Quantum Chromodynamics Quantum Chromodynamics (QCD) is the established theory of strong interactions Gluons hold quarks together to from hadrons Gluons and quarks, or partons, typically exist in a color singlet state Baryon p (uud) meson  (ud)

Matter Under Extreme Conditions New form of strongly interacting nuclear matter?! Nuclei

Predictions from QCD: The QGP Lattice QCD calculations predict a rapid rise in the number of degrees of freedom when T>T c ~ MeV Quark-Gluon Plasma: A thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons

Heat is also a window back in time

The QCD Phase Diagram neutron stars Quark Matter Hadron Resonance Gas Nuclear Matter Color Superconductor RHIC & LHC early universe BB T T C ~ 170 MeV (2*10 12 K) 940 MeV MeV

The Relativistic Heavy Ion Collider STAR PHENIX PHOBOS BRAHMS RHIC Design PerformanceAu + Aup + p Max  s nn 200 GeV500 GeV L [cm -2 s -1 ]2 x x Interaction rates1.4 x 10 3 s -1 6 x 10 5 s -1 Two Superconducting Rings Ions: A = 1 ~ 200, pp, pA, AA, AB

RHIC acceleration scenario for Au beams

The Solenoidal Tracker at RHIC ( STAR ) Detector

The actual STAR detector opened up

The Time Projection Chamber (TPC) Gas P10 10% methane 90% argon E and B parallel to z axis E 133V/cm B 0.5 Tesla electron drift velocity = 5.45 cm/  s number of x/y pads = 136, time buckets 100ns/bucket)

cold nuclear matter p Nz = 100GeV/c p NT ~200MeV/c  < 2x10 -3 rad Reaction plane x z y The STAR trigger for Au-Au collisions

Au+Au Event  One reconstructed central Au+Au collision event at GeV  Thousands of produced particles Beam view Side view

TPC aloneTPC and Time of Flight (TOF) Detector Particle Identification (PID) at STAR one “tray”; 120 trays = full acceptance doubles the p range for PID

K s and  are V0 particles: decay length: K s = 2.69 cm  = 7.89 cm In TPC, neutral Ks and  are reconstructed from charged particles: p, K and  (See above sketch). p+p+ K s and  reconstruction & Topology cuts  -- Primary Vertex Decay point Ks -- ++ Primary Vertex Decay point DcaV0 Decay len DcaImpact Track 1 Track 2 Lambda ( uds ) M = GeV/c 2 Anti-Lambda ( uds ) M = GeV/c 2 mass (GeV/c 2 ) K 0 S (ds and ds) M = GeV/c 2 mass (GeV/c 2 ) BR 64% BR 68%

background subtracted  For 40~100% centrality bin at |y|<0.5 and 0.4<p t <1.3GeV/c. Red line is the same- event distribution. Black line is the normalized mixed- event distribution. STAR Charm Measurement D0D0 D0D0 D*D* D±D± Invariant mass distribution of  meson

A growing STAR dataset STAR has recorded >120M Au+Au, >110M Cu+Cu, >35M d+Au events in first five RHIC runs –Improved RHIC performance, increased luminosity –Increased STAR DAQ capabilities Run I Au+Au 130 Run II Au+Au p+p 200 Run III d+Au 200 Run IV Au+Au 62 & Run V Cu+Cu 62 & 200 *** * pp spin data not included

1 fm/c2 fm/c 10 fm/c 50 fm/c hadronization initial state pre-equilibrium QGP and hydrodynamic expansion hadronic phase Experimental results from STAR/RHIC which bear on evidence for the production and properties of the QGP (1)QCD hard parton scattering,jets jet-medium interactions jet quenching (2) Quark recombination/coalescence

(1) Jets in nuclear collisions High-energy hadronic collisions: collisions of constituent partons –Jets can serve as a calibrated probe of dense nuclear matter –“Hard-scattered” outgoing partons back-to-back in azimuth (  )  Trigger 

Collision systems … Final stateInitial state Au + Au d + Au p + p

Jets: Modified ( Quenched ) by the medium Pedestal&flow subtracted p T (assoc) > 2 GeV/c 4 < p T (trig) < 6 GeV/c

Jets: Back-to-back reappearance More stats → higher p T → Narrow away-side peak emerges in Au+Au! 8 GeV/c < p T (trig) < 15 GeV/c

Trigger-normalized fragmentation function 8 < p T ( trig ) <15 GeV/c Scaling factors Relative to d-Au z T =p T (assoc) / p T (trig)

x z y pxpx pypy y x ● non-central collisions: azimuthal anisotropy in coordinate-space ● interactions  asymmetry in momentum-space ● sensitive to early time in the system’s evolution ● Measurement: Fourier expansion of the azimuthal p T distribution (2) Elliptic flow v 2 and Quark Recombination/Coalescence

Evolution of Source Shape from Hydrodynamic Model of System Au-Au Collisions  s NN = 130 GeV/c Experimental Determination of V 2 In this model the anisotropy in momentum- space measured by v 2 is dominated by the early stages Distribution of charged particles in azimuthal plane with 2 GeV/c < p T < 6GeV/c. The 0 -10%, 10 – 31%, and 31 – 77% represent different classes of centrality where 0 – 10% Is the most central.

Elliptic Flow at low p T for Identified Particles p, Λ baryons (qqq) Hydro calculations: Kolb, Heinz and Huovinen - Clear mass dependence, signature of collective flow - Hydrodynamics gives reasonable description of various mass particle at low transverse momenta - Hydro calculation constrained by particle spectra π, K mesons (qq)

In the p T range 2 GeV/c < p T < 6 GeV/c there is a bifurcation in v 2 between mesons (qq ) and baryons ( qqq ). The  is an important test particle since it is a meson ( ss ) but it has a baryonlike mass 1020 MeV/c 2 Elliptic Flow at Intermediate to High p T for Intentified Particles

Quark Coalescence: mechanism for hadron formation at intermediate p T

Evidence for Quark Coalescence in Hadron Formation Quark-Number Scaling

Dynamics of energy and momentum tell us that medium produced at RHIC is highly opaque: –Jet quenching / energy loss –Elliptic flow Valence quark scaling laws tell us that flow is carried by partons Lattice QCD tells us that flavor quantum numbers are carried by quark-like quasiparticles “If it flows like a QGP, quenches like a QGP, and looks like a QGP, it probably is a QGP ! But what kind of QGP? SUMMARY Introduction to talk by Brendt Muller Strange Quark Matter 2006, UCLA March 2006

England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt India: Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC Netherlands: NIKHEF Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino Switzerland: University of Bern U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan, USTC, Tsinghua, SINR, IMP Lanzhou Croatia: Zagreb University Czech Republic: Nuclear Physics Institute The STAR Collaboration: 51 Institutions, ~ 500 People