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Recent Discoveries at RHIC Do they indicate a new state of matter?

Recent Discoveries at RHIC Do they indicate a new state of matter?. W.A. Zajc Columbia University. It’s In The News. No. 7 Are there new states of matter at ultrahigh temperatures and densities?. From the National Research Council Committee on The Physics of the Universe :

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Recent Discoveries at RHIC Do they indicate a new state of matter?

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  1. Recent Discoveries at RHIC Do they indicate a new state of matter? W.A. ZajcColumbia University W.A. Zajc

  2. It’s In The News No.7Are there new states of matter at ultrahigh temperatures and densities? From the National Research Council Committee on The Physics of the Universe: Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century W.A. Zajc

  3. Fermi’s Vision • (Almost) included RHIC physics • See also remarks in his “statistical model” paper RHIC From Fermi notes on Thermodynamics W.A. Zajc

  4. QCD is not QED • QED (Abelian): • Photons have do not carry charge • Flux is not confined  1/r potential  1/r2 force • QCD (Non-Abelian): • Gluons carry charge (red, green, blue)  (anti-red, anti-green, anti-blue) • Flux tubes form  potential ~ r  constant force • HOW TO LIBERATE ?? + +… W.A. Zajc

  5. The Landscape of QCD W.A. Zajc

  6. Relevant dimensions • Hadron masses ~ 1 GeV • Hadron sizes ~ 10-15 meters aka 1 femtometer aka 1 fermi = 1 fm • Characteristic velocity ~ c • Characteristic time ~ 1 fm/c • Planck’s constant = 0.2 GeV-fm • 1 fm-1 200 MeV • 200 MeV ~ characteristic scale associated with confinement W.A. Zajc

  7. Relevant Nuclear Physics • Nuclei are • (sort of) spherical • contain A=N+Z protons and neutrons • have ~ constant density r0 ~ 0.16 GeV / fm3 • MPROTON ~ MNEUTRON ~ 1 GeV • R(A) = 0.92 A1/3 (rms) , where A = AtomicNumber • <r2PROTON>1/2 ~ <r2NEUTRON>1/2 ~ 0.86 fm • Nuclei ~ close-packed “spheres” of protons and neutrons • Nuclear potential • Short range ( ~ 1 fm) • Modest strength ( ~ 50 MeV depth) • Nuclei are loosely bound • Treat as ~free Fermi gas of protons and neutrons • Nuclear physics is the “Large A, small Q2” limit of QCD W.A. Zajc

  8. Energy density for “g” massless d.o.f 8 gluons, 2 spins;  2 quark flavors, anti-quarks, 2 spins, 3 colors 37 (!) “Reasonable” estimate Relevant Thermal Physics Q. How to liberate quarks and gluons from ~1 fm confinement scale? A. Create an energy density • Need better control of dimensional analysis: W.A. Zajc

  9. Pressure in plasma phase with “Bag constant” B ~ 0.2 GeV / fm3 Pressure of “pure” pion gas at temperature T Slightly More Refined Estimate • Compare • Select system with higher pressure: Phase transition at T ~ 140 MeV with latent heat ~0.8 GeV / fm3 Compare to best estimates (Karsch, QM01)from lattice calculations:T ~ 150-170 MeV latent heat ~ 0.70.3 GeV / fm3 W.A. Zajc

  10. ~1970: An Ultimate Temperature? • The very rapid increase of hadron levels with mass ~ equivalent to an exponential level density • and would thus imply a “limiting temperature”TH ~ 170 MeV Hagedorn, S. Fraustchi, Phys.Rev.D3:2821-2834,1971 W.A. Zajc

  11. 0.66 TC T =0 0.90 TC 1.06 TC (1970) TH  (2000) TC That is: The ‘Hagedorn temperature’ TH is now understood as a precursor of TC TC = Phase transition temperature of QCD Study confining potentialin Lattice QCD at various temperatures Current estimates from lattice calculations:TC ~ 150-170 MeVL ~ 0.70.3 GeV / fm3(latent heat) F. Karsch, hep-ph/0103314 W.A. Zajc

  12. Making Something from Nothing • Explore non-perturbative “vacuum” that confines color flux by melting it • Experimental method: Energetic collisions of heavy nuclei • Experimental measurements:Use probes that are • Auto-generated • Sensitive to all time/length scales • Particle production • Our ‘perturbative’ region is filled with • gluons • quark-antiquark pairs which screen the “bare” interaction • A Quark-Gluon Plasma (QGP) W.A. Zajc

  13. g The Early Universe, Kolb and Turner Previous Attempts First attempt at QGP formation was successful (~1010 years ago) ( Effective number of degrees-of-freedom per relativistic particle ) W.A. Zajc

  14. RHIC Specifications • 3.83 km circumference • Two independent rings • 120 bunches/ring • 106 ns crossing time • Capable of colliding ~any nuclear species on ~any other species • Energy: • 500 GeV for p-p • 200 GeV for Au-Au(per N-N collision) • Luminosity • Au-Au: 2 x 1026 cm-2 s-1 • p-p : 2 x 1032 cm-2 s-1(polarized) W.A. Zajc

  15. RHIC Runs To Date RHIC Successes (to date) based on ability to deliver physics at ~all scales: barn : Multiplicity (Entropy) millibarn: Flavor yields (temperature) microbarn: Charm (transport) nanobarn: Jets (density) picobarn: J/Psi (deconfinement) • Run-1 (2000): • Au-Au at 130 GeV ~ 1 mb-1 (p-p equivalent: ~ 0.04 pb-1) • Run-2 (2001-2): • Au-Au at 200 GeV ~ 24 mb-1 (p-p equivalent: ~ 1 pb-1) • p-p at 200 GeV 0.15 pb-1 • Run-3 (2002-3): • d-Au at 200 GeV 2.7 nb-1 (p-p equivalent: ~ 1 pb-1) • p-p at 200 GeV 0.35 pb-1 W.A. Zajc

  16. How is RHIC Different? • Different from p-p, e-p colliders Atomic weight A introduces new scale Q2 ~ A1/3 Q02 • Different from previous (fixed target) heavy ion facilities • ECM increased by order-of-magnitude • Accessible x (parton momentum fraction)decreases by ~ same factor • Access to perturbative phenomena • Jets • Non-linear dE/dx • Its detectors are comprehensive • ~All final state species measured with a suite of detectors that nonetheless have significant overlap for comparisons Jargon Alert: s = Center-of-mass energy (per nucleon collision) pT = transverse momentum = |p| sin q Q2 = (momentum transfer)2 W.A. Zajc

  17. STAR RHIC’s Experiments W.A. Zajc

  18. 1 RHIC Event Data Taken June 25, 2000. Pictures from STAR Level 3 online display. Q. How to take the measure of such complexity?? (Is it possible?) A. (Yes.) Begin with single-particle momentum spectra W.A. Zajc

  19. Kinematics Dynamics Kinematics 101 Fundamental single-particle observable: Momentum Spectrum W.A. Zajc

  20. BRAHMS Acceptance (PID) Acceptances STAR Acceptance PHOBOS Acceptance W.A. Zajc

  21. Transverse Dynamics • The ability to access “jet” physics also clearly anticipated in RHIC design manual • (vintage: ISAJET) • a new perturbative probe of the colliding matter • Most studies to date have focused on single-particle“high pT” spectra • Please keep in mind: “High pT” is lower than you think W.A. Zajc

  22. Predicting pT Distributions at RHIC • Focus on some slice of the collision: • Assume 3 nucleons struck in A, and 5 in B • Do we weight this contribution as • Npart ( = 3 + 5) ? • Ncoll ( = 3 x 5 ) ? • Answer is a function of pT : • Low pT  large cross sections  yield ~Npart • Soft, non-perturbative, “wounded nucleons”, ... • High pT small cross sectionsyield ~Ncoll • Hard, perturbative, “binary scaling”, point-like, A*B, ... W.A. Zajc

  23. Luminosity • Consider collision of ‘A’ ions per bunchwith ‘B’ ions per bunch: • Luminosity Cross-sectional area ‘S’ A B W.A. Zajc

  24. Change scale by ~ 109 • Consider collision of ‘A’ nucleons per nucleuswith ‘B’ nucleons per nucleus: • ‘Luminosity’ Cross-sectional area ‘S’ A B • Provided: • No shadowing • Small cross-sections W.A. Zajc

  25. Q. Why did we build RHIC? A: To gain access to ‘small’ cross-sections* that are A) Fundamental B) Calculable C) Interesting which then allow us to use Ncoll ( aka A*B or “binary” or “point-like”) scaling of yields as our baseline hypothesis for probing a new state of matter • (This of course one of many possible answers…) p+p → p0+X (200 GeV) } W.A. Zajc

  26. Binary Collisions Spectators Participants Participants Spectators b (fm) Systematizing our Knowledge • All four RHIC experiments have carefully developed techniques for determining • the number of participating nucleons NPARTin each collision(and thus the impact parameter) • The number of binary nucleon-nucleon collisions NCOLL as a function of impact parameter • This effort has been essential in making the QCD connection • Soft physics ~ NPART • Hard physics ~ NCOLL • Often express impact parameter b in terms of “centrality”, e.g., 10-20% most central collisions W.A. Zajc

  27. Example of Ncoll Scaling • Q: Are there rare probes at RHIC that scale as the number of binary collisions? • A: Yes, charm production (for Ncoll from 71 to 975) PHENIX Run-2 Preliminary Data presented at Quark Matter 2002 W.A. Zajc

  28. Jet Axis R ‘Jets’ at RHIC • Tremendous interest in hard scattering (and subsequent energy loss in QGP) at RHIC • Production rate calculable in pQCD • But strong reduction predicted due to dE/dx ~ path-length (due to non-Abelian nature of medium) • However: • “Traditional” jet methodology very difficult at RHIC • Dominated by the soft background • Investigate by (systematics of) high-pT single particles W.A. Zajc

  29. Another Example of Ncoll Scaling • PHENIX (Run-2) data on p0 production in peripheral collisions: • Excellent agreement between PHENIX measured p0’s in p-pandPHENIX measured p0’s in Au-Au peripheralcollisions scaled by the number of collisionsover ~ 5 decades PHENIX Preliminary W.A. Zajc

  30. Central Collisions Are Profoundly Different Q: Do all processes that should scale with Ncoll do just that? A: No! Central collisions are different .(Huge deficit at high pT) • This is a clear discoveryof new behavior at RHIC • Suppression of low-x gluons in the initial state? • Energy loss in a new state of matter? PHENIX Preliminary W.A. Zajc

  31. Energy Loss of Fast Partons • Many approaches • 1983: Bjorken • 1991: Thoma and Gyulassy (1991) • 1993: Brodsky and Hoyer (1993) • 1997: BDMPS- depends on path length(!) • 1998: BDMS • Numerical values range from • ~ 0.1 GeV / fm (Bj, elastic scattering of partons) • ~several GeV / fm (BDMPS, non-linear interactions of gluons) W.A. Zajc

  32. “no effect” Systematizing Our Expectations • Describe in terms of scaled ratio RAA= 1 for “baseline expectations” • Will present most of suppression data in terms of this ratio W.A. Zajc

  33. Is The Suppression Unique to RHIC? • Yes- all previous nucleus-nucleus measurements see enhancement, not suppression. • Effect at RHIC is qualitatively new physics made accessible by RHIC’s ability to produce • (copious) perturbative probes • (New states of matter?) • Run-2 results show that this effect persists (increases) to the highest available transverse momenta • Describe in terms of scaled ratio RAA= 1 for “baseline expectations” SPS 17 GeV ISR 31 GeV RHIC 200 GeV W.A. Zajc

  34. d+Au results from presented at a press conference at BNL on June, 18th, 2003 Is The Suppression Always Seen at RHIC? • NO! • Run-3: a crucial control measurement via d-Au collisions W.A. Zajc

  35. First Conclusion • The combined data from Runs 1-3 at RHIC on p-p, Au-Au and d-Au collisions establish that a new effect (a new state of matter?) is produced in central Au-Au collisions Au + Au Experiment d + Au Control Experiment Final Data Preliminary Data W.A. Zajc

  36. Theoretical Understanding? Both • Au-Au suppression (I. Vitev and M. Gyulassy, hep-ph/0208108) • d-Au enhancement(I. Vitev, nucl-th/0302002) understood in an approach that combines multiple scattering with absorption in a dense partonic medium  Our high pT probeshave been calibratedand are nowbeing used toexplore the precise propertiesof the medium d-Au Au-Au W.A. Zajc

  37. GONE GONE Pedestal&flow subtracted Df Further Evidence • STAR azimuthal correlation function shows ~ complete absence of “away-side” jet • Surface emission only (?) • That is, “partner” in hard scatter is absorbed in the dense medium W.A. Zajc

  38. Recombination • The in vacuofragmentation of a high momentum quark to produce hadrons competes with the in mediumrecombination of lower momentum quarks to produce hadrons • Example: • Fragmentation: Dq→h(z) • produces a 6 GeV/c pfrom a 10 GeV/c quark • Recombination: • produces a 6 GeV/c pfrom two 3 GeV/c quarks • produces a 6 GeV/c protonfrom three 2 GeV/c quarks Fries, et al, nucl-th/0301087 Greco, Ko, Levai, nucl-th/0301093 W.A. Zajc

  39. Recombination Meets Data • Provides a “natural” explanation of • Spectrum of charged hadrons • Enhancements seen in p/p • Momentum scale for same ...requires the assumption of a thermalized parton phase... (which) may be appropriately called a quark-gluon plasma Fries et al., nucl-th/0301087 “Extra” protons sampled from ~pT/3 Fries, et al, nucl-th/0301087 W.A. Zajc

  40. z Hydrodynamic limit STAR: PRL86 (2001) 402 PHOBOS preliminary (scaled) spatial asymmetry y x (PHOBOS : Normalized Paddle Signal) Compilation and Figure from M. Kaneta Hydrodynamics of Elliptic Flow Parameterize azimuthal asymmetryof charged particlesas dn/df ~1 + 2v2cos (2 f) Evidence that initial spatial asymmetry is translatedquicklyto momentum space ( as per a hydrodynamic description) W.A. Zajc

  41. Recombination Tested The complicated observed flow pattern in v2(pT)d2n/dpTdf ~ 1 + 2 v2(pT) cos (2 f) is predicted to be simple at the quark level underpT → pT / n , v2 → v2 / n , n = 2,3 for meson,baryon if the flow pattern is established at the quark level Compilation courtesy of H. Huang W.A. Zajc

  42. Second Conclusions • Suppression at high pT is characteristic of dense matter formation in Au-Au collisions (lack of suppression for heavy quarks, as observed in Ncoll scaling of charm yields, also predicted) • Recombination models operating at the parton level describe • “Anomalous” baryon/meson yields(i.e., jet fragmentation is augmented by “other” partons) • Elliptic flow patterns for different mesons and baryons(results from one primordial flow pattern established at the parton level) • Is there evidence that these (deconfined?) partons are also thermalized? W.A. Zajc

  43. Results on Particle Composition BRAHMS: 10% central PHOBOS: 10% PHENIX: 5% STAR: 5% 200 GeV/A Au+Au Just a sample!There are also results on spectra of p0‘s, K* , f , L , L , X, X , … W.A. Zajc

  44. Longitudinal Dynamics • From the RHIC design manual: • Emphasis on higher beam energy needed to develop “baryon-free” central region • This theoretical argument is nicely confirmed by measurements from BRAHMS • Aids in (future) comparisons to • lattice gauge theory • conditions in the early universe W.A. Zajc

  45. STAR preliminary Systematic errors ~10-20% 130 GeV RHIC : STAR / PHENIX / PHOBOS /BRAHMS 17.4 GeV SPS : NA44, WA97 Central K+/K- BRAHMS PHENIX PHOBOS STAR X+/X- p-/p+ p/p L/L Ratio (chemical fit) K+/p+ K-/p- K+/h- p/p+ p/p- K-/h- K0s/h- K*0/h- L/h- L/h- f/h- X-/h- X+/h- Model:N.Xu and M.Kaneta, nucl-ex/0104021 Ratio (data) Is there a ‘Temperature’? • Apparently: • Assume distributions described by one temperature T and one ( baryon) chemical potential m: • One ratio (e.g., p / p ) determines m / T : • A second ratio (e.g., K / p ) provides T m • Then predict all other hadronic yields and ratios: W.A. Zajc

  46. STAR preliminary Systematic errors ~10-20% 130 GeV RHIC : STAR / PHENIX / PHOBOS /BRAHMS 17.4 GeV SPS : NA44, WA97 Locating RHIC on Phase Diagram • Previous figure  RHIC has net baryon density ~ 0: • TCH = 179 ± 4 MeV, B = 51 ± 4 MeV (M. Kaneta and N. Xu, nucl-ex/0104021) • RHIC is as close as we’ll get to the early universe for some time Previous Heavy Ion Experiments (CERN SPS) W.A. Zajc

  47. Questions • Do those many particles in the final state have anything to do with a state of matter? • For example: Is there a well-defined • Energy density e • Temperature T • Chemical potential m • Size R • Transport coefficient l • Answer: Yes (apparently) • The first round of RHIC experiments have determined ~all of these parameters (and more) W.A. Zajc

  48. RHIC Open Questions • Is the quark-gluon plasma being formed in RHIC collisions? To be determined: • Does charmonium show the expected suppression from (color) Debye screening? • Is there direct (photon) radiation from the plasma? • Do the suppression effects extend to the highest pT’s? • What is the suppression pattern in cold nuclear matter? (proton-nucleus collisions) • What are the gluon and sea-quark contributions to the proton spin? (polarized proton running) First results now available! W.A. Zajc

  49. Screening by the QGP (An explicit test of deconfinement) In pictures: W.A. Zajc

  50. Screening by the QGP In first-order finger physics: • Follow usual derivation of Debye screening • Now put in QGP scales and assumptions: • Hadrons with radii greater than ~ lD will be dissolved • Study “onium” bound states W.A. Zajc

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