Making Quark Soup Out of Gold Lanny Ray

Making Quark Soup Out of Gold! Lanny Ray University of Texas at Austin October 13, 2004 1/6/2022 Rice Colloquium 1

Outline: ØPhysics goals ØHow to accomplish these goals ØSummary of global analysis ØProbing the inner workings using correlations ØHave we made the Quark Gluon Plasma at RHIC? ØConclusions and Acknowledgements 1/6/2022 Rice Colloquium 2

Physics Goals: This talk is about current efforts to better understand the strong interaction and strongly interacting matter, especially at very high energy density and temperature. Quantum Chromodynamics or QCD is theory of the strong interaction. Electrodynamics: one charge, either positive or negative, carried by e. Strong force: three charges, RED or Anti-RED, GREEN or Anti-GREEN, BLUE or Anti-BLUE, carried by quarks (color), anti-quarks (anti-color) and gluons (color-anticolor combinations). 1/6/2022 Rice Colloquium Artist’s view of a nucleus 3

QCD is quite successful but in general is highly non-linear, and therefore very COMPLICATED. jet QCD verified in high energy, high momentum transfer scattering. nucleon Strong interaction systems are compact, color singlets, i. e. white, with color antisymmetric wave functions. parton nucleon Free or deconfined colored objects have not been observed. Can we better understand color confinement from experiment? 1/6/2022 Rice Colloquium 4

Phase Transition from hadron gas to “free” quarks and gluons? Numerical predictions of QCD using a 4 D lattice approximation indicate a phase transition from bound hadrons (mesons and baryons) to color deconfined quark-gluon equilibrated matter – Quark Gluon Plasma (QGP). Tcrit ~ 175 Me. V Ecrit ~ 1 -3 Ge. V/fm 3 From: K. Kanaya, Nucl. Phys. A 715, 233 c (2003) (Quark Matter 2002). 1/6/2022 Rice Colloquium 5

Temperature Tchemical freezeout (Me. V) Phase Diagram for the Strong Interaction early universe 250 quark-gluon plasma 200 RHIC SPS lattice QCD 150 thermal freeze-out deconfinement chiral restauration AGS 100 50 00 1/6/2022 hadron gas SIS neutron stars nuclei 200 400 600 800 1000 1200 Rice Colloquium Baryonic Potential B (Me. V) 6 P. Braun-Munzinger nucl-ex/0007021

Phenomenology can be developed which characterizes the hot, dense medium at T > Tcrit Perhaps effective field theories will result: Equation of State: Temperature Pressure Density What are the effective degrees of freedom and the effective lagrangian, Leff? - Constituent quarks? - Current quarks? - Collective gluon states? - Diquarks? - Dressed q & g, etc. ? Opacity Viscosity 1/6/2022 Rice Colloquium 7

Big Bang! Can phenomenology of hot, dense hadronic matter improve our understanding of the very early universe 1/6/2022 Rice Colloquium 8

QGP? 1 ms 1/6/2022 Rice Colloquium 9

How to Accomplish These Goals: To reach this new regime of temperature and energy density for strongly interacting matter the Relativistic Heavy Ion Collider (RHIC) was constructed along with four detectors to study ultra-relativistic collisions between gold nuclei. 1/6/2022 Rice Colloquium 10

Increasing the collision energy Few to ~100 Ge. V per nucleon E ~ A 1/3 log{s. NN 1/2} QGP? T Baryon debris goes forward down the beam pipe 1/6/2022 nuclei Hot, high energy density central region Rice Colloquium Net r. B 11

Closer look at each stage of the collision: 1/6/2022 Rice Colloquium 12

A general view of RHIC collisions ? pre-equilibrium QGP? hadronization decoupling time initial state t. LAB~5 fm/c Graphics from Steffen Bass and John Harris 1/6/2022 Beam direction Rice Colloquium 13

The RHIC Facility at the Brookhaven National Lab BRAHMS PHOBOS RHIC PHENIX STAR 1/6/2022 Rice Colloquium 14

The STAR detector E-M Calorimeter Projection Chamber Time of Flight 1/6/2022 Rice Colloquium 15

About 2000 charged particles from a single collision! A typical, single Au+Au collision at STAR In a typical run period we obtain about 10 M events like this. 1/6/2022 Rice Colloquium 16

STAR kinematics and acceptance: Full h charged particle distribution measured by the PHOBOS experiment (www. phobos. bnl. gov) Definitions: y Be am di tio c e r n STAR pt x z STAR TPC acceptance 1/6/2022 Rice Colloquium 17

Challenges: ØBig science, large collaborations ØHigh energy Au+Au collisions are messy. ØThe most interesting stage of the collision is hidden from direct observation behind a veil of hadronization, hadro-chemistry, and hadron rescattering. ØSeveral signals of color deconfinement proposed, but none are “smoking guns. ” RHIC has been operating for four years; I will summarize major highlights for global properties of RHIC collision systems. 1/6/2022 Rice Colloquium 18

Summary of Global Analysis Particle Distributions Spectra are thermal (B. E. or M. B. ) distributions plus hard scattering which causes power law behavior at higher pt centrality From: Adler et al. (STAR Collaboration), Phys. Rev. Lett. 89, 202301 (2002). peripheral 1/6/2022 Rice Colloquium 19

Identical Charged Pion Quantum Interferometry 1/6/2022 Rice Colloquium 20

Rside Analysis reveals correlation lengths of an expanding source p- Rout side ou lo Rlong ng t Compilation from: M. Lisa et al. , PRL 84, 2798 (2000) R. Soltz et al. , to be sub PRC C. Adler et al. , PRL 87, 082301 I. G. Bearden et al. , EJP C 18, 317 (2000) 1/6/2022 The decreasing correlation lengths with increasing pair momentum indicate an expanding medium. Rice Colloquium 21

Azimuthal Anisotropy – Elliptic Flow Measures: response of the system to early pressure the system’s ability to convert original spatial anisotropy into momentum anisotropy typical minimum bias event z - midrapidity : |h| < 1. 0 y STAR Model x “almond” PRL 86 (2001) 402 Peripheral Central 1/6/2022 Rice Colloquium 22

Azimuthal correlations in Au+Au at 200 Ge. V peripheral central pedestal and flow subtracted Phys Rev Lett 90, 082302 p-p and peripheral Au+Au similar 1/6/2022 Rice Colloquium ? Suppression of away-side jet; requires high gluon density 23

Summary of bulk properties of final stages of Au+Au collisions at RHIC Energy density ~ 5 -7 Ge. V/fm 3 = 30 -40 times rnuc which is well above Lattice QCD predictions for a phase transition ~1 -3 Ge. V/fm 3. -- highest man-made energy density so far! Very high initial pressure High gluon density ~ 1000/unit rapidity l a n di u it le” g n b n Lo ub sio “H pan ex 1/6/2022 Decoupling T ~ 110 Me. V = 1. 3 trillion K Matter is expanding outward at ½c. Radius ~ 12 fm, twice that of gold nucleus. Total lifetime ~ 10 fm/c = 3 x 10 -23 s Transverse collective expansion plus random thermal motion Two-dimensional, hydrodynamics with hadron-QGP phase transition describes most of the bulk properties of RHIC collisions. Rice Colloquium 24

Probing the inner workings using correlations Correlation measurements provide a window into the internal dynamics of the hot, dense medium: Two-particle correlation in momentum space Two-particle Single-particle densities: density mixed event pair “sibling pair” mixed pair sibling pair Define ratio of densities of the number of pairs of particles: 1/6/2022 Rice Colloquium STAR reports these normalized ratios 25

Proton+proton reference: g Two-Component Model: §Longitudinal color string local momentum fragmentation conservation §Transverse semi-hard parton scattering and fragmentation pt, 2 §Local charge, momentum cons. rin e d r e-o g r a ch pt, 1 p-p 200 Ge. V pt, 2 Semi-hard parton scattering “minijet” (min-bias) minijets Longitudinal color string fragmentation “soft” particles 1/6/2022 Transverse rapidity pt, 1 Rice Colloquium 26

Proton-Proton Correlations in h, f Space: Semi-hard minijets h. D =h -h 1 2 STAR preliminary LS Like sign pairs f 2 f 1 = f. D US Unlike sign pairs Beam CI f Collision “event” in h, f Charge Independent (CI = all charged pairs) 1/6/2022 Rice Colloquium 27

Soft, longitudinal string fragmentation in p-p Manifest as strong, charge-dependent correlations ng r ge a h C d or ing r e alo - + h + HBT Lo cal con mom ser ent vat um ion Like-sign, near-side correlations Unlike-sign, away-side correlations Charge dependent, CD = LS-US, strong STAR preliminary negative correlations on h. D. 1/6/2022 Rice Colloquium 28

Comparing p-p and Au-Au Correlations in Transverse Momentum Space Au-Au 130 Ge. V mid-central p-p 200 Ge. V (nucl-ex/0408012 ) All Charges Au-Au Peripheral 1/6/2022 Evolution of soft medium; dissipation of minijet structure to lower pt. Rice Colloquium Au-Au Central 29

Charge-independent correlations on h, f space for Au-Au 1/6/2022 Rice Colloquium 30

h, f correlations for 130 Ge. V Au-Au: All Charges l tra n e C (correlation amplitude per final state hadron) Features: peak at small relative angles cos(f. D) - soft momentum conservation cos(2 f. D) - elliptic anisotropy 1/6/2022 STAR preliminary l a er h p ri e P Rice Colloquium 31

ntr al ce Subtract cos(f. D) and cos(2 f. D): STAR preliminary Notable Results: • Absence of away-side, h. D dependent structure from soft string fragmentation beginning in most peripheral bin. • Elongation along h. D 1/6/2022 pe rip he ral • Narrowing along f. D e. V G 00 2 p-p Rice Colloquium 32

Possible interpretation… Au de i s y- f D) a w os( a , ft , c So coil re Interaction with longitudinally expanding color fluid drags pre-hadronic matter associated with semi-hard partonic scattering along pseudorapidity. mi nij et (See: Armesto, Salgado, Wiedemann, hep-ph/0405301. ) Au But note that actual, central events have several 10 s of these minijets poking out! 1/6/2022 Rice Colloquium 33

p- 00 2 p V Ge Charge dependent (like-unlike sign pairs) h, f correlations for 62 Ge. V Au-Au STAR preliminary Au-Au Peripheral 1/6/2022 Gaussian to exponential _ opaque medium Rice Colloquium Evolution from 1 D string fragmentation to at least 2 D hadronization 34 Au-Au Central

Possible interpretation… If Au+Au collisions were simply a superposition of independent pp collisions, then we would expect to see one-dimensional charge-ordering on h. D. Au But the system evolves to… + +- + + - Au A system with two-dimensional charge-ordering on h, f, implying that the 1 D color strings have “melted” to form a 2(+)D colored medium. Au 1/6/2022 Au Rice Colloquium 35

What about theoretical predictions or phenomenological models? Generally, there are no theoretical or phenomenological models which describe any of these correlation results. A model (Hijing) by Wang and Gyulassy [Phys. Rev. D 44, 3501 (1991)] based on the high energy jet fragmentation code Pythia, produces some minijet structure like we observe but none of the dissipation effects, strong interaction with the medium, or 2 D hadronization geometry we observe. 1/6/2022 Rice Colloquium 36

Have we made the QGP at RHIC? (a personal, non-STAR opinion) The matter produced: - appears hot enough - has high enough energy density - is in approximate thermal equilibrium - is strongly self-interacting - dissipates energy like crazy - appears to hadronize in the bulk But, - it does not last as long as expected which we do not understand; - we have not yet seen color screening effects which await results from PHENIX (www. phenix. bnl. gov) on J/Y suppression; - we cannot yet rule out a dense medium of compact color singlet objects. I am hopeful but I believe it is premature to declare victory. 1/6/2022 Rice Colloquium 37

Conclusions and Acknowledgements However I cannot over emphasize the fact that: v RHIC is a non-perturbative QCD test facility, searching for the LQCD predicted Quark Gluon Plasma, but RHIC is also studying this hot, dense hadronic matter which may be similar to primordial Big Bang matter. v This field is data driven, theory is way behind. v Experimental results will eventually lead to better phenomenological models. v Ultimately, RHIC data may lead to effective field theories, based on QCD, which are calculable for hot, dense, non-perturbative matter. Given what we know now, what do RHIC events look like? 1/6/2022 Rice Colloquium 38

An updated view of possible deconfined system at fixed time in the lab of about 5 fm/c Au je mini ts Au Incoming nuclei 1/6/2022 Minijets based on correlations per final state particle in Au-Au assuming about 3 -5 hadrons per minijet from p-p; colors indicate strong charge carriers, mainly gluons. Rice Colloquium 39

The STAR Collaboration Brazil: Universidade de Sao Paulo Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino China: IHEP – Beijing IMP - Lanzou IPP – Wuhan USTC SINR – Shanghai Tsinghua University U. S. Laboratories: Argonne Berkeley Brookhaven Great Britain: University of Birmingham France: IRe. S Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University of Rajasthan Jammu University IIT - Bombay VECC – Kolcata 1/6/2022 Poland: Warsaw University of Tech. Rice Colloquium U. S. Universities: UC Berkeley UC Davis UC Los Angeles Carnegie Mellon Creighton University Indiana University Kent State University Michigan State University College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin U. of Washington Wayne State University Yale University 40

The University of Texas High Energy Heavy Ion Nuclear Physics Group http: //www. rhip. utexas. edu Faculty and Research Staff: G. W. Hoffmann, C. F. Moore, Lanny Ray, Jo Schambach Graduate Students: Michael Daugherity, Kohei Kajimoto, Cody Mc. Cain UT STAR Ph. D. s: Curtis Lansdell, Bum Choi, Aya Ishihara, Yiqun Wang 1/6/2022 Rice Colloquium 41

Extra Slides 1/6/2022 Rice Colloquium 42

Can we better understand color confinement from experiment? Effective quark-antiquark interaction potential r q g q “Coulomb”-like interaction, as small, perturbative Asymptotic Freedom as ~ 1 non-perturbative Color Confinement (2004 Nobel Prize in Physics – Wilczek, Gross, Politzer) 1/6/2022 Rice Colloquium 43

Atomic Nucleus protons Energy units: e. V, electron Volt - atoms mesons (carriers of the nuclear force) Me. V = 106 e. V - nuclei Ge. V = 109 e. V - nucleons neutrons quarks 1/6/2022 Rice Colloquium gluons (carriers of the strong force) 44

Hadronic matter (anything containing quarks and gluons) at finite temperature and/or increased net baryon density can be produced in the laboratory via heavy ion collisions. Few 100 Me. V per nucleon The collision compresses the matter to higher density and somewhat higher temperature. QGP? T nuclei Net r. B 1/6/2022 Rice Colloquium 45

red Colors quark gluon yellow antiquark gluon green gluon quark gluon cyan magenta blue gluon antiquark 1/6/2022 Rice Colloquium 46

Chiral Symmetry Restoration? Lattice QCD also predicts that the Chiral symmetry invariance of the Basic QCD Lagrangian, which is Spontaneously broken in the hadonic States of QCD, is restored in QCD Systems above the critical temperature Tc. One consequence is that mass degeneracy in meson multiplets, such as the pseudoscalar pion and rho mesons, will be restored. p- p+ p 0 mass r Chrially symmetric, degenerate pseudoscalar states T > Tc T=0 1/6/2022 Rice Colloquium 47

What is the color screening distance in hot matter Above Tc? This is the QCD analog to the Debeye Screening length in atomic physics. 1/6/2022 Rice Colloquium 48

Phase Transition from hadron gas to “free” quarks and gluons? Numerical predictions of QCD using a 4 D lattice approximation indicate a phase transition from bound hadrons (mesons and baryons) to color deconfined quark-gluon equilibrated matter – Quark Gluon Plasma (QGP). From: K. Kanaya, Nucl. Phys. A 715, 233 c (2003) (QM 2002) 1/6/2022 Rice Colloquium 49

Chemical decoupling temperature and potential inferred from particle ratios and resonances for a thermal model fit Central K+ /K X+ /X p -/ p/p p+ L/ L Ratio (chemical fit) BRAHMS PHENIX PHOBOS STAR K+ /p + K/p p/p + p/p. K*0/h- Chemical freeze-out parameters Tch = 179± 4 Me. V m. B = 51± 4 Me. V K+/h. K -/h - K 0 s/h. L /h - f/h X-/h- Model: M. Kaneta, Thermal Fest (BNL, Jul 2001), N. Xu and M. Kaneta, nucl-ex/0104021 X+/h- 1/6/2022 Ratio (data)Rice Colloquium 50

RAA Suppresion of inclusive hadron yield Au+Au relative to p+p RCP Au+Au central/peripheral nucl-ex/0305015 • central Au+Au collisions: factor ~4 -5 suppression • p. T>5 Ge. V/c: suppression ~ independent of p. T 1/6/2022 Rice Colloquium 51

Jets and two-particle azimuthal distributions p+p dijet • trigger: highest p. T track, p. T>4 Ge. V/c • Df distribution: 2 Ge. V/c<p. Ttrigger • normalize to number of triggers Phys. Rev. Lett 90, 082302 N. B. shifted horizontally by p/2 relative to previous STAR plots! 1/6/2022 Rice Colloquium trigger 52

Azimuthal distributions cont’d pedestal and flow subtracted Near-side: p+p, d+Au, Au+Au similar Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au 1/6/2022 Suppression of the back-to-back correlation in Au+Au is a final-state effect Rice Colloquium 53

Is suppression an initial or final state effect? Initial state? Final state? gluon saturation partonic energy loss How to discriminate? Turn off final state d+Au collisions 1/6/2022 Rice Colloquium 54

What have we learned? (cont. ) Also, the medium produced is very dense and dissipative Suppression of high (few-10 Ge. V/c) transverse momentum spectra in Au+Au relative to p+p and d+Au: Suppression of away-side high pt particles relative to high pt trigger particle: triggered particle suppressed ? But does this require a QGP? NO 1/6/2022 Rice Colloquium 55

A couple of well known, embedded processes Color string fragmentation, charge ordering, local momentum conservation, bulk production at midrapidity from hot, dense medium - Also hard and semi-hard p. QCD processes occur which punch thru medium + How does the hot, dense medium respond? 1/6/2022 Rice Colloquium 56

What’s our game plan? Initial state scattering (soft & p. QCD) Soft processes modified by developing, dissipative medium (another talk) Medium fluctuates as a result of semi-hard punches; focus of this talk We measure the effects of the hot, dense medium on known processes as well as the response of the medium to semi-hard scattering in order to quantify its properties. To do so we measure non-statistical fluctuations and large momentum scale correlations using STAR’s large acceptance; interpretation is in terms of short-range dynamical responses. Better understanding of non-perturbative QCD at finite temperatures. 1/6/2022 Rice Colloquium 57

Semi-hard parton-parton scattering & correlations in p-p n jet to o r p Parton cm Event #1 jet NN cm Event #2 on t o pr Event #3 Use all pairs to construct correlations with NO trigger particle. h. D=h 1 -h 2 -1 0 +1 All events p 0 f. D=f 1 -f 2 Manifest as strong, charge-independent correlations pt > 0. 8 Ge. V/c 1/6/2022 Rice Colloquium 58

Jets at RHIC Find this………. in this p+p jet+jet (STAR@RHIC) jet parton nucleon 1/6/2022 nucleon Rice Colloquium Au+Au ? ? ? (STAR@RHIC) 59

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Centrality dependence of same-side correlation structure Correlation amplitude and volume per final state particle. amplitude & volume widths saturation/ quenching Linear amp. increase “STEP” increase in width along h (beam) n estimates average #collisions/nucleon 1/6/2022 Rice Colloquium 63

View of possible deconfined system at fixed Time in the lab 3 D view of possible deconfined system at fixed lab time of about 5 fm/c (Remove leading beam fragments) Incoming nuclei 1/6/2022 Rice Colloquium 64

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