane particle tracks beam collision vertex particle momentum (px, py, pz) right after the collsion through bending curvature in the magnet field. particle energy (photon, no bending in the magnet field). particle species identification through, e.g. energy loss (dE/dx) and particle speed (time of flight), cerenkov radiation, etc.

How an experiment take data

Take what is necessary: trigger target trigger soft hadron production ……………………………..…………… Minimum-bias trigger Direct photons ………………………………………..…………… photon trigger High pT particles (belong to jet). ………………………………….. High pt trigger J/psi, D meson production. ………………….…………………… J/psi, D meson trigger ……………………….. One can take all the collision events with enough resources. Not every collision is interesting. heavy flavor, photon are very rare.

What is needed for the result to be publishable The result, in principle, need to be independent of a specific experiment. An experiment is specific in it: detector acceptance (Accp): N (accepted by the detector)/N (produced from the collision). Detector efficiency (Eff). HV trip, construction flaw. The efficiency < 100% Experiment trigger efficiency (Trg_eff). Trigger always biased, e.g. photon trigger: only accept events with hits above a certain energy. pT accp x y pT Trg_eff

Example of Publishable Results. cross section (σ): a Lorentz invariant measure of the probability of interactions. It has dimension of area (unit cm 2 or barn ) σ x L = N(events), where L is the luminosity, i.e. the intensity of the beams

How to Study QGP Nuclei is made of protons and neutrons: p+p collision is a natural reference (note: QGP may have already been produced by p+p collisions: ask Rolf and Brijesh) Behavior Quarks and gluons in a static nuclei is different from that in proton. Cold nuclear effect, or initial state nuclear effect, i.e. before collisions p(d)+Au can quantify this effect. New matter is produced after the collisions ( hot or final state effect). time p+p d+Au Au+Au

Study QGP in different Centrality Most Central events (highest multiplicity), e.g. top 5% central, i.e. 5% of the events with largest multiplicity Mid Central events Most Peripheral events From most central to most peripheral event, the collision is more like a p+p collisions. One can also collision smaller size of nuclear, e.g. Cu+Cu, Si+Si, instead of Au+Au to gain more luminosity. N_coll: 8 N_part: 6 Centrality can be quantified by the number of collisions (N_coll) and number of participants (N_part) through the glauber model calculation with

Ways to Reveal the QGP properties---R AA nuclear modification factor (R AA ): R AA ( or R dA ) No medium effect

Au + Au Experiment (200GeV)d + Au Control Experiment (200GeV) Preliminary DataFinal Data Cronin enhancement: parton pT smearing from random kick before collisions (i.e. initial state effect) Energy loss: parton loss lots of energy (dE/dx = ???GeV/fm) through bremsstrahlung when pass through the new state of matter (final state effect)

Ways to Reveal the QGP properties--- Jet correlation Calculate angle between two jet particles trigger Adler et al., PRL90: (2003), STAR near-side away-side Energy dissipated when parton pass through opaque medium. How?

1 < p T (assoc) < 2.5 GeV/c Thanks Andy

Particle ratio is determined by Temperature and chemical potential abundances in hadrochemical equilibrium Ways to Reveal the QGP properties---particle ratio >= critical temperature

Ways to Reveal the QGP properties---flow V1: directed flow Higher order V2: elliptic flow

A Movie of Glass Bead Show Liquid Behavior

Decreasing the number of glass beads in the cross section of the jet changes the behavior of the granular stream after hitting the target from liquid-like pattern to one that looks like fireworks. This latter pattern is more characteristic of how individual particles would behave after hitting a wall.

A Movie of Glass Bead Show Liquid Behavior

More Materials RHIC white paper: for physics understanding –J. Adams et al., Nucl. Phys. A 757, 102 (2005); K. Adcox et al., Nucl. Phys. A 757, 184 (2005) ; I. Arsene et al., Nucl. Phys. A 757, 1 (2005); B. B. Back et al., Nucl. Phys. A 757, 28 (2005). CERN detector and analysis brief book: For nice explanation of jargon in this field. – –