What do we study

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

2. Wood Iron Universe Structure of matter in the Universe Huge scale Gravitational Current building block Leptons: electron, muon, etc scale ~ 10-10 m Electromagnetic scale ~ 10-15 m Strong

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

4. Quarks are Confined inside Particles • Electromagnetic Interaction • Force (r) ~ 1/r2 • Two charges can be broken apart and set free • Strong Interaction (QCD) • Strong interaction is mediated by gluons • Both gluons and quarks has “color” charge. • V(r) = -k1/r + k2r, k2 1 GeV / fm, constant force. 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.

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

6. 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.

7. 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

8. 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

9. 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. 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 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

10. 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.

11. What are Detected particle tracks Detector in Rphi plane beam 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.

12. How an experiment take data

13. Take what is necessary: trigger • One can take all the collision events with enough resources. • Not every collision is interesting. • heavy flavor, photon are very rare. trigger target • 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 • ………………………..

14. 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. accp pT y x Trg_eff pT

15. Example of Publishable Results. • cross section (σ):a Lorentz invariant measure of the probability of interactions. It has dimension of area (unit cm2 or barn ) • σ x L = N(events), where L is the luminosity, i.e. the intensity of the beams

16. How to Study QGP p+p • 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). d+Au Au+Au time

17. 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. Centrality can be quantified by the number of collisions (N_coll) and number of participants (N_part) through the glauber model calculation with N_coll: 8 N_part: 6

18. Ways to Reveal the QGP properties---RAA RAA ( or RdA) No medium effect • nuclear modification factor (RAA):

19. Au + Au Experiment (200GeV) d + Au Control Experiment (200GeV) Final Data Preliminary 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)

20. trigger Adler et al., PRL90:082302 (2003), STAR away-side near-side Ways to Reveal the QGP properties---Jet correlation Calculate angle between two jet particles Energy dissipated when parton pass through opaque medium. How?

21. 1 < pT (assoc) < 2.5 GeV/c Thanks Andy

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

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

24. A Movie of Glass Bead Show Liquid Behavior http://www-news.uchicago.edu/releases/07/071106.liquids.shtml

25. 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.

26. A Movie of Glass Bead Show Liquid Behavior http://www-news.uchicago.edu/releases/07/071106.liquids.shtml

27. 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. • http://physics.web.cern.ch/Physics/DataAnalysis/BriefBook/ • http://physics.web.cern.ch/Physics/ParticleDetector/BriefBook/